OSS cells are related to ovarian follicle cells. (A) Schematic of an individual mature germarium. The germline consists of 15 nurse cells and the developing oocyte; the latter is ensheathed by follicle cells of somatic origin. The accumulation of the three Piwi-class proteins—PIWI, AUB, and AGO3—in these celltypes is indicated. (B) Quantitative RT–PCR analysis of Piwi-class transcripts in OSS cells; ovaries were used as a positive control and female heads as a negative control. Transcript levels were normalized to RpL32 as a control, and expressed as the fold change above the level in heads. OSS cells express high levels of piwi, but not aub or AGO3. (C–E) Immunostaining of OSS cells with antibodies against the three Piwi-class proteins (green) verifies sole expression of PIWI; DNA was counterstained with DAPI (blue).
