OCCURRENCE OF MEMBERS OF THE INSULIN SUPERFAMILY IN CENTRAL-NERVOUS-SYSTEM AND DIGESTIVE-TRACT OF PROTOCHORDATES

Antisera specific for mammalian insulin-like growth factor 1 (IGF-1) a nd mammalian insulin and the double immunofluorescence technique were used for this study. IGF-1-like-immunoreactivity was localized in ente roendocrine cells in the gastro-intestinal tract of the protochordates Ciona intestinalis and Branchiostoma lanceolatum. Some of the specime ns also showed IGF-1-like-immunoreactive (IR) perikarya and fibers in the central nervous system. Whilst in rat endocrine pancreas, IGF-1-IR and insulin-IR occurred in different cell populations, in Ciona and B ranchiostoma the vast majority of entero-endocrine cells and central n eurons were IGF-1-like- +insulin-IR. A minor portion exhibited IGF-1-l ike-IR alone. For further characterization of the IGF-1-like-IR materi al, in Ciona intestinalis, peptides related to IGF-1 were identified b y radioimmunoassay and gel chromatography. In accordance with the immu nohistochemical results, IGF-1-like-IR was detected both in cerebral g anglion and in gastro-intestinal tract. Using acid gel chromatography, in Ciona gastro-intestinal tract the IGF-1-like-IR was found to occur in two peaks, with apparent molecular weights of approximately 16 kDa and 3 kDa. Absorption studies with insulin- and IGF-related peptides, with crude extracts and the peak material obtained after gel chromato graphy, indicated that the IGF-1-like peptides in Ciona are different from mammalian insulin and IGF-1. The findings are in accordance with the presence of a common insulin/IGF precursor molecule in protochorda tes.