Characterization of a cDNA clone encoding molluscan insulin‐related peptide II of Lymnaea stagnalis

A cDNA clone encoding molluscan insulin‐related peptide (MIP) II was isolated from a cDNA library of the central nervous system (CNS) of the freshwater snail, Lymnaea stagnalis, using a heterologous screening with a previously identified MIP cDNA (renamed MIP‐I cDNA). The MIP‐II cDNA encodes a preprohormone resembling the organization of preproinsulin, with a putative signal sequence, and A and B chains; however, in this case connected by two distinct C peptides, Cα and Cβ, instead of a single C peptide, a phenomenon which represents a new development in the prohormone organization of peptides belonging to the insulin superfamily. The A and B chains of MIP II and I differ remarkably in primary structure; in contrast, the Cα peptide domains are fully identical. MIP II has only limited sequence similarity with insulins and related peptides. Both MIP II and I exhibit structural features, which make them a unique class of the insulin superfamily. The MIP I and II genes are expressed in a single type of neuron: the growth‐controlling neuroendocrine light green cells of the Lymnaea CNS. Copyright © 1991, Wiley Blackwell. All rights reserved