Cell-specific expression and heat-shock induction of Hsps during spermatogenesis in Drosophila melanogaster

The developmental and heat-shock-induced expression of two small heat-shock proteins (Hsp23 and Hsp27) was investigated during spermatogenesis in Drosophila melanogaster. Both of these Hsps were expressed in unstressed and stressed male gonads as shown by immunoblotting. Immunostaining of whole-mount organs and thin sections of testes showed that an anti-Hsp23 antibody specifically decorated cells of the somatic lineage, such as the cyst cells and the epithelial cells of the testis and of the seminal vesicle. Hsp27 was expressed in some somatic cells (cyst cells and epithelial cells of the accessory glands) and, in addition, was also visible in the maturing spermatocytes of the germline. The same cell-specific pattern of expression was observed after heat shock, and cells which did not express Hsp23 and Hsp27 in the absence of stress were similarly unable to mount a heat shock response for these s-Hsps. However other Hsps such as Hsp70 and Hsp22 were induced under heat-shock conditions in testes. Actinomycin D prevented the heat-induced accumulation of these Hsps indicating that the induction of Hsps was regulated at the transcriptional level. The heat shock transcriptional factor of Drosophila (DmHSF), present in significantly lower amount in testes when compared to other tissues such as the head, was shown to be required for the heat activation of Hsp22 and Hsp70. Immunostaining revealed that HSF expression was restricted to specific cells such as cyst cells, epithelial pigment cells, spermatogonia and spermatids but not the primary spermatocytes. These data show that the expression and induction of the different small Hsps is regulated in a cell-specific manner under both normal and heat shock conditions and suggest that factors other than the DmHSF are involved in this regulation in male gonads.