Expression of mRNAs encoding FMRFamide-related peptides in adult and embryo 'Helix aspersa'

Abstract

The gastropod mollusc Helix aspersa is known to contain at least seven FMRFamide-related peptides (FaRPs), neuropeptides which fall into two broad classes, distinguished by their primary structure and their physiological actions. We have sought to use the techniques available to us through molecular biology to study the structure and expression of the nucleic acids (RNA and DNA) which encode these peptides in this organism. The two classes of peptide, tetra- and heptapeptides, were found by us to be apparently separated by the stage of mRNA generation: the precursor polypeptides encoded by these mRNAs were also found to have differing structures. Expression of mRNAs specific for the FaRPs were studied during embryogenesis, where there appears to be regulated expression of these mRNAs. In situ hybridization analyses of the central nervous system of adult Helix revealed expression of FaRP-specific mRNAs to be limited to a small number of discrete neurons: it was again observed that there was an apparent distinction between the tetra and extended FaRPs, no ceils being identified in our studies to express both types of mRNA. Confocal scanning microscopy indicated that the distribution of the mRNA, which appeared to be limited to the cytoplasm of cell bodies expressing the peptides, was non-uniform, probably reflecting a functional characteristic of the cells concerned.