Cg. Armstrong et al., DROSOPHILA PPY, A NOVEL MALE-SPECIFIC PROTEIN-SERINE THREONINE PHOSPHATASE LOCALIZED IN SOMATIC-CELLS OF THE TESTIS, Journal of Cell Science, 108, 1995, pp. 3367-3375
Drosophila protein phosphatase Y (PPY) displays 64% amino acid identit
y to protein serine/threonine phosphatase 1 (PP1) and 39% to protein p
hosphatase 2A (PP2A). Here we show by expression of cDNA in bacteria,
that PPY is a protein serine phosphatase and that its biochemical prop
erties are distinct from PP1 in both substrate specificity and regulat
ion by the thermostable inhibitory proteins inhibitor 1 and inhibitor
2. We also demonstrate that PPY is a novel testis specific protein pho
sphatase by analysis of both mRNA and protein distribution. More preci
se 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 l
ocation of PPY is in the nuclei of both head and tail cyst cells throu
ghout the length of the testis except for the apical tip. The distribu
tion of PPY, coupled with its unique biochemical properties, suggests
that PPY may be required to prevent cyst cell division, increase trans
cription for provision of nutrients to the germ cells and/or provide a
signal for spermatocyte differentiation.