The molecular basis of the neuro-endocrine control of egg-laying behaviour in Lymnaea

The biosynthesis, axonal transport and release of multiple peptides by the egg-laying controlling caudodorsal cells (CDC) of Lymnaea stagnalis were studied. High performance gel permeation chromatography was used to resolve newly synthesized peptides after pulse-chase experiments with radioactive amino acids. The precursor is a 35 kd polypeptide which is produced in the CDC somata. It gives rise to intermediate products (20 kd, 10 kd and 7 kd) and a number of end products which include a approximately 4.5 kd (the ovulation hormone, CDCH), a 1.5 kd peptide (the autotransmitter) and other peptides (6 kd, 3.5 kd and 2 kd). The end products are transported in neurosecretory granules to the CDC axon terminals in the cerebral commissure where they are released into the medium during electrical discharges of the CDC system. A cDNA clone encoding part of the CDCH precursor was isolated from a Lymnaea CNS cDNA library by differential hybridisation and use of synthetic oligonucleotide probes. Examination of the deduced amino acid sequence indicates that the precursor contains additional peptides, besides CDCH.