Identification of insulin and glucagon genes in the finless porpoise and the developmental distribution of their producing endocrine cells

BackgroundBoth insulin and glucagon have been extensively studied due to their critical roles in glucose metabolism, development, and disease. However, there is limited information about the molecular characteristics of insulin and glucagon in cetaceans.MethodsTo better understand the information of these key endocrine factors of finless porpoises, we cloned and characterized both of the preproinsulin and preproglucagon genes and determined the islet distribution, architecture, and composition from different growth stages in finless porpoises.ResultsThe coding sequences of the preproinsulin and preproglucagon genes encode the preproinsulin protein of 110 amino acid (aa) residues and the preproglucagon protein of 180 aa residues, respectively. Both of the insulin and glucagon genes exhibited strong conservation in primary structure and synteny to other mammals. The islet area and composition in different stages or gender of finless porpoises were different. The α cells and β cells started to form an islet in the late fetus stage and appeared to be randomly distributed under incompletely mature status. In the pregnant stage, the islets displayed β cells in the islet core, with most α cells in the islet periphery. Interestingly, the area of β cells increased in pregnant female porpoises.ConclusionThese findings provide new insights into the structural conservation of insulin and glucagon genes as well as the developmental distribution of endocrine cells in cetaceans, which may also be useful to their conservation, such as in assessing endocrine-disrupting chemicals’ risks in the future.