Drosophila PPY, a novel male specific protein serine/threonine phosphatase localised in somatic cells of the testis.

Drosophila protein phosphatase Y (PPY) displays 64% amino acid identity to protein serine/threonine phosphatase 1 (PP1) and 39% to protein phosphatase 2A (PP2A). Here we show by expression of cDNA in bacteria, that PPY is a protein serine phosphatase and that its biochemical properties are distinct from PP1 in both substrate specificity and regulation by the thermostable inhibitory proteins inhibitor 1 and inhibitor 2. We also demonstrate that PPY is a novel testis specific protein phosphatase by analysis of both mRNA and protein distribution. More precise immunolocalisation within the testis, using affinity purified anti-PPY protein and anti-PPY peptide antibodies, shows that PPY is present in somatic cyst cells, which encase the germ cells. The predominant location of PPY is in the nuclei of both head and tail cyst cells throughout the length of the testis except for the apical tip. The distribution of PPY, coupled with its unique biochemical properties, suggests that PPY may be required to prevent cyst cell division, increase transcription for provision of nutrients to the germ cells and/or provide a signal for spermatocyte differentiation.