Developmental Dynamics

BackgroundNeural crest cells (NCCs) are migratory embryonic stem cells that give rise to a diverse set of cell types. Here we describe the dynamic distribution of NCCs in developing embryos of the common wall lizard Podarcis muralis inferred from ten markers. Our aim is to provide insights into the NCC development of lacertid lizards and to infer evolutionary modifications by comparisons to other tetrapods. ResultsNCC migration is ongoing at oviposition, following three streams in the head and multiple in the trunk. From 21ss, we observe expression patterns indicating the beginning of differentiation towards mesenchymal and neuronal fates. By 35ss, migration is restricted to caudal levels, and fully differentiated chromaffin cells are observed. ConclusionsWe find that some markers show patterns that differ from other tetrapods. For example, the antibody HNK-1 labels three NCC streams from the hindbrain while some comparable reptile studies describe four. However, the information emerging from all markers combined shows that the overall spatiotemporal distribution of NCCs in the common wall lizard is largely conserved with that of other tetrapods. Our study highlights the dynamic nature of seemingly canonical marker genes and provides the first description of spatiotemporal NCC dynamics in a lacertid lizard.

Centrosome is a key cell signaling hub, orchestrating mitotic events and the distribution of cell fate determinants. Centrosomal dysfunction results in mitotic aberrations such as microtubule disorganization, mitotic spindle anomalies, and orientation defects, leading to cell division errors. Yet, how centrosomal defects are communicated to cell cycle checkpoints during embryogenesis remains unresolved. Centrosomal protein 57 (CEP57) is best known for its role in centrosome organization, where it regulates microtubule nucleation, stabilization, and spindle assembly. Here, we uncover previously undescribed, distinct functions of Cep57 in regulating G1/S progression, centrosome integrity, and DNA damage responses during early embryogenesis. In early zebrafish embryos, Cep57 localizes to both the nucleus and centrosomes, suggesting dual roles in cytoskeletal organization and nuclear cell cycle regulation. Cep57 interacts with Rad21, and its loss results in consequential depletion of Rad21, leading to supernumerary nuclei and defects in pericentriolar material organization. Our results also show that Cep57 interacts with Geminin, and it induces an Rb1-dependent G1 arrest. Hence, lack of Cep57 results in widespread cell cycle defects, genome instability, and increased apoptosis. Quantitative proteomics reveals induction of DNA damage responses and checkpoint pathways, indicating engagement of genome surveillance programs downstream of centrosome dysfunction. Thus, we show that Cep57 functions as a molecular bridge linking centrosome integrity to G1/S checkpoint control in early embryos. These cellular defects precede and likely underlie neural tissue apoptosis and microcephaly-associated characteristics observed in Cep57-deficient embryos. Together, our findings identify Cep57 as a critical integrator of centrosome organization, cell cycle progression, and genome stability, expanding its functional scope beyond canonical centrosome regulation during vertebrate embryogenesis.

The tetrapod limb has long served as a model for elucidating molecular and cellular mechanisms driving tissue patterning, development and evolution. While significant advances have been made in understanding the drivers of limb initiation, outgrowth, and patterning, the early morphogenetic processes that transform the lateral plate mesoderm (LPM) into limb fields remain less resolved. Marsupial mammals provide a unique opportunity to investigate these foundational processes due to their accelerated forelimb development, driven by the functional demands of altricial neonates to crawl into the pouch at birth. Heterochronic formation of the forelimbs occurs prior to development of other surrounding structures, offering unparalleled insights into the plasticity of limb field specification. Here, we reveal that marsupial limb initiation and outgrowth bypasses physical subdivision of the LPM, a process previously considered critical for tetrapod limb formation. Instead, limb development proceeds through early activation of LPM-associated genes and proliferation before coelom formation, demonstrating remarkable morphogenetic plasticity. This evolutionary adaptation enables heterochronic limb development, redefining conserved processes to meet extreme functional constraints. These findings challenge previous models of tetrapod limb specification, highlighting the evolutionary plasticity of limb patterning mechanisms and reshaping our understanding of how selective pressures influence foundational developmental events.

BackgroundEndocytosis constitutes a fundamental cellular process governing development through coordinated regulation of plasma membrane remodeling and ciliogenesis, processes essential for cell shape changes and embryonic development. Although Twist1 null embryos display complete cranial neural tube closure defects and conditional knockout in neuroectoderm disrupts cranial neural crest cell fate determination and delamination, the function of TWIST1 in neural tube morphogenesis remains unknown. We investigated the basis underlying neuroectodermal morphological abnormalities in TWIST1 mutant embryos, specifically the formation of ectopic lateral bending points and cellular disorganization, by examining TWIST1 function in cilia formation, adherens junction integrity, and endocytic vesicle dynamics. ResultsImmunofluorescence analysis revealed that cytosolic TWIST1 colocalizes with {beta}-catenin and endocytic regulators LRP2 and RAB11B along the apical surface of cranial neuroectoderm. Twist1 knockout resulted in reduced ciliary length and number. Quantitative PCR and Western blot analyses demonstrated upregulation of RAB11B and {beta}-catenin at mRNA and protein levels in Twist1 mutants. This molecular dysregulation coincided with increased accumulation of apical endocytic vesicles and altered expression profiles of endocytic component genes, ultimately modifying the apical neuroectodermal cell-cell junctions. ConclusionOur findings establish TWIST1 as a regulator of neuroectodermal morphology, demonstrating its ability to modulate ciliogenesis, endocytic vesicle dynamics, and cell-cell integrity.

BackgroundMorphogenesis depends on spatial and temporal coordination of signaling pathways, yet the colocalization of proteins across pathways remains poorly understood. Here we examine cellular and histological localization of regulatory proteins forming core craniofacial developmental pathways during beak morphogenesis of the zebra finch (Taeniopygia guttata). ResultsWe present an atlas of spatiotemporal coexpression of {beta}-catenin, Bmp4, CaM, Dkk3, Fgf8, Ihh, Tgf{beta}2, and Wnt4 across embryonic stages HH29-42 revealing both established and novel patterns of expression. Overall, in the earliest stages (HH29-32), most proteins show broad and overlapping expression across epithelial and mesenchymal tissues. By stage HH36, expression becomes increasingly compartmentalized, with pronounced differentiation among tissue types. Notably, at later stages, proteins showed tissue-specific distributions in boundary versus core regions of chondrogenic and osteogenic domains indicating coordinated cross-pathway patterning during cartilage and bone formation. ConclusionsOsteogenesis in the zebra finch beak is organized by coordinated signaling between boundary-associated cells and differentiating cores, with cross-pathway feedback establishing bone and cartilage differentiation while maintaining boundaries. Our results corroborated core elements of craniofacial signaling dynamics, while revealing unexpected subcellular localization for several proteins that showed regulatory complexity not captured by prior transcript-level maps. This atlas provides a protein-level baseline for comparative and mechanistic studies of beak morphogenesis.

Embryonic palate development involves bilateral vertical growth of palatal shelves - extensions from the maxillary processes - next to the tongue until embryonic day (E) 13.5. Following vertical growth, palatal shelves elevate and adhere above the tongue by E14.5. Current models indicate that this process of elevation involves a complex vertical to horizontal reorienting of the palatal shelves. While earlier studies have implied that this is a rapid process, the precise timing has not been resolved. To understand the dynamics of palatal shelf elevation, we employed time-restricted pregnancies with a one-hour resolution and magnetic resonance imaging of intermediate stages. Our data showed that in almost all C57BL/6J embryos, palatal shelves have not yet elevated by E14.0. However, six hours later at E14.25, palatal shelves have completed elevation in 80% of embryos. Interestingly, all E14.25 embryos with unelevated palatal shelves (20%) were female, suggesting a delay in female embryos. In FVB/NJ embryos, the elevation window started earlier (E13.875-E14.25) without any noticeable sex differences. We frequently captured an intermediate stage with unilateral elevation of either right or left palatal shelf. Magnetic resonance imaging of various stages showed that palatal shelf elevation began with the formation of bilateral bulges in the posterior. These bulges progressed laterally and anteriorly over time. During elevation, we observed increased cell proliferation in the lingual region of the palatal shelf. Within the bulge, cell orientation was acutely tilted towards the tongue and actomyosin activity was increased, which together may participate in the projection of the bulge in the horizontal direction. Thus, our data reveal novel insights into the rapid dynamic changes in palatal shelf elevation that lay the foundation for future studies of normal and abnormal palatogenesis.

BackgroundActivity of the receptor tyrosine kinase PDGFR and the tyrosine phosphatase SHP2 are critical for vertebrate craniofacial development. We sought to determine the effect of SHP2 binding to PDGFR via phenotypic and biochemical analyses of an allelic series of mouse embryos with combined loss of both proteins in the neural crest lineage. ResultsWe demonstrated that SHP2 preferentially binds PDGFR/ homodimers among the three PDGFR dimers. Analysis of allelic series mutant embryos revealed increased cell death in the lateral nasal and maxillary processes at E10.5, variably penetrant facial blebbing, facial hemorrhaging, midline clefting and loss of the mandibular region at E13.5, and widespread craniofacial bone and cartilage defects at birth. Further, we showed that loss of SHP2 leads to increased phosphorylation of PDGFR and the downstream effector Erk1/2 in E10.5 allelic series mutant embryo lysates. ConclusionsTogether, our findings demonstrate additive effects on craniofacial development upon conditional ablation of PDGFR and SHP2 in the mouse neural crest lineage and indicate that SHP2 may negatively and positively regulate PDGFR signaling through distinct mechanisms.

Light and transmission electron microscopy were used to identify changes in ultrastructure of the olfactory pit of larval zebrafish (Danio rerio) that occur as a result of age and altered environmental light levels. Larvae were reared under control/cyclic light or constant light condition until 4, 8, and 15 days postfertilization (dpf). The larval olfactory pit consisted of an epithelium that varies from simple to pseudostratified to stratified and contained three types of receptor cells: ciliated, microvillar and ciliated crypt. A variety of non-receptor cells were also identified: kinociliate non-sensory supporting cells, vesicular supporting cells, basal cells and an occasional intruder, such as a neutrophil or a lymphocyte. Microvilli projecting from microvillus receptor, kinociliate, and vesicular supporting cells were single, forked, or doubly forked. Junctional complexes were evident between a variety of cells including adjacent epidermal cells, an epidermal cell and a kinociliate cell, a kinociliate and a vesicular supporting cell, and two vesicular supporting cells. Desmosomes were also observed between adjacent cell types. With age, the olfactory epithelium thinned and vesicle number varied. In larvae reared in constant light, mitotic figures were evident, microvillar receptor cells were absent, and, at 4 dpf, some ultrastructural components were similar to those observed in 8 dpf control animals, suggesting precocious development. These findings suggest that constant light rearing alters the timing of receptor replacement, supporting previous work showing that rearing light levels impact sensory system growth and development.

BackgroundPacific saury Cololabis saira is one of the important food resources drawing attention for its recent rapid decline of catch. Their life cycle and embryonic development have been largely unknown. It is important to clarify how the habitat and reproduction of this species have been affected by the global changes of aquatic environment. ResultsWe obtained fertilized eggs of C. saira, by spontaneous spawning and artificial fertilization, and observed the embryonic development up to larval stages. Embryonic stages are documented with major periods of developmental events; cleavage, gastrulation (epiboly) and somitogenesis and organogenesis. Remarkably, segmentation of somites starts in the middle of epiboly, unlike other well-documented teleost species such as zebrafish and medaka. Morphological changes in larval stage up to feeding juvenile is also described. Growth speed of larval Pacific saury is dramatically rapid, in comparison to closely related beloniform fish such as medaka. ConclusionsIn comparison to medaka, early embryogenesis of saury proceeds slowly, although being followed by early onset of somitogenesis. This might be partly responsible for the rapid growth into adult (larger than 20 cm in body length) in only half a year. Further studies on embryonic development will uncover the molecular mechanisms underlying the characteristics of Pacific saury as an excellent source of nutrition and as an indicator of major environmental changes such as global warming.

The mammalian superior colliculus and its non-mammalian homolog, the optic tectum (OT), are midbrain structures that integrate multimodal sensory inputs and guide non-voluntary movements in response to prevalent stimuli. Recent studies have implicated this structure as a possible site affected in Autism Spectrum Disorder (ASD). Interestingly, fetal exposure to valproic acid (VPA) has also been associated with an increased risk of ASD in humans and animal models. Therefore, we took the approach of determining the effects of VPA treatment on zebrafish OT development as a first step in identifying the mechanisms that allow its formation. We describe the normal OT development during the first 5 days of development and show that in VPA treated embryos, while proliferation of the OT neuroepithelium continued, neuronal specification stalled. This was followed by impairment of neurite extension and complexity, suggesting that in addition to neurogenesis, VPA treatment affects axonogenesis and dendritogenesis. VPA treatment was most detrimental during the first three days of development and did not appear to be linked to oxidative stress. In conclusion, our work provides a foundation for research into mechanisms driving OT development, as well as the relationship between the OT, VPA, and ASD.

Despite a wealth of knowledge on the mechanisms underlying craniofacial morphogenesis during gestation, the roles of fetal macrophages and osteoclasts during this process remain less well characterized. Here, we used the pharmacological inhibitor PLX5622 to disrupt colony stimulating factor-1 receptor (CSF1R) signaling, which is essential for macrophage and osteoclast proliferation, differentiation, and survival. Prenatal PLX5622 exposure resulted in [~]50% depletion of CSF1R+ macrophages, with complete loss of osteoclasts. While there were no notable changes in craniofacial nerve or muscle development, prenatal exposure to PLX5622 resulted in skull doming and cranial suture impairments, in addition to disruptions to development of the premaxilla, mandible, ear ossicles, palate, and cranial base. In response to PLX5622 exposure, cytokine and chemokine signaling was altered and neural crest proliferation was impaired. Our data also highlight sex- and strain-specific differences in PLX5622 phenotypes and together demonstrate that CSF1R+ macrophages and osteoclasts are essential for craniofacial morphogenesis.

BackgroundAnterior eye development has been explored in different vertebrate species ranging from fish to mammals. However, missing from this diverse group is a representative of reptiles. A promising candidate to fill this void is the brown anole, Anolis sagrei, which is easily raised in the laboratory and for which genome editing techniques exist. Here we provide a detailed histological analysis of the development of the anterior structures of the eye in A. sagrei, which include the cornea, iris, ciliary body, lens, trabecular meshwork, and sclera ossicles. ResultsDevelopment of the anterior segment in Anoles proceeds as for other vertebrates with the lens forming first followed by the cornea, then the iris, ciliary body, trabecular meshwork, and sclera ossicles. The onset of these latter structures occurs first temporally than nasally. Unlike the eyes of mammals and birds, anoles possess a remarkably thin cornea, flat ciliary body, and a trabecular meshwork that lacks an obvious Schlemms canal. ConclusionsThis study highlights several features present in anoles and represents an important step towards understanding reptile eye development. Key FindingsO_LIThe anole cornea epithelium is thin, composed mainly of a single basal cell layer. C_LIO_LIThe ciliary body lacks a ciliary process. C_LIO_LIIris and ciliary body formation occur in a spatiotemporal fashion, developing first temporally then nasally. C_LIO_LIThe anole trabecular meshwork is composed of a spongiform tissue and lacks a Schlemms canal. C_LI

BackgroundMidline establishment is a fundamental process during early embryogenesis for Bilaterians. Midline patterning in nonamniotes can occur without mitosis, through Planar Cell Polarity (PCP) signaling. By contrast, amniotes utilize both cell proliferation and PCP signaling for patterning early midline landmark, the primitive streak (PS). This study examined their roles for midline patterning at post PS-extension. ResultsIn contrast to PS extension stages, embryos under mitotic arrest during the post PS-extension preserved notochord (NC) extension and Hensens node (HN)/PS regression judged by both morphology and marker genes, although they became shorter, and laterality was lost. Remarkably, no or background level of expression was detected for the majority of PCP core components in the NC-HN-PS area at post PS-extension stages, except for robustly detected prickle-1. Morpholino knockdown of Prickle-1 showed little influence on midline patterning, except for suppressed embryonic growth. Lastly, associated with mitotic arrest-induced size reduction, midline tissue cells displayed hypertrophy. ConclusionThus, the study has identified at least two distinct mitosis sensitivity phases during early midline pattering: One is PS extension that requires both mitosis and PCP, and the other is mitotic arrest-resistant midline patterning with little influence by PCP at post PS-extension stages.

Feathers are the most complex and diverse epidermal appendages found in vertebrates. Their unique hierarchical organization and development is based on a diversity of cell types and morphologies. Despite being well characterized morphologically and extensive molecular developmental research focusing on candidate genes, little is known about the gene regulatory identities of these presumptive feather cell types. Here, we use single cell and single nuclear RNA sequencing with in situ hybridization to identify and characterize cells types in embryonic chicken feathers. We show that the distinct cell morphologies correspond to feather cell types with distinct gene expression profiles. We also describe a previously unidentified cell type, the basal barb ridge epithelium, which appears to play a role in signaling necessary for barb ridge differentiation and pulp cap production. We also analyze RNA velocity trajectories of developing feather cells, and find distinct developmental trajectories for epidermal cells that constitute the mature feather and those that function only in feather development. Finally, we produce an evolutionary tree of feather cell types based on transcription factor expression in order to test prior developmental hypotheses about feather evolution. Our tree is consistent with the developmental model of feather evolution, and sheds light on the influence of ancestral epidermal stratification on feather cell evolution. This transcriptomic approach to study feather cell types helps lay the ground work for understanding the developmental evolutionary complexity and diversity of feathers.

Congenital intestinal atresia (IA) is a birth defect characterised by the absence or closure of part of the intestine. Although genetic factors are implicated, mechanistic understanding has been hindered by the lack of suitable animal models. Here, we describe a medaka (Oryzias latipes) mutant, generated by N-ethyl-N-nitrosourea (ENU) mutagenesis, that develops IA during embryogenesis. Positional cloning identified a nonsense mutation in mypt1, encoding myosin phosphatase target subunit 1. Mutant embryos exhibited ectopic accumulation of F-actin and phosphorylated myosin regulatory light chain (Mrlc) in the intestinal epithelium, consistent with disrupted actomyosin regulation. These cytoskeletal abnormalities were accompanied by epithelial disorganisation without notable alterations in cell proliferation, motility, or apoptosis. Inhibition of myh11a, encoding smooth muscle (SM) myosin heavy chain, ameliorated the IA phenotype but Blebbistatin treatment completely rescued the defect, suggesting a non-contractile role prior to SM maturation. Together, these findings demonstrate that mypt1 loss disrupts intestinal morphogenesis through actomyosin dysregulation. Given the recent clinical identification of IA associated with MYPT1 mutations, this medaka model offers a valuable platform to investigate the developmental and molecular basis of MYPT1-associated IA in human.

BackgroundMaternal nutrition is increasingly recognized as a modulator of offspring skeletal development. While genetics has long been considered the primary determinant of craniofacial morphology, emerging evidence suggests that prenatal and early postnatal dietary exposures also influence facial morphology. However, how maternal diet differentially affects male and female craniofacial structures remains unclear. This study aimed to examine the effects of a maternal high-fat, high-sugar (HFHS) diet on craniofacial and dental morphology in first-(F1) and second-(F2) generation adult mice. Materials and MethodsFemale mice were fed a HFHS diet for six weeks before mating and throughout pregnancy and lactation. F1 offspring were weaned to a standard chow diet, and a subset of female F1 offspring were bred to produce F2 offspring, also maintained on chow. Craniofacial skeletal and dental structures of adult F1 and F2 mice at 1-year of age were assessed using micro-computed tomography for linear and geometric morphometrics. ResultsHFHS diet exposure significantly reduced midfacial and mandibular length in F1 females, and these effects persisted in F2 females. Mandibular shape differences were also observed in both generations of females. In males, skull size remained unchanged, though subtle mandibular shape changes were noted in F1 only. Tooth size was reduced in both sexes of F1 offspring but not in F2. ConclusionMaternal HFHS diet induces sex- and jaw-specific alterations in craniofacial morphology, with skeletal changes persisting in females across generations, while dental effects did not persist beyond one generation. These findings highlight the potential for maternal dietary habits to exert lasting, intergenerational influences on offspring facial form.

BackgroundDuring development, axons are organized into bundles, a process known as axonal fasciculation. The zebrafish lateral line nerve has been used as a model to study axonal fasciculation; however, the underlying mechanisms are not yet fully understood. Although Fgf3 and Fgf10a are well known to regulate the migration of the lateral line primordium along which the lateral line nerve projects, their roles in the organization of the lateral line nerve itself have not been clarified. Resultsfgf3,10a double mutants exhibited lateral line axonal defasciculation accompanied by an increased number of Schwann cells. Live imaging revealed a marked increase in Schwann cell proliferation and demonstrated that newly divided Schwann cells migrate along axons and infiltrate interaxonal spaces, thereby expanding these spaces and disrupting axonal fasciculation. Pharmacological manipulations further implicated a contribution of Nrg1-ErbB signaling to this phenotype. ConclusionsOur findings suggest that Fgf3 and Fgf10a are required to restrict Schwann cell proliferation and infiltration, thereby ensuring axonal fasciculation during lateral line development.

Craniofacial birth defects, such as cleft lip and palate, are among the most common congenital anomalies and often arise from disruptions in early facial patterning. Many of these defects are linked to environmental teratogens, yet such exposures cannot be directly tested in humans, making animal models essential for evaluating developmental risks. Xenopus laevis offers a powerful solution: its tadpoles develop externally, share deeply conserved craniofacial patterning mechanisms with humans, and provide an accessible platform for uncovering how environmental exposures reshape facial structures during development. Here, we present the XenCart Protocol, a reproducible workflow for Alcian Blue staining and quantitative morphometric analysis of Xenopus craniofacial cartilage. This method provides clear visualization of individual cartilage elements and can be readily applied to investigate genetic or environmental perturbations. The Xenopus craniofacial skeleton contains distinct cartilaginous structures that perform key biomechanical functions and share strong homology with regions of the human craniofacial skeleton. These similarities allow direct comparison of developmental outcomes across vertebrates. As part of a CURE-based undergraduate course, the XenCart Protocol was used to measure jaw cartilage dimensions in tadpoles exposed to an emerging teratogen, e-liquids used in vaping. E-liquid exposure caused consistent reductions across major craniofacial cartilages, including shorter Meckels cartilage, narrowed infrarostral width, decreased basihyobranchial and ceratohyal dimensions, and reduced suprarostral angles, reflecting an overall shift toward a smaller, more compact craniofacial morphology. These patterns suggest potential disruption of neural crest cell migration or signaling pathways for craniofacial cartilage development, mechanisms that, if similarly affected in humans, could contribute to midfacial narrowing, jaw underdevelopment, or increased vulnerability to conditions such as orofacial clefts. The ability to detect robust, structure-specific differences highlights the sensitivity of the protocol and its strong alignment with student-led research. These findings also pinpoint the precise regions of the jaw most affected by e-liquid exposure, providing a foundation for uncovering the developmental mechanisms driving these craniofacial changes. In summary, the XenCart Protocol provides a standardized, scalable method for quantifying craniofacial cartilage development and offers a powerful platform for both mechanistic research and undergraduate training in developmental biology and toxicology.

The orientation and distribution of fibrillar collagen are critical determinants of the shape and mechanical properties of bones and organs.1-3 However, how they are spatially organized within tissues is still poorly understood,4-7 as visualizing these collagen architectures remains challenging. Actinotrichia (AT), the spear-shaped fibrillar collagen structures located at the distal tips of fish fins, are easily observable due to their large size and distinctive morphology8-14 and have recently emerged as a model system for studying collagen fiber organization.15-19 In this study, we generated knockout lines for the fish-specific extracellular matrix (ECM) genes actinodin1 and actinodin2 (and1/2), which are lost in tetrapods.12 Loss of these genes dramatically altered the orientation of collagen fibers, thereby inducing changes in fin morphology. In the wild-type fins, AT are orderly arranged beneath the epidermis, forming layers parallel to the fin surface, and their individual fibers radiate distally toward the fin tip. In contrast, double knockout (dKO) of and1/2 results in overall fin reduction accompanied by increased thickness. Examination of the collagen structure distribution revealed the presence of aberrant collagen fibers oriented perpendicular to the fin epidermis. Moreover, the vertically oriented fibers contributed to thickening of the mesenchymal region in which they were distributed. The number of abnormal fibers increased with the severity of and1/2 deficiency, suggesting that collagen fibers in fins inherently tend to align perpendicular to the epidermis when these genes are absent. Furthermore, in tetrapods lacking the and gene family--specifically amphibians, the tetrapod group most closely related to fish20--examination of the developing limb, the organ homologous to paired fins in fish,21 revealed collagen fibers oriented perpendicular to the epidermis. The distribution pattern also resembled that observed in the fin buds of and1/2 dKO fish. Together, these findings highlight collagen patterning alterations as a previously unrecognized factor contributing to the evolutionary divergence between thinned fins and thickened limbs. Moreover, the identification of mutants that dramatically alter collagen fiber orientation is unprecedented, suggesting that analysis of Actinodin (And) function unveil the mechanisms underlying collagen matrix formation.22-28

Chondrichthyans (cartilaginous fishes) form the sister group to osteichthyans (bony fishes) and therefore occupy a key phylogenetic position for comparative studies of early vertebrate evolution. Despite their importance, chondrichthyan development remains understudied relative to established model systems such as mouse, chick, and zebrafish, in part because of limited embryo accessibility and the lack of standardized laboratory resources for rearing. Here, we present the epaulette shark Hemiscyllium ocellatum, a small, oviparous shark as a tractable laboratory system for studying shark development. We provide an overview of epaulette shark husbandry requirements and generate a comprehensive micro-computed tomography imaging series spanning embryonic development through hatching. This dataset provides a three-dimensional anatomical atlas of development for a representative chondrichthyan species. By preserving whole embryos in three dimensions, micro-CT imaging enables developmental morphologies to be visualized at high resolution and in near-native anatomical context. Together with the recently published epaulette shark genome, this developmental atlas helps establish the Epaulette shark for comparative anatomical, developmental, and genomic studies.