REGULATION OF HSP EXPRESSION DURING RODENT SPERMATOGENESIS

Spermatogenesis is the process by which immature male germ cells, thro ugh a complex series of events involving mitosis, meiosis, and cellula r differentiation, eventually become mature spermatozoa capable of fer tilizing an ovum. This process involves the developmental progression of male germ cells through a number of spermatogenetic cell types, eac h of which is characterized by unique features of morphology, cellular associations, and specialized functions. The unique features of each germ cell type are dictated, to a large degree, by the patterns of pro tein expression characteristic of each cell type. This review will exa mine two different aspects of the regulated expression of heat shock p roteins in spermatogenic cells. First, we will review studies showing that the expression of several different members of both the hsp70 as well as hsp90 families of heat shock proteins is regulated during the differentiation of these cells. Second, we will review studies which h ave examined the induction of hsp expression in spermatogenic cells fo llowing exposure to elevated temperatures. Next, we will review the ro le of the transcription factors, heat shock factor 1 (HSF1) and HSF2 i n the regulation of expression of hsps in the testis. One interesting and unique function of the male reproductive system in many species is the maintenance of the testes at a temperature below that of the othe r tissues of the animal. The importance of precise thermoregulation of the testis is evidenced by the fact that even slight elevations of sc rotal temperature are associated with infertility. The results of rece nt studies have suggested a potential involvement of the cellular stre ss response in the mechanism responsible for these inhibitory effects of elevated testis temperature on spermatogenesis. Possible mechanisms are discussed.