Journal of Neuroscience, Vol 13, 2719-2729, Copyright © 1993 by Society for Neuroscience
Mutually exclusive expression of alternatively spliced FMRFamide transcripts in identified neuronal systems of the snail Lymnaea
K Bright, E Kellett, SE Saunders, M Brierley, JF Burke and PR Benjamin
Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Brighton, United Kingdom.
The FMRFamide gene of the snail Lymnaea encodes tetrapeptides
(FMRFamide/FLRFamide) and heptapeptides (GDPFLRFamide/SDPFLRFamide) on
separate exons. In situ hybridization probes specific to these exons were
used to map the expression of the two exons in identified neuronal systems
of the CNS. Analysis of more than 200 preparations showed that cytoplasmic
expression of mRNA was exclusively of one type, with individual neurons
expressing either the tetrapeptide or heptapeptide exon. Of the
approximately 340 neurons expressing the two exons, the majority (80%)
expressed the tetrapeptide exon. The tetrapeptide exon was more widespread,
occurring in neurons from all 11 ganglia of the CNS. The heptapeptide was
mainly confined to two ganglia (visceral and right parietal), with a small
number of cells in three other ganglia. Mapping studies combined with dye
marking of identified neurons showed the presence of the tetrapeptide exon
in several behaviorally important networks: heart motoneurons, whole body
withdrawal response motoneurons, and probably penis motoneurons as well as
giant identified neurons (LP1, RPD1). The heptapeptides were prominent in
two main clusters of cells (Bgp and Fgp) together with a smaller number of
tetrapeptide-expressing cells.