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Homology in vertebrate body plans is traditionally ascribed to the high-level conservation of regulatory components within the genetic programs governing them, particularly during the "phylotypic stage." However, advancements in embryology and molecular phylogeny have unveiled the dynamic nature of gene repertoires responsible for early development. Notably, the Nodal and Lefty genes, members of the transforming growth factor-beta superfamily producing intercellular signaling molecules and crucial for left-right (L-R) symmetry breaking, exhibit distinctive features within their gene repertoires. These features encompass among-species gene repertoire variations resulting from gene gain and loss, as well as gene conversion. Despite their significance, these features have been largely unexplored in a phylogenetic context, but accumulating genome-wide sequence information is allowing the scrutiny of these features. It has exposed hidden paralogy between Nodal1 and Nodal2 genes resulting from differential gene loss in amniotes. In parallel, the tandem cluster of Lefty1 and Lefty2 genes, which was thought to be confined to mammals, is observed in sharks and rays, with an unexpected phylogenetic pattern. This article provides a comprehensive review of the current understanding of the origins of these vertebrate gene repertoires and proposes a revised nomenclature based on the elucidated history of vertebrate genome evolution., (© 2024 The Authors. Developmental Dynamics published by Wiley Periodicals LLC on behalf of American Association for Anatomy.)

Background: Studying cartilaginous fishes (chondrichthyans) has helped us understand vertebrate evolution and diversity. However, resources such as genome sequences, embryos, and detailed staging tables are limited for species within this clade. To overcome these limitations, we have focused on a species, the brownbanded bamboo shark (Chiloscyllium punctatum), which is a relatively common aquarium species that lays eggs continuously throughout the year. In addition, because of its relatively small genome size, this species is promising for molecular studies., Results: To enhance biological studies of cartilaginous fishes, we establish a normal staging table for the embryonic development of the brownbanded bamboo shark. Bamboo shark embryos take around 118 days to reach the hatching period at 25°C, which is approximately 1.5 times as fast as the small-spotted catshark (Scyliorhinus canicula) takes. Our staging table divides the embryonic period into 38 stages. Furthermore, we found culture conditions that allow early embryos to grow in partially opened egg cases., Conclusions: In addition to the embryonic staging table, we show that bamboo shark embryos exhibit relatively fast embryonic growth and are amenable to culture, key characteristics that enhance their experimental utility. Therefore, the present study is a foundation for cartilaginous fish research. Developmental Dynamics 247:712-723, 2018. © 2017 Wiley Periodicals, Inc., (© 2018 The Authors Developmental Dynamics published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.)

Background: The inner ear and epibranchial ganglia of vertebrates arise from a shared progenitor domain that is induced by FGF signalling, the posterior placodal area (PPA), before being segregated by Wnt signalling. One of the first genes activated in the PPA is the transcription factor Pax2. Loss-of- and gain-of function studies have defined a role for Pax2 in placodal morphogenesis and later inner ear development, but have not addressed the role Pax2 plays during the formation and maintenance of the PPA., Results: To understand the role of Pax2 during the development of the PPA, we used over-expression and repression of Pax2. Both gave rise to a smaller otocyst and repressed the formation of epibranchial placodes. In addition, cell cycle analysis revealed that Pax2 suppression reduced proliferation of the PPA., Conclusions: Our results suggest that Pax2 functions in the maintenance but not the induction of the PPA. One role of Pax2 is to maintain proper cell cycle proliferation in the PPA., (Copyright © 2012 Wiley Periodicals, Inc.)

We have isolated four homologs of Engrailed genes from the Japanese lamprey, Lethenteron japonicum, an agnathan that occupies a critical phylogenic position between cephalochordates and gnathostomes. We named these four genes LjEngrailedA, LjEngrailedB, LjEngrailedC, and LjEngrailedD. LjEngrailedA, LjEngrailedB, and LjEngrailedD share a major expression domain in the presumptive midbrain-hindbrain boundary region of the central nervous system, although their levels and timing of expression differed. On the other hand, LjEngrailedC transcripts were in the pharyngeal ectoderm and the ventral ectoderm of the body wall. In addition, LjEngrailedA was expressed in the ventral side of the epibranchial muscle precursors. LjEngrailedD transcripts were seen in the mesodermal cells of the mandibular arch and later in a group of cells responsible for the formation of the upper lip, lower lip, and velum. Our results provide clues to the evolution of these structures as well as a possible scenario for duplication events of Engrailed genes.

Turtles have a body plan unique among vertebrates in that their ribs have shifted topographically to a superficial layer of the body and the trunk muscles are greatly reduced. Identifying the developmental factors that cause this pattern would further our understanding of the evolutionary origin of the turtles. As the first step in addressing this question, we replaced newly developed epithelial somites of the chicken at the thoracic level with those of the Chinese soft-shelled turtle Pelodiscus sinensis (P. sinensis somites into a chicken host) and observed the developmental patterning of the grafted somites in the chimera. The P. sinensis somites differentiated normally in the chicken embryonic environment into sclerotomes and dermomyotomes, and the myotomes differentiated further into the epaxial and hypaxial muscles with histological morphology similar to that of normal P. sinensis embryos and not to that of the chicken. Epaxial dermis also arose from the graft. Skeletal components, however, did not differentiate from the P. sinensis sclerotome, except for small fragments of cartilage associated with the host centrum and neural arches. We conclude that chicken and P. sinensis share the developmental programs necessary for the early differentiation of somites and that turtle-specific traits in muscle patterning arise mainly through a cell-autonomous developmental process in the somites per se. However, the mechanism for turtle-specific cartilage patterning, including that of the ribs, is not supported by the chicken embryonic environment.