Reptile genomes open the frontier for comparative analysis of amniote development and regeneration

Abstract

Developmental genetic studies of vertebrates have focused primarily on zebrafish, frog and mouse models, which have clear application to medicine and well-developed genomic resources. In contrast, reptiles represent the most diverse amniote group, but have only recently begun to gather the attention of genome sequencing efforts. Extant reptilian groups last shared a common ancestor ~280 million years ago and include lepidosaurs, turtles and crocodilians. This phylogenetic diversity is reflected in great morphological and behavioral diversity capturing the attention of biologists interested in mechanisms regulating developmental processes such as somitogenesis and spinal patterning, regeneration, the evolution of "snake-like" morphology, the formation of the unique turtle shell, and the convergent evolution of the four-chambered heart shared by mammals and archosaurs. The complete genome of the first non-avian reptile, the green anole lizard, was published in 2011 and has provided insights into the origin and evolution of amniotes. Since then, the genomes of multiple snakes, turtles, and crocodilians have also been completed. Here we will review the current diversity of available reptile genomes, with an emphasis on their evolutionary relationships, and will highlight how these genomes have and will continue to facilitate research in developmental and regenerative biology.

Identification and comparative analysis of the epidermal differentiation complex in snakes

“…In snakes, the superficial layers of the epidermis are detached as a single, coherent sheet whereas other squamates (lizards and geckos) shed multiple smaller flakes. While the dynamic regulation and composition of snake skin has been partially revealed over the past fifty years789, the recent availability of whole genome sequences of snakes and other reptiles allows, for the first time, to identify genes that encode epidermal proteins and, by comparative genomics, to establish a basis for building hypotheses on the molecular evolution of the epidermis in snakes101112.…”

Current Understanding on Tail Regeneration in Green Anoles (Anolis carolinensis)

“…Differentially expressed genes related to Wnt signaling and lizard tail tip regeneration also show similarity with regeneration of salamander tail tip and mouse digit tip. This suggests that genes responsible for regeneration is conserved in all tetrapod vertebrates [14]. [38].…”

“…In regenerated tails, muscles are irregular and elongated whereas muscles of original tails are arranged into nested cones forming myomeres attached to myosepta [14]. Regeneration of muscle tissues during tail regrowth in lizards is characterized by segmental myomeres [3] located beneath the dermis of new tail [42].…”

“…Further, muscles within quadrants are attached to the vertebral column (via robust tendons) with regular patterns [21,31] and cover central myoseptum (absent in regenerated tail) [31]. Abundance of connective tissue is also identified in regenerated tails than in original tail [14,21].…”

“…Previously, genetic studies of developmental process were mainly based on frog, mouse or zebrafish models [14]. Now reptiles, particularly lizards, are coming into the mainstream because of their diversity and unique feature of regeneration.…”