CLONING OF A MOLLUSCAN G-PROTEIN ALPHA-SUBUNIT OF THE GQ CLASS WHICH IS EXPRESSED DIFFERENTIALLY IN IDENTIFIED NEURONS

Through molecular cloning we have identified a molluscan G protein a s ubunit which belongs to the G alpha(q) family and is expressed in the central nervous system (CNS) of the pond snail, Lymnaea stagnalis. The deduced protein product shares a very high degree of amino acid seque nce identity with vertebrate and invertebrate G alpha(q)/G alpha(11) s ubunits (80-82% and 76-77%, respectively). Large parts of the protein have been completely conserved, among which are residues 25-58, includ ing the nucleotide-binding A domain. Especially the C-terminal half (a mino acids 195-353), implicated in receptor and effector interactions, is highly conserved (94% sequence identity with murine sequences). Th is region includes the nucleotide-binding C, G, and I domains, which a re identical to cognate motifs of vertebrate G alpha(q/11). Like the l atter proteins, the Lymnaea G alpha(q) C-terminus lacks a cysteine tha t could serve as a substrate for pertussis toxin. In situ hybridizatio n reveals G alpha(q)-encoding mRNA(s) to be present throughout the CNS . Interestingly, however, close inspection of two identified cell type s in the cerebral ganglia, the light-green cells, involved in the regu lation of growth and metabolism and the anterior lobe cells which are involved in the control of male aspects of reproduction, indicates tha t they express the mRNA(s) at significantly different levels. Even wit hin the heterologous cluster of light-green cells there appears to be differential expression of the pertinent mRNA. Such observations have hitherto not been reported for specific cell types occurring in vivo.