TISSUE-SPECIFIC EXPRESSION OF PHOSPHOLIPASE-C ENCODED BY THE NORPA GENE OF DROSOPHILA-MELANOGASTER

Mutations in the norpA gene of Drosophila melanogaster severely affect the light-evoked photoreceptor potential with strong mutations render ing the fly blind. Molecular cloning of the norpA gene revealed that i t encodes phosphatidylinositol-specific phospholipase C, which enzymes play a pivotal role in one of the largest classes of signaling pathwa ys known. We have used Northern analysis, Western blots, phospholipase C activity assays, and immunohistochemical staining of tissues to exa mine the tissue-specific expression of the norpA gene and found that i t is expressed in a variety of tissues besides the eye. Hybridization of norpA cRNA probe to blots of poly(A+) RNA reveals that the gene enc odes at least four transcripts: a 7.5-kilobase (kb) transcript that is expressed in eye and 6.5-, 5.5-, and 5.0-kb transcripts that are expr essed in adult body or early stages of development. Antiserum generate d against the major gene product of norpA recognizes a 130-kDa protein that is abundant in eyes but severely reduced or absent in norpA muta nts, a result which is consistent with previous conclusions that the n orpA gene encodes an essential component of the visual system. However , the norpA antiserum also recognizes a 130-kDa protein in adult legs, thorax, and male abdomen, but not female abdomen. These localizations are supported by results of phospholipase C activity assays which sho w that the norpA mutation reduces phospholipase C activity in each of the tissues in which norpA protein can be detected. Furthermore, immun ohistochemical staining of tissue sections with the norpA antiserum de monstrates that the norpA protein is abundant in the retina and ocelli and is present to a lesser extent in the brain and thoracic nervous s ystem. Since some of the above mentioned tissues that express norpA (s uch as thorax, legs, and abdomen) have no known photoreceptor tissue, we conclude that the norpA gene product is also likely to have a role in signaling pathways other than phototransduction.