[The heat shock response and HSP70 gene expression in male germ cells]

Apoptosis of spermatogenic cells is an essential process that allows to maintain correct proportion between somatic and germ cells. In addition, apoptosis induced by cellular stress is an important checkpoint mechanism that eliminates damaged male germ cells. The response to cellular stress (e.g. hyperthermia) in somatic cells includes activation of the heat shock transcription factor 1 (HSF1) leading to induction and accumulation of the heat shock proteins (HSPs), mainly HSP70i, which allows cell survival. In major contrast, in meiotic and post-meiotic germ cells Hsp70i genes are not induced in elevated temperature. Instead, activation of HSF1 leads to caspase-3-dependent apoptosis and spermatogenic cells are actively eliminated. Although HSP70i proteins are repressed in spermatocytes and spermatids, another HSP70 proteins are specifically expressed in those cells, which are necessary for spermatogenesis. However, Hsp70.2/Hst70 gene, the major testis-specific Hsp70 expressed mostly in spermatocytes, is down-regulated by HSF1 and spermatogenic cells undergoing stress-induced apoptosis lack HSP70.2/HST70 protein.