Evolutionary conservation of the leucine-rich repeat transmembrane protein Gp150 in Drosophila and Bombyx

Gp150 is a transmembrane glycoprotein belonging to the leucine-rich repeat (LRR) superfamily. Here we report the molecular characterization of a Gp150 homolog in Drosophila virilis, which is separated from Drosophila melanogaster by about 60 million years. A silkworm Bombyx mori Gp150 homolog was identified through a sequence database search. Sequence analysis revealed high conservation in the LRRs and cysteine motifs flanking the LRR region in the extracellular domain of Gp150. Using an in vivo assay, we demonstrated that the extracellular domain is essential for Gp150 function. Moreover, structural features unique to the Gp150 proteins were identified that include an incomplete carboxy-flanking cysteine motif, acidic regions on both sides of the LRR region in the extracellular domain, and a short cytoplasmic domain with three putative tyrosine phosphorylation motifs, which might be involved in interaction with SH2 domains. Thus, Gp150 defines a new subfamily of LRR proteins and may be involved in signal transduction. Sequence comparison of the two Drosophila gp150 genes demonstrated a high degree of conservation of genome organization downstream of the gp150 gene. Interestingly, D. virilis gp150 coding region appears to have an additional intron, an uncommon feature in homologs of other genes. The expression pattern of gp150 during embryogenesis in D. melanogaster and D. virilis was found to be identical. gp150 transcripts were localized generally to regions where cells are undergoing dramatic morphogenetic movements. This is further corroborated by the localization of gp150 transcripts in eye imaginal discs in the region spanning the morphogenetic furrow.