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Just as in clay moulding or glass blowing, physically sculpting biological structures requires the constituent material to locally flow like a fluid while maintaining overall mechanical integrity like a solid. Disordered soft materials, such as foams, emulsions and colloidal suspensions, switch from fluid-like to solid-like behaviours at a jamming transition.sup.1-4. Similarly, cell collectives have been shown to display glassy dynamics in 2D and 3D.sup.5,6 and jamming in cultured epithelial monolayers.sup.7,8, behaviours recently predicted theoretically.sup.9-11 and proposed to influence asthma pathobiology.sup.8 and tumour progression.sup.12. However, little is known about whether these seemingly universal behaviours occur in vivo.sup.13 and, specifically, whether they play any functional part during embryonic morphogenesis. Here, by combining direct in vivo measurements of tissue mechanics with analysis of cellular dynamics, we show that during vertebrate body axis elongation, posterior tissues undergo a jamming transition from a fluid-like behaviour at the extending end, the mesodermal progenitor zone, to a solid-like behaviour in the presomitic mesoderm. We uncover an anteroposterior, N-cadherin-dependent gradient in yield stress that provides increasing mechanical integrity to the presomitic mesoderm, consistent with the tissue transiting from a wetter to a dryer foam-like architecture. Our results show that cell-scale stresses fluctuate rapidly (within about 1 min), enabling cell rearrangements and effectively 'melting' the tissue at the growing end. Persistent (more than 0.5 h) stresses at supracellular scales, rather than cell-scale stresses, guide morphogenetic flows in fluid-like tissue regions. Unidirectional axis extension is sustained by the reported rigidification of the presomitic mesoderm, which mechanically supports posterior, fluid-like tissues during remodelling before their maturation. The spatiotemporal control of fluid-like and solid-like tissue states may represent a generic physical mechanism of embryonic morphogenesis. Cell collectives in embryonic tissues undergo a fluid-to-solid jamming transition, similar to those that occur in soft materials such as foams, emulsions and colloidal suspensions, to physically sculpt the vertebrate body axis., Author(s): Alessandro Mongera [sup.1] [sup.2] [sup.7] , Payam Rowghanian [sup.1] [sup.2] , Hannah J. Gustafson [sup.1] [sup.2] [sup.3] , Elijah Shelton [sup.1] [sup.2] , David A. Kealhofer [sup.4] , Emmet [...]

Fossils of early gnathostomes (or jawed vertebrates) have been the focus of study for nearly two centuries. They yield key clues about the evolutionary assembly of the group's common body plan, as well the divergence of the two living gnathostome lineages: the cartilaginous and bony vertebrates. A series of remarkable new palaeontological discoveries, analytical advances and innovative reinterpretations of existing fossil archives have fundamentally altered a decades-old consensus on the relationships of extinct gnathostomes, delivering a new evolutionary framework for exploring major questions that remain unanswered, including the origin of jaws., Jawed vertebrates (gnathostomes) comprise more than 99% of living vertebrate species, including humans. This diversity is built on features including jaws, teeth, paired appendages, and specialized embryonic and skeletal tissues [...]

Over the past 200 years, almost every invertebrate phylum has been proposed as a starting point for evolving vertebrates. Most of these scenarios are outdated, but several are still seriously considered. The short-range transition from ancestral invertebrate chordates (similar to amphioxus and tunicates) to vertebrates is well accepted. However, longer-range transitions leading up to the invertebrate chordates themselves are more controversial. Opinion is divided between the annelid and the enteropneust scenarios, predicting, respectively, a complex or a simple ancestor for bilaterian animals. Deciding between these ideas will be facilitated by further comparative studies of multicellular animals, including enigmatic taxa such as xenacoelomorphs., Biologists have considered nearly every major taxon of animals as the key starting point for the evolution of vertebrates. We survey these ideas, many of which are no longer tenable [...]

Abrupt collapse of the tropical rainforest biome (Coal Forests) drove rapid diversification of Carboniferous tetrapods (amphibians and reptiles) in Euramerica. This finding is based on analysis of global and alpha diversity databases in a precise geologic context. From Visean to Moscovian time, both diversity measures steadily increased, but following rainforest collapse in earliest Kasimovian time (ca. 305 Ma), tetrapod extinction rate peaked, alpha diversity imploded, and endemism developed for the first time. Analysis of ecological diversity shows that rainforest collapse was also accompanied by acquisition of new feeding strategies (predators, herbivores), consistent with tetrapod adaptation to the effects of habitat fragmentation and resource restriction. Effects on amphibians were particularly devastating, while amniotes ('reptiles') fared better, being ecologically adapted to the drier conditions that followed. Our results demonstrate, for the first time, that Coal Forest fragmentation influenced profoundly the ecology and evolution of terrestrial fauna in tropical Euramerica, and illustrate the tight coupling that existed between vegetation, climate, and trophic webs. doi: 10.1130/G31182.1

A new colosteid, Deltaherpeton hiemstrae gen. et sp. nov., is described from the Mississippian Upper Visean site at Delta, Iowa. Deltaherpeton is represented by a skull roof and both jaws. The new taxon is unique among colosteids in having an internasal and single midline postparietal. An additional midline pair of cf. 'interfrontonasals' may be present. Characters previously used to define the colosteids are reviewed and a refined diagnosis for the family Colosteidae is presented. Synapomorphies which unite Deltaherpeton, Colosteus, Greererpeton, and Pholidogaster as Colosteidae are: premaxilla with fang pair; dentary with notch for receipt of premaxillary fang; mandible with single elongate exomeckelian fenestra; pre-narial infraorbital lateral line terminating at ventral margin of premaxilla just anterior to external naris; and post-narial infraorbital lateral line terminating at the ventral margin of the maxilla just posterior to the external naris. Our review of dermal bones in the colosteid snout concludes that no specimen is sufficiently free of distortions or breakage to indicate clearly whether or not the prefrontal borders the external naris, or that an anterior tectal is present. The morphology of Deltaherpeton and the revised data presented for colosteids do not clarify the relationship of colosteids to other early tetrapods.

In vertebrates, Hedgehog (Hh) signaling initiated in primary cilia activates the membrane protein Smoothened (Smo) and leads to activation of Gli proteins, the transcriptional effectors of the pathway. In the absence of signaling, Gli proteins are inhibited by the cytoplasmic protein Suppressor of Fused (SuFu). It is unclear how Hh activates Gli and whether it directly regulates SuFu. We find that Hh stimulation quickly recruits endogenous SuFu--Gli complexes to cilia, suggesting a model in which Smo activates Gli by relieving inhibition by SuFu. In support of this model, we find that Hh causes rapid dissociation of the SuFu--Gli complex, thus allowing Gli to enter the nucleus and activate transcription. Activation of protein kinase A (PKA), an inhibitor of Hh signaling, blocks ciliary localization of SuFu--Gli complexes, which in turn prevents their dissociation by signaling. Our results support a simple mechanism in which Hh signals at vertebrate cilia cause dissociation of inactive SuFu--Gli complexes, a process inhibited by PKA. doi/ 10.1083/jcb.201004108

Segmentation of the vertebrate head emerges out of earlier processes that establish the anterior-posterior (A-P) axis. Recent genetic studies and comparisons across species have led to a better understanding of the links between A-P patterning and segmentation. These point to similar signals acting on both head and trunk, such as retinoic acid and fibroblast growth factors. These form interacting networks of diffusible morphogen gradients that pattern both hindbrain rhombomeres and mesodermal somites. New computational models, particularly for retinoic acid, have revealed how morphogen gradients are established and made robust to changes in signaling levels. However, the orientations of these gradients, as well as how they interact to generate segments, differ remarkably between germ layers and body regions. Thus, the vertebrate head is, in part, built through modifications of the same processes that link A-P patterning and segmentation in the trunk, but fundamental differences in how these processes are deployed lend further doubt to the notion that head and trunk segments are homologous.

The fossil record has been an invaluable aid for reconstructing the major events of vertebrate evolution. There is no comparable record for protochordates, however, which severely limits our knowledge of their ancestral morphology, habits, and mode of life. The alternative is inference based on an interpretation of living protochordates but this is fraught with problems, not least being our own biases of what we think an ancestral chordate ought to look like. Relevant to the present symposium is the problem of head/trunk relationships and whether or not the myotomes of the trunk originally extended into the head in vertebrates. I will review what is currently known of patterns of innervation in tunicates and amphioxus in relation to Romer's somaticovisceral concept of the vertebrate body to show how little progress has been made in resolving this problem. There are, in contrast, surprisingly good prospects for solving some other puzzles concerning chordate origins. Dorsoventral inversion provides a good example. A consensus is now emerging, based largely on molecular data from hemichordates that casts new light on the asymmetry of the head in amphioxus. Specifically, the morphogenetic growth process that reestablishes symmetry in late-stage larvae can now be seen, at least in part, as a recapitulation of past evolutionary events, and this has important implications for the origin and basic organization of the brain.

The gene network that directs the development of the first population of endoderm progenitor cells and enables both rapidity and speed of endoderm development are described. The better understanding of core endoderm network could be applied to efficiently direct the differentiation of mouse and human ES cell cultures into definitive endoderm-like cells by activating the Nodal pathway with recombinant Activin (a Nodal-like TGF[beta] ligand).

Amiloride-sensitive [Na.sup.+] absorption is a well-described feature of numerous transporting epithelia in vertebrates. Yet, very little is known about this important physiological process regarding invertebrates. In the present paper, we compare vertebrate [Na.sup.+] absorption mediated by the amiloride-sensitive epithelial [Na.sup.+] channel (ENaC) and its invertebrate counterpart. We used the dorsal skin of the annelid Hirudo medicinalis as a model for the [Na.sup.+] absorption of invertebrate epithelia. In applying electrophysiological, molecular, and biochemical techniques we found striking functional and structural differences between vertebrate and invertebrate amiloride-sensitive [Na.sup.+] absorption. Using modified Ussing chambers, we analyzed the influence of different known blockers and effectors of vertebrate ENaC on leech epithelial [Na.sup.+] absorption. We demonstrate that the serine protease trypsin had no effect on the [Na.sup.+] transport across leech integument, while it strongly activates vertebrate ENaC. While protons, and the divalent cations [Ni.sup.2+] and [Zn.sup.2+] stimulate vertebrate ENaC, amiloride-sensitive [Na.sup.+] currents in leech integument were substantially reduced. For molecular studies, we constructed a cDNA library of Hirudo medicinalis and screened it with specific ENaC antibodies. We performed numerous PCR approaches using a vast number of different degenerated and specific ENaC primers to identify ENaC-like structures. Yet, both strategies did not reveal any ENaC-like sequence in leech integument. From these data we conclude that amiloride-sensitive [Na.sup.+] absorption in leech skin is not mediated by an ENaC-like [Na.sup.+] channel but by a still unknown invertebrate member of the ENaC/DEG family that we termed 1ENaTP (leech epithelial [Na.sup.+] transporting protein). epithelial [Na.sup.+] channel/degenerin superfamily; invertebrate epithelial transport doi:10.1152/ajpregu.00549.2006

Short-term elevation of circulating glucocorticosteroids (GCs) in vertebrates facilitates the adoption of a distinct emergency life history state, which allows individuals to cope with perturbations and recover homeostasis at the expense of temporarily suppressing nonessential activities. Although GC responses are viewed as a major evolutionary mechanism to maximize fitness through stress management, phenotypic variability exists within animal populations, and it remains unclear whether interindividual differences in stress physiology can explain variance in unequivocal components of fitness. We show that the magnitude of the adrenocortical response to a standardized perturbation during development is negatively related to survival and recruitment in a wild population of long lived birds. Our results provide empirical evidence for a link between stress response, not exposure to stressors, and fitness in a vertebrate under natural conditions. Recent studies suggest that variability in the adrenocortical response to stress may be maintained if high and low GC responders represent alternative coping strategies, with differential adaptive value depending on environmental conditions. Increased fitness among low GC responders, having a proactive personality, is predicted under elevated population density and availability of food resources, conditions that characterize our study population. animal personality | conticosterone | glucocorticosteroids | reproduction | survival

Evolutionary dynamics of vertebrate body mass range were studied by regression equations, which are used to predict the origin age, initial body mass and body mass range. The results suggested that dynamics of phenotypic characteristic can help molecular clock and fossil models in dating evolutionary years.

The skeletal muscles and axial skeleton of vertebrates derive from the embryonic paraxial mesoderm. In amniotes, paraxial mesoderm is formed bilaterally to the nerve cord as a result of primitive streak and tail-bud regression during body axis formation. In chick and mouse embryos, paraxial mesoderm was proposed to derive from a population of resident cells located in the regressing primitive streak and tail bud. In contrast, in lower vertebrates, paraxial mesoderm is formed as a result of the continuation of ingression movements of gastrulation. Here, we reinvestigate paraxial mesoderm formation in the chicken embryo and demonstrate that these two modes are concomitantly at work to set up the paraxial mesoderm. Although the medial part of somites derives from stem cells resident in the primitive streak/tail bud, the lateral part derives from continuous ingression of epiblastic material. Our fate mapping further shows that the paraxial mesoderm territory in the epiblast is regionalized along the anteroposterior axis as in lower vertebrates. These observations suggest that the mechanisms responsible for paraxial mesoderm formation are largely conserved across vertebrates. vertebrate | epiblast | primitive streak | tail bud | body axis formation

In mammals, growth hormone-releasing hormone (GHRH) is the most important neuroendocrine factor that stimulates the release of growth hormone (GH) from the anterior pituitary. In nonmammalian vertebrates, however, the previously named GHRH-like peptides were unable to demonstrate robust GH-releasing activities. In this article, we provide evidence that these GHRH-like peptides are homologues of mammalian PACAP-related peptides (PRP). Instead, GHRH peptides encoded in cDNAs isolated from goldfish, zebrafish, and African clawed frog were identified. Moreover, receptors specific for these GHRHs were characterized from goldfish and zebrafish. These GHRHs and GHRH receptors (GHRH-Rs) are phylogenetically and structurally more similar to their mammalian counterparts than the previously named GHRH-like peptides and GHRH-like receptors. Information regarding their chromosomal locations and organization of neighboring genes confirmed that they share the same origins as the mammalian genes. Functionally, the goldfish GHRH dose-dependently activates cAMP production in receptor-transfected CHO cells as well as GH release from goldfish pituitary cells. Tissue distribution studies showed that the goldfish GHRH is expressed almost exclusively in the brain, whereas the goldfish GHRH-R is actively expressed in brain and pituitary. Taken together, these results provide evidence for a previously uncharacterized GHRH-GHRH-R axis in nonmammalian vertebrates. Based on these data, a comprehensive evolutionary scheme for GHRH, PRP-PACAP, and PHI-VIP genes in relation to three rounds of genome duplication early on in vertebrate evolution is proposed. These GHRHs, also found in flounder, Fugu, medaka, stickleback, Tetraodon, and rainbow trout, provide research directions regarding the neuroendocrine control of growth in vertebrates. molecular evolution | genome duplication | pituitary adenylate cyclase-activating polypeptide

Otx2 is a paired type homeobox gene that plays essential roles in each step and site of head development in vertebrates. In the mouse, Otx2 expression in the anterior neuroectoderm is regulated primarily by two distinct enhancers: anterior neuroectoderm (AN) and forebrain/midbrain (FM) enhancers at 92 kb and 75 kb 5'of the Otx2 locus, respectively. The AN enhancer has activity in the entire anterior neuroectoderm at headfold and early somite stages, whereas the FM enhancer is subsequently active in the future caudal forebrain and midbrain ectoderm. In tetrapods, both AN and FM enhancers are conserved, whereas the AN region is missing in teleosts, despite overt Otx2 expression in the anterior neuroectoderm. Here, we show that zebrafish and fugu FM regions drive expression not only in the forebrain and midbrain but also in the anterior neuroectoderm at headfold stage. The analysis of coelacanth and skate genomic Otx2 orthologues suggests that the utilization of the two enhancers, AN and FM, is an ancestral condition. In contrast, the AN enhancer has been specifically lost in the teleost lineage with a compensatory establishment of AN activity within the FM enhancer. Furthermore, the AN activity in the fish FM enhancer was established by recruiting upstream factors different from those that direct the tetrapod AN enhancer, yet zebrafish FM enhancer is active in both mouse and zebrafish anterior neuroectoderm at the headfold stage. anterior neuroectoderm | coelacanth | enhancer | tetrapod | chondrichthyes

Inhibition of Notch signaling by Numb is critical for many cell fate decisions. In this study, we demonstrate a more complex relationship between Notch and the two vertebrate Numb homologues Numb and Numblike. Although Numb and Numblike at low levels of Notch signaling negatively regulated Notch, high levels of Notch signaling conversely led to a reduction of Numb and Numblike protein levels in cultured cells and in the developing chick central nervous system. The Notch intracellular domain but not the canonical Notch downstream proteins Hes 1 and Hey 1 caused a reduction of Numb and Numblike. The Notch-mediated reduction of Numblike required the PEST domain in the Numblike protein and was blocked by the proteasome inhibitor MG132. Collectively, these observations reveal a reciprocal negative regulation between Notch and Numb/ Numblike, which may be of relevance for stabilizing asymmetric cell fate switches and for tumor development.

The role of specific cell surface carbohydrates in the development of nerves in olfactory systems in vertebrates is studied.

The Tol2 element is a naturally occurring active transposable element found in vertebrate genomes. The Tol2 transposon system has been shown to be active from fish to mammals and considered to be a useful gene transfer vector in vertebrates. However, cis-sequences essential for transposition have not been characterized. Here we report the characterization of the minimal cis-sequence of the Tol2 element. We constructed Tol2 vectors containing various lengths of DNA from both the left (5') and the right (3') ends and tested their transpositional activities both by the transient excision assay using zebrafish embryos and by analyzing chromosomal transposition in the zebrafish germ lineage. We demonstrated that Tol2 vectors with 200 bp from the left end and 150 bp from the right end were capable of transposition without reducing the transpositional efficiency and found that these sequences, including the terminal inverted repeats (TIRs) and the subterminal regions, are sufficient and required for transposition. The left and right ends were not interchangeable. The Tol2vector carrying an insert of > 11 kb could transpose, but a certain length of spacer, 18 bp, between the left and right ends was necessary for excision. Furthermore, we found that a 5-bp sequence, 5'-(A/G)AGTA-3', is repeated 33 times in the essential subterminal region. Mutations in the repeat sequence at 13 different sites in the subterminal region, as well as mutations in TIRs, severely reduced the excision activity, indicating that they play important roles in transposition. The identification of the minimal c/s-sequence of the Tol2 element and the construction of mini-Tol2 vectors will facilitate development of useful transposon tools in vertebrates. Also, our study established a basis for further biochemical and molecular biological studies for understanding roles of the repetitive sequence in the subterminal region in transposition.

A study investigating the reasons for the anchoring of a transcription factor, ATCE1 on the inner membrene of the acrosome of sperms of vertebrates is presented.

The role of p57 and Hes1 genes in controlling the number of pancreatic progenitors in the cell cycle during organogenesis in vertebrates is discussed.

Despite longstanding interest in parallel evolution, little is known about the genes that control similar traits in different lineages of vertebrates. Pelvic reduction in stickleback fish (family Gasterosteidae) provides a striking example of parallel evolution in a genetically tractable system. Previous studies suggest that cis-acting regulatory changes at the Pitx1 locus control pelvic reduction in a population of threespine sticklebacks (Gasterosteus aculeatus). In this study, progeny from intergeneric crosses between pelvic-reduced threespine and ninespine (Pungitius pungitius) sticklebacks also showed severe pelvic reduction, implicating a similar genetic origin for this trait in both genera. Comparative sequencing studies in complete and pelvic-reduced Pungitius revealed no differences in the Pitx1 coding sequences, but Pitx1 expression was absent from the prospective pelvic region of larvae from pelvic-reduced parents. A much more phylogenetically distant example of pelvic reduction, loss of hindlimbs in manatees, shows a similar left--right size bias that is a morphological signature of Pitx1-mediated pelvic reduction in both sticklebacks and mice. These multiple lines of evidence suggest that changes in Pitx1 may represent a key mechanism of morphological evolution in multiple populations, species, and genera of sticklebacks, as well as in distantly related vertebrate lineages. development | limb | parallel evolution | Pitx1 | stickleback

Orthologous gene structures in eight vertebrate species were compared on a genomic scale to detect the birth and maturation of new internal exons during the course of evolution. We found that 40% of new human exons are alternatively spliced, and most of these are cassette exons (exons that are either included or skipped in their entirety) with low inclusion rates. This proportion decreases steadily as older and older exons are examined, even as splicing efficiency increases. Remarkably, the great majority of new cassette exons are composed of highly repeated sequences, especially Alu. Many new cassette exons are 5' untranslated exons; the proportion that code for protein increases steadily with age. New protein-coding exons evolve at a high rate, as evidenced by the initially high substitution rates ([K.sub.s] and [K.sub.a]), as well as the SNP density compared with older exons. This dynamic picture suggests that de novo recruitment rather than shuffling is the major route by which exons are added to genes, and that species-specific repeats could play a significant role in recent evolution. repeats | splicing

Knowledge of relatedness between pairs of individuals plays an important role in many research areas including evolutionary biology, quantitative genetics, and conservation. Pairwise relatedness estimation methods based on genetic data from highly variable molecular markers are now used extensively as a substitute for pedigrees. Although the sampling variance of the estimators has been intensively studied for the most common simple genetic relationships, such as unrelated, half- and full-sib, or parent--offspring, little attention has been paid to the average performance of the estimators, by which we mean the performance across all pairs of individuals in a sample. Here we apply two measures to quantify the average performance: first, misclassification rates between pairs of genetic relationships and, second, the proportion of variance explained in the pairwise relatedness estimates by the true population relatedness composition (i. e., the frequencies of different relationships in the population). Using simulated data derived from exceptionally good quality marker and pedigree data from five long-term projects of natural populations, we demonstrate that the average performance depends mainly on the population relatedness composition and may be improved by the marker data quality only within the limits of the population relatedness composition. Our five examples of vertebrate breeding systems suggest that due to the remarkably low variance in relatedness across the population, marker-based estimates may often have low power to address research questions of interest.

During vertebrate evolution there has been a shift in the way in which the heart varies cardiac output (the product of heart rate and stroke volume). While mammals, birds, and amphibians increase cardiac output through large increases in heart rate and only modest increases (~30%) in stroke volume, fish and some reptiles use modest increases in heart rate and very large increases in stroke volume (up to 300%). The cellular mechanisms underlying these fundamentally different approaches to cardiac output modulation are unknown. We hypothesized that the divergence between volume modulation and frequency modulation lies in the response of different vertebrate myocardium to stretch. We tested this by progressively stretching individual cardiac myocytes from the fish heart while measuring sarcomere length (SL), developed tension, and intracellular [Ca.sup.2+] ([[Ca.sup.2+].sub.i]) transients. We show that in fish cardiac myocytes, active tension increases at SLs greater than those previously demonstrated for intact mammalian myocytes, representing a twofold increase in the functional ascending limb of the length-tension relationship. The mechanism of action is a length-dependent increase in myofilament [Ca.sup.2+] sensitivity, rather than changes in the [[Ca.sup2+]].sub.i] transient or actin filament length in the fish cell. The capacity for greater sarcomere extension in fish myocardium may be linked to the low resting tension that is developed during stretch. These adaptations allow the fish heart to volume modulate and thus underpin the fundamental difference between the way fish and higher vertebrates vary cardiac output.

A study on vertebrate and invertebrate organisms to understand the structure and function of the large molecular complexes that are involved in focal adhesions in cytoplasm is presented.

An overview of function of spalt genes in the development of vertebrates and also diseases in humans is presented.

The existence of a universal molecular clock has been called into question by observations that substitution rates vary widely between lineages. However, increasing empirical evidence for the systematic effects of different life history traits on the rate of molecular evolution has raised hopes that rate variation may be predictable, potentially allowing the 'correction' of the molecular clock. One such example is the body size trend observed in vertebrates; smaller species tend to have faster rates of molecular evolution. This effect has led to the proposal of general predictive models correcting for rate heterogeneity and has also been invoked to explain discrepancies between molecular and paleontological dates for explosive radiations in the fossil record. Yet, there have been no tests of an effect in any nonvertebrate taxa. In this study, we have tested the generality of the body size effect by surveying a wide range of invertebrate metazoan lineages. DNA sequences and body size data were collected from the literature for 330 species across five phyla. Phylogenetic comparative methods were used to investigate a relationship between average body size and substitution rate at both interspecies and interfamily comparison levels. We demonstrate significant rate variation in all phyla and most genes examined, implying a strict molecular clock cannot be assumed for the Metazoa. Furthermore, we find no evidence of any influence of body size on invertebrate substitution rates. We conclude that the vertebrate body size effect is a special case, which cannot be simply extrapolated to the rest of the animal kingdom. comparative method | generation time | metabolic rate | Metazoa

The role of intercellular calcium ion signals in different phases of muscle development including myofibrillogenesis in vertebrate embryos is studied.

The regulation of the transcription factor Olig2 by elements that are of a particular lineage during spinal cord development in vertebrates is studied.

A study on the role of antioxidant enzymes in defining areas with high levels of reactive oxygen species (ROS) during vertebrate limb development is presented.

Among ectothermic tetrapods, amphibians are by far the most diverse group at high elevations in the tropical Andes. This article asks whether this pattern reflects intrinsic aspects of amphibian natural history. An interdisciplinary analysis suggests that amphibians have a long evolutionary history at moderate Andean elevations and that adaptation for activity at low temperature occurred frequently and independently in different taxa. One conclusion is that temperature is unlikely to be the only or the main factor constraining some unrepresented anuran taxa that do not reach high elevations. Other physical variables (e.g. the effects of ultraviolet radiation on egg development) could better explain anuran diversity along tropical altitudinal gradients. In contrast, heliothermic taxa, such as lizards, might indeed be constrained by the low and variable temperatures that characterize high tropical elevations. Ecological gradients, therefore, might not affect ectothermic tetrapods in a similar manner, and differential susceptibility to biotic and abiotic factors that change with elevation might help to explain current patterns of distribution and diversity.

Glia are the most abundant cell type in the mammalian nervous system and they have vital roles in neural development, function and health. However our understanding of the biology of glia is in its infancy. How do glia develop and interact with neurons? How diverse are glial populations? What are the primary functions of glia in the mature nervous system? These questions can be addressed incisively in the Drosophila nervous system--this contains relatively few glia, which are well-defined histologically and amenable to powerful molecular-genetic analyses. Here, we highlight several developmental, morphological and functional similarities between Drosophila and vertebrate glia. The striking parallels that emerge from this comparison argue that invertebrate model organisms such as Drosophila have excellent potential to add to our understanding of fundamental aspects of glial biology.

The central nervous system (CNS) of terrestrial vertebrates underwent a prominent molecular change when a tetraspan membrane protein, myelin proteolipid protein (PLP), replaced the type I integral membrane protein, [P.sub.0], as the major protein of myelin. To investigate possible reasons for this molecular switch, we genetically engineered mice to express [P.sub.0] instead of PLP in CNS myelin. In the absence of PLP, the ancestral [P.sub.0] provided a periodicity to mouse compact CNS myelin that was identical to mouse PNS myelin, where [P.sub.0] is the major structural protein today. The PLP-[P.sub.0] shift resulted in reduced myelin internode length, degeneration of myelinated axons, severe neurological disability, and a 50% reduction in lifespan. Mice with equal amounts of [P.sub.0] and PLP in CNS myelin had a normal lifespan and no axonal degeneration. These data support the hypothesis that the [P.sub.0]-PLP shift during vertebrate evolution provided a vital neuroprotective function to myelin-forming CNS glia.

The characteristics of retinal stem cells present in the epithelium of iris pigments are studied.

The role of the primary capillary plexus formed due to elongation of cells, in the development of the circulatory system in vertebrate embryos, is studied.

Techniques for fast noninvasive control of neuronal excitability will be of major importance for analyzing and understanding neuronal networks and animal behavior. To develop these tools we demonstrated that two light-activated signaling proteins, vertebrate rat rhodopsin 4 (RO4) and the green algae channelrhodospin 2 (ChR2), could be used to control neuronal excitability and modulate synaptic transmission. Vertebrate rhodopsin couples to the Gi/o, pertussis toxin-sensitive pathway to allow modulation of G protein-gated inward rectifying potassium channels and voltage-gated [Ca.sup.2+] channels. Light-mediated activation of RO4 in cultured hippocampal neurons reduces neuronal firing within ms by hyperpolarization of the somato-dendritic membrane and when activated at presynaptic sites modulates synaptic transmission and paired-pulse facilitation. In contrast, somato-dendritic activation of ChR2 depolarizes neurons sufficiently to induce immediate action potentials, which precisely follow the ChR2 activation up to light stimulation frequencies of 20 Hz. To demonstrate that these constructs are useful for regulating network behavior in intact organisms, embryonic chick spinal cords were electroporated with either construct, allowing the frequency of episodes of spontaneous bursting activity, known to be important for motor circuit formation, to be precisely controlled. Thus light-activated vertebrate RO4 and green algae ChR2 allow the antagonistic control of neuronal function within ms to s in a precise, reversible, and noninvasive manner in cultured neurons and intact vertebrate spinal cords.

Gonadotropin-releasing hormone (GnRH) is an important regulator of reproduction in all vertebrates through its actions on the production and secretion of pituitary gonadotropin hormones (GtHs). Most vertebrate species express at least two GnRHs, including one form, designated chicken (c)GnRH-II or type II GnRH, which has been well conserved throughout evolution. The goldfish brain and pituitary contain salmon GnRH and cGnRH-II. In goldfish, GnRH-induced luteinizing hormone (LH) secretion involves PKC; however, whether PKC mediates GnRH stimulation of GtH subunit mRNA levels is unknown. In this study, we used inhibitors and activators of PKC to examine its possible involvement in GnRH-induced increases in GtH-[alpha], follicle-stimulating hormone (FSH)-[beta] and LH-[beta] mRNA levels in primary cultures of dispersed goldfish pituitary cells. Treatment with PKC inhibitors calphostin C and GF109203X unmasked a basal repression of GtH subunit mRNA levels by PKC; both inhibitors increased GtH subunit mRNA levels in a dose-dependent manner. PKC activators, 12-Otetradecanoylphorbol 13-acetate (TPA), and 1,2-dioctanoyl-sn-glycerol, stimulated GtH subunit mRNA levels, whereas an inactive phorbol ester (4-[alpha]-TPA) was without effect. Thus, a dual, inhibitory and stimulatory, influence for PKC in the regulation of GtH subunit mRNA levels is suggested. In contrast, PKC inhibitor- and activatorinduced effects were, for the most part, additive to those of GnRH, suggesting that conventional and novel PKCs are unlikely to be involved in GnRH-stimulated increases in GtH subunit mRNA levels. Our data illustrate major differences in the signal transduction of GnRH effects on GtH secretion and gene expression in the goldfish pituitary. pituitary; gene expression; goldfish; gonadotropes; neuroendocrinology; protein kinase C

Dendrites represent arborising neurites in both vertebrates and invertebrates. However, in vertebrates, dendrites develop on neuronal cell bodies, whereas in higher invertebrates, they arise from very different neuronal structures, the primary neurites, which also form the axons. Is this anatomical difference paralleled by principal developmental and/or physiological differences? We address this question by focussing on one cellular model, motorneurons of Drosophila and characterise the compartmentalisation of these cells. We find that motorneuronal dendrites of Drosophila share with typical vertebrate dendrites that they lack presynaptic but harbour post-synaptic proteins, display calcium elevation upon excitation, have distinct cytoskeletal features, develop later than axons and are preceded by restricted localisation of Par6-complex proteins. Furthermore, we demonstrate in situ and culture that Drosophila dendrites can be shifted from the primary neurite to their soma, i.e. into vertebrate-like positions. Integrating these different lines of argumentation, we propose that dendrites in vertebrates and higher invertebrates have a common origin, and differences in dendrite location can be explained through translocation of neuronal cell bodies introduced during the evolutionary process by which arthropods and vertebrates diverged from a common urbilaterian ancestor. Implications of these findings for studies of dendrite development, neuronal polarity, transport and evolution are discussed. Keywords: Dendrite; Compartmentalisation; Mosaic analysis; Cytoskeleton; Transmitter receptors; Drosophila

The tetrapod limb, which has served as a paradigm for the study of development and morphological evolution, is becoming a paradigm for developmental evolution as well. In its origin and diversification, the tetrapod limb has undergone a great deal of remodeling. These morphological changes and other evolutionary phenomena have produced variation in mechanisms of tetrapod limb development. Here, we review that variation in the four major clades of limbed tetrapods. Comparisons in a phylogenetic context reveal details of development and evolution that otherwise may have been unclear. Such details include apparent differences in the mechanisms of dorsal ventral patterning and limb identity specification between mouse and chick and mechanistic novelties in amniotes, anurans, and urodeles. As we gain a better understanding of the details of limb development, further differences among taxa will be revealed. The use of appropriate comparative techniques in a phylogenetic context thus sheds light on evolutionary transitions in limb morphology and the generality of developmental models across species and is therefore important to both evolutionary and developmental biologists. Keywords: Tetrapod; Limb evolution; Developmental evolution; Fin-limb transition; Limb bud; Evolutionary transitions; Comparative development

The sex-specific slopes of Bateman's gradients have important implications for understanding animal mating systems, including patterns of sexual selection and reproductive competition. Intersexual differences in the fitness benefits derived from mating with multiple partners are expected to yield distinct patterns of reproductive success for males and females, with variance in direct fitness predicted to be greater among males. These analyses assume that typically all adults are reproductive and that failure to produce offspring is non-adaptive. Among some species of cooperatively breeding birds and mammals, however, nonbreeding adult alloparents are common and may comprise the majority of individuals in social groups. The presence of a large number of non-breeding adults, particularly when coupled with greater social suppression of reproduction among females, may alter the relative variance in direct fitness between the sexes, thereby generating an apparent contradiction to Bateman's Paradigm. To explore quantitatively the effects of nonbreeding alloparents on variance in reproductive success, we used genetic estimates of parentage and reproductive success drawn from the literature to calculate the relative variability in direct fitness for females and males in alloparental and 'other' societies of birds and mammals. Our analyses indicate that in mammals and, to a lesser extent, in birds, variability in direct fitness is greater among females in species characterized by the presence of non-breeding alloparents. These data suggest that social interactions, including social suppression of reproduction, are powerful determinants of individual direct fitness that may modify sex-specific patterns of reproductive variance from those described by Bateman.

Virus replication in higher vertebrates is restrained by IFNs that cause cells to transcribe genes encoding antiviral proteins, such as 2'-5' oligoadenylate synthetases. 2'-5' oligoadenylate synthetase is stimulated by dsRNA to produce 5'-phosphorylated, 2'-5'-linked oligoadenylates (2-5A), whose function is to activate RNase L. Although RNase L is required for a complete IFN antiviral response and mutations in the RNase L gene (RNASEL or HPC1) increase prostate cancer rates, it is unknown how 2-5A affects these biological endpoints through its receptor, RNase L. Presently, we show that 2-5A activation of RNase L produces a remarkable stimulation of transcription ([greater than or equal to] 20-fold) for genes that suppress virus replication and prostate cancer. Unexpectedly, exposure of DU145 prostate cancer cells to physiologic levels of 2-5A (0.1 [micro]M) induced approximately twice as many RNA species as it down-regulated. Among the 2-5A-induced genes are several IFN-stimulated genes, including IFN-inducible transcript 1/P56, IFN-inducible transcript 2/P54, IL-8, and IFN-stimulated gene 15. 2-5A also potently elevated RNA for macrophage inhibitory cytokine-1/nonsteroidal antiinflammatory drug-activated gene-1, a TGF-[beta] super-family member implicated as an apoptotic suppressor of prostate cancer. Transcriptional signaling to the macrophage inhibitory cytokine-1/nonsteroidal antiinflammatory drug-activated gene-1 promoter by 2-5A was deficient in HeLa cells expressing a nuclease-dead mutant of RNase L and was dependent on the mitogen-activated protein kinases c-Jun N-terminal kinase and extracellular signal-regulated kinase, both of which were activated in response to 2-5A treatments. Because 2-5A and RNase L participate in defenses against viral infections and prostate cancer, our findings have implications for basic cellular mechanisms that control major pathogenic processes. prostate | macrophage inhibotory cytokine 1 | HPC1 | RNASEL

In vertebrates, the senses of hearing and balance depend on hair cells, which transduce sounds with their hair bundles, containing actin-based stereocilia and microtubule-based kinocilia. A long-standing question in auditory science is the identity of the mechanically sensitive transduction channel of hair cells, thought to be localized at the tips of their stereocilia. Experiments in zebrafish implicated the transient receptor potential (TRP) channel NOMPC (drTRPN1) in this role; TRPN1 is absent from the genomes of higher vertebrates, however, and has not been localized in hair cells. Another candidate for the transduction channel, TRPA1, apparently is required for transduction in mammalian and nonmammalian vertebrates. This discrepancy raises the question of the relative contribution of TRPN1 and TRPA1 to transduction in nonmammalian vertebrates. To address this question, we cloned the TRPN1 ortholog from the amphibian Xenopus laevis, generated an antibody against the protein, and determined the protein's cellular and subcellular localization. We found that TRPN1 is prominently located in lateral-line hair cells, auditory hair cells, and ciliated epidermal cells of developing Xenopus embryos. In ciliated epidermal cells TRPN1 staining was enriched at the tips and bases of the cilia. In saccular hair cells, TRPN1 was located prominently in the kinocilial bulb, a component of the mechanosensory hair bundles. Moreover, we observed redistribution of TRPN1 upon treatment of hair cells with calcium chelators, which disrupts the transduction apparatus. This result suggests that although TRPN1 is unlikely to be the transduction channel of stereocilia, it plays an essential role, functionally related to transduction, in the kinocilium. ciliary | mechanosensory | transduction | transient receptor potential channel