Lighting up lizard islets: A fluorescent map of pancreatic hormones before hatching

This study investigates the organization of pancreatic endocrine islets in lizard embryos before hatching. Immunohistochemical staining was performed on "pre-hatching" embryos from three species representing major squamate clades: Lacerta agilis (Lacertoidea), Eublepharis macularius (Gekkota), and Anolis sagrei (Iguania). Four distinct endocrine cell types were identified within the pancreas of the studied species: glucagon-producing α-cells, insulin-producing β-cells, somatostatin-producing δ cells, and pancreatic polypeptide (γ) cells. Each of these cell types exhibited a unique distribution pattern across the upper, lower, and splenic lobes, as well as within the pancreatic head. The observed variation in the spatial distribution of endocrine cells appears to be related to several factors, including the developmental origins of the pancreatic regions from specific embryonic primordia, their subsequent differentiation driven by distinct developmental mechanisms, and paracrine interactions. The marked interspecific variations in islet cell topography and composition of the analyzed species could represent adaptations to dietary specialization or other ecological pressures. It has been proposed that the anatomical variation of the pancreas and, consequently its topographical relationship with the other organs, may be, to some extent, evolutionarily conservative within certain major squamate clades. In fact, at least some of the endocrine cell distribution patterns among the investigated species appear to be related to the proximity of certain pancreatic regions to the spleen, determined by pancreas shape. This suggests a potential regulatory influence on pancreatic islet differentiation and implies an indirect phylogenetic influence on endocrine cell distribution through the diverse pancreatic morphology. Further comparative research is required to clarify the potential phylogenetic, ecological, and developmental impact on pancreatic islet formation and composition.