Effect of age and busulphan treatment on the hsp70 gene-related transcript level in rat testes

Expression, function, and regulation of the testis-enriched heat shock HSPA2 gene in rodents and humans

The HSPA2 gene is a poorly characterized member of the HSPA (HSP70) family. HSPA2 was originally described as testis-specific and expressed at the highest level in pachytene spermatocytes of rodents, the expression of which is not induced by heat shock. HSPA2 is crucial for male fertility. However, recent advances have shown that HSPA2 is expressed in various tumors and in certain types of somatic tissues. In this review, we summarize the current knowledge on the HSPA2 expression pattern, including information on transcriptional, translational, posttranslational, and epigenetic mechanisms which regulate HSPA2 expression. We also present and discuss the current views concerning the functions of the HSPA2 protein in spermatogenetic, somatic, and cancer cells. The knowledge of the properties of HSPA2, although limited, shows this protein as a unique member of the HSPA family. However, understanding whether this protein could become a relevant cancer biomarker or a therapeutically applicable target requires extensive further studies.

Chaperones come of age

Chaperone function plays a key role in repairing proteotoxic damage, in the maintenance of cell architecture, and in cell survival. Here, we summarize our current knowledge about changes in chaperone expression and function in the aging process, as well as their involvement in longevity and cellular senescence.

Stage-specific expression and cellular localization of the heat shock factor 2 isoforms in the rat seminiferous epithelium

Heat shock transcription factors (HSFs) are generally known as regulators of cellular stress response. The mammalian HSF1 functions as a classical stress factor, whereas HSF2 is active during certain developmental processes, including embryogenesis and spermatogenesis. In the present study, we examined HSF2 expression at specific stages of the rat seminiferous epithelial cycle. We found that expression of the alternatively spliced HSF2-alpha and HSF2-beta isoforms is developmentally regulated in a stage-specific manner. Studies on cellular localization demonstrated that HSF2 is present in the nuclei of early pachytene spermatocytes at stages I-IV and in the nuclei of round spermatids at stages V-VIIab. In contrast a strong HSF2 immunoreactivity was detected in small distinct cytoplasmic regions from zygotene spermatocytes to maturation phase spermatids. Immunoelectron microscopic analysis revealed that these structures are mainly cytoplasmic bridges between germ cells. Our results on cellular localization of HSF2 and stage-specific expression of the HSF2 isoforms indicate that HSF2, in addition to its function as a nuclear transcription factor, may be involved in other cellular processes during spermatogenesis, possibly in the sharing process of gene products between the germ cells.

Distinct transcripts are recognized by sense and antisense riboprobes for a member of the murine HSP70 gene family, HSP70.2, in various reproductive tissues

The expression of hsp70.2, an hsp70 gene family member, originally characterized by its high levels of expression in germ cells in the adult mouse testis, was detected in several other reproductive tissues, including epididymis, prostate, and seminal vesicles, as well as in extraembryonic tissues of mid-gestation fetuses. In addition, hybridization with RNA probes transcribed in the sense orientation surprisingly indicated the presence of slightly larger "antisense" transcripts in several tissues. The levels of antisense transcripts varied among the tissues, with the highest signal detected in the prostate and no signal being detectable in the testis. Consistent with these results, in situ hybridization analysis clearly localized the sense-orientation transcripts to pachytene spermatocytes, while no antisense-orientation transcripts were observed in adjacent sections of the same tubules. Our findings have thus shown that although hsp70.2 was expressed abundantly and in a highly stage-specific manner in the male germ line, it was also expressed in other murine tissues. Furthermore, we have made the surprising observation of antisense transcription of the hsp70.2 gene in several mouse tissues, revealing another level of complexity in the regulation and function of heat shock proteins.

Characterization of the heat shock protein P70 in rat spermatogenic cells

A number of hsp70-like proteins are associated with developing male germ cells. One of these molecules, P70, is not sensitive to heat stress and is germ cell-specific, and its expression is developmentally regulated. We have characterized the association of the rat P70(rP70) with differentiating germ cells in the testis and with posttesticular sperm. An antibody originally raised against human sperm proacrosin (designated C3; Sigel et al., 1987: J Reprod Immunol 11:307-319) was found to immunostain rP70 by immunoblot analysis and was used in subsequent studies of the rP70 molecule. The C3 antibody reacted with P70 isoforms in rat, human, mouse, guinea pig, boar, and rooster testicular homogenates. In the developing rat testis, abundant rP70 protein levels were first detected on postnatal day 22, with upregulation to adult levels occurring after postnatal day 28. Purified populations of adult rat pachytene spermatocytes, round spermatids, and elongating spermatids, isolated by unit gravity velocity sedimentation, all expressed rP70. Posttesticular sperm exhibited a loss of the rP70 molecule; caput epididymal sperm were weakly immunoreactive for rP70, but no immunoreactivity was observed in either cauda epididymal sperm or epididymal fluid. In contrast to human ejaculated sperm, rat ejaculated sperm did not express rP70. The loss of P70 from rat posttesticular sperm may reflect species-specific differences in P70 functions, which are thought to include a role in the structural modifications that occur during germ cell differentiation.

Effect of busulphan treatment and elevated temperature on the expression of the beta-pol gene in rat testis

Changes in the expression pattern of the DNA polymerase beta gene during inhibition of spermatogenesis by busulphan and by temperature (artificial cryptorchidism) have been studied. Transient arrest of spermatogenesis in two-month-old rats after injection of a single dose of busulphan (10 mg/kg) resulted in parallel but transient decrease in the 1.4 kb of beta-pol mRNA level to an undetectable value, followed by its reappearance after resumption of spermatogenesis. An artificial cryptorchidism also caused a drastic decrease of beta-pol mRNA level. Both results as well as morphological examination of testis after busulphan injection and artificial cryptorchidism revealed that spermatocytes and spermatids represent the testicular cell fraction containing the elevated amount of beta-pol mRNA. Involvement of DNA polymerase beta in meiotic recombination is discussed.

Isolation and nucleotide sequence analysis of the rat testis-specific major heat-shock protein (HSP70)-related gene

The isolation of a rat hsp 70-related gene which is specifically and highly expressed in testis is described together with the complete nucleotide sequence of the transcription unit (2947 bp), 5' flanking (about 1 kbp) and 3' flanking (about 0.3 kbp) regions. The sequence analysis and nuclease S1 mapping revealed that the isolated gene (referred to as the hst70 gene) represents a novel, distinct member of the hsp70 multigene family. Its transcription unit lacks introns and a single open reading frame encodes a protein of 69.5 kDa. The predicted amino acid sequence of this protein is highly similar (only four out of 633 amino acids are different) to that encoded by the mouse testis-specific hsp70.2 gene (Zakeri, Z.F., Wolgemuth, D.J. and Hunt, C.R. (1988) Mol. Cell. Biol. 8, 2925-2932). The functional significance of multiple potentially regulatory sequences (e.g. TATA-boxes, heat-shock element and estrogen receptor binding site) present in the 5' flanking region of the rat hst70 gene is discussed.