Reptile Embryology and Regeneration

Does the pancreas of gekkotans differentiate similarly? Developmental structural and 3D studies of the mourning gecko (Lepidodactylus lugubris) and the leopard gecko (Eublepharis macularius)

This study investigated the pancreas differentiation of two species of gekkotan families-the mourning gecko Lepidodactylus lugubris (Gekkonidae) and the leopard gecko Eublepharis macularius (Eublepharidae)-based on two-dimensional (2D) histological samples and three-dimensional (3D) reconstructions of the position of the pancreatic buds and the surrounding organs. The results showed that at the moment of egg laying, the pancreas of L. lugubris is composed of three distinct primordia: one dorsal and two ventral. The dorsal primordium differentiates earlier than either ventral primordium. The right ventral primordium is more prominent and distinctive, starting to form earlier than the left one. Moreover, at this time, the pancreas of the leopard gecko is composed of the dorsal and right ventral primordium and the duct of the left ventral primordium. It means that the leopard gecko's left primordium is a transitional structure. These results indicate that the early development of the gekkotan pancreas is species specific. The pancreatic buds of the leopard and mourning gecko initially enter the duodenum by separate outlets, similar to the pancreas of other vertebrates. The pancreatic buds (3 of the mourning gecko and 2 of the leopard gecko) fuse quickly and form an embryonic pancreas. After that, the structure of this organ changes. After fusion, the pancreas of both gekkotans comprises four parts: the head of the pancreas (central region) and three lobes: upper, splenic, and lower. This organ develops gradually and is very well distinguished at hatching time. In both gekkotan species, cystic, hepatic, and pancreatic ducts enter the duodenum within the papilla. During gekkotan pancreas differentiation, the connection between the common bile duct and the dorsal pancreatic duct is associated with intestinal rotation, similar to other vertebrates.

Avian cardiomyocyte architecture and what it reveals about the evolution of the vertebrate heart

Bird cardiomyocytes are long, thin and lack transverse (t)-tubules, which is akin to the cardiomyocyte morphology of ectothermic non-avian reptiles, who are typified by low maximum heart rates and low pressure development. However, birds can achieve greater contractile rates and developed pressures than mammals, whose wide cardiomyocytes contain a dense t-tubular network allowing for uniform excitation-contraction coupling and strong contractile force. To address this apparent paradox, this paper functionally links recent electrophysiological studies on bird cardiomyocytes with decades of ultrastructure measurements. It shows that it is the strong transsarcolemmal Ca2+ influx via the L-type Ca2+ current (ICaL) and the high gain of Ca2+-induced Ca2+ release from the sarcoplasmic reticulum (SR), coupled with an internal SR Ca2+ release relay system, that facilitates the strong fast contractions in the long thin bird cardiomyocytes, without the need for t-tubules. The maintenance of an elongated myocyte morphology following the post-hatch transition from ectothermy to endothermy in birds is discussed in relation to cardiac load, myocyte ploidy, and cardiac regeneration potential in adult cardiomyocytes. Overall, the paper shows how little we know about cellular Ca2+ dynamics in the bird heart and suggests how increased research efforts in this area would provide vital information in our quest to understand the role of myocyte architecture in the evolution of the vertebrate heart. This article is part of the theme issue 'The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease'. Please see glossary at the end of the paper for definitions of specialized terms.

Convergent developmental patterns underlie the repeated evolution of adhesive toe pads among lizards

How developmental modifications produce key innovations, which subsequently allow for rapid diversification of a clade into new adaptive zones, has received much attention. However, few studies have used a robust comparative framework to investigate the influence of evolutionary and developmental constraints on the origin of key innovations, such as the adhesive toe pad of lizards. Adhesive toe pads evolved independently at least 16 times in lizards, allowing us to examine whether the patterns observed are general evolutionary phenomena or unique, lineage-specific events. We performed a high-resolution comparison of plantar scale development in 14 lizard species in Anolis and geckos, encompassing five independent origins of toe pads (one in Anolis, four in geckos). Despite substantial evolutionary divergence between Anolis and geckos, we find that these clades have undergone similar developmental modifications to generate their adhesive toe pads. Relative to the ancestral plantar scale development, in which scale ridges form synchronously along the digit, both padded geckos and Anolis exhibit scansor formation in a distal-to-proximal direction. Both clades have undergone developmental repatterning and, following their origin, modifications in toe pad morphology occurred through relatively minor developmental modifications, suggesting that developmental constraints governed the diversification of the adhesive toe pad in lizards.

Genomic evidence of adaptive evolution in the reptilian SOCS gene family

The suppressor of the cytokine signaling (SOCS) family of proteins play an essential role in inhibiting cytokine receptor signaling by regulating immune signal pathways. Although SOCS gene functions have been examined extensively, no comprehensive study has been performed on this gene family's molecular evolution in reptiles. In this study, we identified eight canonical SOCS genes using recently-published reptilian genomes. We used phylogenetic analysis to determine that the SOCS genes had highly conserved evolutionary dynamics that we classified into two types. We identified positive SOCS4 selection signals in whole reptile lineages and SOCS2 selection signals in the crocodilian lineage. Selective pressure analyses using the branch model and Z-test revealed that these genes were under different negative selection pressures compared to reptile lineages. We also concluded that the nature of selection pressure varies across different reptile lineages on SOCS3, and the crocodilian lineage has experienced rapid evolution. Our results may provide a theoretical foundation for further analyses of reptilian SOCS genes' functional and molecular mechanisms, as well as their roles in reptile growth and development.