Different neuroendocrine cell types in thepars intercerebralisofPeriplaneta americanaproduce their own specific IGF-related peptides
AbstractOf the nine genes of the American cockroach,Periplaneta americana, coding for peptides related to insulin and insulin-like growth factor, seven show significant expression in the central nervous system as demonstrated by the polymerase chain reaction on reverse transcribed RNA.In situhybridisation shows that five of those are expressed by cells in thepars intercerebralis. Antisera raised to the predicted peptides show that these cells are neuroendocrine in nature and project to thecorpora cardiaca. Interestingly, there are at least three cell types that each express different genes. This contrasts withDrosophilawhere a single cell type expresses a number of genes expressing several such peptides. Whereas inDrosophilathe neuroendocrine cells producing insulin-like peptides also express sulfakinins, the arthropod orthologs of gastrin and cholecystokinin, inPeriplanetathe sulfakinins are produced by different cells. Other neuropeptides known to be produced by thepars intercerebralisinPeriplanetaand other insect species, such as the CRF-like diuretic hormone, neuroparsin, leucokinin or myosuppressin, neither colocalize with an insulin-related peptide. The separate cellular localization of these peptides and the existence of multiple insulin receptors in this species implies a more complex regulation by insulin and IGF-related peptides in cockroaches than in the fruit fly.