Inhibition of testicular germ cell apoptosis and differentiation in mice misexpressing Bcl-2 in spermatogonia

[Sperm apoptosis: myth or reality?]

Apoptosis has become a popular biologic concept, for many reasons. From embryonic development to adult tissues, apoptosis is necessary to maintain tissues homeostasis in most organ systems during organogenesis and in the adult. Human spermatogenetic epithelium is also concerned. Dysregulations of this process are involved in many pathologies (leukaemia, auto-immune diseases, etc...), and some forms of male infertility also. Apoptotic features have been found in human semen from infertile patients, and could become useful in order to appreciate semen quality, especially in Assisted Reproductive Technology (ART). Despite numerous studies, some questions remain, especially about meaning of apoptotic damages of spermatozoa.

The Bcl-2 family in autoimmune and degenerative disorders

Members of the Bcl-2 family are essential regulators of programmed cell death and thus play a major role in the development and function of many tissues. The balance between pro-survival and pro-apoptotic members of the family decides whether a cell will live or die. This mechanism allows organisms to get rid of cells that are no longer needed or have become dangerous. Deregulation of apoptosis is a major contributing factor in the development of many diseases. A deeper understanding of how the Bcl-2 family proteins orchestrate death in normal and pathologic conditions is thus relevant not only for disease etiology, but also to try to prevent these various disorders. Experiments with transgenic and gene-ablated mice have helped elucidate the function of the different members of the Bcl-2 family and their physiological roles. The present review highlights the role of Bcl-2 family members in autoimmune and degenerative disorders, with a particular focus on the mouse models that have been used to study their function.

Diethyl maleate-induced oxidative stress leads to testicular germ cell apoptosis involving Bax and Bcl-2

Testicular germ cell apoptosis is normally a continuous process throughout life. However, massive testicular germ cell loss is known to result from a wide variety of cellular stresses including toxicant exposure. Thus, the present study was aimed to investigate the mechanisms of germ cell loss under stress conditions following diethyl maleate (DEM) exposure. Stress conditions were generated in male Balb/c mice by depleting glutathione by DEM administration. The germ cell apoptosis was found to be increased as assessed by terminal deoxynucleotidyl transferase (TdT)-mediated deoxy-UTP biotin nick end labeling (TUNEL) staining, evaluation of histoarchitechture of testis, and germ cell numbers. It was found that the germ cell number was significantly reduced in DEM-treated sections. RT-PCR was carried out to assess Bax/Bcl-2 mRNA expression levels. Immunohistochemistry of Bax and Bcl-2 revealed Bax activation. The prevalence and cellular localization of the above markers in testicular tissues of DEM-treated animals suggest the possible involvement of Bax/Bcl-2 in the male germ cell apoptosis.

Testis atrophy and reduced sperm motility in transgenic mice overexpressing c-FLIP(L)

OBJECTIVE

To study the effect of c-FLIP overexpression in testicular germ cells.

DESIGN

A novel transgenic mouse model overexpressing the apoptotic modulator c-FLIP in the testis was generated.

SETTING

Animal facility and university research laboratory.

ANIMAL(S)

Transgenic mice overexpressing the long isoform of c-FLIP (c-FLIP(L)) under the transcriptional control of a 400 bp long regulatory region of the Stra8 promoter.

INTERVENTION(S)

Spermatozoa motility and testis histological, immunohistochemical, and Western blot analyses were carried out in transgenic and control derived specimens.

MAIN OUTCOME MEASURE(S)

Testis morphology, sperm motility, and germ cell apoptosis were assayed.

RESULTS

Stra8 promoter was found to activate the ectopic overexpression of c-FLIP(L) in round and elongated spermatids. As a consequence of such overexpression, a dramatic loss of germ cells was observed, resulting in testicular atrophy associated with reduced sperm motility.

CONCLUSION(S)

The data show that c-FLIP(L) forced expression in haploid male germ cells has detrimental effects on spermatogenesis and sperm quality and reveal a possible mechanism underlying the onset of testicular atrophy.

Two-step oligoclonal development of male germ cells

During mouse development, primordial germ cells (PGCs) that give rise to the entire germ line are first identified within the proximal epiblast. However, long-term tracing of the fate of the cells has not been done wherein all cells in and around the germ-cell lineage are identified. Also, quantitative estimates of the number of founder PGCs using different models have come up with various numbers. Here, we use tetrachimeric mice to show that the progenitor numbers for the entire germ line in adult testis, and for the initiating embryonic PGCs, are both 4 cells. Although they proliferate to form polyclonal germ-cell populations in fetal and neonatal testes, germ cells that actually contribute to adult spermatogenesis originate from a small number of secondary founder cells that originate in the fetal period. The rest of the "deciduous" germ cells are lost, most likely by apoptosis, before the reproductive period. The second "actual" founder germ cells generally form small numbers of large monoclonal areas in testes by the reproductive period. Our results also demonstrate that there is no contribution of somatic cells to the male germ cell pool during development or in adulthood. These results suggest a model of 2-step oligoclonal development of male germ cells in mice, the second step distinguishing the heritable germ line from cells selected not to participate in forming the next generation.

[Could apoptotic markers help the exploration of male infertility?]

Apoptosis is a cell death program involved in different steps of spermatogenesis, first at puberty, at the beginning of spermatogenesis, then in adult testicles by controlling normal spermatogenesis. As a result, apoptosis deregulation can affect spermatogenesis. Many studies have provided evidence that apoptosis deregulation in germinal cells resulted in male infertility. In addition, apoptosis detection in ejaculated spermatozoa arouses a growing interest in research as a reliable marker of spermatozoon quality. The aim of this review is to summarize our knowledge on physiological apoptosis during spermatogenesis, and then analyse the possibility of using apoptotic markers as selective markers of spermatozoon quality to optimize the rate of success of in vitro fertilization.

Sohlh2 knockout mice are male-sterile because of degeneration of differentiating type A spermatogonia

The spermatogenesis and oogenesis-specific transcription factor Sohlh2 is normally expressed only in premeiotic germ cells. In this study, Sohlh2 and several other germ cell transcripts were found to be induced in mouse embryonic stem cells when cultured on a feeder cell line that overexpresses bone morphogenetic protein 4. To study the function of Sohlh2 in germ cells, we generated mice harboring null alleles of Sohlh2. Male Sohlh2-deficient mice were infertile because of a block in spermatogenesis. Although normal prior to birth, Sohlh2-null mice had reduced numbers of intermediate and type B spermatogonia by postnatal day 7. By day 10, development to the preleptotene spermatocyte stage was severely disrupted, rendering seminiferous tubules with only Sertoli cells, undifferentiated spermatogonia, and degenerating colonies of differentiating spermatogonia. Degenerating cells resembled type A2 spermatogonia and accumulated in M-phase prior to death. A similar phenotype was observed in Sohlh2-null mice on postnatal days 14, 21, 35, 49, 68, and 151. In adult Sohlh2-mutant mice, the ratio of undifferentiated type A spermatogonia (DAZL+/PLZF+) to differentiating type A spermatogonia (DAZL+/PLZF-) was twice normal levels. In culture, undifferentiated type A spermatogonia isolated from Sohlh2-null mice proliferated normally but linked the mutant phenotype to aberrant cell surface expression of the receptor-tyrosine kinase cKit. Thus, Sohlh2 is required for progression of differentiating type A spermatogonia into type B spermatogonia. One conclusion originating from these studies would be that testicular factors normally regulate the viability of differentiating spermatogonia by signaling through Sohlh2. This regulation would provide a crucial checkpoint to optimize the numbers of spermatocytes entering meiosis during each cycle of spermatogenesis. Disclosure of potential conflicts of interest is found at the end of this article.

Regulation of early wave of germ cell apoptosis and spermatogenesis by deubiquitinating enzyme CYLD

Spermatogenesis involves an early wave of germ cell apoptosis, which is required for maintaining the balance between germ cells and supporting Sertoli cells. However, the signaling mechanism regulating this apoptotic event is poorly defined. Here we show that genetic deficiency of Cyld, a recently identified deubiquitinating enzyme, attenuates the early wave of germ cell apoptosis and causes impaired spermatogenesis in mice. Interestingly, the loss of CYLD in testicular cells leads to activation of the transcription factor NF-kappaB and aberrant expression of antiapoptotic genes. We further show that CYLD negatively regulates a ubiquitin-dependent NF-kappaB activator, RIP1. CYLD binds to RIP1 and inhibits its ubiquitination and signaling function. These findings establish CYLD as a pivotal deubiquitinating enzyme (DUB) that regulates germ cell apoptosis and spermatogenesis and suggest an essential role for CYLD in controlling the RIP1/NF-kappaB signaling axis in testis.

Expression of Aire and the early wave of apoptosis in spermatogenesis

Expression of the autoimmune regulator (Aire) protein in mice and humans is thought to be restricted to the medullary epithelial and monocyte-dendritic cells of the thymus. There it mediates expression and presentation of a large variety of proteins, including those that are peripheral organ-specific and are not expressed by other thymocytes. In this way, self-reactive T lymphocytes that would attack peripheral cells producing these proteins are confronted with the self-Ags and, as a consequence, are deleted. In this study, we show that Aire mRNA is also expressed in the testis--another tissue with promiscuous gene expression. Aire protein, however, is expressed only sporadically in spermatogonia and spermatocytes. Transcription of genes that are under Aire control in the thymus is unaffected by Aire in the testis. However, in mice with a disrupted Aire gene, the scheduled apoptotic wave of germ cells, which is necessary for normal mature spermatogenesis, is reduced, and sporadic apoptosis in adults is increased. Because Rag-1 deficiency does not abolish the effect, the adaptive immune system is not involved. We suggest that there is a link between the scheduled and sporadic apoptotic processes and propose that scheduled apoptosis provides a counterselection mechanism that keeps the germline stable.

Sperm nuclear DNA fragmentation and mitochondrial activity in men with varicocele

OBJECTIVE

To verify the impact of varicocele on semen quality and sperm function (DNA integrity and mitochondrial activity).

DESIGN

Prospective study.

SETTING

Patients in an academic research environment.

PATIENT(S)

Seventeen patients with a clinical diagnosed varicocele of grade II or III and 20 men without a varicocele.

MAIN OUTCOME MEASURE(S)

Rate of sperm DNA fragmentation as assessed by the Comet assay and categorized as classes I (no DNA fragmentation), II (little DNA fragmentation), III (meaningful DNA fragmentation), and IV (high DNA fragmentation). Rate of mitochondrial activity as assessed by the diaminobenzidine (DAB) assay and categorized as grades I (all mitochondria active), II (most mitochondria active), III (most mitochondria inactive), and IV (all mitochondria inactive).

RESULT(S)

No statistically significant differences were found between the study and control groups with respect to age, ejaculatory abstinence, and round cell count. Men with varicocele had significantly higher ejaculate volume, concentration of immotile sperm, and neutrophil count and lower mean percentage of sperm concentration, progressive motility, and morphology than men in the control group. The study group presented a lower percentage of sperm with little DNA fragmentation (class II) and a higher percentage of sperm with DNA fragmentation (class IV). In addition, the study group presented a greater percentage of sperm with inactive mitochondria (class III).

CONCLUSION(S)

Compared with men without varicocele, men with varicocele had a higher percentage of cells with DNA fragmentation and sperm with inactive mitochondria. Indeed, varicocele causes a decrease in motility, concentration, and morphology and an increase in volume and concentration of immotile sperm and neutrophils. The sperm functional evaluation (DNA fragmentation and mitochondrial activity) could be important factors in deciding treatment options for men with varicocele.

Induction of apoptosis involving multiple pathways is a primary response to cyclin A1-deficiency in male meiosis

The meiotic arrest in male mice null for the cyclin A1 gene (Ccna1) was associated with apoptosis of spermatocytes. To determine whether the apoptosis in spermatocytes was triggered in response to the arrest at G2/M phase, as opposed to being a secondary response to overall disruption of spermatogenesis, we examined testes during the first wave of spermatogenesis by terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) staining. We observed enhanced apoptosis coinciding with the arrest point in postnatal day 22 tubules, with no overt degeneration. Along with activation of caspase-3, an increase in the levels and change of subcellular localization of Bax protein was observed in cyclin A1-deficient spermatocytes, which coincided with the detection of apoptosis. As p53 is implicated in the activation of Bax-mediated cell death, we generated mice lacking both cyclin A1 and p53. Although the absence of p53 did not rescue the meiotic arrest, there was a decrease in the number of apoptotic cells in the double-mutant testes. This finding suggested that p53 may be involved in the process by which the arrested germ cells are removed from the seminiferous tubules but that other pathways function as well to ensure removal of the arrested spermatocytes.

Clinical relevance of sperm DNA damage in assisted reproduction

Many studies have shown how a 'paternal effect' can cause repeated assisted reproduction failures. In particular, with increasing experience of intracytoplasmic sperm injection (ICSI), it became evident that spermatozoa from some patients repeatedly fail to form viable embryos, although they can fertilize the oocyte and trigger early preimplantation development. Many authors have shown how this paternal effect can be traced back to anomalies in sperm chromatin organization: the spermatozoa of subfertile men are characterized by numerical abnormalities in spermatozoal chromosome content, Y chromosome microdeletions, alterations in the epigenetic regulation of paternal genome and non-specific DNA strand breaks. In particular, pathologically increased sperm DNA fragmentation is one of the main paternal-derived causes of repeated assisted reproduction failures in the ICSI era. The intention of this review is to describe nuclear sperm DNA damage, with emphasis on its clinical significance and its relationship with male infertility. Assessment of sperm DNA damage appears to be a potential tool for evaluating semen samples prior to their use in assisted reproduction, helping to select spermatozoa with intact DNA or with the least amount of DNA damage for use in assisted conception.

Up-regulation of CD95 (Apo-1/Fas) is associated with spermatocyte apoptosis during the first round of spermatogenesis in the rat

Apoptosis plays a major role in controlling both the rate of sperm production and chromosomal abnormalities in adult male testes. However, little is known on the mechanisms controlling induction and execution of apoptosis under physiological conditions. In this work we have uncovered a major role for the cell death receptor Fas in both the extrinsic and intrinsic pathways in normal germ cell apoptosis. We show here that Fas levels increased significantly in a group of germ cell in 25 d old rats, which were identified as spermatocytes and only a few spermatogonia. In addition, we show that isolated spermatocytes expressing high levels of Fas display activation of caspase-8, -9, -3, -6 and -2, as well as increased levels of intracellular calcium and decreased pH, which coincides with stabilization of p53, and transcriptional activation of PUMA and Fas. Therefore, our data strongly suggests that transcriptional up regulation of Fas could predispose a group of spermatocytes to Fas ligand triggering apoptosis by the extrinsic and intrinsic pathway.

Proliferation of spermatogonial stem cells and spermatogenesis in vitro

Detection of spermatogonial stem cells (SSC) became possible 10 years ago, with the transplantation of germ cells into the seminiferous tubules of mice. Using this assay system, attempts to maintain and expand SSC in vitro finally bore fruit. Gonocytes from neonatal mice and spermatogonial stem cells from adult mice were plated on feeder cells in a medium supplemented with Glial cell line-derived neurotrophic factor (GDNF) along with certain other factors. The germ cells that emerged under such conditions, named germline stem (GS) cells, proliferated exponentially through self-renewing division. GS cells in vitro show features of differentiation as well. Some expressed c-kit, which is a cell surface marker of differentiating spermatogonia. Therefore, it seems that GS cells undergo both self-renewing and differentiating cell divisions in vitro. There is a century of history behind attempts to reproduce spermatogenesis in vitro and significant progress has been made. Nonetheless, there are few established culture-based protocols for recreating spermatogenesis in vitro. GS cells would be an ideal starting material in this regard. (Reprod Med Biol 2006; 5: 169-174).

Sperm DNA fragmentation: paternal effect on early post-implantation embryo development in ART

BACKGROUND

The relationship between early embryo post-implantation development in couples undergoing assisted reproductive techniques (ARTs) and sperm chromatin alterations has not been satisfactorily explained. The aim of this study was to assess the relationship between sperm DNA fragmentation in IVF/ICSI patients, sperm parameters (concentration, motility and morphology) and ART outcome, especially with regard to clinical pregnancy and pregnancy loss (spontaneous miscarriage or biochemical pregnancy).

METHODS

DNA fragmentation was evaluated by TUNEL assay, performed on sperm suspensions after density gradient separation, in 132 men undergoing an ART cycle (82 IVF and 50 ICSI) and correlated with sperm parameters and ART outcome.

RESULTS

A highly significant negative correlation was found between DNA fragmentation and sperm parameters. There was a close relationship between DNA fragmentation and post-implantation development in ICSI patients: the clinical pregnancy and pregnancy loss rates significantly differed between patients with high and low sperm DNA fragmentation (P = 0.007 and P = 0.009, respectively).

CONCLUSIONS

Sperm DNA fragmentation seems to affect embryo post-implantation development in ICSI procedures: high sperm DNA fragmentation can compromise 'embryo viability', resulting in pregnancy loss.

DNA damage-induced programmed cell death: potential roles in germ cell development

The detection of DNA damage is necessary to protect against proliferation of potentially harmful cells and often results in cell cycle arrest and programmed cell death. Key components of DNA damage signaling networks include ATM, CHK2, p53, and Bax. Mutations in these damage signaling systems are linked to tumorigenesis and developmental abnormalities. Expression of some of these genes in primordial germ cells (PGCs) argues that PGCs may utilize DNA damage-induced signaling mechanisms to select against germ cells that are genetically defective, thus maintaining the integrity of the germline. This paper summarizes the roles of these DNA damage signaling molecules and addresses their potential involvement in germ cell development.

Transcriptome analyses of male germ cells with serial analysis of gene expression (SAGE)

Serial analysis of gene expression (SAGE) provides an alternative with additional advantages to microarrays for studying gene expression during spermatogenesis. The digitized transcriptome provided by SAGE of purified mouse germ cells identified 27,504 species of transcripts expressed in type A spermatogonia, pachytene spermatocytes, and round spermatids. Over 2700 of these transcripts were novel. Computational analyses allowed the identification of clusters of co-regulated genes, cell-specific promoter modules, cell-specific biological processes, as well as "preferential" biological networks in different cell types. These analyses provided potential drug targets for interference of specific pathways at different stages of spermatogenesis. Analyses of the transcriptomes revealed the prominent role of cytochrome c oxidase in germ cells and suggest a novel role for this enzyme in cytochrome c-mediated apoptosis in spermatogonia. A number of genes were shown to undergo differential splicing during spermatogenesis giving rise to cell-specific splice variants.

Effects of TGF-betas and a specific antagonist on apoptosis of immature rat male germ cells in vitro

Massive apoptosis of pubertal male germ cells is important for the development of functional spermatogenesis in the adult testis. Although the trigger(s) for male germ cell loss at puberty remain undefined, we have hypothesized that transforming growth factor-betas (TGF-betas) play an active role. Here we demonstrate that the three mammalian TGF-beta isoforms, TGF-beta1, TGF-beta2 and TGF-beta3, induce distinct apoptosis of pubertal spermatogonia and spermatocytes in a dose-dependent manner. Induction of male germ cell death by activation of caspase-3 was most pronounced with TGF-beta2 compared to TGF-beta1 and TGF-beta3. Furthermore, we found colocalization of activated caspase-3 with apoptotic protease-activating factor-1 (Apaf-1) in apoptotic germ cells, thus indicating the importance of the intrinsic mitochondrial pathway in TGF-beta-induced apoptosis. The specificity of the TGF-beta effects was proven by addition of recombinant latency-associated peptide against TGF-beta1 (rLAP-TGF-beta1) which completely abolished TGF-beta1-induced and TGF-beta3-induced germ cell apoptosis. Although TGF-beta2-triggered germ cell death also was significantly reduced by rLAP-TGF-beta1, inhibition was not maximal. Our results suggest that the three TGF-beta isoforms induce apoptosis of pubertal male germ cells via the mitochondrial pathway in vitro and are thus likely candidates involved in the excessive first wave of apoptosis of male germ cells during puberty.

Follicular expression of a human beta-cell leukaemia/lymphoma-2 (Bcl-2) transgene does not decrease atresia or increase ovulation rate in swine

Transgenic (TG) gilts carrying a human Bcl-2 cDNA transgene driven by mouse inhibin-alpha subunit promoter were produced and evaluated to determine if ectopic expression of Bcl-2 in the ovaries would decrease the frequency of atresia in antral follicles and increase ovulation rate. Immunohistochemical analysis showed that the Bcl-2 transgene protein was expressed in granulosa and theca cells, in 86% of healthy and 54% of atretic follicles analysed in TG prepubertal and Day 50 pregnant gilts combined (n = 24). In contrast, Bcl-2 transgene protein was expressed in only 1.4% of healthy and 0% of atretic follicles in non-TG littermates (n = 13). Real-time reverse transcription-polymerase chain reaction analysis confirmed that human Bcl-2 was expressed in follicles of TG gilts. The atresia rate for the TG and non-TG groups did not differ (P > 0.05) for prepubertal (45 v. 59%) and Day 50 pregnant gilts (53 v. 52%) respectively. The mean +/- s.e.m. ovulation rate did not differ (P > 0.5) between TG (15.9 +/- 0.8, n = 12) and non-TG (16.4 +/- 0.6, n = 7) Day 50 pregnant gilts. The molecular basis of the failure of ectopic Bcl-2 expression to increase the ratio of healthy to atretic follicles is unknown, but it is possible that the activity of the mitochondrial-dependent cell death pathway was not neutralized by ectopic expression of human Bcl-2 or that other cell death pathways compensated for the decreased mitochondrial-dependent cell death.

The Niche for Spermatogonial Stem Cells in the Mammalian Testis

The theory of the "stem cell niche" was originally proposed for the hematopoietic system, and the existence of the niche as an actual entity was proved in the Drosophila germ cell system. Historically, mammalian spermatogenesis has been studied extensively as a prime example of a stem cell system, and studies have established a stem-progenitor hierarchical order of spermatogonia. In the niche on the basal lamina of seminiferous tubules, spermatogonial stem cells (SSCs) are secluded from the outside world and divide constantly to self-renew and differentiate. During the last 10 years, the development and exploitation of the germ cell transplantation method has expanded our understanding of the nature of SSCs and their niches. The ability to maintain and expand SSCs in vitro, which recently became possible, has further reinforced this research area as a mecca of stem cell biology. Nonetheless, the mammalian germ stem cell and its niche remain to be defined more strictly and precisely. We are still on a journey in search of the real stem cell and its true niche.

Short-type PB-cadherin promotes survival of gonocytes and activates JAK-STAT signalling

Neonatal development of the rat testis involves a number of critical events including re-entry of gonocytes into the cell cycle and eventual loss of many of these cells and their progeny via apoptosis. Since surviving gonocytes give rise to subsequent generations of germ cells, regulation of their fate is critical for adult testicular function. Here, we have identified a role for short-type PB-cadherin (STPB-C) in promoting survival of gonocytes in neonatal rats and we have linked its expression to the JAK-STAT signaling pathway. These findings were obtained with varied approaches including use of transgenic rats overexpressing STPB-C which were studied with protein microarrays and other techniques, direct examination of germ cell apoptosis and survival in gonocyte-Sertoli cell co-cultures, and direct study of the JAK-STAT pathway in these models and in L cells transfected with STPB-C. These data provide new information on the regulation of gonocyte fate and exciting new evidence supporting a link between the JAK-STAT pathway and cadherin-based cell-cell interactions.

Expression levels of the inhibitor of apoptosis survivin in testes of patients with normal spermatogenesis and spermatogenic failure

OBJECTIVE

To determine the expression of the inhibitor of apoptosis survivin in men with and without spermatogenic failure.

DESIGN

Prospective case study.

SETTING

Two university-based infertility clinics.

PATIENT(S)

Forty-nine infertile men presenting with azoospermia.

INTERVENTION(S)

Testicular biopsies for histopathological assessment and analyses of survivin expression levels by real-time reverse transcription-polymerase chain reaction. Survivin levels were normalized to expression of the housekeeping porphobilinogen deaminase gene.

MAIN OUTCOME MEASURE(S)

Correlation of the histological findings with normalized survivin expression levels.

RESULTS(S)

Testicular survivin mRNA expression was highest in normal spermatogenesis (n = 14). Decreased expression was observed in patients with spermatogenesis disorders. The expression level correlated with the degree of spermatogenic failure. While it was reduced in postmeiotic maturation arrest (n = 11), a lack of expression was seen in most specimens (10 of 12) with premeiotic maturation arrest and in all of those with Sertoli cell-only syndrome (n = 12).

CONCLUSION(S)

These data indicate that survivin is expressed in human germ cells and might be involved in apoptosis control during spermatogenesis. Decreased survivin expression in spermatogenic disorders may contribute to the accelerated germ cell apoptosis observed in male idiopathic infertility.

The significance of sperm nuclear DNA strand breaks on reproductive outcome

PURPOSE OF REVIEW

A growing body of evidence indicates that ejaculated spermatozoa from men being treated with intracytoplasmic sperm injection contain nuclear abnormalities. Many of these nuclear anomalies manifest themselves as breaks in the sperm nuclear DNA. This review examines the mechanisms involved in generating DNA strand breaks during spermatogenesis in the human, the main techniques used to assess the sperm nucleus and the evidence, in relation to assisted reproduction, showing that sperm nuclear DNA strand breaks may impact on reproductive outcome.

RECENT FINDINGS

Techniques such as the TUNEL assay and the sperm chromatin structure assay both show increased levels of DNA abnormalities in spermatozoa from men who have poor semen parameters. The reproductive parameters affected by an increased presence of DNA abnormalities in ejaculated spermatozoa include fertilization, blastocyst development, and pregnancy rates.

SUMMARY

There is accumulating evidence linking sperm nuclear DNA anomalies to poor reproductive outcome in relation to assisted reproduction technologies. The tests currently available only provide an inkling of the impact of sperm nuclear DNA abnormalities on reproductive outcomes. Although the impact an abnormal paternal genome may have on reproductive outcome is unquestionably less than that of its female counterpart, it cannot be ignored.

Overexpression of anti-apoptotic Mcl-1 in testicular germ cell tumours

AIMS

To determine the expression of Mcl-1 in testicular germ cell tumours in order to clarify the role of this anti-apoptotic factor in these tumours. Various members of the Bcl-2 family have been implicated in the apoptotic mechanisms regulating germ cell apoptosis. Mcl-1 is an anti-apoptotic Bcl-2 family member and has recently been reported to be related to the progression of malignancy; however, the involvement of Mcl-1 in the development of germ cell tumours is still unknown.

METHODS AND RESULTS

Mcl-1 expression in testicular germ cell tumours was investigated by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR). By immunohistochemistry, overexpression of Mcl-1 was present in all germ cell tumours that were studied, including embryonal carcinoma and yolk sac tumour, as well as choriocarcinoma and teratoma. In teratomas, Mcl-1 was widely distributed in the epithelial, myogenic, neural and mesenchymal components. RT-PCR analysis after microdissection revealed high levels of Mcl-1 mRNA in all tumour variants compared with non-neoplastic germ cells.

CONCLUSION

Overexpression of anti-apoptotic Mcl-1 may function to enhance the viability of testicular germ cells, thereby leading to tumorigenesis.

Ubiquitin C-terminal hydrolase L-1 is essential for the early apoptotic wave of germinal cells and for sperm quality control during spermatogenesis

Ubiquitination is required throughout all developmental stages of mammalian spermatogenesis. Ubiquitin C-terminal hydrolase (UCH) L1 is thought to associate with monoubiquitin to control ubiquitin levels. Previously, we found that UCHL1-deficient testes of gad mice have reduced ubiquitin levels and are resistant to cryptorchid stress-related injury. Here, we analyzed the function of UCHL1 during the first round of spermatogenesis and during sperm maturation, both of which are known to require ubiquitin-mediated proteolysis. Testicular germ cells in the immature testes of gad mice were resistant to the early apoptotic wave that occurs during the first round of spermatogenesis. TUNEL staining and cell quantitation demonstrated decreased germ cell apoptosis and increased numbers of premeiotic germ cells in gad mice between Postnatal Days 7 and 14. Expression of the apoptotic proteins TRP53, Bax, and caspase-3 was also significantly lower in the immature testes of gad mice. In adult gad mice, cauda epididymidis weight, sperm number in the epididymis, and sperm motility were reduced. Moreover, the number of defective spermatozoa was significantly increased; however, complete infertility was not detected. These data indicate that UCHL1 is required for normal spermatogenesis and sperm quality control and demonstrate the importance of UCHL1-dependent apoptosis in spermatogonial cell and sperm maturation.

Ontogenesis and cell specific localization of Fas ligand expression in the rat testis

Over the past few years, a number of experimental evidences suggested the involvement of Fas Ligand (FasL) expressing Sertoli cells to induce apoptosis of Fas bearing germ cells. However, the FasL expression during testicular development and its cell specific localization within the testis is still a matter of debate. In the present study, we have monitored FasL expression during rat testis development by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and evaluated cell specific localization of FasL expression, by in situ RT-PCR and immunohistochemistry, on adult rat testis. RT-PCR analysis, performed on total RNA from rat testes obtained from 1 day up to 1-year-old animals, demonstrated the presence of FasL transcripts at all developmental stages examined. In situ RT-PCR analysis clearly indicated the presence of FasL mRNA in Sertoli cells of adult testis, while we could never detect FasL transcripts in germ cells. Immunohistochemistry experiments showed a strong immunostaining for FasL in Sertoli cells of adult testis and again, no immunopositivity was observed in germ cells. In conclusion, our data suggest that FasL expression in rat testis is present from the early postnatal days up to the adult, and the Sertoli cells is the main FasL expressing cell within the seminiferous tubule.

Effects of Acid Sphingomyelinase Deficiency on Male Germ Cell Development and Programmed Cell Death1

Deficiency of acid sphingomyelinase (ASM), an enzyme responsible for producing a pro-apoptotic second messenger ceramide, has previously been shown to promote the survival of fetal mouse oocytes in vivo and to protect oocytes from chemotherapy-induced apoptosis in vitro. Here we investigated the effects of ASM deficiency on testicular germ cell development and on the ability of germ cells to undergo apoptosis. At the age of 20 weeks, ASM knock-out (ASMKO) sperm concentrations were comparable with wild-type (WT) sperm concentrations, whereas sperm motility was seriously affected. ASMKO testes contained significantly elevated levels of sphingomyelin at the age of 8 weeks as detected by high-performance, thin-layer chromatography. Electron microscopy revealed that the testes started to accumulate pathological vesicles in Sertoli cells and in the interstitium at the age of 21 days. Irradiation of WT and ASMKO mice did not elevate intratesticular ceramide levels at 16 h after irradiation. In situ end labeling of apoptotic cells also showed a similar degree of cell death in both groups. After a 21-day recovery period, the numbers of primary spermatocytes and spermatogonia at G2 as well as spermatids were essentially the same in the WT and ASMKO testes, as detected by flow cytometry. In serum-free cultures both ASMKO and WT germ cells showed a significant increase in the level of ceramide, as well as massive apoptosis. In conclusion, ASM is required for maintenance of normal sphingomyelin levels in the testis and for normal sperm motility, but not for testicular ceramide production or for the ability of the germ cells to undergo apoptosis.

Advantage of combining magnetic cell separation with sperm preparation techniques

The selection of vital, non-apoptotic spermatozoa is a prerequisite for achieving optimal conception rates in assisted reproductive techniques. Magnetic cell sorting using annexin-V microbeads can effectively separate apoptotic and non-apoptotic spermatozoa. The objective of the present study was to optimize the integration of magnetic cell sorting in standard sperm preparations and to correlate the effect of different sperm preparation procedures on apoptotic markers. Semen specimens collected from 15 healthy donors were prepared by either density gradient centrifugation or by one-step sperm wash technique separately and in combination with magnetic cell sorting. The preparation methods were evaluated by assessment of semen parameters (motility, viability and morphology) as well as markers of apoptosis (levels of active caspase-3, integrity of membrane mitochondrial potential and externalization of phosphatidylserine). The apoptotic markers were measured using fluorochrome dyes coupled with flow cytometry. The results showed that the combination of density gradient centrifugation and annexin-V magnetic cell sorting was superior to all other sperm preparation methods in terms of providing motile, viable and non-apoptotic spermatozoa. This study clearly shows the advantage of integrating magnetic cell sorting as a part of sperm preparation, which in turn may positively affect the success rates of assisted reproductive techniques.

Overexpression of ubiquitin carboxyl-terminal hydrolase L1 arrests spermatogenesis in transgenic mice

Ubiquitin carboxyl-terminal hydrolase 1 (UCH-L1) can be detected in mouse testicular germ cells, mainly spermatogonia and somatic Sertoli cells, but its physiological role is unknown. We show that transgenic (Tg) mice overexpressing EF1alpha promoter-driven UCH-L1 in the testis are sterile due to a block during spermatogenesis at an early stage (pachytene) of meiosis. Interestingly, almost all spermatogonia and Sertoli cells expressing excess UCH-L1, but little PCNA (proliferating cell nuclear antigen), showed no morphological signs of apoptosis or TUNEL-positive staining. Rather, germ cell apoptosis was mainly detected in primary spermatocytes having weak or negative UCH-L1 expression but strong PCNA expression. These data suggest that overexpression of UCH-L1 affects spermatogenesis during meiosis and, in particular, induces apoptosis in primary spermatocytes. In addition to results of caspases-3 upregulation and Bcl-2 downregulation, excess UCH-L1 influenced the distribution of PCNA, suggesting a specific role for UCH-L1 in the processes of mitotic proliferation and differentiation of spermatogonial stem cells during spermatogenesis.

Spatial analysis of germ stem cell development in Oct-4/EGFP transgenic mice

Questions persist regarding male germ stem cells and how they mature during the prespermatogenic period of testicular development. We successfully labeled the prespermatogonia with green fluorescence protein (GFP) by using Oct-4 enhancer/promoter. This study shows that GFP was specifically expressed in prespermatogonia, spermatogonia and spermatids that faithfully reproduce the endogenous expression of Oct-4. Histochemical analysis revealed that most of the TRA98-positive gonocytes are also positive for GFP. However, the frequency of GFP expressing cells out of TRA98 expressing cells decreased together with the maturation of gonocytes in the first week after birth. To compare the stem cell activity between GFP-positive and -negative populations, we performed a transplantation of sorted cells into testes from an individual population. Colonization efficiency of germ cells from a GFP-positive population resulted in a 30-fold increase in colonization compared with a GFP-negative population. Since the expression of Oct-4 in prespermtogonia correlates well with the stem activity, Oct-4 might be a crucial molecule in the stem cell property of spermatogonia but not in cell survival.

Expression of the apoptosis inhibitor survivin in testicular tissue of infertile patients

Summary Apoptosis is a common phenomenon during spermatogenesis, and its dysregulation has been associated with male infertility. Survivin is an inhibitor of apoptosis protein that regulates apoptosis at cell division and is overexpressed in common human cancers. We investigated whether survivin mRNA expression is detectable in testicular biopsies from patients with infertility of varying aetiology. The aim of this study was to examine the testicular survivin expression in azoospermic men with normal spermatogenesis and in those with specific spermatogenic disorders. Survivin mRNA expression was detected by reverse transcriptase-polymerase chain reaction in histologically classified testicular biopsy specimens from 30 azoospermic men. Survivin was found to be expressed in normal spermatogenesis (n = 10), in post-meiotic spermatogenic arrest (n = 6), and in specimens showing a mixed picture of pre-meiotic maturation arrest with sparse islands of post-meiotic arrest (n = 2). In contrast, a lack of survivin expression was seen in specimens without haploid germ cells (pre-meiotic maturation arrest, n = 2) and in those with Sertoli-cell-only syndrome (SCOS, n = 10). These data indicate for the first time that survivin is expressed in human testis. Moreover, its expression seems to correlate with the stage of maturation arrest in patients presenting with spermatogenic disorders. Survivin mRNA expression was not found in SCOS specimens, possibly indicating germ-cell-specific expression in human testicular tissue. Thus, survivin is a potential molecular marker of spermatogenesis, whose expression is altered in specific spermatogenic disorders.

Transient DNA Strand Breaks During Mouse and Human Spermiogenesis:New Insights in Stage Specificity and Link to Chromatin Remodeling1

In the course of mammalian spermiogenesis, a unique chromatin remodeling process takes place within elongating and condensing spermatid nuclei. The histone-to-protamine exchange results in efficient packaging and increased stability of the paternal genome. Although not fully understood, this change in chromatin architecture must require a global but transient appearance of endogenous DNA strand breaks because most of the DNA supercoiling is eliminated in the mature sperm. To establish the extent of DNA strand breakage and the stage specificity at which these breaks are created and repaired, we performed a sensitive terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) assay to detect in situ DNA strand breaks on both mice and human testis cross sections. In the mouse, we established that DNA strand breaks are indeed detected in the whole population of elongating spermatids between stages IX and XI of the seminiferous epithelium cycle perfectly coincident with the chromatin remodeling as revealed by histone H4 hyperacetylation. Similarly, TUNEL analyses performed on human testis sections revealed an elevated and global increase in the levels of DNA strand breaks present in nuclei of round-shaped spermatids also coincident with chromatin remodeling. The demonstration of the global character of the transient DNA strand breaks in mammalian spermiogenesis suggests that deleterious consequences on genetic integrity of the male gamete may arise from any disturbance in the process. In addition, this investigation may shed some light on the origin of the low success rate that has been encountered so far with intracytoplasmic injection procedures making use of round spermatids in humans.

Protection from Radiation-Induced Male Germ Cell Loss by Sphingosine-1-Phosphate1

Male germ cells are susceptible to radiation-induced injury, and infertility is a common problem after total-body irradiation. Here we investigated, first, the effects of irradiation on germ cells in mouse testis and, second, the role of sphingosine-1-phosphate (S1P) treatment in radiation-induced male germ cell loss. Irradiation of mouse testes mainly damaged the early developmental stages of spermatogonia. The damage was seen by means of DNA flow cytometry 21 days after irradiation as decreasing numbers of spermatocytes and spermatids with increasing amounts of ionizing radiation (0.1-2.0 Gy). Intratesticular injections of S1P given 1-2 h before irradiation (0.5 Gy) did not protect against short-term germ cell loss as measured by in situ end labeling of DNA fragmentation 16 h after irradiation. However, after 21 days, in the S1P-treated testes, the numbers of primary spermatocytes and spermatogonia at G2 (4C peak as measured by flow cytometry) were higher at all stages of spermatogenesis compared with vehicle-treated testes, indicating protection of early spermatogonia by S1P, whereas the spermatid (1C) populations were similar. In conclusion, S1P appears to protect partially (16%-47%) testicular germ cells against radiation-induced cell death. This warrants further studies aimed at development of therapeutic agents capable of blocking sphingomyelin-induced pathways of germ cell loss.

Dysfunctional spermatogenesis in transgenic mice overexpressing bHLH-Zip transcription factor, Spz1

Spz1, a previously identified basic helix-loop-helix-leucine zipper (bHLH-Zip) transcription factor, is expressed specifically in the testis and epididymis of adult mice. However, Spz1's in vivo function is unclear. To study the function of Spz1 in vivo, we established Spz1 transgenic mice. Using this model, we were able to demonstrate that overexpression of Spz1 in the testis destroys tissue homeostasis at an early stage of spermatogenesis, which in turn induces apoptosis in germ cells and thus reduces male fertility. We identified that Spz1 is ectopically expressed in multiple tissues of transgenic male mice by Western blot analysis. In the testes of transgenic mice, Spz1 proteins were found to be overexpressed in both germ and somatic cells as determined by immunofluorescence staining. This upregulated cell proliferation was confirmed by in vivo BrdU incorporation in multinucleated gonocytes of 1-week-old transgenic mice. However, histological and immunohistochemical analyses indicated that these multinucleated germ cells in seminiferous tubules subsequently underwent apoptosis at 2 and 4 weeks of age through Fas/FasL- and ER stress-signaling pathways. Furthermore, germ cells surviving two cycles of meiosis suffered aberrant spermiogenesis, generating a large pool of abnormal spermatozoa. The transgenic male mice with reduced populations of normal spermatozoa produced offsprings of smaller litter sizes and became infertile at 6 months of age. These results suggest that cell proliferation in early spermatogenesis is critically regulated by multisignal pathways and unregulated cell proliferation at this stage, as induced by Spz1, leads to germ cell apoptosis. These results imply that Spz1 plays an important regulatory role during spermatogenesis.

Increased Apoptosis Occurring During the First Wave of Spermatogenesis Is Stage-Specific and Primarily Affects Midpachytene Spermatocytes in the Rat Testis1

The physiological apoptosis that occurs in immature testis appears to be necessary for the maturation of this tissue. Thus, inhibition of the early apoptotic wave associated with the first round of spermatogenesis is followed by accumulation of spermatogonia and infertility later in life. To identify the cell types undergoing apoptosis in immature rat testis and to characterize the relationship between this apoptosis and progression of the first wave of spermatogenesis, sequential viable segments of seminiferous tubules from 8-, 18-, and 26-day-old rats were examined under a phase-contrast microscope. One novel observation was the existence of pronounced stage-specificity during the peak of apoptosis at the very early postnatal ages of 18 and 26 days. Increased apoptosis of pachytene spermatocytes in stages VII-VIII was the major feature that distinguished immature spermatogenesis from the corresponding adult process. The frequency of apoptosis among type A spermatogonia in immature stages IX-I was also elevated in comparison to the corresponding mature stages. The age-related peak of apoptosis was mediated by caspase 3; furthermore, stage-dependent expression of Bax in midpachytene spermatocytes was observed in the 18- and 26-day-old testis. These observations suggest that this Bax-regulated, caspase 3-mediated, increased apoptosis of midpachytene spermatocytes during the first wave of immature spermatogenesis represents a major difference in comparison to apoptosis occurring in the mature testis, and it may play an important regulatory role in establishing spermatogenesis in the rat testis.

Caspase activity inhibition delays programmed spermatogenic cell death in vitro

Programmed cell death or apoptosis was analyzed in rat Sertoli-spermatogonial cell cocultures prepared from 2-9 day old rats using time-lapse video microscopy, a cell viability fluorescence microscopy assay, immunocytochemical markers, and cell-permeable caspase inhibitory peptides with reversible and irreversible effects. We show that apoptosis can initially affect a single member of a spermatogonial cell cohort and that single non-viable spermatogonial cells can remain conjoined to viable spermatogonial cells. The integrity of the cytoskeletal F-actin network and the presence on Bcl-2 immunoreactivity are valuable markers of spermatogonial cell viability. Apoptotic bodies released into the culture medium are generally eliminated after culture medium replenishment; however, spermatogonial apoptotic cell remnants can be taken up by Sertoli cells, which are known to represent a phagocytic somatic population within the seminiferous epithelium. Cell permeable caspase-1 and caspase-4 inhibitory peptides with reversible and irreversible action were supplemented to a serum-free hormone-growth factor-supplemented medium. In the absence of the caspase inhibitory peptide, the viability of spermatogonial cells decreases gradually with time in coculture. However, the addition of caspase inhibitory peptides causes a significant accumulation of spermatogenic cells per unit surface area. Although inhibition of caspases, the executors of spermatogonial cell death, results in a substantial increase of spermatogonial cells in the cocultures, it remains to be determined what the differentiation potential of caspase-inhibited spermatogonial cell cohorts is.

Apoptosis in male germ cells in response to cyclin A1-deficiency and cell cycle arrest

Male mice homozygous for a mutated allele of the cyclin A1 gene (Ccna1) are sterile due to a block in cell cycle progression before the first meiotic division. Meiosis arrest in Ccna1(-/-) spermatocytes is associated with desynapsis abnormalities, lowered MPF activity, and apoptosis as evidenced by TUNEL-positive staining. With time, adult testicular tubules exhibit severe degeneration: some tubules in the older animals are almost devoid of germ cells at various stages of spermatogenesis. The mechanisms by which the cells sense the cell cycle arrest and the regulation of the decision to undergo cell death are under investigation.

Expression of the mouse Aven gene during spermatogenesis, analyzed by subtraction screening using Mvh-knockout mice

As an attempt to investigate the function of the mouse Vasa-homolog (MVH) protein, a germ cell-specific RNA helicase, we have cloned genes that fail to be expressed in homozygous Mvh-knockout testes. One of the cDNA clones obtained by selective PCR subtraction cloning matched two cDNA sequences in the mouse testis cDNA database, and was highly homologous to Aven, a human gene regulating cell death. Sequences of the two mouse testis cDNAs in the database revealed that they share an 800 bp sequence but have quite different 5'-regions; the latter are derived from different exons by alternative use of transcription initiation sites. The shorter (mAven-S) and longer (mAven-L) transcripts encode 216 and 342 amino acids, respectively, and both isoforms are predominantly expressed in adult testes. However, mAven-L is not completely testis-specific and is expressed in testes during all developmental stages, whereas the expression of mAven-S is restricted to the testis and is barely detectable in Mvh-homozygous testes. In situ hybridization showed that mAven-S is expressed specifically in post-meiotic cells, mainly in round spermatids.

Overexpression of Bcl-W in the testis disrupts spermatogenesis: revelation of a role of BCL-W in male germ cell cycle control

To explore physiological roles of BCL-W, a prosurvival member of the BCL-2 protein family, we generated transgenic (TG) mice overexpressing Bcl-w driven by a chicken beta-actin promoter. Male Bcl-w TG mice developed normally but were infertile. The adult TG testes displayed disrupted spermatogenesis with various severities ranging from thin seminiferous epithelium containing less germ cells to Sertoli cell-only appearance. No overpopulation of any type of germ cells was observed during testicular development. In contrast, the developing TG testes displayed decreased number of spermatogonia, degeneration, and detachment of spermatocytes and Sertoli cell vacuolization. The proliferative activity of germ cells was significantly reduced during testicular development and spermatogenesis, as determined by in vivo and in vitro 5'-bromo-2'deoxyuridine incorporation assays. Sertoli cells were structurally and functionally normal. The degenerating germ cells were TUNEL-negative and no typical apoptotic DNA ladder was detected. Our data suggest that regulated spatial and temporal expression of BCL-W is required for normal testicular development and spermatogenesis, and overexpression of BCL-W inhibits germ cell cycle entry and/or cell cycle progression leading to disrupted spermatogenesis.

The attractive Achilles heel of germ cell tumours: an inherent sensitivity to apoptosis-inducing stimuli

Testicular germ cell tumours (TGCTs) are extremely sensitive to cisplatin-containing chemotherapy. The rapid time course of apoptosis induction after exposure to cisplatin suggests that TGCT cells are primed to undergo programmed cell death as an inherent property of the cell of origin. In fact, apoptosis induction of germ cells in the testis is an important physiological mechanism to control the quality and quantity of the gametes produced. Although p53 protein is highly expressed in the majority of TGCTs, almost no p53 mutations have been detected. Interestingly, p53 overexpression is associated with loss of p21 and gain of mdm2 expression, which might indicate a partial loss in functionality of the p53 regulatory pathway in TGCTs. Besides p21, TGCTs often show low expression of other proteins involved in the regulation of cell cycle progression, such as the retinoblastoma protein and members of the INK4 family. It can be postulated that the deregulated G(1)-S phase checkpoint results in premature entry into the S phase upon DNA damage. In addition to Bcl-2 family members that are involved in the regulation of germ cell apoptosis in the normal testis via the mitochondrial death pathway, the Fas death pathway is also known to regulate apoptosis of germ cells in the testis. Since chemotherapy has been shown to activate the Fas death pathway and TGCTs co-express both Fas and its ligand FasL, TGCT cells might undergo apoptosis upon cisplatin treatment via autocrine or paracrine activation of the Fas system by FasL. The hypothesis suggested here is that the lack of cell cycle arrest following a cisplatin-containing treatment, together with the activation of the Fas death pathway and the mitochondrial death pathway, explains the rapid and efficient apoptosis of TGCT cells. Defining the mechanisms involved in the cisplatin sensitivity of TGCTs will provide tools to increase cisplatin sensitivity in other human tumours with acquired or intrinsic resistance.

Maintenance of mouse male germ line stem cells in vitro

The proliferation and differentiation of a stem cell are regulated intrinsically by the stem cell and extrinsically by the stem cell niche. Elucidation of regulatory mechanisms of spermatogonial stem cells (SSCs), the stem cell of the postnatal male germ line, would be facilitated by in vitro studies that provide a defined microenvironment reconstituted ex vivo. We analyzed the effect of in vitro environment on the maintenance of adult and immature SSCs in a 7-day culture system. Although the number of adult and immature SSCs decreased in a time-dependent manner, nearly one in four stem cells (24%) could be maintained in vitro for 7 days. Stem cell maintenance was enhanced by coculture with OP9 bone marrow stroma or L fibroblast cell lines, addition of glial cell line-derived neurotrophic factor, or utilization of specific culture medium. In contrast, coculture with TM4 or SF7 Sertoli cell lines and addition of activin A or bone morphogenetic protein 4 (BMP4) reduced stem cell maintenance in vitro. Only 4% of the stem cells remained when cultured with TM4 cells or activin A, and 6% remained when cultured with SF7 cells or BMP4. These results lead to the hypothesis that suppression of germ cell differentiation improves in vitro maintenance of SSCs by interrupting the unidirectional cascade of spermatogenesis and blocking stem cell differentiation.

Caspase activity and a specific cytochrome C are required for sperm differentiation in Drosophila

The final stage of spermatid terminal differentiation involves the removal of their bulk cytoplasm in a process known as spermatid individualization. Here we show that apoptotic proteins play an essential role during spermatid individualization in Drosophila melanogaster. Several aspects of sperm terminal differentiation, including the activation of caspases, are reminiscent of apoptosis. Notably, caspase inhibitors prevent the removal of bulk cytoplasm in spermatids and block sperm maturation in vivo, causing male sterility. We further identified loss-of-function mutations in one of the two Drosophila cyt-c genes, cyt-c-d, which block caspase activation and subsequent spermatid terminal differentiation. Finally, a giant ubiquitin-conjugating enzyme, dBruce, is required to protect the sperm nucleus against hypercondensation and degeneration. These observations suggest that an apoptosis-like mechanism is required for spermatid differentiation in Drosophila.

Germ cell apoptosis and its molecular trigger in mouse testes

Germ cell apoptosis is very common during various stages of mammalian testicular development. However, our understanding of the mechanisms underlying male germ cell apoptosis is still limited. This review firstly covers the general features of germ cell death in normal testes of fetal, neonatal, and adult mice from electron microscopy (EM) and terminal dUTP nick-end labeling (TUNEL) staining. The issue of whether the Fas and Fas ligand (FasL) system and/or the Bax and Bcl-2 system is involved in the induction of germ cell apoptosis in normal and damaged testes will then be addressed, including a special consideration of the ischemia-reperfusion model, the endocrine disruptor-treated model, and others. Finally, this review will propose that the process of normal spermatogenesis seems skillfull in taking advantage of apoptotic processes of germ cells and that different molecular pathways may be triggered to induce male germ cell apoptosis, depending upon the physiological and pathological states of germ cells.

Apoptosis during spermatogenesis in the spotted ray Torpedo marmorata

This article is a cytological and molecular investigation on the occurrence of apoptosis during spermatogenesis in Torpedo, a cartilaginous fish characterised by a typical cystic testis. Using DNA fragmentation and Bak gene expression, it demonstrated that germ cells undergo apoptosis only at the stages of spermatocyte and spermatid, and degeneration also involves Sertoli but not Leydig cells. In immature cysts, this cellular process probably occurs when the ratio of germ cells to the only Sertoli cell (SC) forming the spermatoblast changes. Apoptosis also takes place in mature cysts after sperm release to eliminate most of the SCs. Few of them, however, become cytoplasts and probably continue secreting androgens so as to control the final events of spermatogenesis, i.e., passage of spermatozoa through the ductus deferentes. Finally, the present investigation demonstrated that, in Torpedo testis, Bak mRNA is expressed during spermatogenesis, thus suggesting that the mitochondrial pathway might be active. This observation in one of the oldest vertebrate classes indicates that, in all vertebrates, the apoptotic process during spermatogenesis is conserved, contributing to testicular homeostasis.

Biological significance of phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) in mammalian cells

Reactive oxygen species (ROS) are known mediators of intracellular signal cascades. Excessive production of ROS may lead to oxidative stress, loss of cell function, and cell death by apoptosis or necrosis. Lipid hydroperoxides are one type of ROS whose biological function has not yet been clarified. Phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a unique antioxidant enzyme that can directly reduce phospholipid hydroperoxide in mammalian cells. This contrasts with most antioxidant enzymes, which cannot reduce intracellular phospholipid hydroperoxides directly. In this review, we focus on the structure and biological functions of PHGPx in mammalian cells. Recently, molecular techniques have allowed overexpression of PHGPx in mammalian cell lines, from which it has become clear that lipid hydroperoxides also have an important function as activators of lipoxygenase and cyclooxygenase, participate in inflammation, and act as signal molecules for apoptotic cell death and receptor-mediated signal transduction at the cellular level.

Abnormal spermatozoa in the ejaculate: abortive apoptosis and faulty nuclear remodelling during spermatogenesis

The mechanisms responsible for producing abnormal spermatozoa in the ejaculate are relatively unknown. Numerous studies have now shown the presence of nuclear DNA strand breaks in human ejaculated spermatozoa and the abnormal persistence of apoptotic marker proteins. The reason why human spermatozoa, in particular from men with abnormal semen parameters, possess these abnormalities is still not clear. Two processes that have been linked to the presence of nuclear DNA strand breaks in spermatozoa are anomalies in apoptosis during spermatogenesis or problems in the replacement of histones with protamines during spermiogenesis. Understanding the mechanisms responsible for producing abnormal spermatozoa in the human will improve knowledge about certain causes of male infertility.