A novel hsp70-like protein (P70) is present in mouse spermatogenic cells

What's Genetic Variation Got to Do with It? Starvation-Induced Self-Fertilization Enhances Survival in Paramecium

The pervasiveness of sex despite its well-known costs is a long-standing puzzle in evolutionary biology. Current explanations for the success of sex in nature largely rely on the adaptive significance of the new or rare genotypes that sex may generate. Less explored is the possibility that sex-underlying molecular mechanisms can enhance fitness and convey benefits to the individuals that bear the immediate costs of sex. Here, we show that the molecular environment associated with self-fertilization can increase stress resistance in the ciliate Paramecium tetraurelia. This advantage is independent of new genetic variation, coupled with a reduced nutritional input, and offers fresh insights into the mechanistic origin of sex. In addition to providing evidence that the molecular underpinnings of sexual reproduction and the stress response are linked in P. tetraurelia, these findings supply an integrative explanation for the persistence of self-fertilization in this ciliate.

Analysis of Drosophila melanogaster testis transcriptome

Background

The formation of matured and individual sperm involves a series of molecular and spectacular morphological changes of the developing cysts in Drosophila melanogaster testis. Recent advances in RNA Sequencing (RNA-Seq) technology help us to understand the complexity of eukaryotic transcriptomes by dissecting different tissues and developmental stages of organisms. To gain a better understanding of cellular differentiation of spermatogenesis, we applied RNA-Seq to analyse the testis-specific transcriptome, including coding and non-coding genes.

Results

We isolated three different parts of the wild-type testis by dissecting and cutting the different regions: 1.) the apical region, which contains stem cells and developing spermatocytes 2.) the middle region, with enrichment of meiotic cysts 3.) the basal region, which contains elongated post-meiotic cysts with spermatids. Total RNA was isolated from each region and analysed by next-generation sequencing. We collected data from the annotated 17412 Drosophila genes and identified 5381 genes with significant transcript accumulation differences between the regions, representing the main stages of spermatogenesis. We demonstrated for the first time the presence and region specific distribution of 2061 lncRNAs in testis, with 203 significant differences. Using the available modENCODE RNA-Seq data, we determined the tissue specificity indices of Drosophila genes. Combining the indices with our results, we identified genes with region-specific enrichment in testis.

Conclusion

By multiple analyses of our results and integrating existing knowledge about Drosophila melanogaster spermatogenesis to our dataset, we were able to describe transcript composition of different regions of Drosophila testis, including several stage-specific transcripts. We present searchable visualizations that can facilitate the identification of new components that play role in the organisation and composition of different stages of spermatogenesis, including the less known, but complex regulation of post-meiotic stages.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5085-z) contains supplementary material, which is available to authorized users.

Heat shock factor function and regulation in response to cellular stress, growth, and differentiation signals

Heat shock factors (HSF) activate the transcription of genes encoding products required for protein folding, processing, targeting, degradation, and function. Although HSFs have been extensively studied with respect to their role in thermotolerance and the activation of gene expression in response to environmental stress, the involvement of HSFs in response to stresses associated with cell growth and differentiation, and in response to normal physiological processes is becoming increasingly clear. In this work, we review recent advances toward understanding how cells transmit growth control and developmental signals, and interdigitate cellular physiology, to regulate HSF function.

Heat Shock Protein A2 (HSPA2): Regulatory Roles in Germ Cell Development and Sperm Function

Among the numerous families of heat shock protein (HSP) that have been implicated in the regulation of reproductive system development and function, those belonging to the 70 kDa HSP family have emerged as being indispensable for male fertility. In particular, the testis-enriched heat shock 70 kDa protein 2 (HSPA2) has been shown to be critical for the progression of germ cell differentiation during spermatogenesis in the mouse model. Beyond this developmentally important window, mounting evidence has also implicated HSPA2 in the functional transformation of the human sperm cell during their ascent of the female reproductive tract. Specifically, HSPA2 appears to coordinate the remodelling of specialised sperm domains overlying the anterior region of the sperm head compatible with their principle role in oocyte recognition. The fact that levels of the HSPA2 protein in mature spermatozoa tightly correlate with the efficacy of oocyte binding highlight its utility as a powerful prognostic biomarker of male fertility. In this chapter, we consider the unique structural and biochemical characteristics of HSPA2 that enable this heat shock protein to fulfil its prominent roles in orchestrating the morphological differentiation of male germ cells during spermatogenesis as well as their functional transformation during post-testicular sperm maturation.

Malfunction of spermatogenesis in experimental ischemic mice

An experimental ischemia (EI)-induced mouse model was used to analyze pathological and biochemical alterations in testes. Initial morphological changes were observed in Sertoli cells of EI testes at the light microscopic level. Examination of the ultrastructure using transmission electron microscopy confirmed that Sertoli cells were partially detached from the basement membrane of the seminiferous epithelium and that the cell membranes of adjacent Sertoli cells were not joined. The functional integrity of the blood-testis barrier (BTB) was assessed using the lanthanum tracer technique. Lanthanum had penetrated into the spaces between adjacent Sertoli cells in the adluminal compartment up to the lumen of the seminiferous epithelium in EI testes. Proteome analysis showed that the expression of heat shock protein (HSP) 70 was significantly upregulated in EI testes. Western blot analysis confirmed that the expression of HSP70 increased in a time-dependent manner after the EI procedure. HSP70 immunostaining was observed in spermatocytes and in round and elongated spermatids in EI testes. Our results suggest that a change in the junctions between adjacent Sertoli cells on the basal compartment is involved in the BTB disruption in EI testes. Therefore, male infertility caused by the BTB disruption could be associated with heat stress induced by ischemia.

Reporter mice express green fluorescent protein at initiation of meiosis in spermatocytes

Transgenic mice were generated using a heat shock protein 2 (Hspa2) gene promoter to express green fluorescent protein (GFP) at the beginning of meiotic prophase I in spermatocytes. Expression was confirmed in four lines by in situ fluorescence, immunohistochemistry, western blotting, and PCR assays. The expression and distribution of the GFP and HSPA2 proteins co-localized in spermatocytes and spermatids in three lines, but GFP expression was variegated in one line (F46), being present in some clones of meiotic and post-meiotic germ cells and not in others. Fluorescence activated cell sorting (FACS) was used to isolate purified populations of spermatocytes and spermatids. Although bisulfite sequencing revealed differences in the DNA methylation patterns in the promoter regions of the transgene of the variegated expressing GFP line, a uniformly expressing GFP reporter line, and the Hspa2 gene, these differences did not correlate with variegated expression. The Hspa2-GFP reporter mice provide a novel tool for studies of meiosis by allowing detection of GFP in situ and in isolated spermatogenic cells. They will allow sorting of meiotic and post-meiotic germ cells for characterization of molecular features and correlation of expression of GFP with stage-specific spermatogenic cell proteins and developmental events.

Molecular chaperones, cochaperones, and ubiquitination/deubiquitination system: involvement in the production of high quality spermatozoa

Spermatogenesis is a complex process in which mitosis, meiosis, and cell differentiation events coexist. The need to guarantee the production of qualitatively functional spermatozoa has evolved into several control systems that check spermatogenesis progression/sperm maturation and tag aberrant gametes for degradation. In this review, we will focus on the importance of the evolutionarily conserved molecular pathways involving molecular chaperones belonging to the superfamily of heat shock proteins (HSPs), their cochaperones, and ubiquitination/deubiquitination system all over the spermatogenetic process. In this respect, we will discuss the conserved role played by the DNAJ protein Msj-1 (mouse sperm cell-specific DNAJ first homologue) and the deubiquitinating enzyme Ubpy (ubiquitin-specific processing protease-y) during the spermiogenesis in both mammals and nonmammalian vertebrates.

Mutation of Eif4g3, encoding a eukaryotic translation initiation factor, causes male infertility and meiotic arrest of mouse spermatocytes

The ENU-induced repro8 mutation was identified in a screen to uncover genes that control mouse gametogenesis. repro8 causes male-limited infertility, with failure of spermatocytes to exit meiotic prophase via the G2/MI transition. The repro8 mutation is in the Eif4g3 gene, encoding eukaryotic translation initiation factor 4, gamma 3. Mutant germ cells appear to execute events of meiotic prophase normally, and many proteins characteristic of the prophase-to-metaphase transition are not obviously depleted. However, activity of CDC2A (CDK1) kinase is dramatically reduced in mutant spermatocytes. Strikingly, HSPA2, a chaperone protein for CDC2A kinase, is absent in mutant spermatocytes in spite of the presence of Hspa2 transcript, consistent with the observation that the repro8 phenotype is markedly similar to the phenotype of the Hspa2 knockout. Thus, EIF4G3 is required for HSPA2 translation in spermatocytes, a finding that provides the first genetic evidence for selective translational control of meiotic exit in mammalian spermatocytes.

Effect of 43 degrees treatment on expression of heat shock proteins 105, 70 and 60 in cultured monkey Sertoli cells

AIM

To examine the possible effect of heat treatment on expression of heat shock proteins (Hsps) 105, 70, and 60 in primary monkey Sertoli cells and to evaluate the possible signal pathways.

METHODS

Western blot analysis, real-time polymerase chain reaction (PCR), and confocal immunohistochemistry were used to analyze mRNA and protein levels of the Hsps in response to 43 degrees treatment of Sertoli cells isolated from pubertal monkey testes.

RESULTS

Staining with Hoechst 33342 indicated Sertoli cells did not undergo apoptosis after heat treatment. Hsp105 was expressed in cytoplasm of untreated Sertoli cells. Both Hsp105 mRNA and protein levels were increased approximately 20-fold compared to those of the untreated controls at 12 h after heat treatment. Untreated Sertoli cells did not express Hsp70, but heat stress induced its expression in the cell cytoplasm. The time-course of changes in Hsp70 was similar to that of Hsp105. In contrast to Hsp105 and Hsp70, the change in Hsp60 expression was much less obvious. The protein level between 12 h and 48 h after heat treatment was only approximately 1.5-fold that of the untreated control. Extracellular regulated kinase (ERK) 1/2 inhibitor (U0126) or phosphoinositide kinase-3 (PI3K) inhibitor (LY294002) could partially block the response of Hsp105 and Hsp70 induced by heat treatment.

CONCLUSION

These results indicate that the heat-induced expression of the three types of Hsp in monkey Sertoli cells might be regulated by ERK and/or PI3K signal pathways, but the profile of their expression is different, suggesting that they might have different regulatory functions in Sertoli cells.

A reference map and identification of porcine testis proteins using 2-DE and MS

The development of the testis is essential for maturation of male mammals. A complete understanding of proteins expressed in the testis will provide biological information on many reproductive dysfunctions in males. The purposes of this study were to apply a proteomic approach to investigating protein composition and to establish a 2-D PAGE reference map for porcine testis proteins. MALDI-TOF MS was performed for protein identification. When 1 mg of total proteins was assayed by 2-D PAGE and stained with colloidal CBB, more than 400 proteins with a pI of pH 3-10 and M(r) of 10-200 kDa could be detected. Protein expression varied among individuals, with CV between 4.7 and 131.5%. A total of 447 protein spots were excised for identification, among which 337 spots were identified by searching the mass spectra against the NCBInr database. Identification of the remaining 110 spots was unsuccessful. A 2-D PAGE-based porcine testis protein database has been constructed on the basis of the results and will be published on the WWW. This database should be valuable for investigating the developmental biology and pathology of porcine testis.

Developmental changes of heat-shock proteins in porcine testis by a proteomic analysis

Heat-shock proteins (HSPs) are important in spermatogenesis. This study investigated developmental changes in the expression of major HSPs in porcine testis. The testis from five immature (mean age 2.9+/-0.1 months) and five mature boars (35.7+/-14.0 months) were examined. Two-dimensional polyacrylamide gel electrophoresis was conducted and proteins were identified by Western blotting and/or matrix-assisted laser desorption/ionization mass spectrometry. Moreover, the 90, 70, and 60 kDa HSPs, 70 kDa heat-shock cognate protein (HSC 70), tubulin, and actin were quantified on two-dimensional gels. Protein spots were quantified by densitometry, combined with a computer-assisted image analysis system. Immunohistochemistry was performed to analyze the expression pattern of major HSPs and beta-tubulin in testis. One isoform of HSP 90 (HSP 90 alpha), two isoforms of HSC 70 (HSC 70a and HSC 70c), one isoform of HSP70 (HSP 70e), and tubulin increased after sexual maturation (P<0.05). A testis-specific HSP70 (P70t) was markedly increased in the testes of sexually mature boars. Meanwhile, levels of actin and some isoforms of HSPs including 60 kDa HSP remained similar in both groups. These observations were further confirmed by immunohistochemistry; therefore, the upregulation of protein expression in the adult testis could be attributed to a higher level of protein expression and the number of cells that were HSPs-positive already resided in the immature testis. The differential expression of major HSPs suggested that they may be important in porcine spermatogenesis.

Characterization of multiple members of the HSP70 family in platyfish culture cells: molecular evolution of stress protein HSP70 in vertebrates

A shift from 28 to 37 degrees C in the incubation temperature of a culture of the platyfish fibroblast cell line, EHS cells (platyfish fibroblast cell line), induced a set of stress proteins. A two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) analysis showed that the cells expressed three genetically distinct forms of heat-shock protein 70 (HSP70) family proteins: heat-inducible forms of HSP70, the constitutively expressed heat-shock cognate protein 70 (HSC70) and its phosphorylated isoform, and the glucose-regulated protein 78 (GRP78). Three different clones encoding two major isoforms of heat-inducible HSP70, platyfish HSP70-1 and HSP70-2, and of the HSC70 were isolated from a platyfish cDNA library. We compared the deduced amino acid sequences of the platyfish HSP70 and HSC70 proteins with those of other vertebrates. Phylogenetic analysis showed that vertebrate HSP70 could be classified into four cluster groups: (a) fish HSP70, with two isoforms of heat-inducible HSP70 in fish, fish HSP70-1 and HSP70-2; (b) the mammalian testis-specific HSP70-related protein HST70; (c) the mammalian heat-inducible HSP70B'; and (d) the mammalian major histocompatibility complex (MHC)-linked HSP70, including the MHC-linked heat-inducible HSP70 and the testis-specific HSP70-related protein. These findings suggest that vertebrate HSP70 was derived from a single ancestral HSP70 gene during vertebrate evolution and that multiple copies of heat-inducible HSP70 were probably evolved during genetic divergence in fish and higher vertebrates.

HSP70 protects against TNF-induced lethal inflammatory shock

The heat shock (HS) response is a universal response activated after exposure to various stimuli. The major HS protein (HSP) is the 72 kDa HSP70 with strong homology in different eukaryotic species. We demonstrate that HS treatment of mice leads to a strong induction of HSP70 in several organs and confers significant protection against lethality induced by tumor necrosis factor (TNF). HS prevents high production of interleukin-6 and nitric oxide and reduces severe damage and apoptosis of the enterocytes in the bowel. Mice deficient in the inducible hsp70.1 gene were no longer protected by HS treatment. We show that HS can be applied successfully in an antitumor protocol based on TNF and interferon-gamma, leading to a significant inhibition of lethality but not to a reduction of antitumoral capacity.

Expression of Apg-1, a member of the Hsp110 family, in the human testis and sperm

BACKGROUND

Apg-1 encodes a heat shock protein belonging to the Hsp110 family and is inducible by a 32 degrees C to 39 degrees C heat shock in somatic cells. In mouse testicular germ cells Apg-1 mRNA is constitutively expressed depending on the developmental stage. As human Apg-1 has recently been identified, the expression of Apg-1 in the human testis and sperm was investigated.

METHODS

Expression and heat-inducibility of Apg-1 in the human testicular germ cell tumor cell line, NEC8, was analyzed. Using an antimouse Apg-1 antibody, expression of Apg-1 in the human testis and sperm was examined by western blotting after confirmation of the specificity of the antibody. The cells expressing Apg-1 in the testis were further determined by immunohistochemistry.

RESULTS

Slight induction of Apg-1 mRNA was detected in NEC8 cells after 32 degrees C to 39 degrees C temperature shift. In the human testis, the antibody specifically recognized Apg-1, which was absent in the testis without germ cells (Sertoli-cell-only syndrome) or arrested at spermatogonia. Spermatocytes and spermatids, but not testicular somatic cells, were positively stained with the anti-Apg-1 antibody. By western blot analysis, Apg-1 was detected in the preparation enriched for sperm from normal volunteers and infertile patients, but not from azoospermia patients.

CONCLUSION

Apg-1 is developmentally expressed in human testicular germ cells and sperm, suggesting its role in spermatogenesis and fertilization. Identification of substrates for Apg-1 chaperone activity will help elucidate its function.

Heat-shock resistance in experimental cryptorchid testis of mice

Cryptorchidism is commonly used for research on spermatogenesis. However, there are few comparative investigations about the strain differences in mice, especially in long-term experiments. In the present study, the authors demonstrate its specific dynamics in the MRL/MpJ mouse strain, and discuss the cause of strain differences. In the mouse strains A/J BALB/c, C3H/He, and C57BL/6, after 2 weeks of experimental cryptorchidism, the ratios of the cryptorchid testis weight against the intact one were 0.38+/-0.05, 0.43+/-0.05, 0.38+/- 0.02, and 0.44+/-0.14, respectively. On the other hand, in the MRL/MpJ strain it was shifted to 0.69+/-0.08. The details of this strain difference were compared by calculation of germ cells with the Sertoli cell index at 2 weeks after operation. The indices of spermatogonia in all strains were not significantly different; however, in MRL/MpJ mice remarkable numbers of late spermatocytes and round spermatids were detected. The decrease of the testis weight ratio was similar until 10 days in the C57BL/6 and MRL/MpJ strains, but continued in C57BL/6 until 21 days, whereas in MRL/MpJ mice it plateaued after 10 days. Northern blot analysis for heat shock protein 70-2 using total RNA prepared from the cryptorchid and intact testes at 2 weeks after operation revealed that the expression was decreased in the cryptorchid testis of C57BL/6, but not MRL/MpJ mice. The results suggested that heat-resistant germ cells were present in MRL/MpJ, originating possibly from the genetic background.

Testicular germ cell apoptosis in Bcl6-deficient mice

Bcl6 protein has been detected in testicular germ cells, mainly spermatocytes, of normal mice, but its physiological role is largely unknown. The number of spermatozoa in the cauda epididymis of adult Bcl6-deficient (Bcl6−/−) mice is lower than that of Bcl6+/+ mice. We have found numerous apoptotic spermatocytes at the metaphase I stage with induction of Bax protein in adult Bcl6−/− testes. Developmentally, the incidence of germ cell apoptosis of Bcl6−/− mice was similar to that of Bcl6+/+ mice until six weeks of age and increased after eight weeks of age. The incidence of apoptosis in heterozygous Bcl6+/− mice was also higher than that of Bcl6+/+ mice. Since the activated form of p38 MAP kinase was detected in spermatocytes of adult Bcl6−/− mice, the germ cell apoptosis may be induced by stressors. Treatment of testes of adult Bcl6+/+ mice with a mild hyperthermia resulted in germ cell apoptosis predominantly in metaphase I spermatocytes with induction of Bax protein and activation of p38 MAP kinase and this apoptosis mimics that in adult Bcl6−/− mice. Thus, Bcl6 may play a role as a stabilizer in protecting spermatocytes from apoptosis induced by stressors.

Putative creatine kinase M-isoform in human sperm is identifiedas the 70-kilodalton heat shock protein HspA2

We previously described a putative creatine kinase M isoform in human sperm that is developmentally regulated and expressed during late spermiogenesis, simultaneous with cytoplasmic extrusion. We have now identified this protein as the testis-expressed 70-kDa heat shock protein chaperone known as HspA2 (the human homologue of mouse Hsp70-2). We have isolated and characterized HspA2 (formerly CK-M) by amino acid sequencing and have localized it by immunocytochemistry to spermatocytes at low levels, to spermatids, and in the tail of mature sperm. The specificity of the CK-M/HspA2 antiserum to HspA2 was demonstrated on immunoblots of one- and two-dimensional SDS-PAGE. In agreement with our earlier biochemical data, immunocytochemistry of testicular tissue indicated that HspA2 is selectively expressed in mature spermatids and in sperm about to be released in the seminiferous tubuli. The identity of HspA2 has been further confirmed by cross-absorption of the mouse HSP70-2 antibody by the HspA2/CK-M fraction, and by identical immunostaining patterns of human testicular tissue using either the anti-CK-M/HspA2 or an anti-mouse Hsp70-2 antisera. During spermiogenesis, both cytoplasmic extrusion and plasma membrane remodeling, which facilitate the formation of the zona pellucida binding site, involve major intrasperm protein transport, which may be chaperoned by HspA2. Accordingly, in immature human sperm, which fail to express HspA2, there is cytoplasmic retention and lack of zona pellucida binding. The present findings provide the biological rationale for the role of the human HspA2 as an objective biochemical marker of sperm function and male fertility, which we have established in earlier clinical studies.

Repression of hspA2 messenger RNA in human testes with abnormal spermatogenesis

OBJECTIVE

To evaluate the messenger RNA (mRNA) expression of hspA2 in testes of infertile men with azoospermia.

DESIGN

Prospective study.

SETTING

Center for Reproduction and Genetics, Pundang Je-Saeng General Hospital, Dae-Jin Medical Center, Korea.

PATIENT(S)

Azoospermic patients (n = 15) undergoing testicular biopsy for pathologic evaluation were selected.

INTERVENTION(S)

After pathologic evaluation, testicular biopsy specimens were subdivided into three groups: group 1, normal spermatogenesis (n = 5); group 2, spermatocyte arrest (n = 5); and group 3, Sertoli cell-only syndrome (n = 5). The levels of hspA2 mRNA expression were compared in testes of group 1, group 2, and group 3 with the use of a competitive reverse transcription polymerase chain reaction (RT-PCR) technique.

MAIN OUTCOME MEASURE(S)

Comparison of hspA2 mRNA levels in testes.

RESULT(S)

On competitive RT-PCR analyses for hspA2 mRNA, significant hspA2 expression was observed in group 1, whereas a very low level of hspA2 was expressed in groups 2 and 3.

CONCLUSION(S)

This study demonstrates that hspA2 gene expression is down-regulated in human testes with abnormal spermatogenesis, which in turn suggests that the hspA2 gene might play a specific role during meiosis in human testes.

Molecular chaperones in cilia and flagella: implications for protein turnover

The mechanisms of protein incorporation and turnover in 9+2 ciliary axonemes are not known. Previous reports of an HSP70-related protein, first in Chlamydomonas flagella and then in sea urchin embryonic cilia, suggested a potential role in protein transport or incorporation. The present study further explores this and other chaperones in axonemes from a representative range of organisms. Two-dimensional gel electrophoresis proved identity between the sea urchin ciliary 78 kDa HSP and a constitutive cytoplasmic HSP70 cognate (pI = 5.71). When isolated flagella from mature sea urchin sperm were analyzed, the same total amount and distribution of 78 kDa protein as in cilia were found. Antigens of similar size were detected in ctenophore comb plate, molluscan gill, and rabbit tracheal cilia. Absent from sea urchin sperm flagella, TCP-1alpha was detected in sea urchin embryonic and rabbit tracheal cilia; the latter also contained HSP90, detected by two distinct antibodies. Tracheal cilia were shown to undergo axonemal protein turnover while tracheal cells mainly synthesized ciliary proteins. TCP-1alpha progressively appeared in regenerating embryonic cilia only as their growth slowed, suggesting a regulatory role in incorporation or turnover. These results demonstrate that chaperones are widely distributed ciliary and flagellar components, potentially related to axonemal protein dynamics.

Hepatoma-derived growth factor-related protein (HRP)-1 gene in spermatogenesis in mice

Hepatoma-derived growth factor (HDGF)-related protein (HRP)-1, a member of the HDGF gene family, showed testis-specific expression in mice. HRP-1 expression in spermatogenesis was analyzed in the testis of normal and azoospermic mice by Northern blot and immunohistochemistry. HRP-1 gene message was not expressed in the ovary and its product was detected only in the nuclei of germ cells, not in somatic cells. The HRP-1 gene is expressed through pachytene spermatocyte to round spermatid. HRP-1 gene expression was not detected in the testis of cryptorchid mice or in some strains of mutant mice. These findings suggest that the testis-specific HRP-1 gene may play an important role in the phase around meiotic cell division.

The Hsp70 homolog gene, Hsc70t, is expressed under translational control during mouse spermiogenesis

Hsc70t is a member of the Hsp70 family of genes and is constitutively expressed after meiosis in mouse spermatogenesis. Immunohistochemistry and in situ hybridization techniques were used to examine the precise localization of the Hsc70t product during the various stages of spermatogenesis. A rabbit antiserum raised againstthe mouse Hsc70t-lacZ fusion protein detected the Hsc70t protein in the late spermatid-enriched fraction after two-dimensional Western blot analyses. On histological sections, the protein appears in the cytoplasm of spermatids as they progress from step 9 to the final step of spermatogenesis. An antisense RNA probe generated from the 3' untranslated region of Hsc70t cDNA detected Hsc70t mRNA in late round spermatids from step 7 onward with the signal disappearing in spermatids at step 15. Thus, Hsc70t mRNA first appears after meiosis in haploid cells but is not translated effectively until these cells progress to the transcriptionally inactive stage which coincides with chromatin condensation. These results establish that the synthesis of Hsc70t protein is under strict translational control.

Molecular cloning and developmental pattern of expression of MSJ-1, a new male germ cell-specific DNAJ homologue

A cDNA encoding a new member of the DnaJ protein family has been isolated by screening a mouse testicular expression library. The predicted protein, named MSJ-1, is 242 amino acid residues-long, containing the fingerprinting J domain in the NH2 terminus. A wide tissutal Northern blot analysis reveals that MSJ-1 is expressed only in the testis, while in situ hybridization analyses demonstrate that the mRNA is first transcribed in spermatids. The antiserum developed against a MSJ-1/GST fusion protein recognizes a protein of 30 kDa in germ cell protein extracts.

Protective mechanisms in germ cells: stress proteins in spermatogenesis

A wide range of environmental exposures trigger protective mechanisms in reproductive tissues which are mediated by stress or heat shock proteins (HSPs). These stress proteins maintain normal cellular functions such as protein synthesis, as well as assist in resisting and recovering from toxicant-induced cellular damage. Over the past decade a number of laboratories have examined the expression and potential functions of these stress proteins during gametogenesis (reviewed in Dix, 1997a) and in reproductive toxicology (Dix, 1997b). This paper reviews the expression of HSPs in testes, presents a detailed analysis of the function of Hsp70-2 during the meiotic phase of spermatogenesis, and concludes with a discussion of stress-inducible HSPs and putative protective mechanisms.

Expression of heat shock protein 70 blocks thymic differentiation of T cells in transgenic mice

Heat shock protein 70 (HSP70) is involved not only in protein folding, but also in processes of differentiation and cell-cycle progression. Recently, HSP70 has been implicated in mediation of functions of some immunosuppressive agents. To study the role of HSP70 in differentiation of haematopoietic cells, we generated transgenic mice using the human inducible hsp70 gene fused to the mouse H-2K promoter. These mice develop a T-cell deficiency that is characterized by thymic hypoplasia and a significant reduction in peripheral T cells. The total number of thymocytes is about 100-fold less than that in normal mice. The majority of the thymocytes are immature T cells that express neither CD4 nor CD8 molecules, indicating that T cells are affected at an early stage of thymic differentiation. Expression of the transgenic HSP70 was detected both in bone marrow cells and in thymocytes. Furthermore, injection of normal bone marrow cells into the T-cell deficient mice led to the generation of mature T cells indicating that the T-cell deficiency was caused by the action of HSP70 in T cells. The blockage of differentiation occurred only in T cells, both alphabeta- and gammadelta-T-cell receptor (TCR)-bearing cells, but not in B cells, granulocytes, and monocytes. The observations suggest that HSP70 may inhibit a cellular process that is essential for the differentiation of early stage T cells. Further experiments using this model system will widen our understanding of HSP70 and its function on a molecular level.

Marked differences between avian and mammalian testicular cells in the heat shock induction and polyadenylation of Hsp70 and ubiquitin transcripts

Mammalian male germ cells undergo apoptosis at the body's internal temperature of 37 degrees C. Birds, however, are unique among homeothermic animals in developing spermatogenesis at the elevated avian internal body temperature of 40-41 degrees C. To shed light on the mechanisms that maintain an efficient avian spermatogenesis at elevated temperatures we compared, in mouse and chicken testicular cells, the expression of genes that are essential for stress resistance: Hsp70 and ubiquitin. While the expression of Hsp70 and ubiquitin did not change upon heat shock in mouse testicular cells, both the amount and polyadenylation of Hsp70 and ubiquitin transcripts increased when male germ cells from adult chicken testis were exposed to elevated temperatures.

Isolation of antiSLIP1-reactive boar sperm P68/62 and its binding to mammalian zona pellucida

Single-step purification of boar sperm P68/62 that is cross-reactive with a polyclonal antibody against sulfolipidimmobilizing protein 1 (SLIP1) was achieved by chromatofocusing. This method is useful for obtaining P68/62 in quantity. The two proteins, P68 and P62, were antigenically related, since the antibody generated specifically against the 68-kDa band reacted with both the 68- and 62-kDa bands. Like rat testis SLIP1, purified boar sperm P68/62 bound to sulfogalactosylglycerolipid (SGG) and inhibited sperm-egg binding in a dose-dependent manner when added exogenously to sperm-egg coincubates. This inhibitory effect occurred at the level of the zona pellucida (ZP), and further studies showed that biotinylated boar sperm P68/62 bound to the ZP of unfertilized mouse eggs. Furthermore, biotinylated boar sperm P68/62 bound to isolated ZP of unfertilized eggs from other species, including pig, rat, cat, dog, and human, as well as to ZP of intact fertilized mouse eggs and preimplantation embryos of various developmental stages, although the degree of its binding to the ZP of intact eight-cell embryos, morulae, and blastocysts was much lower than that of fertilized eggs and two-cell embryos. These results suggest that P68/62 of capacitated sperm must act together with other sperm surface proteins/molecules that regulate zona binding specificity within homologous species and in unfertilized eggs. Together with our previous findings, we suggest that rather than being a true ZP receptor, sperm P68/62 may be involved in the initial step of sperm-ZP binding that is adhesive in nature.

HSP70-2 is required for CDC2 kinase activity in meiosis I of mouse spermatocytes

Cyclin B-dependent CDC2 kinase activity has a key role in triggering the G2/M-phase transition during the mitotic and meiotic cell cycles. The Hsp70-2 gene is expressed only in spermatogenic cells at a significant level. In Hsp70-2 gene knock-out (Hsp70-2(−/−)) mice, primary spermatocytes fail to complete meiosis I, suggesting a link between HSP70-2 heat-shock protein and CDC2 kinase activity during this phase of spermatogenesis. Members of the HSP70 protein family are molecular chaperones that mediate protein de novo folding, translocation and multimer assembly. This study used immunoprecipitation-coupled western blot and in vitro reconstitution experiments to show that HSP70-2 interacts with CDC2 in the mouse testis, appears to be a molecular chaperone for CDC2, and is required for CDC2/cyclin B1 complex formation. Previous studies reported that most CDC2 kinase activity in the mouse testis is present in pachytene spermatocytes. Although CDC2 kinase activity for histone H1 was present in the testis of wild-type mice, it was nearly absent from the testis of Hsp70-2(−/−) mice, probably due to defective CDC2/cyclin B1 complex formation. Furthermore, addition of HSP70-2 to freshly prepared extracts of testis from Hsp70-2(−/−) mice not only restored CDC2/cyclin B1 complex formation but also reconstituted CDC2 kinase activity in vitro. It appears that one cause of failure to complete meiosis I during spermatogenesis in Hsp70-2(−/−) mice is disruption of CDC2/cyclin B1 assembly in pachytene spermatocytes, thereby preventing development of the CDC2 kinase activity required to trigger G2/M-phase transition. These studies provide novel in vivo evidence for a link between an HSP70 molecular chaperone and CDC2 kinase activity essential for the meiotic cell cycle in spermatogenesis.

Members of the 70 kDa heat shock protein family specifically recognize sulfoglycolipids: role in gamete recognition and mycoplasma-related infertility

We have previously shown that several mycoplasma species associated with infertility bind specifically to sulfated glycolipids isolated from the mammalian reproductive tract. We now show that a germ cell-specific sulfoglycolipid binding protein (SLIP 1), which is a potent inhibitor of sperm/egg binding in vitro, is immunologically related to the heat shock protein(Hsp) 70 family of stress proteins and that Hsps are surface antigens in male germ cells. Our present data demonstrate that several mycoplasma and mammalian Hsps share this glycolipid binding specificity in vitro, and suggest that surface Hsps can function as adhesins which mediate sulfoglycolipid recognition in infectious disease and normal reproductive physiology.

Male germ cell-specific alteration in temperature set point of the cellular stress response

Heat shock factor (HSF), a transcriptional regulator with heat-activatable DNA binding ability, mediates the stress-induced expression of eukaryotic heat shock protein genes. Previous results from this laboratory demonstrated that a preparation of mixed male germ cell types from mouse testis exhibited a lower temperature threshold for activation of HSF1 DNA binding relative to other mouse cell types (Sarge, K.D., Bray, A.E., and Goodson, M.L. (1995) Nature 374, 126). The purpose of the present study was to determine whether the phenomenon of reduced HSF1 activation temperature is common to all testis cell types, both somatic and germ cell types, or whether it is a special property of male germ cells. The results show that a purified population of pachytene spermatocytes, one of the male germ cell types, exhibits a profile of reduced HSF1 activation temperature identical to that observed for the mixed germ cell preparation, with a threshold HSF1 activation temperature of 35 degrees C. Activation of HSF1 DNA binding in male germ cells by incubation at 38 degrees C is accompanied by the classic cellular stress response parameters of heat-induced HSF1 phosphorylation and increased expression of the hsp72 stress protein. In contrast, a preparation of somatic testis cell types exhibits HSF1 activation only at temperatures of 42 degrees C and above, a profile identical to that observed for mouse liver cells and mammalian cell lines. These results demonstrate that the phenomenon of reduced HSF1 activation temperature is a unique property of male germ cell types within the mammalian testis and demonstrate that HSF1 activated at this lower temperature threshold is fully capable of mediating a productive cellular stress response in these cell types.

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.

Genetic aspects of the hsp70 multigene family in vertebrates

The family of genes encoding heat shock proteins of about 70 kDa (hsp70) in vertebrates is reviewed under genetic aspects. After a detailed description of the various hsp70 genes more general characteristics of the organization and evolution of the multigene family are discussed.

Characterization of a testis specific protein localized to endoplasmic reticulum of spermatogenic cells

BACKGROUND

In order to understand the mechanism of spermiogenesis, it is important to characterize germ cell specific genes and proteins expressed during spermatogenesis. We previously reported that a mouse monoclonal antibody, 1C9, raised against golden hamster testis homogenate, recognized a 103 kDa protein in hamster spermatogenic cells (Ohsako et al.; J. Vet. Med. Sci., 53:969-974, 1991). In the present study, we have determined the precise stage and intracellular localization of this protein.

MATERIALS AND METHODS

Hamster, mouse, and rat tissues were used for immunocytochemistry, SDS-PAGE, and immunoblotting. Immunoelectron microscopy was performed using Lowicryl K4M embedded hamster testis and colloidal gold conjugated second antibody. Furthermore, immuno-affinity purification was carried out using a 1C9-Sepharose column.

RESULTS

In immunoblot analysis, 1C9 also recognized a 103 kDa protein and a 101 kDa protein in the rat and the mouse testes, respectively. Ten different hamster tissues other than testis did not show reactivity against 1C9. In immunostained paraffin sections of hamster testis, the initial staining appeared in middle pachytene spermatocytes and persisted until maturation phase spermatids (step 15). However, it was no longer detectable in the subsequent steps of spermatids. In addition, strong staining was observed in the post-nuclear region of elongated spermatids. Immunoelectron microscopic analysis showed that the protein was localized to the endoplasmic reticulum (ER) and nuclear envelope of spermatogenic cells, but not in the other organelles, such as Golgi apparatus and acrosome of the spermatids. This protein appears to be associated with ER membrane. Furthermore, this protein is found exclusively in the testicular microsomal fraction, not in the cytosol. By affinity purification, approximately 320 micrograms of the 103 kDa protein was obtained from 10 hamster testes. The purified 103 kDa protein was unaffected by N-glycanase, indicating it does not have asparagine-linked glycoconjugates.

CONCLUSIONS

These results indicate that the protein recognized by 1C9 appears to be a unique protein that is localized in the ER and nuclear envelope of spermatogenic cells.

An upstream region of the rat spermatogenesis-specific heat-shock-like Hst70 gene confers testis-specific expression in transgenic mice

In order to study the temporal and spatial regulation of a rat testis-specific heat-shock-like hst70 gene, an 0.8-kb fragment of its upstream DNA was fused to the lacZ gene and microinjected into one-cell murine embryos. Independent tgHST1 and tgHST2 transgenic mice strains were established, containing about 5-7 and 40-60 transgene copies/haploid genome, respectively. Enzyme assays in various tissues showed that transgene-encoded beta-galactosidase accumulates exclusively in testes of transgenic animals and cannot be detected until 16-17 days after birth. In-situ assays revealed that the enzyme accumulates mainly in pachytene primary spermatocytes. Our data complement previous studies on the endogenous rat hst70 and suggest that its 0.8-kb upstream region contains sufficient information to function as an active spermatogenesis-specific promoter.

Tissue-specific expression of heat shock proteins of the mouse in the absence of stress

The steady-state levels of four members of the heat shock proteins families (HSP84, HSC73, HSP71, and HSP25) were examined by immunoblot analysis of several different tissues of young and adult mice in the absence of stress. These hsps were detected in all tissues but their level was variable. The levels of HSC73 and HSP84 varied only slightly between different tissues in either young or adult mice, with the exception of skin where these hsps were found in reduced amounts. In contrasts, the stress-inducible member of the HSP70 family, HSP71, was found to be expressed in all tissues but in amounts which differed by as much as two orders of magnitude between tissues. In general, the levels of both HSP71 and HSP25 were found to be tissue dependent, with higher levels found in tissues such as stomach, intestine, colon and bladder, tissues which are exposed to toxic environmental or metabolic products, and which may concentrate these substances by water resorption and/or be exposed to them for longer periods. The levels of HSP71 and HSP25 were generally positively correlated both in young and adult mice although this correlation was not found in certain tissues such as kidney, testes, and bone. Tissues of young mice contained lower amounts of HSP25 and HSP71 than were found in the same tissues from adults. We conclude that hsps are expressed in all tissues of the mouse in the absence of stress and that some organs, particularly those exposed to potentially toxic metabolites, show a higher level of expression of HSP71 and HSP25.

HSP86 and HSP84 exhibit cellular specificity of expression and co-precipitate with an HSP70 family member in the murine testis

This study extends to the protein level our previous observations, which had established the stage and cellular specificity of expression of hsp86 and hsp84 in the murine testis in the absence of exogenous stress. Immunoblot analysis was used to demonstrate that HSP86 protein was present throughout testicular development and that its levels increased with the appearance of differentiating germ cells. HSP86 was most abundant in the germ cell population and was present at significantly lower levels in the somatic cells. By contrast, the HSP84 protein was detected in the somatic cells of the testis rather than in germ cells. The steady-state levels of HSP86 and HSP84 paralleled the pattern of the expression of their respective mRNAs, suggesting that regulation at the level of translation was not a major mechanism controlling hsp90 gene expression in testicular cells. Immunoprecipitation analysis revealed that a 70-kDa protein coprecipitated with the HSP86/HSP84 proteins in testicular homogenates. This protein was identified as an HSP70 family member by immunoblot analysis, suggesting that HSP70 and HSP90 family members interact in testicular cells.

In situ localization of male germ cell-associated kinase (mak) mRNA in adult mouse testis: specific expression in germ cells at stages around meiotic cell division

Biochemical analysis of the male germ cell-associated kinase (mak) gene, which was isolated recently by using weak cross-hybridization with the v-ros tyrosine kinase gene, revealed that the gene was highly expressed in mammalian testicular germ cells, but not in ovarian cells. In order to identify the cells which express the mak gene in more detail, we localized mak mRNA in frozen sections of mouse testis by non-radioactive in situ hybridization. In this study, we utilized thymine-thymine (T-T) dimerized mak cDNA as a haptenic, non-radioactive probe, and the signal was detected enzyme-immunohistochemically by using an anti-T-T antibody. As a result, mak mRNA was localized intensely in late pachytene (stage X) and diplotene (stage XI) spermatocytes, and faintly in dividing spermatocytes (stage XII) and early round spermatids (stage I-II), suggesting that the gene may play an important role in the phase around meiotic cell division, but not throughout the entire meiosis.

Identification of the gene for the developmentally expressed 70 kDa heat-shock protein (P70) of mouse spermatogenic cells

Mouse spermatogenic cells synthesize a 70-kDa protein (P70) closely related to the major heat-shock protein (hsp70) of mammalian cells (R. L. Allen, D. A. O'Brien, and E. M. Eddy, Mol. Cell. Biol. 8, 828-832, 1988). Expression of P70 is developmentally regulated while hsp70 is induced in response to stress, suggesting that P70 is the product of a unique member of the Hsp70 multigene family transcribed in spermatogenic cells. A strong candidate for this gene was the Hsp70.2 gene (Z. F. Zakeri, D. J. Wolgemuth, and C. R. Hunt, Mol. Cell. Biol. 8, 2925-2932, 1988). A DNA segment from the 5' region of Hsp70.2 hybridized to a 2.7-kb transcript with a temporal pattern of expression in mouse spermatogenic cells similar to the P70 protein. We used a polyclonal antiserum generated against a synthetic peptide predicted from the Hsp70.2 sequence to characterize its protein product and to isolate cDNA clones from a pachytene spermatocyte expression library. The antiserum reacted specifically with meiotic and postmeiotic spermatogenic cells on sections of mouse testis. It recognized the P70 protein on Western blots of two-dimensional gels and did not bind to other heat-shock proteins of spermatogenic or somatic cells. The cDNAs hybridized to a 2.7-kb mRNA that was abundant in unstressed pachytene spermatocytes and round spermatids but was not detected in other cell types. Two cDNAs were sequenced and found to be 99% homologous to the 3' end of the Hsp70.2 gene. These data strongly supported the hypothesis that P70 is the expressed product of the Hsp70.2 gene in mouse spermatogenic cells.

Developmental regulation of heat-shock response in mouse oogenesis: identification of differentially responsive oocyte classes during Graafian follicle development

The response to heat (hs response) of dictyate mouse oocytes at various differentiation stages was analyzed in vitro, by determining patterns of oocyte heat-shock (hs) gene expression and heat-shock protein (HSP) synthesis, under both normal conditions and after an hs. Growing oocytes constitutively synthesized HSP89 and HSC70, and, in contrast to preovulatory oocytes which do not display an hs response, displayed a heat-elicited, transcription-dependent synthesis of two HSP68 isoforms, but not of other inducible HSPs. To determine the developmental schedule of hs response disappearance during oogenesis, fully grown oocytes from Graafian follicles were morphologically sorted into three discrete classes related to the follicle development, namely, loosely associated with granulosa cells (LA oocytes, from small Graafian follicles), intermediately associated with granulosa cells (IA oocytes, from medium-sized Graafian follicles), and cumulus-associated (CA oocytes, from mature follicles). LA oocytes displayed an hs response qualitatively similar to, but smaller in extent than, that of growing oocytes, and were able to resume and complete spontaneous meiotic maturation in vitro at a high rate after hs. We conclude that hs response of mouse dictyate oocytes is maximal during growth period, significantly declines with acquisition of full oocyte size and antrum formation within the follicle, and is finally shut off with oocyte/follicle terminal differentiation.

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.

Cloning of a hsp70-related gene expressed in mouse spermatids

A cDNA library of spermatids was screened by a differential hybridization in order to isolate genes expressed in haploid cells of the mouse male germ line. A clone was found that encoded a protein related to the heat shock protein 70. A genomic DNA clone comparable to this cDNA clone was also isolated from a mouse genomic library. This gene had only one continuous open reading frame capable of coding a 630 amino-acid protein. There was an excellent match of the sequence with the heat shock protein 70 family but a difference from any previous 70 kilodalton heat shock protein. A 2.7kb transcript derived from this gene was expressed in spermatids but not in other testicular germ cells and somatic tissues. We have referred to this gene as hsc70t.