MULTIPLE SUBTYPES OF PHOSPHOLIPASE-C ARE ENCODED BY THE NORPA GENE OFDROSOPHILA-MELANOGASTER

The norpA gene of Drosophila melanogaster encodes a phosphatidylinosit ol-specific phospholipase C that is essential for phototransduction. B esides being found abundantly in retina, norpA gene products are expre ssed in a variety of tissues that do not contain phototransduction mac hinery, implying that norpA is involved in signaling pathways in addit ion to phototransduction. We have identified a second subtype of norpA protein that is generated by alternative splicing of norpA RNA The al ternative splicing occurs at a single exon that is excluded from matur e norpA transcripts when a substitute exon of equal size is retained. The net difference between the two subtypes of norpA protein is 14 ami no acid substitutions occurring between amino acid positions 130 and 1 55 of the enzyme. Results from Northern analyses suggest that norpA su btype I transcripts are most abundantly expressed in adult retina, whi le subtype II transcripts are most abundant in adult body. Moreover, n orpA subtype I RNA can be detected by the reverse transcription-polyme rase chain reaction in extracts of adult head tissue but not adult bod y nor at earlier stages of Drosophila development. Conversely, norpA s ubtype II RNA can be detected by reverse transcription-polymerase chai n reaction throughout development as well as in heads and bodies of ad ults. Furthermore, norpA subtype I RNA is easily detected in retina us ing tissue in situ hybridization analysis, while subtype II RNA is not detectable in retina but is found in brain. Since only norpA subtype I RNA is found in retina, we conclude that subtype I protein is utiliz ed in phototransduction. Since norpA subtype IE RNA is not found in re tina but is expressed in a variety of tissues not known to contain pho totransduction machinery, subtype II protein is likely to be utilized in signaling pathways other than phototransduction, The amino acid dif ferences between the two subtypes of norpA protein may reflect the nee d for each subtype to interact with signaling components of different signal-generating pathways.