DROSOPHILA PHOSPHOLIPASE C-GAMMA EXPRESSED PREDOMINANTLY IN BLASTODERM CELLS AT CELLULARIZATION AND IN ENDODERMAL CELLS DURING LATER EMBRYONIC STAGES

A Drosophila gene encoding a gamma-type isozyme of phosphoinositide-sp ecific phospholipase C (PLC) was isolated and characterized. The gene, termed plc-gamma d, was mapped at position 14B-C of the X chromosome. The encoded protein, termed PLC-gamma D, contains X and Y regions, co mmon to all known PLC isozymes. The two re- gions are split by a Z reg ion that comprises two src homology 2 and one src homology 3 domains a nd is characteristic of gamma-type mammalian PLC (PLC-gamma 1 and -gam ma 2). The deduced amino acid sequence of PLC-gamma D shows overall si milarity to mammalian PLC-gamma s; no large dele- tion was observed ex cept the short C-terminal extended region. In particular, the two spli t catalytic domains (X and Y regions) and the regulatory Z region incl uding the src homology 2 and src homology 3 domains are well conserved . The mRNA is expressed throughout development, but expression is rela tively higher during the embryonic stage, suggesting fundamental and i mportant roles in both cell proliferation and differentiation. Distrib ution of the mRNA during embryogenesis, as analyzed by whole mount in situ hybridization, revealed that the mRNA emerges and reaches maximum levels at the cellular blastoderm stage and then decreases rapidly to a lower level. In later embryonic stages, invaginated anterior and po sterior midgut primordia show high levels of mRNA expression, and fuse d midgut also maintains a high level of expression. In other tissues a nd cells, the mRNA was detected at lower levels. These results indicat e that Drosophila PLC-gamma may be involved in universal cellular proc esses mediated possibly by receptor tyrosine kinases during embryogene sis and may also play specific roles during cellularization and midgut differentiation.