Search

Larvacean tunicates feature a spectacular innovation not seen in other animals - the trunk oikoplastic epithelium (OE). This epithelium produces a house, a large and complex extracellular structure used for filtering and concentrating food particles. Previously we identified several homeobox transcription factor genes expressed during early OE patterning. Among these are two Pax3/7 copies that we named pax37A and pax37B. The vertebrate homologs, PAX3 and PAX7 are involved in developmental processes related to neural crest and muscles. In the ascidian tunicate Ciona intestinalis , Pax3/7 plays a role in the development of cells deriving from the neural plate border, including trunk epidermal sensory neurons and tail nerve cord neurons, as well as in the neural tube closure. Here we have investigated the roles of Oikopleura dioica pax37A and pax37B in the development of the OE, by using CRISPR-Cas9 mutant lines and analyzing scRNA-seq data from wild-type animals. We found that pax37B but not pax37A is essential for the differentiation of cell fields that produce the food concentrating filter of the house: the anterior Fol, giant Fol and Nasse cells. Trajectory analysis supported a neuroepithelial-like or a preplacodal ectoderm transcriptional signature in these cells. We propose that the highly specialized secretory epithelial cells of the Fol region either maintained or evolved neuroepithelial features. This is supported by a fragmented gene regulatory network involved in their development that also operates in ascidian epidermal neurons. [Display omitted] • pax37B controls the development of the Fol region of the oikoplastic epithelium. • The pax37B TF network is similar to that of ascidian trunk epidermal neurons. • The pax37B + cells are secretory cells with a neuroepithelial-like origin. [ABSTRACT FROM AUTHOR]

Gastrulation is a critical event whose molecular mechanisms are thought to be conserved among vertebrates. However, the morphological movement during gastrulation appears to be divergent across species, making it difficult to discuss the evolution of the process. Previously, we proposed a novel amphibian gastrulation model, the "subduction and zippering (S&Z) model". In this model, the organizer and the prospective neuroectoderm are originally localized in the blastula's blastocoel roof, and these embryonic regions move downward to make physical contact of their inner surfaces with each other at the dorsal marginal zone. The developmental stage when contact between the head organizer and the anterior-most neuroectoderm is established is called "anterior contact establishment (ACE)." After ACE, the A-P body axis elongates posteriorly. According to this model, the body axis is derived from limited regions of the dorsal marginal zone at ACE. To investigate this possibility, we conducted stepwise tissue deletions using Xenopus laevis embryos and revealed that the dorsal one-third of the marginal zone had the ability to form the complete dorsal structure by itself. Furthermore, a blastocoel roof explant of the blastula, which should contain the organizer and the prospective neuroectoderm in the S&Z model, autonomously underwent gastrulation and formed the complete dorsal structure. Collectively, these results are consistent with the S&Z gastrulation model and identify the embryonic region sufficient for construction of the complete dorsal structure. Finally, by comparing amphibian gastrulation to gastrulation of protochordates and amniotes, we discuss the gastrulation movement evolutionarily conserved among chordates. [ABSTRACT FROM AUTHOR]

Due to similarities in iodine concentrations and peroxidase activities, the thyroid in vertebrates is considered to originate from the endostyle of invertebrate chordates even though it is a glandular (mucus-producing) organ for aquatic suspension feeding. Among chordates with an endostyle, urochordates are useful evolutionary research models for the study of vertebrate traits. The ascidian Ciona intestinalis forms an endostyle with specific components of glandular- and thyroid-related elements, and molecular markers have been identified for these components. Since we previously examined a simple endostyle in the larvacean Oikopleura dioica, the expression of the thyroid-related transcription factor genes, Ciona Nkx2-1 and FoxE, was perturbed by TALEN-mediated gene knockout in the present study to elucidate the shared and/or divergent features of a complex ascidian endostyle. The knockout of Ciona Nkx2-1 and FoxE exerted different effects on the morphology of the developing endostyle. The knockout of Nkx2-1 eliminated the expression of both glandular and thyroidal differentiation marker genes, e.g., vWFL1, vWFL2, CiEnds1, TPO, and Duox, while that of FoxE eliminated the expression of the differentiation marker genes, TPO and CiEnds1. The supporting element-related expression of Pax2/5/8a, Pax2/5/8b, FoxQ1, and β-tubulin persisted in the hypoplastic endostyles of Nkx2-1- and FoxE-knockout juveniles. Although the gene regulation of ascidian-specific CiEnds1 remains unclear, these results provide insights into the evolution of the vertebrate thyroid as well as the urochordate endostyle. [ABSTRACT FROM AUTHOR]

The endostyle is a ventral pharyngeal organ used for internal filter feeding of basal chordates and is considered homologous to the follicular thyroid of vertebrates. It contains mucus-producing (glandular) and thyroid-equivalent regions organized along the dorsoventral (DV) axis. Although thyroid-related genes (Nkx2-1 , FoxE , and thyroid peroxidase (TPO)) are known to be expressed in the endostyle, their roles in establishing regionalization within the organ have not been demonstrated. We report that Nkx2-1 and FoxE are essential for establishing DV axial identity in the endostyle of Oikopleura dioica. Genome and expression analyses showed von Willebrand factor-like (vWFL) and TPO/dual oxidase (Duox)/Nkx2-1/FoxE as orthologs of glandular and thyroid-related genes, respectively. Knockdown experiments showed that Nkx2-1 is necessary for the expression of glandular and thyroid-related genes, whereas FoxE is necessary only for thyroid-related genes. Moreover, Nkx2-1 expression is necessary for FoxE expression in larvae during organogenesis. The results demonstrate the essential roles of Nkx2-1 and FoxE in establishing regionalization in the endostyle, including (1) the Nkx2-1-dependent glandular region, and (2) the Nkx2-1/FoxE-dependent thyroid-equivalent region. DV axial regionalization may be responsible for organizing glandular and thyroid-equivalent traits of the pharynx along the DV axis. [Display omitted] • Nkx2-1 and FoxE establish regional identity of the endostyle in chordates. •These TFs establish glandular and thyroid-related traits of the larvacean O. dioica. • vWFL and TPO/Duox marks differentiations of glandular and thyroid-equivalent regions. •This is the first study to demonstrate functions of Nkx2-1/FoxE in organizing the endostyle. [ABSTRACT FROM AUTHOR]

c-Jun N-terminal kinase (JNK) is a multi-functional protein involved in a diverse array of context-dependent processes, including apoptosis, cell cycle regulation, adhesion, and differentiation. It is integral to several signalling cascades, notably downstream of non-canonical Wnt and mitogen activated protein kinase (MAPK) signalling pathways. As such, it is a key regulator of cellular behaviour and patterning during embryonic development across the animal kingdom. The cephalochordate amphioxus is an invertebrate chordate model system straddling the invertebrate to vertebrate transition and is thus ideally suited for comparative studies of morphogenesis. However, next to nothing is known about JNK signalling or cellular processes in this lineage. Pharmacological inhibition of JNK signalling using SP600125 during embryonic development arrests gastrula invagination and causes convergence extension-like defects in axial elongation, particularly of the notochord. Pharynx formation and anterior oral mesoderm derivatives like the preoral pit are also affected. This is accompanied by tissue-specific transcriptional changes, including reduced expression of six3/6 and wnt2 in the notochord, and ectopic wnt11 in neurulating embryos treated at late gastrula stages. Cellular delamination results in accumulation of cells in the gut cavity and a dorsal fin-like protrusion, followed by secondary Caspase-3-mediated apoptosis of polarity-deficient cells, a phenotype only partly rescued by co-culture with the pan-Caspase inhibitor Z-VAD-fmk. Ectopic activation of extracellular signal regulated kinase (ERK) signalling in the neighbours of extruded notochord and neural cells, possibly due to altered adhesive and tensile properties, as well as defects in cellular migration, may explain some phenotypes caused by JNK inhibition. Overall, this study supports conserved functions of JNK signalling in mediating the complex balance between cell survival, apoptosis, differentiation, and cell fate specification during cephalochordate morphogenesis.

During animal ontogenesis, body axis patterning is finely regulated by complex interactions among several signaling pathways. Nitric oxide (NO) and retinoic acid (RA) are potent morphogens that play a pivotal role in vertebrate development. Their involvement in axial patterning of the head and pharynx shows conserved features in the chordate phylum. Indeed, in the cephalochordate amphioxus, NO and RA are crucial for the correct development of pharyngeal structures. Here, we demonstrate the functional cooperation between NO and RA that occurs during amphioxus embryogenesis. During neurulation, NO modulates RA production through the transcriptional regulation of Aldh1a.2 that irreversibly converts retinaldehyde into RA. On the other hand, RA directly or indirectly regulates the transcription of Nos genes. This reciprocal regulation of NO and RA pathways is essential for the normal pharyngeal development in amphioxus and it could be conserved in vertebrates.

The Earth's oceans brim with an incredible diversity of microscopic lifeforms, including motile planktonic larvae, whose survival critically depends on effective dispersal in the water column and subsequent exploration of the seafloor to identify a suitable settlement site. How their nervous systems mediate sensing of diverse multimodal cues remains enigmatic. Here, we uncover that the tunicate Ciona intestinalis larvae employ ectodermal sensory cells to sense various mechanical and chemical cues. Combining whole-brain imaging and chemogenetics, we demonstrate that stimuli encoded at the periphery are sufficient to drive global brain-state changes to promote or impede both larval attachment and metamorphosis behaviors. The ability of C. intestinalis larvae to leverage polymodal sensory perception to support information coding and chemotactile behaviors may explain how marine larvae make complex decisions despite streamlined nervous systems. • Long- and short-range chemical cues influence larval attachment and metamorphosis • Ciona larvae use polymodal sensory cells to sense mechanical and chemical cues • Individual sensory neurons can encode stimulus-specific information • Brain dynamics act as a framework for stimulus-driven behavioral action choice Ciona is a marine chordate with a biphasic life cycle. Hoyer et al. identify a set of short- and long-range chemical cues that influence attachment and metamorphosis of Ciona larvae. These cues are detected by polymodal sensory cells, which encode the valence of the stimulus and drive brain-wide dynamics to elicit robust behavioral actions. [ABSTRACT FROM AUTHOR]

The heart of ascidians (marine invertebrate chordates) has a tubular structure, and heartbeats propagate from one end to the other. The direction of pulsation waves intermittently reverses in the heart of ascidians and their relatives; however, the underlying mechanisms remain unclear. We herein performed a series of experiments to characterize the pacemaker systems in isolated hearts and their fragments, and applied a mathematical model to examine the conditions leading to heart reversals. The isolated heart of Ciona robusta autonomously generated pulsation waves at ∼20 to 25 beats min-1 with reversals at ∼1 to 10 min intervals. Experimental bisections of isolated hearts revealed that independent pacemakers resided on each side and also that their beating frequencies periodically changed as they expressed bimodal rhythms, which comprised an ∼1.25 to 5.5 min acceleration/deceleration cycle of a beating rate of between 0 and 25 beats min-1. Only fragments including 5% or shorter terminal regions of the heart tube maintained autonomous pulsation rhythms, whereas other regions did not. Our mathematical model, based on FitzHugh-Nagumo equations applied to a one-dimensional alignment of cells, demonstrated that the difference between frequencies expressed by the two independent terminal pacemakers determined the direction of propagated waves. Changes in the statuses of terminal pacemakers between the excitatory and oscillatory modes as well as in their endogenous oscillation frequencies were sufficient to lead to heart reversals. These results suggest that the directions of pulsation waves in the Ciona heart reverse according to the changing rhythms independently expressed by remotely coupled terminal pacemakers., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Metameric somites are a novel character of chordates with unclear evolutionary origins. In the early branching chordate amphioxus, anterior somites are derived from the paraxial mesodermal cells that bud off the archenteron (i.e., enterocoely) at the end of gastrulation. Development of the anterior somites requires FGF signaling, and distinct somite compartments express orthologs of vertebrate non-axial mesodermal markers. Thus, it has been proposed that the amphioxus anterior somites are homologous to the vertebrate head mesoderm, paraxial mesoderm and lateral plate mesoderm. To trace the evolutionary origin of somites, it is essential to study the chordates' closest sister group, Ambulacraria, which includes hemichordates and echinoderms. The anterior coeloms of hemichordate and sea urchin embryos (respectively called protocoel and coelomic pouches) are also formed by enterocoely and require FGF signals for specification and/or differentiation. In this study, we applied RNA-seq to comprehensively screen for regulatory genes associated with the mesoderm-derived protocoel of the hemichordate Ptychodera flava. We also used a candidate gene approach to identify P. flava orthologs of chordate somite markers. In situ hybridization results showed that many of these candidate genes are expressed in distinct or overlapping regions of the protocoel, which indicates that molecular compartments exist in the hemichordate anterior coelom. Given that the hemichordate protocoel and amphioxus anterior somites share a similar ontogenic process (enterocoely), induction signal (FGF), and characteristic expression of orthologous genes, we propose that these two anterior coeloms are indeed homologous. In the lineage leading to the emergence of chordates, somites likely evolved from enterocoelic, FGF-dependent, and molecularly compartmentalized anterior coeloms of the deuterostome last common ancestor., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Abstract Background Lateral gene transfer (LGT), also known as horizontal gene transfer, into multicellular eukaryotes with differentiated tissues, particularly gonads, continues to be met with skepticism by many prominent evolutionary and genomic biologists. A detailed examination of 26 animal genomes identified putative LGTs in invertebrate and vertebrate genomes, concluding that there are fewer predicted LGTs in vertebrates/chordates than invertebrates, but there is still evidence of LGT into chordates, including humans. More recently, a reanalysis of a subset of these putative LGTs into vertebrates concluded that there is not horizontal gene transfer in the human genome. One of the genes in dispute is an N-acyl-aromatic-L-amino acid amidohydrolase (ENSG00000132744), which encodes ACY3. This gene was initially identified as a putative bacteria-chordate LGT but was later debunked as it has a significant BLAST match to a more recently deposited genome of Saccoglossus kowalevskii, a flatworm, Metazoan, and hemichordate. Results Using BLAST searches, HMM searches, and phylogenetics to assess the evidence for LGT, gene loss, and rate variation in ACY3/ASPA homologues, the most parsimonious explanation for the distribution of ACY3/ASPA genes in eukaryotes involves both gene loss and bacteria-animal LGT, albeit LGT that occurred hundreds of millions of years ago prior to the divergence of gnathostomes. Conclusions ACY3/ASPA is most likely a bacteria-animal LGT. LGTs at these time scales in the ancestors of humans are not unexpected given the many known, well-characterized, and adaptive LGTs from bacteria to insects and nematodes.

The chemical composition of fossil soft tissues is a potentially powerful and yet underutilized tool for elucidating the affinity of problematic fossil organisms. In some cases, it has proven difficult to assign a problematic fossil even to the invertebrates or vertebrates (more generally chordates) based on often incompletely preserved morphology alone, and chemical composition may help to resolve such questions. Here, we use in situ Raman microspectroscopy to investigate the chemistry of a diverse array of invertebrate and vertebrate fossils from the Pennsylvanian Mazon Creek Lagerstätte of Illinois, and we generate a ChemoSpace through principal component analysis (PCA) of the in situ Raman spectra. Invertebrate soft tissues characterized by chitin (polysaccharide) fossilization products and vertebrate soft tissues characterized by protein fossilization products plot in completely separate, non‐overlapping regions of the ChemoSpace, demonstrating the utility of certain soft tissue molecular signatures as biomarkers for the original soft tissue composition of fossil organisms. The controversial problematicum Tullimonstrum, known as the Tully Monster, groups with the vertebrates, providing strong evidence of a vertebrate rather than invertebrate affinity. [ABSTRACT FROM AUTHOR]

Larvaceans are chordates with a tadpole-like morphology. In contrast to most chordates of which early embryonic morphology is bilaterally symmetric and the left-right (L-R) axis is specified by the Nodal pathway later on, invariant L-R asymmetry emerges in four-cell embryos of larvaceans. The asymmetric cell arrangements exist through development of the tailbud. The tail thus twists 90° in a counterclockwise direction relative to the trunk, and the tail nerve cord localizes on the left side. Here, we demonstrate that larvacean embryos have nonconventional L-R asymmetries: 1) L- and R-cells of the two-cell embryo had remarkably asymmetric cell fates; 2) Ca2+ oscillation occurred through embryogenesis; 3) Nodal, an evolutionarily conserved left-determining gene, was absent in the genome; and 4) bone morphogenetic protein gene (Bmp) homolog Bmp.a showed right-sided expression in the tailbud and larvae. We also showed that Ca2+ oscillation is required for Bmp.a expression, and that BMP signaling suppresses ectopic expression of neural genes. These results indicate that there is a chordate species lacking Nodal that utilizes Ca2+ oscillation and Bmp.a for embryonic L-R patterning. The right-side Bmp.a expression may have arisen via cooption of conventional BMP signaling in order to restrict neural gene expression on the left side. [ABSTRACT FROM AUTHOR]

Development in the colonial ascidian genus Diplosoma is unusual in producing two zooids already during the free-swimming larval period. The development of D. listerianum had been investigated in two studies. The present study reports embryonic development of a second species D. migrans. In D. migrans the pharynx of the oozooid develops from two separate primordia. The intestinal tract develops as well from two distinct primordia that fuse and subsequently connect to the prospective pharynx. The pharynx of the blastozooid develops from the paired epicardia of the oozooid. In the oozooid the primordia of the peribranchial sacs often derive from the endodermal wall of the prospective pharynx, but occasionally develop from thickenings of the ectodermal epidermis. No atrial siphon is formed; instead, the body wall retracts and the gill slits open directly to the exterior. In the oozooid the rectum develops from the initial prospective intestine, while the remaining intestine develops from a diverticulum of the stomach. In the blastozooid the main part of the intestinal tract develops from the initial prospective intestine, whereas the rectum develops as a diverticulum of the initial intestine. Due to this developmental mode, the intestinal tracts of oozooid and blastozooid are transitorily connected at the respective border of rectum and proximal part of posterior intestinal tract. The paired epicardia of the two zooids derive from the epicardial outgrowths of the pharyngeal primordia of the oozooid that are also the primordia of the heart and pericardia. Budding in the larva and the adult is highly similar, in particular concerning the development of a new thorax and the heart from paired epicardial Anlagen and the origin of the distal part of the posterior intestine. Discrepancies in the descriptions of the embryonic development of D. listerianum and differences to the development in D. migrans are discussed. The development of the pericardium-heart-complex from epithelially organized tissue constitutes the plesiomorphic condition within Didemnidae and Aplousobranchiata. The development from mesenchymatic cell masses is a secondarily derived simplification. [ABSTRACT FROM AUTHOR]

The bHLH transcription-factor Mesp has an essential but ambiguous role in early chordate heart development. Here, we employ the genetic and morphological simplicity of the basal chordate Ciona intestinalis to elucidate Mesp regulation and function. Characterization of a minimal cardiac enhancer for the Ciona Mesp gene demonstrated direct activation by the T-box transcription factor Tbx6c. The Mesp enhancer was fused to GFP, permitting high-resolution visualization of heart cells as they migrate and divide. The enhancer was also used to drive targeted expression of an activator form of Mesp, which induces heart formation without migration. We discuss the implications of Tbx6-Mesp interactions for the evolution of cardiac mesoderm in invertebrates and vertebrates.

Abstract Background Because phylogenetic inference is an important basis for answering many evolutionary problems, a large number of algorithms have been developed. Some of these algorithms have been improved by integrating gene evolution models with the expectation of accommodating the hierarchy of evolutionary processes. To the best of our knowledge, however, there still is no single unifying model or algorithm that can take all evolutionary processes into account through a stepwise or simultaneous method. Results On the basis of three existing phylogenetic inference algorithms, we built an integrated pipeline for inferring the evolutionary history of a given gene family; this pipeline can model gene sequence evolution, gene duplication-loss, gene transfer and multispecies coalescent processes. As a case study, we applied this pipeline to the STIMATE (TMEM110) gene family, which has recently been reported to play an important role in store-operated Ca2+ entry (SOCE) mediated by ORAI and STIM proteins. We inferred their phylogenetic trees in 69 sequenced chordate genomes. Conclusions By integrating three tree reconstruction algorithms with diverse evolutionary models, a pipeline for inferring the evolutionary history of a gene family was developed, and its application was demonstrated.

This study was carried out to determine the effects of sewage pollution on the fish assemblages found in the Klang River. Samples were collected between July 2012 and April 2013 with a total of 102 specimens belonging to 5 freshwater fish species, Puntius hexazona, Betta livida, Neohomaloptera johorensis, Parosphromenus harveyi and the dominant species, Rasbora sumatrana, with the highest dominance value (Di%=36.66). Multiregression revealed a statistically insignificant relationship among the physical, chemical and biochemical parameters of water and sediment and Puntius hexazona, Betta livida, Neohomaloptera johorensis and Parosphromenus harveyi. Based on multiple regression tests, a significant relationship with R2 = 92.2% and F= 7.876 (p= 0.000) was found between six water and sediment quality constituents and the numbers of Rasbora sumatrana this species at the stations studied at Site 8. On the other hand, water temperature (β= -0.114; t= -2.811 (p= 0.016)); sediment organic matter (β= -0.011; t= -2.406 (p= 0.033)) and water phosphorus (PO4) (β= 0.323; t= 3.444 (p= 0.005)) were found to be the most important water and sediment parameters effecting Rasbora sumatrana.

During embryogenesis, chromatin accessibility profiles control lineage-specific gene expression by modulating transcription, thus impacting multipotent progenitor states and subsequent fate choices. Subsets of cardiac and pharyngeal/head muscles share a common origin in the cardiopharyngeal mesoderm, but the chromatin landscapes that govern multipotent progenitors competence and early fate choices remain largely elusive. Here, we leveraged the simplicity of the chordate model Ciona to profile chromatin accessibility through stereotyped transitions from naive Mesp+ mesoderm to distinct fate-restricted heart and pharyngeal muscle precursors. An FGF-Foxf pathway acts in multipotent progenitors to establish cardiopharyngeal-specific patterns of accessibility, which govern later heart vs. pharyngeal muscle-specific expression profiles, demonstrating extensive spatiotemporal decoupling between early cardiopharyngeal enhancer accessibility and late cell-type-specific activity. We found that multiple cis-regulatory elements, with distinct chromatin accessibility profiles and motif compositions, are required to activate Ebf and Tbx1/10, two key determinants of cardiopharyngeal fate choices. We propose that these ‘combined enhancers’ foster spatially and temporally accurate fate choices, by increasing the repertoire of regulatory inputs that control gene expression, through either accessibility and/or activity.

During embryogenesis, chromatin accessibility profiles control lineage-specific gene expression by modulating transcription, thus impacting multipotent progenitor states and subsequent fate choices. Subsets of cardiac and pharyngeal/head muscles share a common origin in the cardiopharyngeal mesoderm, but the chromatin landscapes that govern multipotent progenitors competence and early fate choices remain largely elusive. Here, we leveraged the simplicity of the chordate model Ciona to profile chromatin accessibility through stereotyped transitions from naive Mesp+ mesoderm to distinct fate-restricted heart and pharyngeal muscle precursors. An FGF-Foxf pathway acts in multipotent progenitors to establish cardiopharyngeal specific patterns of accessibility, which govern later heart vs. pharyngeal muscle-specific expression profiles, demonstrating extensive spatiotemporal decoupling between early cardiopharyngeal enhancer accessibility and late cell-type-specific activity. We found that multiple cis-regulatory elements, with distinct chromatin accessibility profiles and motif compositions, are required to activate Ebf and Tbx1/10, two key determinants of cardiopharyngeal fate choices. We propose that these "combined enhancers" foster spatially and temporally accurate fate choices, by increasing the repertoire of regulatory inputs that control gene expression, through either accessibility and/or activity. [ABSTRACT FROM AUTHOR]

MDM2 regulates a variety of cellular processes through its dual protein:protein interaction and ubiquitin ligase activities. One major function of MDM2 is to bind and ubiquitinate P53, thereby regulating its proteasomal degradation. This function is in turn controlled by the cell fate determinant NUMB, which binds to and inhibits MDM2 via a short stretch of 11 amino acids, contained in its phosphotyrosine-binding (PTB) domain, encoded by exon 3 of the NUMB gene. The NUMB-MDM2-P53 circuitry is relevant to the specification of the stem cell fate and its subversion has been shown to be causal in breast cancer leading to the emergence of cancer stem cells. While extensive work on the evolutionary aspects of the MDM2/P53 circuitry has provided hints as to how these two proteins have evolved together to maintain conserved and linked functions, little is known about the evolution of the NUMB gene and, in particular, how it developed the ability to regulate MDM2 function. Here, we show that NUMB is a metazoan gene, which acquired exon 3 in the common ancestor of the Chordate lineage, first being present in the Cephalochordate and Tunicate subphyla, but absent in invertebrates. We provide experimental evidence showing that since its emergence, exon 3 conferred to the PTB domain of NUMB the ability to bind and to regulate MDM2 functions. [ABSTRACT FROM AUTHOR]

Unlike other carcinomas, hepatocellular carcinoma (HCC) metastasizes to distant organs relatively rarely. In contrast, it routinely metastasizes to liver vasculature/liver, affecting portal veins 3-10 times more often than hepatic veins. This portal metastatic predominance is traditionally rationalized within the model of a reverse portal flow, due to accompanying liver cirrhosis. However, this intuitive model is not coherent with facts: 1) reverse portal flow occurs in fewer than 10% of cirrhotic patients, while portal metastasis occurs in 30-100% of HCC cases, and 2) portal vein prevalence of HCC metastasis is also characteristic of HCC in non-cirrhotic livers. Therefore, we must assume that the route for HCC metastatic dissemination is the same as for other carcinomas: systemic dissemination via the draining vessel, i.e., via the hepatic vein. In this light, portal prevalence versus hepatic vein of HCC metastasis appears as a puzzling pattern, particularly in cases when portal HCC metastases have appeared as the sole manifestation of HCC. Considering that other GI carcinomas (colorectal, pancreatic, gastric and small bowel) invariably disseminate via portal vein, but very rarely form portal metastasis, portal prevalence of HCC metastasis appears as a paradox. However, nature does not contradict itself; it is rather our wrong assumptions that create paradoxes. The 'portal paradox' becomes a logical event within the hypothesis that the formation of the unique portal venous system preceded the appearance of liver in evolution of chordates. The analysis suggests that the appearance of the portal venous system, supplying hormones and growth factors of pancreatic family, which includes insulin, glucagon, somatostatin, and pancreatic polypeptide (HGFPF) to midgut diverticulum in the early evolution of chordates (in an Amphioxus-like ancestral animal), promoted differentiation of enterocytes into hepatocytes and their further evolution to the liver of vertebrates. These promotional-dependent interactions are conserved in the vertebrate lineage. I hypothesize that selective homing and proliferation of malignant hepatocytes (i.e., HCC cells) in the portal vein environment are due to a uniquely high concentration of HGFPF in portal blood. HGFPF are also necessary for liver function and renewal and are significantly extracted by hepatocytes from passing blood, creating a concentration gradient of HGFPF between the portal blood and hepatic vein outflow, making post-liver vasculature and remote organs less favorable spaces for HCC growth. It also suggested that the portal vein environment (i.e., HGFPF) promotes the differentiation of more aggressive HCC clones from already-seeded portal metastases, explaining the worse outcome of HCC with the portal metastatic pattern. The analysis also offers new hypothesis on the phylogenetic origin of the hepatic diverticulum of cephalochordates, with certain implications for the modeling of the chordate phylogeny. [ABSTRACT FROM AUTHOR]

Conodont elements are the earliest mineralized vertebrate dental tools and the only ones capable of extensive repair. Two models of conodont growth, aswell as the presence of a larval stage, have been hypothesized. We analysed normally and pathologically developed elements to test these hypotheses and identified three ontogenetic stages characterized by different anisometric growth and morphology. The distinction of these stages is independently corroborated by differences in tissue strontium (Sr) content. The onset of the last stage is marked by the appearance of wear resulting from mechanical food digestion. At least five episodes of damage and repair could be identified in the normally developed specimen. In the pathological element, functionwas compromised by the development of abnormal denticles. This development can be reconstructed as addition of new growth centres out of the main growth axis during an episode of renewed growth. Our findings support the model of periodic retraction of elements and addition of new growth centres. Changes in Sr content coincident with distinct morphology and lack of wear in the early life stage indicate that conodonts might have assumed their mature feeding habit of predators or scavengers after an initial larval stage characterized by a different feeding mode. [ABSTRACT FROM AUTHOR]

Neuropeptides that possess the Arg-Phe-NH 2 motif at their C-termini (i.e., RFamide peptides) have been characterized in the nervous system of both invertebrates and vertebrates. In vertebrates, RFamide peptides make a family and consist of the groups of gonadotropin-inhibitory hormone (GnIH), neuropeptide FF (NPFF), prolactin-releasing peptide (PrRP), kisspeptin (kiss1 and kiss2), and pyroglutamylated RFamide peptide/26RFamide peptide (QRFP/26RFa). It now appears that these vertebrate RFamide peptides exert important neuroendocrine, behavioral, sensory, and autonomic functions. In 2000, GnIH was discovered as a novel hypothalamic RFamide peptide inhibiting gonadotropin release in quail. Subsequent studies have demonstrated that GnIH acts on the brain and pituitary to modulate reproductive physiology and behavior across vertebrates. To clarify the origin and evolution of GnIH, the existence of GnIH was investigated in agnathans, the most ancient lineage of vertebrates, and basal chordates, such as tunicates and cephalochordates (represented by amphioxus). This review first summarizes the structure and function of GnIH and other RFamide peptides, in particular NPFF having a similar C-terminal structure of GnIH, in vertebrates. Then, this review describes the evolutionary origin of GnIH based on the studies in agnathans and basal chordates. [ABSTRACT FROM AUTHOR]

Background: Lateral gene transfer (LGT), also known as horizontal gene transfer, into multicellular eukaryotes with differentiated tissues, particularly gonads, continues to be met with skepticism by many prominent evolutionary and genomic biologists. A detailed examination of 26 animal genomes identified putative LGTs in invertebrate and vertebrate genomes, concluding that there are fewer predicted LGTs in vertebrates/chordates than invertebrates, but there is still evidence of LGT into chordates, including humans. More recently, a reanalysis of a subset of these putative LGTs into vertebrates concluded that there is not horizontal gene transfer in the human genome. One of the genes in dispute is an N-acyl-aromatic-L-amino acid amidohydrolase (ENSG00000132744), which encodes ACY3. This gene was initially identified as a putative bacteria-chordate LGT but was later debunked as it has a significant BLAST match to a more recently deposited genome of Saccoglossus kowalevskii, a flatworm, Metazoan, and hemichordate. Results: Using BLAST searches, HMM searches, and phylogenetics to assess the evidence for LGT, gene loss, and rate variation in ACY3/ASPA homologues, the most parsimonious explanation for the distribution of ACY3/ASPA genes in eukaryotes involves both gene loss and bacteria-animal LGT, albeit LGT that occurred hundreds of millions of years ago prior to the divergence of gnathostomes. Conclusions: ACY3/ASPA is most likely a bacteria-animal LGT. LGTs at these time scales in the ancestors of humans are not unexpected given the many known, well-characterized, and adaptive LGTs from bacteria to insects and nematodes. [ABSTRACT FROM AUTHOR]

Ciona larvae display a number of behaviors, including negative phototaxis. In negative phototaxis, the larvae first perform short spontaneous rhythmic casting swims. As larvae are cast in a light field, their photoreceptors are directionally shaded by an associated pigment cell, providing a phototactic cue. This then evokes an extended negative taxis swim. We report here that the larval forebrain of Ciona has a previously uncharacterized single slow-oscillating inhibitory neuron (neuron cor-assBVIN78) that projects to the midbrain, where it targets key interneurons of the phototaxis circuit known as the photoreceptor relay neurons. The anatomical location, gene expression, and oscillation of cor-assBVIN78 suggest homology to oscillating neurons of the vertebrate hypothalamus. Ablation of cor-assBVIN78 results in larvae showing extended phototaxis-like swims, even in the absence of phototactic cues. These results indicate that cor-assBVIN78 has a gating activity on phototaxis by projecting temporally oscillating inhibition to the photoreceptor relay neurons. However, in intact larvae, the frequency of cor-assBVIN78 oscillation does not match that of the rhythmic spontaneous swims, indicating that the troughs in oscillations do not themselves initiate swims but rather that cor-assBVIN78 may modulate the phototaxis circuit by filtering out low-level inputs while restricting them temporally to the troughs in inhibition. [Display omitted] • Ciona larvae have a single slow-oscillating GABAergic forebrain neuron • This neuron projects to cholinergic midbrain interneurons of the phototaxis circuit • Ablation of this neuron evokes phototaxis-like swims in the absence of light cues • This oscillating inhibitory neuron has gating activity on the phototaxis circuit Ciona is a model for chordate neural circuit analysis. Chung et al. identify a single slow-oscillating GABAergic neuron in the Ciona larval forebrain, which, when ablated, leads to extended spontaneous swim bouts. The Ciona connectome predicts that this neuron inhibits the negative phototaxis circuit via cholinergic midbrain interneurons. [ABSTRACT FROM AUTHOR]

Regeneration is a variable trait in chordates, with some species capable of impressive abilities, and others of only wound healing with scarring. Regenerative capacity has been reported in the literature for 5 species from two cephalochordate genera, Branchiostoma and Asymmetron. Its cellular and molecular bases have been studied in some detail in only two species: tail regeneration in the European amphioxus B. lanceolatum; and oral cirrus regeneration in the Asian species B. japonicum. Gene expression analyses of germline formation and posterior elongation in cephalochordate embryos provide some insight into regulation of progenitor and stem cell function. When combined with functional studies of gene function, including overexpression and knockdown, these will open the door to amphioxus as a good model not only for understanding the evolution of regeneration, but also for biomedical purposes. [ABSTRACT FROM AUTHOR]

Studies on amphioxus, representing the most basal group of chordates, can give insights into the evolution of vertebrate traits. The present review of amphioxus research is focused on the physiology of light-guided behavior as well as on the fine structure, molecular biology, and electrophysiology of the nervous system, with special attention being given to the photoreceptive organs. The amphioxus visual system is especially interesting because four types of receptors are involved in light detection - dorsal ocelli and Joseph cells (both rhabdomeric photoreceptors) and the frontal eye and lamellar body (both ciliary photoreceptors). Here, we consider how the available information on photoreceptive organs and light-guided behavior in amphioxus helps generate hypotheses about the history of these features during chordate and subsequently vertebrate evolution. [ABSTRACT FROM AUTHOR]

Cranial placodes are an evolutionary novelty of vertebrates that give rise to many cranial sense organs and ganglia, as well as to the neurosecretory anterior pituitary. Although amphioxus does not have placodes, it shares with vertebrates several of the ectodermal patterning mechanisms and cell types that are important in placode development. Comparisons between amphioxus, vertebrates and other groups provide us with important insights into what the last common chordate ancestor probably looked like and allow us to propose a scenario for how placodes evolved by rewiring of gene regulatory networks. After reviewing ectodermal patterning and the cytodifferentiation of neurosecretory and sensory cells in amphioxus, this review will argue that the evolutionary origin of cranial placodes involved 1) the concentration of sensory and neurosecretory cell types in the head by linking their development to ancient cranial ectodermal patterning mechanisms; and 2) the formation of high density arrays of sensorineural precursors by intercalating a progenitor expansion module into the gene regulatory network driving differentiation of sensory or neurosecretory cells. [ABSTRACT FROM AUTHOR]

How the embryonic body axis is generated is a fundamental question in developmental biology. The molecular mechanisms involved in this process have been the subject of intensive studies using traditional model organisms during the last few decades, and the results have provided crucial information for understanding the formation of animal body plans. In particular, studies exploring the molecular nature of Spemann's organizer have revealed the intricate interactions underlying several signaling pathways (namely the Wnt/β-catenin, Nodal and Bmp pathways) that pattern the dorsoventral (DV) axis in vertebrate embryos. Furthermore, recent comparative studies have shown that many of these signaling interactions are also employed in other non-vertebrate model organisms for their early embryonic axis patterning. These results suggest that there is deep homology in DV patterning mechanisms among bilaterian animals and that these mechanisms may be traced back to the common ancestor of cnidarians and bilaterians. However, the mechanism by which the DV axis became inverted in the chordate lineage relative to the DV axis in other bilaterian animals remains unclear. Cephalochordata (i.e., amphioxus) represent a basal chordate group which occupies a key phylogenetic position for explorations of the origin of the chordate body plan. In this review, we summarize what is currently known regarding the developmental mechanisms that establish the DV axis in amphioxus embryos. By comparing this to what is known in vertebrates, we can start to hypothesize about the ancestral DV patterning mechanisms in chordates and discuss their possible evolutionary origins. [ABSTRACT FROM AUTHOR]

Summary Comparing synaptic circuits and networks between brains of different animal groups helps us derive an understanding of how nervous systems might have evolved. The circuits of the startle response pathway in the brains of tailed vertebrates are known from electrophysiological studies on the giant reticulospinal Mauthner cells (M-cells). To identify morphological counterparts in chordate tunicates, a sister group of vertebrates [ 1, 2 ], we have compiled a densely reconstructed connectome (defined in [ 3 ]) for the CNS in the tadpole larva of Ciona intestinalis (L.), using ssEM [ 4 ]. The dorsal, tubular CNS of the ∼1-mm tadpole larva is built on a similar plan to vertebrates, its neurons distributed rostrocaudally in three centers, a brain vesicle, motor ganglion, and caudal nerve cord [ 5 ]. A single pair of descending decussating neurons, ddNs, found in the motor ganglion, have similarities to reticulospinal neurons descending from the vertebrate hindbrain to the spinal cord. The pre- and postsynaptic connections and circuits of these ddNs support their homology with decussating vertebrate M-cells. Network analysis reveals that, like M-cells, ddNs receive mechanosensory input from the peripheral nervous system and provide input to motoneurons, premotor interneurons, and ascending commissural inhibitory neurons (ACINs). These circuits uncover a putative homologous startle network in the Ciona tadpole. However, differences in circuits, including a lack of bilateral symmetry in their network, and convergence of inputs from left and right sides, raise questions about the relationship between form and function, and are a possible outcome of the tiny number of neurons in ascidian larvae. [ABSTRACT FROM AUTHOR]

The appendicularian, Oikopleura dioica, is a planktonic tunicate that retains a swimming tadpole shape throughout its life. It has relatively few cells and exhibits fast development, yet it has a basic chordate body plan. In this study, the morphology of adults was investigated using scanning electron microscopy (SEM) and fine 3D images of most organs were taken. The trunk epidermis is organized into bilateral territories secreting the house that includes the food-trapping filter. The pharynx extends ventrally and posteriorly to the gill openings and esophagus, respectively. The endostyle, with a morphologically distinct ciliated band, is embedded in the pharynx. The digestive tract showed left-right asymmetry as the connection between the pharynx and esophagus tilts leftward. The heart is located ventrally between the left stomach and the intestine and consists of a left muscular sheet and a right thin, non-muscular sheet. The brain is connected to the oral and ventral sensory organs, ciliary funnels and sensory vesicles and axons descend from it that eventually innervate the caudal ganglion. In the tail, a nerve cord with sporadically distributed neuronal somata runs along the left side of the notochord. The gonad is a single syncytium of thousands of gametes. In the ovary, an abundance of cortical membrane invaginate into the cytoplasm during oogenesis and the growing oocytes are interconnected via common cytoplasm through a ring canal. Spermatogenesis progresses synchronously within the common cytoplasm. These descriptions provide a valuable anatomical atlas for studying development and physiology using this simple organism with a chordate body plan. [ABSTRACT FROM AUTHOR]

The third complement component (C3) in ascidian was reported to function as an opsonin to enhance phagocytosis and as a chemotactic factor for phagocytes, indicating that ascidian C3 works in mesodermal cavity as a humoral factor like vertebrate C3s. In the basal Eumetazoa, Cnidaria lacking mesodermal tissues, C3 was reported to work in an endodermal cavity. Evolution of structure and function of C3 is still to be clarified. Here we report the identification of the third C3 gene, CiC3-3, in the genome of an ascidian, Ciona intestinalis. Phylogenetic analysis using the entire amino acid sequences of Eumetazoan C3s indicated that CiC3-3 possess a closer relationship to vertebrate C3, C4 and C5 than other ascidian C3s. Although CiC3-3 retained the α-β processing site and 6 cysteine residues in the C3a region, it lacked the intra-molecular thioester bond and the catalytic histidine residue. Instead, CiC3-3 had a unique insertion of about 70 residues long Lys/Arg-rich sequence. CiC3-3 was expressed highly in the embryonic stages, but little in the adult in contradistinction to CiC3-1 and CiC3-2. The expression of CiC3-3 in early embryonic stages was restricted to endoderm similar to cnidarian C3s. Thus, the ascidian complement system could represent a unique evolutionary stage sharing a primitive endodermal function with Cnidaria, and newly developed humoral function with vertebrates.

The paper analyzes the comparative effectiveness of Computer-Assisted Learning (CAL) and the traditional teaching method in biology on primary school pupils. A stratified random sample consisted of 214 pupils from two primary schools in Novi Sad. The pupils in the experimental group learned the biology content (Chordate) using CAL, whereas the pupils in the control group learned the same content using traditional teaching. The research design was the pretest-posttest equivalent groups design. All instruments (the pretest, the posttest and the retest) contained the questions belonging to three different cognitive domains: knowing, applying, and reasoning. Arithmetic mean, standard deviation, and standard error were analyzed using the software package SPSS 14.0, and t-test was used in order to establish the difference between the same statistical indicators. The analysis of results of the post­test and the retest showed that the pupils from the CAL group achieved significantly higher quantity and quality of knowledge in all three cognitive domains than the pupils from the traditional group. The results accomplished by the pupils from the CAL group suggest that individual CAL should be more present in biology teaching in primary schools, with the aim of raising the quality of biology education in pupils. [Projekat Ministarstva nauke Republike Srbije, br. 179010: Quality of Educational System in Serbia in the European Perspective]