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How the timing of development is linked to organismal size is a longstanding question. Although numerous studies have reported a correlation of temporal and spatial traits, the developmental or selective constraints underlying this link remain largely unexplored. We address this question by studying the periodic process of embryonic axis segmentation in-vivo in Oryzias fish. Interspecies comparisons reveal that the timing of segmentation correlates to segment, tissue and organismal size. Segment size in turn scales according to tissue and organism size. To probe for underlying causes, we genetically hybridised two closely related species. Quantitative analysis in ~600 phenotypically diverse F2 embryos reveals a decoupling of timing from size control, while spatial scaling is preserved. Using developmental quantitative trait loci (dev QTL) mapping we identify distinct genetic loci linked to either the control of segmentation timing or tissue size. This study demonstrates that a developmental constraint mechanism underlies spatial scaling of axis segmentation, while its spatial and temporal control are dissociable modules. Synopsis: The molecular relationships that link developmental timing and organismal size remain underexplored. Here, a cross-species analysis in Oryzias fish measures the timing of embryonic body axis segmentation and overall organismal size, providing evidence that timing and size control are dissociable modules. Real-time imaging of the segmentation clock in F2 embryos from interspecies crosses of Oryzias fish reveals a broad phenotypic spectrum. F2 embryos exhibit a linear relationship between PSM and somite size, indicating that a developmental constraint mechanism underlies spatial scaling. developmental quantitative trait loci (dev QTL) analysis of F2 embryos identifies distinct genomic loci correlated with segmentation timing and tissue size, respectively. Interspecies comparison in rice fish (Orzyias spp.) shows that both the rate and size of embryonic segmentation increase in proportion to fish size but are regulated by independent mechanisms. [ABSTRACT FROM AUTHOR]

The pharyngeal arch (PA) is a transient structure of vertebrate embryos. Their number varies from species to species; nine in lampreys, seven in teleosts, and six in amniotes. Each pharyngeal arch contains a nerve and an artery as well as skeletomuscular elements. There has been a long-standing controversy about the formation of the fifth PA. Here, we investigated the formation of the fifth PA by tracking the distribution of neural crest cells in pharyngeal arches in chick embryos. Fertilized chick and quail eggs were used. Neural crest cells were detected by using quail-chick cell tracing technique and in ovo electroporation of EGFP constructs. Our results showed that neural crest cells from the post-otic level contributed to all post-otic pharyngeal arches (PA3-6). In contrast, neural crest cells from the somite 1-3 level avoided to invade the third pharyngeal arch, although they gave rise post-otic pharyngeal arches. Based on the trajectory of neural crest cells, the fifth pharyngeal arch was visible between the fourth and sixth pharyngeal arch, although it was considerably smaller compared to other arches. The fifth PA forms during early development at least in avian species. It is closer to the sixth PA than the fourth PA. This is in line with the formation of the fifth PAA, which can form a bypass and even fuse with the sixth PAA. [ABSTRACT FROM AUTHOR]

Cobb syndrome is a rare neurocutaneous disease characterized by vascular anomalies involving the skin and spinal cord at the same metamere. The most common initial symptoms are neurological manifestations such as pain, monoparesis, headache, scoliosis, and motor damage. We present two patients with Cobb syndrome and severe disease burden harboring somatic mutations in KRAS. The two patients were subsequently treated with the MEK inhibitor trametinib, indicating the potential therapeutic benefit of this treatment for patients with life‐threatening Cobb syndrome who are currently considered incurable. [ABSTRACT FROM AUTHOR]

Background: Numerous studies have shown that somite development is a necessary stage of myogenesis chondrogenesis and osteogenesis. Our previous study has established a stable presomitic mesoderm progenitor cell line (UiPSM) in vitro. Naturally, we wanted to explore whether UiPSM cell can develop bone and myogenic differentiation. Results: Selective culture conditions yielded PAX3 and PAX7 positive skeletal muscle precursors from UiPSM cells. The skeletal muscle precursors undergo in vitro maturation resulting in myotube formation. MYOD effectively promoted the maturity of the skeletal myocytes in a short time. We found that UiPSM and MYOD mediated UiPSM cell-derived skeletal myocytes were viable after transplantation into the tibialis anterior muscle of MITRG mice, as assessed by bioluminescence imaging and scRNA-seq. Lack of teratoma formation and evidence of long-term myocytes engraftment suggests considerable potential for future therapeutic applications. Moreover, UiPSM cells can differentiate into osteoblast and chondroblast cells in vitro. Conclusions: UiPSM differentiation has potential as a developmental model for musculoskeletal development research and treatment of musculoskeletal disorders. [ABSTRACT FROM AUTHOR]

Reproducible tissue morphology is a fundamental feature of embryonic development. To ensure such robustness during tissue morphogenesis, inherent noise in biological processes must be buffered. While redundant genes, parallel signaling pathways and intricate network topologies are known to reduce noise, over the last few years, mechanical properties of tissues have been shown to play a vital role. Here, taking the example of somite shape changes, I will discuss how tissues are highly plastic in their ability to change shapes leading to increased precision and reproducibility. [ABSTRACT FROM AUTHOR]

Derived from axial structures, Sonic Hedgehog (Shh) is secreted into the paraxial mesoderm, where it plays crucial roles in sclerotome induction and myotome differentiation. Through conditional loss-of-function in quail embryos, we investigate the timing and impact of Shh activity during early formation of sclerotome-derived vertebrae and ribs, and of lateral mesoderm-derived sternum. To this end, Hedgehog interacting protein (Hhip) was electroporated at various times between days 2 and 5. While the vertebral body and rib primordium showed consistent size reduction, rib expansion into the somatopleura remained unaffected, and the sternal bud developed normally. Additionally, we compared these effects with those of locally inhibiting BMP activity. Transfection of Noggin in the lateral mesoderm hindered sternal bud formation. Unlike Hhip, BMP inhibition via Noggin or Smad6 induced myogenic differentiation of the lateral dermomyotome lip, while impeding the growth of the myotome/rib complex into the somatic mesoderm, thus affirming the role of the lateral dermomyotome epithelium in rib guidance. Overall, these findings underscore the continuous requirement for opposing gradients of Shh and BMP activity in the morphogenesis of proximal and distal flank skeletal structures, respectively. Future research should address the implications of these early interactions to the later morphogenesis and function of the musculo-skeletal system and of possible associated malformations. [ABSTRACT FROM AUTHOR]

Proper embryonic development depends on the timely progression of a genetic program. One of the key mechanisms for achieving precise control of developmental timing is to use gene expression oscillations. In this Review, we examine how gene expression oscillations encode temporal information during vertebrate embryonic development by discussing the gene expression oscillations occurring during somitogenesis, neurogenesis, myogenesis and pancreas development. These oscillations play important but varied physiological functions in different contexts. Oscillations control the period of somite formation during somitogenesis, whereas they regulate the proliferation-to-differentiation switch of stem cells and progenitor cells during neurogenesis, myogenesis and pancreas development. We describe the similarities and differences of the expression pattern in space (i.e. whether oscillations are synchronous or asynchronous across neighboring cells) and in time (i.e. different time scales) of mammalian Hes/zebrafish Her genes and their targets in different tissues. We further summarize experimental evidence for the functional role of their oscillations. Finally, we discuss the outstanding questions for future research. [ABSTRACT FROM AUTHOR]

Congenital scoliosis (CS), affecting approximately 0.5 to 1 in 1,000 live births, is commonly caused by congenital vertebral malformations (CVMs) arising from aberrant somitogenesis or somite differentiation. While Wnt/ß- catenin signaling has been implicated in somite development, the function of Wnt/planar cell polarity (Wnt/PCP) signaling in this process remains unclear. Here, we investigated the role of Vangl1 and Vangl2 in vertebral development and found that their deletion causes vertebral anomalies resembling human CVMs. Analysis of exome sequencing data from multiethnic CS patients revealed a number of rare and deleterious variants in VANGL1 and VANGL2, many of which exhibited loss- of- function and dominant- negative effects. Zebrafish models confirmed the pathogenicity of these variants. Furthermore, we found that Vangl1 knock- in (p.R258H) mice exhibited vertebral malformations in a Vangl gene dose- and environment- dependent manner. Our findings highlight critical roles for PCP signaling in vertebral development and predisposition to CVMs in CS patients, providing insights into the molecular mechanisms underlying this disorder. [ABSTRACT FROM AUTHOR]

During vertebrate embryo development, the body is progressively segmented along the anterior-posterior (A-P) axis early in development. The rate of somite formation is controlled by the somitogenesis embryo clock (EC), which was first described as gene expression oscillations of hairy1 (hes4) in the presomitic mesoderm of chick embryos with 15–20 somites. Here, the EC displays the same periodicity as somite formation, 90 min, whereas the posterior-most somites (44–52) only arise every 150 minutes, matched by a corresponding slower pace of the EC. Evidence suggests that the rostral-most somites are formed faster, however, their periodicity and the EC expression dynamics in these early stages are unknown. In this study, we used time-lapse imaging of chicken embryos from primitive streak to somitogenesis stages with high temporal resolution (3-minute intervals). We measured the length between the anterior-most and the last formed somitic clefts in each captured frame and developed a simple algorithm to automatically infer both the length and time of formation of each somite. We found that the occipital somites (up to somite 5) form at an average rate of 75 minutes, while somites 6 onwards are formed approximately every 90 minutes. We also assessed the expression dynamics of hairy1 using half-embryo explants cultured for different periods of time. This showed that EC hairy1 expression is highly dynamic prior to somitogenesis and assumes a clear oscillatory behaviour as the first somites are formed. Importantly, using ex ovo culture and live-imaging techniques, we showed that the hairy1 expression pattern recapitulates with the formation of each new pair of somites, indicating that somite segmentation is coupled with EC oscillations since the onset of somitogenesis. [ABSTRACT FROM AUTHOR]

Background: Noncanonical Wnts are morphogens that can elevate intracellular Ca2+, activate the Ca2+/calmodulin‐dependent protein kinase, CaMKII, and promote cell movements during vertebrate gastrulation. Results: Zebrafish express seven CaMKII genes during embryogenesis; two of these, camk2b1 and camk2g1, are necessary for convergent extension (CE) cell movements. CaMKII morphant phenotypes were observed as early as epiboly. At the 1–3 somite stage, neuroectoderm and paraxial cells remained unconverged in both morphants. Later, somites lacked their stereotypical shape and were wider, more closely spaced, and body gap angles increased. At 24hpf, somite compression and notochord undulation coincided with a shorter and broader body axis. A camk2b1 crispant was generated which phenocopied the camk2b1 morphant. The levels of cell proliferation, apoptosis and paraxial and neuroectodermal markers were unchanged in morphants. Hyperactivation of CaMKII during gastrulation by transient pharmacological intervention (thapsigargin) also caused CE defects. Mosaically expressed dominant‐negative CaMKII recapitulated these phenotypes and showed significant midline bifurcation. Finally, the introduction of CaMKII partially rescued Wnt11 morphant phenotypes. Conclusions: Overall, these data support a model whereby cyclically activated CaMKII encoded from two genes enables cell migration during the process of CE. Key Findings: CaMKII morphants phenocopy Wnt11 CE defects.CaMKII rescues Wnt11 morphants.Hyperactivated CaMKII induces CE defects.Dominant negative CaMKII causes midline bifurcation.CaMKII crispant phenocopies morphant. [ABSTRACT FROM AUTHOR]

The trunk axial skeleton develops from paraxial mesoderm cells. Our recent study demonstrated that conditional knockout of the stem cell factor Sall4 in mice by TCre caused tail truncation and a disorganized axial skeleton posterior to the lumbar level. Based on this phenotype, we hypothesized that, in addition to the previously reported role of Sall4 in neuromesodermal progenitors, Sall4 is involved in the development of the paraxial mesoderm tissue. Analysis of gene expression and SALL4 binding suggests that Sall4 directly or indirectly regulates genes involved in presomitic mesoderm differentiation, somite formation and somite differentiation. Furthermore, ATAC-seq in TCre; Sall4 mutant posterior trunk mesoderm shows that Sall4 knockout reduces chromatin accessibility. We found that Sall4-dependent open chromatin status drives activation and repression of WNT signaling activators and repressors, respectively, to promote WNT signaling. Moreover, footprinting analysis of ATAC-seq data suggests that Sall4-dependent chromatin accessibility facilitates CTCF binding, which contributes to the repression of neural genes within themesoderm. This study unveils multiple mechanisms by which Sall4 regulates paraxial mesoderm development by directing activation of mesodermal genes and repression of neural genes. [ABSTRACT FROM AUTHOR]

Purpose: The present paper describes two new genera and species of the parasitic copepod family Chondracanthidae Milne Edwards, 1840 based on specimens collected from two species of deep-sea fishes at a depth of 212 m off Suruga Bay, Japan. Avatar nishidaigen. et sp. nov. is described from the host fish Chaunax abei Le Danois, 1978 (Chaunacidae). Kokeshioides surugaensisgen. et sp. nov. is described from the host fish Setarches longimanus (Alcock, 1894) (Setarchidae). Methods: Fresh specimens of chondracanthids were collected from the buccal cavity of two species of deep-sea fishes (fish hosts were frozen), Chaunax abei Le Danois, 1978 (Lophiiformes: Chaunacidae) and Setarches longimanus (Alcock, 1894) (Perciformes: Setarchidae), caught at a depth of 212 m in Suruga Bay, Japan (34° 37′48.87″ N, 138° 43′2.958″ E). Both the species are described and illustrated based on ovigerous females. Results: The genus Avatargen. nov. can readily be distinguished from all other chondracanthid genera by the following combination of features: cephalothorax slightly wider than long with anterior pair of large and posterior pair of small lateral lobes, and two pairs of ventro-lateral processes; the very posteriormost part of the first pedigerous somite contributes to the neck; cylindrical trunk with two pairs of blunt proximal fusiform processes; antennule with small knob terminally; antenna bearing distal endopodal segment; labrum protruding ventrally; two pairs of biramous legs each with 2-segmented rami. Kokeshioidesgen. nov. has the following combinations of features that distinguish it from other chondracanthid genera: body flattened, without lateral processes; cephalothorax much wider than long, with paired anterolateral and posterolateral lobes, folded ventrally; the very posteriormost part of the first pedigerous somite contributes to the neck; mandible elongate; legs unique, heavily sclerotized, represented by two pairs of acutely pointed processes. Conclusion: With the addition of two new genera presently reported, the family Chondracanthidae currently includes 52 valid genera. Among the described genera Avatargen. nov. seems to be very primitive, while Kokeshioidesgen. nov. is highly advanced. The deduced evolutionary history of chondracanthid genera is also discussed. [ABSTRACT FROM AUTHOR]

Somitogenesis is a hallmark feature of all vertebrates and some invertebrate species that involves the periodic formation of block-like structures called somites. Somites are transient embryonic segments that eventually establish the entire vertebral column. A highly conserved molecular oscillator called the segmentation clock underlies this periodic event and the pace of this clock regulates the pace of somite formation. Although conserved signaling pathways govern the clock in most vertebrates, the mechanisms underlying the speciesspecific divergence in various clock characteristics remain elusive. For example, the segmentation clock in classical model species such as zebrafish, chick, and mouse embryos tick with a periodicity of ~30, ~90, and ~120 min respectively. This enables them to form the species-specific number of vertebrae during their overall timespan of somitogenesis. Here, we perform a systematic review of the species-specific features of the segmentation clock with a keen focus on mouse embryos. We perform this review using three different perspectives: Notchresponsive clock genes, ligand-receptor dynamics, and synchronization between neighboring oscillators. We further review reports that use non-classical model organisms and in vitro model systems that complement our current understanding of the segmentation clock. Our review highlights the importance of comparative developmental biology to further our understanding of this essential developmental process. [ABSTRACT FROM AUTHOR]

During embryonic development, the timing of events at the cellular level must be coordinated across multiple length scales to ensure the formation of a well-proportioned body plan. This is clear during somitogenesis, where progenitors must be allocated to the axis over time whilst maintaining a progenitor population for continued elaboration of the body plan. However, the relative importance of intrinsic and extrinsic signals in timing progenitor addition at the single-cell level is not yet understood. Heterochronic grafts from older to younger embryos have suggested a level of intrinsic timing whereby later staged cells contribute to more posterior portions of the axis. To determine the precise step at which cells are delayed, we performed single-cell transcriptomic analysis on heterochronic grafts of somite progenitors in the chicken embryo. This revealed a previously undescribed cell state within which heterochronic grafted cells are stalled. The delayed exit of older cells from this state correlates with expression of posterior Hox genes. Using grafting and explant culture, we find that both Hox gene expression and the migratory capabilities of progenitor populations are intrinsically regulated at the population level. However, by grafting varied sizes of tissue, we find that small heterochronic grafts disperse more readily and contribute to more anterior portions of the body axis while still maintaining Hox gene expression. This enhanced dispersion is not replicated in explant culture, suggesting that it is a consequence of interaction between host and donor tissue and thus extrinsic to the donor tissue. Therefore, we demonstrate that the timing of cell dispersion and resulting axis contribution is impacted by a combination of both intrinsic and extrinsic cues. [ABSTRACT FROM AUTHOR]

The digestive system structure in pre-zoea and zoea I larvae of the red king crab Paralithodes camtschaticus has been examined. During this development period, the digestive system consists of an esophagus, a stomach, a midgut (where the hepatopancreas ducts open), and a hindgut. The esophagus begins from the oral slit on the animal's ventral side and extends vertically up to the junction with the cardiac stomach. The latter is followed by the pyloric stomach. At the stages under study, crabs have a cardiac-pyloric valve and a pyloric filter in the stomach already developed. The midgut begins with an expansion in the cephalothorax, enters the pleon, grows narrower there, and extends to somite 3 of pleon. The hepatopancreas is represented by a symmetrical paired gland which occupies almost the entire cephalothorax space and opens with its ducts at the junction of the pyloric stomach with the midgut. The hepatopancreas is divided into the anterior and posterior lobes. At the pre-zoea stage, the anterior lobes are large and filled with yolk. At the zoea I stage, the anterior lobes are smaller relative to the entire hepatopancreas, and the posterior lobes increase and form tubular outgrowths. It has been shown that during the transition from pre-zoea to zoea I, the number of mitochondria in enterocytes increases and a peritrophic membrane forms in the midgut. These changes are probably associated with the transition to independent living and feeding. [ABSTRACT FROM AUTHOR]

Cobb syndrome is a rare genetic disorder characterized by dermatomal pattern, with corresponding muscular, osseous, paraspinal, and/or spinal vascular lesions occurring at the same body somite (metamere). It is also known as spinal arteriovenous metameric syndrome (SAMS) and cutaneous meningospinal angiomatosis. We present a case of a 36 years old male presented to OPD with Complain of progressive weakness of Right upper limb for 5 years. On examination, Patient had large cutaneous port wine stain on the right side of the chest, nape of neck, and along the whole right upper limb in a dermatomal distribution with ulnar claw hand wasting of thenar muscles on right side. MRI cervical spine with contrast showed aggressive vertebral hemangioma involving anterior and posterior arch of C1 vertebra, vertebral body of C2 to C5, right half of vertebral body of C2 and C6 and right pedicle of C2 to C5 vertebra. Abnormal thickened and T2WI /STIR hyperintense skin and subcutaneous tissue involving right half of scalp and right half of neck which showing post contrast enhancement, possibility of subcutaneous hemangioma. Cobb syndrome was diagnosed based on the dermatomal distribution of the cutaneous vascular lesions and the corresponding vertebral, epidural, and paraspinal vascular lesions occurring at the same metamere. Treatment decision is guided by the patient's symptoms and imaging features. [ABSTRACT FROM AUTHOR]

The body colour variation in response to different background colours is associated with camouflage, increasing efficiency against predation. In our study, we investigated the body colour variation of the freshwater shrimp Macrobrachium jelskii in response to different background colours. For this, we collected specimens of M. jelskii in the Thomás Osterne Reservoir, Municipality of Crato, State of Ceará, Brazil. For the experiment, we used six aquariums divided into three treatment groups: white background; black background; red background; with two replicates for each group. Before the experiment, we photographed 30 specimens of M. jelskii in dorsal view. Then, we distributed five shrimps in each aquarium, totalling 10 shrimps per treatment. After 30 days, we obtained new images of the shrimps, under the same settings used before the experiment. We used ImageJ software to obtain the RGB values (Red, Green, Blue) of the dorsal region of the first abdominal somite of the shrimps. Before the experiment, the body pigmentation of M. jelskii was homogeneous, with overlap between the groups. After the experiment, the RGB of M. jelskii varied according to each background colour, differing between the white and black, between the white and red, and not differing between the black and red. Our results show that M. jelskii adjusted its pigmentation to different background colours, evidencing a mechanism that may favour the camouflage of the species in different habitats and provide more chances of survival against visual predators. [ABSTRACT FROM AUTHOR]

Polyploidy is an extended phenomenon in biology. However, its physiological significance and whether it defines specific cell behaviors is not well understood. Here we study its connection to macroautophagy/autophagy, using the larval respiratory system of Drosophila as a model. This system comprises cells with the same function yet with notably different ploidy status, namely diploid progenitors and their polyploid larval counterparts, the latter destined to die during metamorphosis. We identified an association between polyploidy and autophagy and found that higher endoreplication status correlates with elevated autophagy. Finally, we report that tissue histolysis in the trachea during Drosophila metamorphosis is mediated by autophagy, which triggers the apoptosis of polyploid cells. Abbreviations: APF: after pupa formation; Atg: autophagy related; btl: breathless; CycE: Cyclin E; DT: dorsal trunk; fzr: fizzy-related; L3: larval stage 3; PBS: phosphate-buffered saline; RI: RNAi; Tr: tracheal metamere; yki: yorkie. [ABSTRACT FROM AUTHOR]

Somitogenesis is a hallmark feature of all vertebrates and some invertebrate species that involves the periodic formation of block-like structures called somites. Somites are transient embryonic segments that eventually establish the entire vertebral column. A highly conserved molecular oscillator called the segmentation clock underlies this periodic event and the pace of this clock regulates the pace of somite formation. Although conserved signaling pathways govern the clock in most vertebrates, the mechanisms underlying the species-specific divergence in various clock characteristics remain elusive. For example, the segmentation clock in classical model species such as zebrafish, chick, and mouse embryos tick with a periodicity of ∼30, ∼90, and ∼120 min respectively. This enables them to form the species-specific number of vertebrae during their overall timespan of somitogenesis. Here, we perform a systematic review of the species-specific features of the segmentation clock with a keen focus on mouse embryos. We perform this review using three different perspectives: Notch-responsive clock genes, ligand-receptor dynamics, and synchronization between neighboring oscillators. We further review reports that use non-classical model organisms and in vitro model systems that complement our current understanding of the segmentation clock. Our review highlights the importance of comparative developmental biology to further our understanding of this essential developmental process.

Mutations of several genes cause incomplete penetrance and variable expressivity of phenotypes, which are usually attributed to modifier genes or gene-environment interactions. Here, we show stochastic gene expression underlies the variability of somite segmentation defects in embryos mutant for segmentation clock genes her1 or her7. Phenotypic strength is further augmented by low temperature and hypoxia. By performing live imaging of the segmentation clock reporters, we further show that groups of cells with higher oscillation amplitudes successfully form somites while those with lower amplitudes fail to do so. In unfavorable environments, the number of cycles with high amplitude oscillations and the number of successful segmentations proportionally decrease. These results suggest that individual oscillation cycles stochastically fail to pass a threshold amplitude, resulting in segmentation defects in mutants. Our quantitative methodology is adaptable to investigate variable phenotypes of mutant genes in different tissues. Mutations of several genes cause variable phenotypes. Here, the authors show stochastic her1 and her7 gene expression, which is affected by environmental conditions, underlies variability of somite segmentation defects. [ABSTRACT FROM AUTHOR]

Fibroblast growth factor (FGF) signaling is conserved from cnidaria to mammals (Ornitz and Itoh, 2022) and it regulates several critical processes such as differentiation, proliferation, apoptosis, cell migration, and embryonic development. One pivotal process FGF signaling controls is the division of vertebrate paraxial mesoderm into repeated segmented units called somites (i.e., somitogenesis). Somite segmentation occurs periodically and sequentially in a head-to-tail manner, and lays down the plan for compartmentalized development of the vertebrate body axis (Gomez et al., 2008). These somites later give rise to vertebrae, tendons, and skeletal muscle. Somite segments form sequentially from the anterior end of the presomitic mesoderm (PSM). The periodicity of somite segmentation is conferred by the segmentation clock, comprising oscillatory expression of Hairy and enhancer-of-split (Her/Hes) genes in the PSM. The positional information for somite boundaries is instructed by the double phosphorylated extracellular signal-regulated kinase (ppERK) gradient, which is the relevant readout of FGF signaling during somitogenesis (Sawada et al., 2001; Delfini et al., 2005; Simsek and Ozbudak, 2018; Simsek et al., 2023). In this review, we summarize the crosstalk between the segmentation clock and FGF/ppERK gradient and discuss how that leads to periodic somite boundary formation. We also draw attention to outstanding questions regarding the interconnected roles of the segmentation clock and ppERK gradient, and close with suggested future directions of study. [ABSTRACT FROM AUTHOR]

In development, tissue shape changes and gene expression patterns give rise to morphogenesis. Understanding tissue shape changes requires the analysis of mechanical properties of the tissue such as tissue rigidity, cell influx from neighboring tissues, cell shape changes and cell proliferation. Local and global gene expression patterns can be influenced by neighbor exchange and tissue shape changes. Here we review recent studies on the mechanisms for tissue elongation and its influences on dynamic gene expression patterns by focusing on vertebrate somitogenesis. We first introduce mechanical and biochemical properties of the segmenting tissue that drive tissue elongation. Then, we discuss patterning in the presence of cell mixing, scaling of signaling gradients, and dynamic phase waves of rhythmic gene expression under tissue shape changes. We also highlight the importance of theoretical approaches to address the relation between tissue shape changes and patterning. [ABSTRACT FROM AUTHOR]

Shisa represents a type of single-transmembrane adaptor protein containing an N-terminal cysteine-rich domain and a proline-rich C-terminal region. Nine shisa subfamily genes have been proposed in most vertebrates; however, some might be species-specific. The number of shisa genes present in zebrafish remains unclear. This study aimed to investigate the evolutionary relationships among shisa family genes in zebrafish (TU strain) using phylogenetic and syntenic analyses. The function of shisa-2 was preliminarily examined via CRISPR/Cas13d-mediated knockdown. Following identification in zebrafish, 10 shisa family genes, namely shisa-1, 2, 3, 4, 5, 6, 7, 8, 9a, and 9b, were classified into three main clades and six subclades. Their encoding proteins contained a cysteine-rich N-terminal domain and a proline-rich C-terminal region containing different motifs. A specific syntenic block containing atp8a2 and shisa-2 was observed to be conserved across all species. Furthermore, all these genes were expressed during embryogenesis. Shisa-2 was expressed in the presomitic mesoderm, somites, and so on. Shisa-2 was identified as a regulator of the expression of the somite formation marker mesp-ab. Overall, our study provides new insights into the evolution of shisa family genes and the control of shisa-2 over the convergent extension cells of somitic precursors in zebrafish. [ABSTRACT FROM AUTHOR]

Both male and female of Hirodai ohtsukaigen. n. et sp. n. (Crustacea: Copepoda: Cyclopoida) are described based on specimens recovered from the Dollfus' stargazer Uranoscopus guttatus Cuvier, 1829 (Actinopteri: Perciformes: Uranoscopidae) collected from Colachel, Tamil Nadu, south-west coast of India. Based on the unique morphology of the copepod, which is not similar in characteristics to any of the known cyclopoid families, a new family, Uranoscopicolaidae fam. n., has been proposed to accommodate its only known species, Hirodai ohtsukaigen. n. et sp. n. The genus Hirodai gen. n. has the following combination of characters: (1) general cyclopoid body, possessing four pairs of ventrolateral processes corresponding to the first four pedigerous somites; (2) antennule 6-segmented; (3) antenna 2-segmented, the basal segment with one accessory process, armed with two papillae, one basally and the other terminally and having three setae; distal segment modified into a terminally bent hook; (4) genital double somite is 0.7 times as wide as 5th somite, and 2.1 times as wide as long; genital opening ventral; (5) egg sac multiseriate; (6) maxilliped vestigial in adult female; (7) 2-segmented maxilla, the terminal segment with a ventral robust seta at the middle, the rounded apex armed with a bunch of spinules on both surface, except in the inner middle portion; (8) caudal ramus with two long and two small terminal papillae; and (9) legs 1 to 4 biramous with 3-segmented rami possessing setae, leg 5 uniramous and unsegmented, and leg 6 absent. Ecological remarks on Hirodai ohtsukaigen. n. et sp. n. are also provided. [ABSTRACT FROM AUTHOR]

Monstrilloid copepods are protelean endoparasites of benthic invertebrates. Their adult free-living stage is chiefly found in the plankton of shallow coastal systems, estuaries and coral reefs; there are no previous records of monstrilloids from deeper marine habitats including epipelagic or mesopelagic waters. Two new species of the monstrilloid copepod genus Cymbasoma Thompson, 1888 are described based on adult females incidentally captured by an epibenthic sledge operated at a depth range of 118–302 m off north-west Iceland and the Norway Channel. Cymbasoma norvegicum sp. nov. is distinguished by a combination of characters including a long, constricted anal somite, bilobed fifth legs with long inner lobe, antennules with fused segments, and first antennule segment unarmed. Cymbasoma pedroi sp. nov. has a pair of rounded posterolateral protuberances on the genital somite, fused fifth legs lobes, and an anteriorly produced, ornamented forehead. Both species are considered new members of the Cymbasoma rigidum species group, widely distributed in different geographic areas but not previously known from epi-mesopelagic depths. The finding of these new species represents the first discovery of monstrilloids at epi-mesopelagic depths in the Pacific Ocean and it significantly adds to our knowledge of this copepod order, thus highlighting their potentially high yet unstudied diversity in deeper waters. [ABSTRACT FROM AUTHOR]

The Holocene fossil crab genus Arges De Haan, 1833, is here shown to be a senior subjective synonym of the pilumnid crab Typhlocarcinops Rathbun, 1909. Both genera possess the diagnostic character of an extremely wide first male pleonal somite that reaches across the wide thoracic sternum to the base of the coxae of the fourth pair of ambulatory legs. Arges parallelus (De Haan, 1833), is also here regarded as a senior subjective synonym of Typhlocarcinops decrescens Rathbun, 1904, a species known from Japan, China, Hong Kong, the Philippines and Indonesian Papua. [ABSTRACT FROM AUTHOR]

Background: Tramadol hydrochloride or tramadol is an opioid analgesic that acts on the central nervous system. The pregnancy category of tramadol is determined as "C" according to the Food and Drug Administration. There are no adequate and well‐controlled studies in pregnant women. In this study, we aimed to reveal the effects of tramadol on neural tube (midline) closure by analyzing morphologically, histologically and genetically in chick embryos. Methods: Ninety White Leghorn species, fertile and 0‐day‐old specific pathogen‐free eggs (60 ± 5 g) were used in the study. Eggs were divided into a total of six groups (control, sham, and drug groups). Four different doses of tramadol (1, 2.5, 5, and 7.5 mg/egg) were administered subblastodermically at the 28th hour of the incubation. All eggs were opened at the 48th hour of incubation and evaluated. Results: Embryos in the control group according to Hamburger–Hamilton classification were compatible with stages 13 and 14. In the groups treated with tramadol, it was determined that the embryos had neural tube closure defects (such as neck, tail regions) and some embryos showed developmental retardation due to the increase in the drug dose. In the statistical analysis performed, a significant difference was found between the control group and the group receiving the highest dose of tramadol in terms of crown‐rump length and number of somites (p <.05). The brain and reproductive expression gene expression was upregulated in embryos at each of tramadol doses compared to control group. Conclusions: It was determined that tramadol causes neural tube closure defects in embryos depending on the dose. [ABSTRACT FROM AUTHOR]

Elongation of the posterior body axis is distinct from that of the anterior trunk and head. Early drivers of posterior elongation are the neural plate/tube and notochord, later followed by the presomitic mesoderm (PSM), together with the neural tube and notochord. In axolotl, posterior neural plate-derived PSM is pushed posteriorly by convergence and extension of the neural plate. The PSM does not go through the blastopore but turns anteriorly to join the gastrulated paraxial mesoderm. To gain a deeper understanding of the process of axial elongation, a detailed characterization of PSM morphogenesis, which precedes somite formation, and of other tissues (such as the epidermis, lateral plate mesoderm and endoderm) is needed. We investigated these issues with specific tissue labelling techniques (DiI injections and GFP+ tissue grafting) in combination with optical tissue clearing and 3D reconstructions. We defined a spatiotemporal order of PSM morphogenesis that is characterized by changes in collective cell behaviour. The PSM forms a cohesive tissue strand and largely retains this cohesiveness even after epidermis removal. We show that during embryogenesis, the PSM, as well as the lateral plate and endoderm move anteriorly, while the net movement of the axis is posterior. [ABSTRACT FROM AUTHOR]

Abstract Background Human pluripotent stem cell‐derived muscle models show great potential for translational research. Here, we describe developmentally inspired methods for the derivation of skeletal muscle cells and their utility in skeletal muscle tissue engineering with the aim to model skeletal muscle regeneration and dystrophy in vitro. Methods Key steps include the directed differentiation of human pluripotent stem cells to embryonic muscle progenitors followed by primary and secondary foetal myogenesis into three‐dimensional muscle. To simulate Duchenne muscular dystrophy (DMD), a patient‐specific induced pluripotent stem cell line was compared to a CRISPR/Cas9‐edited isogenic control line. Results The established skeletal muscle differentiation protocol robustly and faithfully recapitulates critical steps of embryonic myogenesis in two‐dimensional and three‐dimensional cultures, resulting in functional human skeletal muscle organoids (SMOs) and engineered skeletal muscles (ESMs) with a regeneration‐competent satellite‐like cell pool. Tissue‐engineered muscle exhibits organotypic maturation and function (up to 5.7 ± 0.5 mN tetanic twitch tension at 100 Hz in ESM). Contractile performance could be further enhanced by timed thyroid hormone treatment, increasing the speed of contraction (time to peak contraction) as well as relaxation (time to 50% relaxation) of single twitches from 107 ± 2 to 75 ± 4 ms (P

The metameric pattern of somites is created based on oscillatory expression of clock genes in presomitic mesoderm. However, the mechanism for converting the dynamic oscillation to a static pattern of somites is still unclear. Here, we provide evidence that Ripply/Tbx6 machinery is a key regulator of this conversion. Ripply1/Ripply2-mediated removal of Tbx6 protein defines somite boundary and also leads to cessation of clock gene expression in zebrafish embryos. On the other hand, activation of ripply1/ripply2 mRNA and protein expression is periodically regulated by clock oscillation in conjunction with an Erk signaling gradient. Whereas Ripply protein decreases rapidly in embryos, Ripply-triggered Tbx6 suppression persists long enough to complete somite boundary formation. Mathematical modeling shows that a molecular network based on results of this study can reproduce dynamic-to-static conversion in somitogenesis. Furthermore, simulations with this model suggest that sustained suppression of Tbx6 caused by Ripply is crucial in this conversion. During somitogenesis, the dynamic oscillation of the molecular clock is converted into static spatial patterns. Here, the authors show that persistent suppression of Tbx6 expression triggered by periodical Ripply1/2 gene expression is a key to this conversion. [ABSTRACT FROM AUTHOR]

The cichlid fishes comprise the largest extant vertebrate family and are the quintessential example of rapid "explosive" adaptive radiations and phenotypic diversification. Despite low genetic divergence, East African cichlids harbor a spectacular intra‐ and interspecific morphological diversity, including the hyper‐variable, neural crest (NC)‐derived traits such as coloration and craniofacial skeleton. Although the genetic and developmental basis of these phenotypes has been investigated, understanding of when, and specifically how early, in ontogeny species‐specific differences emerge, remains limited. Since adult traits often originate during embryonic development, the processes of embryogenesis could serve as a potential source of species‐specific variation. Consequently, we designed a staging system by which we compare the features of embryogenesis between three Malawi cichlid species—Astatotilapia calliptera, Tropheops sp. 'mauve' and Rhamphochromis sp. "chilingali"—representing a wide spectrum of variation in pigmentation and craniofacial morphologies. Our results showed fundamental differences in multiple aspects of embryogenesis that could underlie interspecific divergence in adult adaptive traits. First, we identified variation in the somite number and signatures of temporal variation, or heterochrony, in the rates of somite formation. The heterochrony was also evident within and between species throughout ontogeny, up to the juvenile stages. Finally, the identified interspecific differences in the development of pigmentation and craniofacial cartilages, present at the earliest stages of their overt formation, provide compelling evidence that the species‐specific trajectories begin divergence during early embryogenesis, potentially during somitogenesis and NC development. Altogether, our results expand our understanding of fundamental cichlid biology and provide new insights into the developmental origins of vertebrate morphological diversity. Research highlights: This work details the early development of three divergent Lake Malawi cichlids. A comparative analysis reveals anatomical and timing differences during embryogenesis and indicates divergence of species' morphologies before their overt formation. [ABSTRACT FROM AUTHOR]

Somites are transient structures derived from the pre‐somitic mesoderm (PSM), involving mesenchyme‐to‐epithelial transition (MET) where the cells change their shape and polarize. Using Scanning electron microscopy (SEM), immunocytochemistry and confocal microscopy, we study the progression of these events along the tail‐to‐head axis of the embryo, which mirrors the progression of somitogenesis (younger cells located more caudally). SEM revealed that PSM epithelialization is a gradual process, which begins much earlier than previously thought, starting with the dorsalmost cells, then the medial ones, and then, simultaneously, the ventral and lateral cells, before a somite fully separates from the PSM. The core (internal) cells of the PSM and somites never epithelialize, which suggests that the core cells could be 'trapped' within the somitocoele after cells at the surfaces of the PSM undergo MET. Three‐dimensional imaging of the distribution of the cell polarity markers PKCζ, PAR3, ZO1, the Golgi marker GM130 and the apical marker N‐cadherin reveal that the pattern of polarization is distinctive for each marker and for each surface of the PSM, but the order of these events is not the same as the progression of cell elongation. These observations challenge some assumptions underlying existing models of somite formation. [ABSTRACT FROM AUTHOR]

We evaluated the elasticity of live tissues of zebrafish embryos using label‐free optical elastography. We employed a pair of custom‐built elastic microcantilevers to gently compress a zebrafish embryo and used optical‐tracking analysis to obtain the induced internal strain. We then built a finite element method (FEM) model and matched the strain with the optical analysis. The elastic moduli were found by minimizing the root‐mean‐square errors between the optical and FEM analyses. We evaluated the average elastic moduli of a developing somite, the overlying ectoderm, and the underlying yolk of seven zebrafish embryos during the early somitogenesis stages. The estimation results showed that the average elastic modulus of the somite increased from 150 to 700 Pa between 4‐ and 8‐somite stages, while those of the ectoderm and the yolk stayed between 100 and 200 Pa, and they did not show significant changes. The result matches well with the developmental process of somitogenesis reported in the literature. This is among the first attempts to quantify spatially‐resolved elasticity of embryonic tissues from optical elastography. [ABSTRACT FROM AUTHOR]

Introduction: practical anatomical studies using cadavers of large animals, such as equines, pose difficulties due to their volume, weight and the conditions required for handling and storage of certain groups of organs. This paper describes a way to overcome these problems by using cryodehydration for the preparation of a set of organs. This description includes the metamere formed by the abdominal segment of the oesophagus, stomach, duodenum, pancreas, liver, spleen, adrenal glands and kidneys, as well as the vascular segment associated with these organs. It also describes the preparation of the organs in the thoracic cavity. Material and Methods: after fixation, the abdominal cavity is opened to expose a wide caudal view of the organs mentioned above. A layer of polyurethane foam is applied to this surface to form a mold. When dry, this mold is removed. The organs are dissected, removed as a unit and immediately placed back on this mold to preserve their morphology and positions relative to each other. The side that was exposed undergoes cryodehydration. When completed, this surface is molded again and cryodehydration is repeated, now to the newly exposed side. For the organs in the thoracic cavity, the diaphragm is removed and the first polyurethane mold is prepared on the diaphragmatic surface of the lungs, and the second, on their dorsal edge, alternating the cryodehydration techniques at all times. Dissections to expose specific structures may be conducted during all the procedure and, at the end of this process, each organ may be painted in a characteristic colour. Results: these units last longer and have the advantage of being lighter and easier to handle and store. Conclusion: as teaching aids, the thoracic set may be re-connected to the abdominal set, which facilitates learning, preserving the original topography and morphology. These same sets are also excellent material for museums. [ABSTRACT FROM AUTHOR]

Although integrins are known to be mechanosensitive and to possess many subtypes that have distinct physiological roles, single molecule studies of force exertion have thus far been limited to RGD-binding integrins. Here, we show that integrin α4β1 and RGD-binding integrins (αVβ1 and α5β1) require markedly different tension thresholds to support cell spreading. Furthermore, actin assembled downstream of α4β1 forms cross-linked networks in circularly spread cells, is in rapid retrograde flow, and exerts low forces from actin polymerization. In contrast, actin assembled downstream of αVβ1 forms stress fibers linking focal adhesions in elongated cells, is in slow retrograde flow, and matures to exert high forces (>54-pN) via myosin II. Conformational activation of both integrins occurs below 12-pN, suggesting that post-activation subtype-specific cytoskeletal remodeling imposes the higher threshold for spreading on RGD substrates. Multiple layers of single integrin mechanics for activation, mechanotransduction and cytoskeleton remodeling revealed here may underlie subtype-dependence of diverse processes such as somite formation and durotaxis. Integrins come in subtypes that bind distinct ligands. This work reveals and quantifies subtype-specific mechanical force transmission and assembly of cytoskeleton architectures. [ABSTRACT FROM AUTHOR]

Bioelectricity is defined as endogenous electrical signaling mediated by the dynamic distribution of charged molecules. Recently, increasing evidence has revealed that cellular bioelectric signaling is critical for regulating embryonic development, regeneration, and congenital diseases. However, systematic real-time in vivo dynamic electrical activity monitoring of whole organisms has been limited, mainly due to the lack of a suitable model system and voltage measurement tools for in vivo biology. Here, we addressed this gap by utilizing a genetically stable zebrafish line, Tg (ubiquitin: ASAP1), and ASAP1 (Accelerated sensor of action potentials 1), a genetically encoded voltage indicator (GEVI). With light-sheet microscopy, we systematically investigated cell membrane potential (Vm) signals during different embryonic stages. We found cells of zebrafish embryos showed local membrane hyperpolarization at the cleavage furrows during the cleavage period of embryogenesis. This signal appeared before cytokinesis and fluctuated as it progressed. In contrast, whole-cell transient hyperpolarization was observed during the blastula and gastrula stages. These signals were generally limited to the superficial blastomere, but they could be detected within the deeper cells during the gastrulation period. Moreover, the zebrafish embryos exhibit tissue-level cell Vm signals during the segmentation period. Middle-aged somites had strong and dynamic Vm fluctuations starting at about the 12-somite stage. These embryonic stage-specific characteristic cellular bioelectric signals suggest that they might play a diverse role in zebrafish embryogenesis that could underlie human congenital diseases. [ABSTRACT FROM AUTHOR]

We describe and diagnose a new species of Acanthephyra (Acanthephyridae: Caridea: Decapoda) and provide an amended key to all species of the genus. In order to assess the taxonomic position of the new species, we examined and coded 55 characters in available specimens of Acanthephyra and ran morphological phylogenetic analyses. We also used a COI gene marker for molecular analyses of the new species and other available specimens of Acanthephyra. Both analyses retrieved an unexpected grouping of species that contradicted a recently accepted morphological grouping. We tested a new, quantitative, set of characters and found that three of them may explain the molecular grouping of the genus. These characters are linked to: (1) proportions of the 6th pleonic somite, (2) length of the same against carapace length, and (3) length of the same against length of two preceding somites. We suggest that these characters mirror evolutionary traits in Acanthephyra and discuss their possible adaptive sense. [ABSTRACT FROM AUTHOR]

Avermectin is a highly effective insecticide that has been widely used in agriculture since the 1990s. In recent years, the safety of avermectin for non-target organisms has received much attention. The vasculature is important organs in the body and participate in the composition of other organs. However, studies on the vascular safety of avermectin are lacking. The vasculature of zebrafish larvae is characterized by ease of observation and it is a commonly used model for vascular studies. Therefore, zebrafish larvae were used to explore the potential risk of avermectin on the vasculature. The results showed that avermectin induced vascular damage throughout the body of zebrafish larvae, including the head, eyes, intestine, somite, tail and other vasculature. The main forms of damage are reduction in vascular diameter, vascular area and vascular abundance. Meanwhile, avermectin induced a decrease in the number of endothelial cells and apoptosis within the vasculature. In addition, vascular damage may be related to impairment of mitochondrial function and mitochondria-mediated apoptosis. Finally, exploration of the molecular mechanisms revealed abnormal alterations in the expression of genes related to the VEGF/Notch signaling pathway. Therefore, the VEGF/Notch signaling pathway may be an important mechanism for avermectin-induced vascular damage in zebrafish larvae. This study demonstrates the vascular toxicity of avermectin in zebrafish larvae and reveals the possible molecular mechanism, which would hopefully draw more attention to the safety of avermectin in non-target organisms. [Display omitted] • Avermectin induced systemic vascular damage in zebrafish larvae. • Avermectin induced endothelial cells damage in zebrafish larvae. • Vascular damage was associated with apoptosis and mitochondrial damage. • Vascular damage was regulated by the VEGF/Notch signaling pathway. [ABSTRACT FROM AUTHOR]

Living systems exhibit an unmatched complexity, due to countless, entangled interactions across scales. Here, we aim to understand a complex system, that is, segmentation timing in mouse embryos, without a reference to these detailed interactions. To this end, we develop a coarse-grained approach, in which theory guides the experimental identification of the segmentation clock entrainment responses. We demonstrate period- and phase-locking of the segmentation clock across a wide range of entrainment parameters, including higher-order coupling. These quantifications allow to derive the phase response curve (PRC) and Arnold tongues of the segmentation clock, revealing its essential dynamical properties. Our results indicate that the somite segmentation clock has characteristics reminiscent of a highly non-linear oscillator close to an infinite period bifurcation and suggests the presence of long-term feedbacks. Combined, this coarse-grained theoretical-experimental approach reveals how we can derive simple, essential features of a highly complex dynamical system, providing precise experimental control over the pace and rhythm of the somite segmentation clock. [ABSTRACT FROM AUTHOR]

Hematopoietic stem and progenitor cells emerge from the aorta and migrate to the caudal hematopoietic tissue (CHT) of zebrafish larvae, the hematopoietic equivalent of the mammalian fetal liver, for their proliferation and differentiation. We previously reported that somitederived stromal cells were a key component of the CHT niche. Here, we found that the cell adhesion protein Protocadherin 18a (Pcdh18a) is expressed in the stromal cell progenitors (SCPs) emigrating from somites toward the future CHT. Deletion of most of the Pcdh18a intracellular domain caused a decrease in the number of SCPs, the directionality of their migration, and the cell-contact mediated repulsion that normally occurs between migrating SCPs. These defects were followed by abnormal morphogenesis of the venous plexus that forms the CHT framework, and the inability of the CHT to function as a niche for hematopoietic stem and progenitor cells. Finally, we found that the extracellular domain of Pcdh18a mediates trans heterophilic adhesion of stromal cells to endothelial cells in vivo and thereby the reticular versus perivascular fate of SCPs. Thus, Pcdh18a expression in SCPs is essential for the proper development of the hematopoietic niche. [ABSTRACT FROM AUTHOR]

Objectives: Mesoderm, derived from a new layer between epiblast and hypoblast during gastrulation, can differentiate into various tissues, including muscles, bones, kidneys, blood, and the urogenital system. However, systematic elucidation of mesoderm characteristics and specific markers remains a challenge. This study aims to screen and identify candidate genes important for mesoderm development. Materials and Methods: Cells originating from the three germ layers were obtained by laser capture microdissection, followed by microcellular RNA sequencing. Mesoderm‐specific differentially expressed genes (DEGs) were identified by using a combination of three bioinformatics pipelines. Candidate mesoderm‐specific genes expression were verified by real‐time quantitative polymerase chain reaction analysis and immunohistochemistry. Functional analyses were verified by ESCs‐EBs differentiation and colony‐forming units (CFUs) assay. Results: A total of 1962 differentially expressed mesoderm genes were found, out of which 50 were candidate mesoderm‐specific DEGs which mainly participate in somite development, formation of the primary germ layer, segmentation, mesoderm development, and pattern specification process by GO analysis. Representative genes Cdh2, Cdh11, Jag1, T, Fn‐1, and Pcdh7 were specifically expressed in mesoderm among the three germ layers. Pcdh7 as membrane‐associated gene has hematopoietic‐relevant functions identified by ESCs‐EBs differentiation and CFUs assay. Conclusions: Spatial transcriptomic profiling with multi‐method analysis and confirmation revealed candidate mesoderm progenitors. This approach appears to be efficient and reliable and can be extended to screen and validate candidate genes in various cellular systems. [ABSTRACT FROM AUTHOR]

The copepod Nemesissanthadevii sp. nov. (Siphonostomatoida: Eudactylinidae), which is parasitizing the gill filaments of the Coral catshark Atelomycterus marmoratus (Anonymous (Bennett), 1830) off Kota Kinabalu waters, Malaysia, is described and illustrated in this article. The new species Nemesis santhadevii prominently differs from its congeners in the following features: (1) the cephalothorax sub-circular is 1.3 times as wide as long and overlapping the second pedigerous somite; (2) the fifth somite is 0.4 times the width of the fourth; (3) the genital double somite is slightly narrower than the fifth; (4) the lowest cephalothoracic shield's body length (0.20:1) proportion; (5) the caudal rami is ovate, it has two large and three small setae; (6) and the second somite has antenna with a patch of 34–38 spinules. It is the first record of parasitic eudactilinid copepod from Sabah, East Malaysia. A checklist of global valid species of Nemesis Risso, 1826, is provided. [ABSTRACT FROM AUTHOR]

The fascinating world of leeches (Annelida: Hirudinea) has more than 700 species. On the other hand, India possesses 82 species. There is a record of only one terrestrial leech species Haemadipsa satyanarayanai Mandal et al., 2020. The authors had the opportunity to establish a new leech for science Haemadipsa zeylanica dhritii n. ssp. from Nagaland, India due to somite VII 3 annulate and VIII 4 annulate; eyes 3 and 4 are on contiguous annuli so it is a subspecies of Haemadadipsa zeylanica due to presence of single pair of chain stripes on the mid-dorsal region; two-thirds of the posterior dorsal part of the body bears 4 large black spots; male pore between segments 32-33; female pore between segments 37-38 and annuli 102 which are not similar with rest of the subspecies of Haemadipsa zeylanica. [ABSTRACT FROM AUTHOR]

The genus Metridia Boeck, 1864 is widely distributed in the global ocean, but only 9 species of Metridia have been recorded from the China seas. Here we report the rare copepod Metridia bicornuta Davis, 1949 for the first time for the South China Sea. One specimen was collected from the southern basin of the South China Sea (13°0.21′N 113°0.21′E) at depths of 500-800 m. Females of this species differ from those of congeneric species by the following features: (i) Prosome 1.5 times as long as urosome; (ii) forehead with lateral points projecting on both sides; (iii) genital somite 1.8 times as long as the second somite; (iv) distal segment of fifth swimming leg (P5) with a small outer marginal spine and 3 subequal robust terminal setae. This finding expands the known global distribution of M. bicornuta , and increases the number of copepod species in the China seas. Résumé: Le genre Metridia Boeck, 1864 est largement réparti dans l'océan mondial, mais seulement 9 espèces de Metridia ont été rapportées des mers de Chine. Nous signalons ici la présence du copépode rare Metridia bicornuta Davis, 1949 en mer de Chine méridionale pour la première fois. Un spécimen a été collecté du bassin Sud de la Mer de Chine méridionale (13°0.21′N 113°0.21′E) à la profondeur de 500-800 m. Les femelles de cette espèce diffèrent de celles des autres espèces du genre par les caractères suivants : (i) Prosome 1,5 fois aussi long que l'urosome ; (ii) partie frontale avec des pointes latérales faisant saillie des deux côtés ; (iii) somite génital 1,8 fois aussi long que le deuxième somite ; (iv) segment distal de la cinquième patte natatoire (P5) avec une petite épine marginale externe et 3 soies terminales robustes subégales. Cette trouvaille étend la répartition mondiale connue de M. bicornuta , et augmente le nombre des espèces de copépodes des mers de Chine. [ABSTRACT FROM AUTHOR]

The river lamprey (L. fluviatilis) is a representative of the ancestral jawless vertebrate group. We performed a histological analysis of trunk muscle fiber differentiation during embryonal, larval, and adult musculature development in this previously unstudied species. Investigation using light, transmission electron (TEM), and confocal microscopy revealed that embryonal and larval musculature differs from adult muscle mass. Here, we present the morphological analysis of L. fluviatilis myogenesis, from unsegmented mesoderm through somite formation, and their differentiation into multinucleated muscle lamellae. Our analysis also revealed the presence of myogenic factors LfPax3/7 and Myf5 in the dermomyotome. In the next stages of development, two types of muscle lamellae can be distinguished: central surrounded by parietal. This pattern is maintained until adulthood, when parietal muscle fibers surround the central muscles on both sides. The two types show different morphological characteristics. Although lampreys are phylogenetically distant from jawed vertebrates, somite morphology, especially dermomyotome function, shows similarity. Here we demonstrate that somitogenesis is a conservative process among all vertebrates. We conclude that river lamprey myogenesis shares features with both ancestral and higher vertebrates. [ABSTRACT FROM AUTHOR]

The article discusses the process of segmentation in the early embryo, which involves the formation of repeated epithelial blocks called somites. The authors focus on the mechanism underlying the slowing oscillations of the segmentation clock, a gene regulatory network that coordinates somite formation. Through in vitro and in vivo experiments, they propose that the slowing of clock oscillations is a cell-autonomous property and suggest a model of segmentation governed by an intrinsic timer that can be influenced by extrinsic factors. The authors also explore the relationship between clock dynamics and the onset of segmental differentiation, providing insights into the spatial dynamics of oscillations along the presomitic mesoderm. They propose that the intrinsic timer could provide positional information for somite formation. The article highlights the need for further research to understand how the intrinsic timer model relates to existing models of segmentation. [Extracted from the article]

In mammalian development, oscillatory activation of Notch signaling is required for segmentation clock function during somitogenesis. Notch activity oscillations are synchronized between neighboring cells in the presomitic mesoderm (PSM) and have a period that matches the rate of somite formation. Normal clock function requires cyclic expression of the Lunatic fringe (LFNG) glycosyltransferase, as well as expression of the inhibitory Notch ligand Delta-like 3 (DLL3). How these factors coordinate Notch activation in the clock is not well understood. Recent evidence suggests that LFNG can act in a signal-sending cell to influence Notch activity in the clock, raising the possibility that in this context, glycosylation of Notch pathway proteins by LFNG may affect ligand activity. Here we dissect the genetic interactions of Lfng and Dll3 specifically in the segmentation clock and observe distinctions in the skeletal and clock phenotypes of mutant embryos showing that paradoxically, loss of Dll3 is associated with strong reductions in Notch activity in the caudal PSM. The patterns of Notch activity in the PSM suggest that the loss of Dll3 is epistatic to the loss of Lfng in the segmentation clock, and we present direct evidence for the modification of several DLL1 and DLL3 EGF-repeats by LFNG. We further demonstrate that DLL3 expression in cells co-expressing DLL1 and NOTCH1 can potentiate a cell's signal-sending activity and that this effect is modulated by LFNG, suggesting a mechanism for coordinated regulation of oscillatory Notch activation in the clock by glycosylation and cis -inhibition. [Display omitted] • Axial skeletal phenotypes after loss of DLL3 or LFNG are similar except in the sacrum. • Loss of DLL3 in the mouse PSM counterintuitively leads to a reduction in Notch signaling. • Both EGF repeats 2 and 5 of DLL3 are efficiently modified by LFNG. • When cells co-express NOTCH1 and DLL1, induction of DLL3 expression potentiates signal-sending activities. • LFNG blocks DLL3's effect on signal-sending activity, providing cyclic regulation of cis -interactions during somitogenesis. [ABSTRACT FROM AUTHOR]

Fibronectin is essential for somite formation in the vertebrate embryo. Fibronectin matrix assembly starts as cells emerge from the primitive streak and ingress in the unsegmented presomitic mesoderm (PSM). PSM cells undergo cyclic waves of segmentation clock gene expression, followed by Notch-dependent upregulation of meso1 in the rostral PSM which induces somite cleft formation. However, the relevance of the fibronectin matrix for these molecular processes remains unknown. Here, we assessed the role of the PSM fibronectin matrix in the spatio-temporal regulation of chick embryo somitogenesis by perturbing (1) extracellular fibronectin matrix assembly, (2) integrin–fibronectin binding, (3) Rho-associated protein kinase (ROCK) activity and (4) non-muscle myosin II (NM II) function. We found that integrin–fibronectin engagement and NM II activity are required for cell polarization in the nascent somite. All treatments resulted in defective somitic clefts and significantly perturbed meso1 and segmentation clock gene expression in the PSM. Importantly, inhibition of actomyosin-mediated contractility increased the period of hairy1/hes4 oscillations from 90 to 120 min. Together, our work strongly suggests that the fibronectin–integrin–ROCK–NM II axis regulates segmentation clock dynamics and dictates the spatio-temporal localization of somitic clefts. [ABSTRACT FROM AUTHOR]

The fibroblast growth factor (FGF) signalling pathway plays various roles during vertebrate embryogenesis, from mesoderm formation to brain patterning. This diversity of functions relies on the fact that vertebrates possess the largest FGF gene complement among metazoans. In the cephalochordate amphioxus, which belongs to the chordate clade together with vertebrates and tunicates, we have previously shown that the main role of FGF during early development is the control of rostral somite formation. Inhibition of this signalling pathway induces the loss of these structures, resulting in an embryo without anterior segmented mesoderm, as in the vertebrate head. Here, by combining several approaches, we show that the anterior presumptive paraxial mesoderm cells acquire an anterior axial fate when FGF signal is inhibited and that they are later incorporated in the anterior notochord. Our analysis of notochord formation in wild type and in embryos in which FGF signalling is inhibited also reveals that amphioxus anterior notochord presents transient prechordal plate features. Altogether, our results give insight into how changes in FGF functions during chordate evolution might have participated to the emergence of the complex vertebrate head. [ABSTRACT FROM AUTHOR]

T is the founding member of the T-box family of transcription factors; family members are critical for cell fate decisions and tissue morphogenesis throughout the animal kingdom. T is expressed in the primitive streak and notochord with mouse mutant studies revealing its critical role in mesoderm formation in the primitive streak and notochord integrity. We previously demonstrated that misexpression of Tbx6 in the paraxial and lateral plate mesoderm results in embryos resembling Tbx15 and Tbx18 nulls. This, together with results from in vitro transcriptional assays, suggested that ectopically expressed Tbx6 can compete with endogenously expressed Tbx15 and Tbx18 at the binding sites of target genes. Since T-box proteins share a similar DNA binding domain, we hypothesized that misexpressing T in the paraxial and lateral plate mesoderm would also interfere with the endogenous Tbx15 and Tbx18, causing embryonic phenotypes resembling those seen upon Tbx6 expression in the somites and limbs. Interestingly, ectopic T expression led to distinct embryonic phenotypes, specifically, reduced-sized somites in embryos expressing the highest levels of T , which ultimately affects axis length and neural tube morphogenesis. We further demonstrate that ectopic T leads to ectopic expression of Tbx6 and Mesogenin 1 , known targets of T. These results suggests that ectopic T expression contributes to the phenotype by activating its own targets rather than via a straight competition with endogenous T-box factors. [Display omitted] • Generation of 3-component transgenic mouse system to inducibly express T under Cre recombinase and Doxycycline control. • Ectopic T expression in the mouse paraxial mesoderm affects somite maturation. • Somites can differentiate into dermomyotome and sclerotome but these are often irregular. • Secondary effects include undulating neural tube, compaction of the axis, and fusion of fore- and hindlimb buds. • Ectopic expression of a subset of T target genes potentially contributes to the phenotype. [ABSTRACT FROM AUTHOR]