The spatial distribution of endocrine cells in the pancreas of the mourning gecko ( <i>Lepidodactylus lugubris</i> ) reflects their embryonic origins

The pancreas of the mourning gecko (Lepidodactylus lugubris) develops from three anlagen that fuse into a gland with a head and three lobes: splenic, upper, and lower. Endocrine islets are mainly found in the splenic lobe and the pancreatic head. The purpose of this study is to investigate the spatial distribution of endocrine cell types within the pancreatic islets of the pre-hatched embryo of the mourning gecko. This study used immunohistochemistry to examine pancreatic endocrine organization in pre-hatch embryos. Four endocrine cell types were identified: glucagon-producing α cells, insulin-producing β cells, somatostatin-producing δ cells and pancreatic polypeptide (γ) cells, each with distinct distributions. β cells were concentrated in the splenic lobe and head, absent in the lower lobe, and often co-localized with α cells in large islets. δ cells were found only in the splenic and upper lobes, primarily at islet edges and within exocrine tissue. γ cells appeared throughout the pancreas, most densely in the upper and lower lobes, as individual cells or small clusters. Some cells showed dual immunoreactivity for glucagon and pancreatic polypeptide, suggesting a shared progenitor and complex functional integration. The spatial distribution of endocrine cells correlated with embryonic origin, with the splenic lobe (from the dorsal bud) showing higher insulin cell density and functional maturity than ventral bud-derived regions. These findings support that endocrine cell differentiation in reptiles is shaped by regional pancreatic origin. The co-expression and lobe-specific patterns provide valuable insights into the evolutionary and developmental mechanisms of endocrine regulation in the reptilian pancreas.