p53-mediated germ cell quality control in spermatogenesis

Exacerbation of diabetes-induced testicular apoptosis by zinc deficiency is most likely associated with oxidative stress, p38 MAPK activation, and p53 activation in mice

Since diabetes induces testicular oxidative damage and cell death, and zinc (Zn) plays an important role in the spermatogenesis, the objective of the present study was to define the effects of Zn deficiency on diabetes-induced testicular apoptosis and associated mechanisms. Zn deficiency was induced by chronic treatment of normal and diabetic mice with N,N,N',N'-tetrakis (2-pyridylemethyl) ethylenediamine (TPEN) chelation. After diabetes onset, mice were given intraperitoneally TPEN at 5mg/kg daily for four months, which, like diabetes, induced a significant decrease in testicular Zn level. TUNEL staining revealed that testicular apoptosis was significantly increased along with an increased Bax/Bcl-2 ratio, in diabetic mice and TPEN-treated normal mice. Zn deficiency significantly exacerbated diabetes-induced testicular apoptosis, along with significantly increased oxidative and nitrosative damage and down-regulation of antioxidant Nrf2 expression. Increased oxidative stress was associated with an increase in activation of p38 MAPK and p53 protein in diabetic testis, which was worsened in the testes of diabetic mice with Zn deficiency. Diabetes also induced a significant increase in endoplasmic reticulum stress and associated cell death, which was not affected by Zn deficiency. These results suggest that like diabetes, chronic depletion of Zn with TPEN induces testicular oxidative stress and damage, along with the activation of p38 MAPK and p53 signaling and mitochondria-related apoptotic cell death. Therefore, prevention of Zn deficiency for diabetic patients is important in order to avoid the exacerbation of diabetic effects on testicular cells death.

A genome-scale protein interaction profile of Drosophila p53 uncovers additional nodes of the human p53 network

The genome of the fruitfly Drosophila melanogaster contains a single p53-like protein, phylogenetically related to the ancestor of the mammalian p53 family of tumor suppressors. We reasoned that a comprehensive map of the protein interaction profile of Drosophila p53 (Dmp53) might help identify conserved interactions of the entire p53 family in man. Using a genome-scale in vitro expression cloning approach, we identified 91 previously unreported Dmp53 interactors, considerably expanding the current Drosophila p53 interactome. Looking for evolutionary conservation of these interactions, we tested 41 mammalian orthologs and found that 37 bound to one or more p53-family members when overexpressed in human cells. An RNAi-based functional assay for modulation of the p53 pathway returned five positive hits, validating the biological relevance of these interactions. One p53 interactor is GTPBP4, a nucleolar protein involved in 60S ribosome biogenesis. We demonstrate that GTPBP4 knockdown induces p53 accumulation and activation in the absence of nucleolar disruption. In breast tumors with wild-type p53, increased expression of GTPBP4 correlates with reduced patient survival, emphasizing a potential relevance of this regulatory axis in cancer.

Initial insights regarding the role of p53 in maintaining sperm DNA integrity following treatment of mice with ethylnitrosourea or cyclophosphamide

If p53 is essential to eliminate damaged spermatogenic cells, then mutagen exposure in the absence of p53 would increase sperm containing damaged DNA. p53 knockout (-/-, NULL) and wild-type (+/+, WT) mice (five/group) were exposed to ethylnitrosourea (ENU) or cyclophosphamide (CP). In phase I, mice were exposed by gavage to 0 or 60 mg/kg/day ENU or CP for four days and examined on test day (TD) 4, and in phase II, mice were exposed to 0, 6, 20, or 60 mg/kg/day ENU or CP for four days and evaluated on TD 36 when exposed spermatocytes matured. In phase I, mutagens were not directly cytotoxic to mature sperm. In phase II, WT mice were more sensitive to decreases in reproductive organ weights, whereas both genotypes had decreased sperm counts. Testicular histology revealed similar CP responses, but genotype-specific ENU responses (WT mice had depletion of elongating spermatids; NULL mice had late-stage spermatocyte/early stage spermatid loss). Ethylnitrosourea increased DNA strand breaks in WT mice. Thus, mice responded similarly to CP, suggesting a primarily p53-independent response, whereas the ENU response differed by zygosity, suggesting a role for p53. As DNA damage increased at higher ENU doses, compensatory repair pathways may operate in NULL mice.

Study of apoptosis-related markers in ram spermatozoa

Certain features of capacitated or frozen-thawed spermatozoa have been considered to be an apoptosis-like phenomenon, and, it has been suggested that the presence of apoptotic sperm in seminal doses could be one of the reasons for poor fertility. The objective of this study was to determine whether phosphatidylserine (PS) translocation, caspase activity and DNA fragmentation, which are considered to be apoptotic markers in somatic cells, occur in ram sperm. Fresh ejaculates and sperm samples in different physiological state (cold-shocked, in vitro capacitated and acrosome-reacted (AR)) were compared. Simultaneous staining with 6-carboxifluorescein diacetate (6-CFDA) and Annexin V-Cy3.18 (AnnV) revealed four different sperm subpopulations in ejaculates. The main subpopulation was composed of viable cells without PS exposure (CFDA+/AnnV-). A total of 40.8% of sperm showed inverted PS, with two levels of alteration: CFDA+/AnnV+ in midpiece ("type I AnnV+"), and in acrosome and midpiece ("type II AnnV+"). The fewest subpopulation contained non-viable cells showing Annexin labelling in the entire cell (CFDA-/AnnV+). Labeling of caspases-3 and -7 by immunocytochemistry revealing different sperm subtypes depending on their localization in apical, equatorial, post-acrosomal regions and tail. The results obtained by western-blot showed, for the first time to our knowledge, that caspase-like proteins are present in fresh ram semen as both inactive and active forms. The proportion of sperm with fragmented DNA [terminal transferase-mediated dUDP nick end-labeling (TUNEL)-positive] were found rarely (2.7+/-0.5%) in all fresh ejaculates involved in this study. The analysis of total activity of both caspases by a fluorometric method showed a decrease in vitro capacitated and acrosome-reacted samples as well as in cryoinjured samples. However, the percentage of TUNEL-positive sperm demonstrating DNA fragmentation was significantly increased after in vitro induced capacitation and acrosome reaction, as well as after cold-shock although this augment was not significant. PS exposure is not totally dependent on caspases in ram spermatozoa as the addition of a caspase inhibitor prevented the increase in PS inversion due to incubation in capacitating conditions but not to the ionophore-induced acrosome reaction or cold-shock.

MAGE-A, mMage-b, and MAGE-C proteins form complexes with KAP1 and suppress p53-dependent apoptosis in MAGE-positive cell lines

The MAGE-A, MAGE-B, and MAGE-C protein families comprise the class-I MAGE/cancer testes antigens, a group of highly homologous proteins whose expression is suppressed in all normal tissues except developing sperm. Aberrant expression of class I MAGE proteins occurs in melanomas and many other malignancies, and MAGE proteins have long been recognized as tumor-specific targets; however, their functions have largely been unknown. Here, we show that suppression of class I MAGE proteins induces apoptosis in the Hs-294T, A375, and S91 MAGE-positive melanoma cell lines and that members of all three families of MAGE class I proteins form complexes with KAP1, a scaffolding protein that is known as a corepressor of p53 expression and function. In addition to inducing apoptosis, MAGE suppression decreases KAP1 complexing with p53, increases immunoreactive and acetylated p53, and activates a p53 responsive reporter gene. Suppression of class I MAGE proteins also induces apoptosis in MAGE-A-positive, p53wt/wt parental HCT 116 colon cancer cells but not in a MAGE-A-positive HCT 116 p53-/- variant, indicating that MAGE suppression of apoptosis requires p53. Finally, treatment with MAGE-specific small interfering RNA suppresses S91 melanoma growth in vivo, in syngenic DBA2 mice. Thus, class I MAGE protein expression may suppress apoptosis by suppressing p53 and may actively contribute to the development of malignancies and by promoting tumor survival. Because the expression of class I MAGE proteins is limited in normal tissues, inhibition of MAGE antigen expression or function represents a novel and specific treatment for melanoma and diverse malignancies.

Programmed cell death of primordial germ cells in Drosophila is regulated by p53 and the Outsiders monocarboxylate transporter

Primordial germ cell development uses programmed cell death to remove abnormal, misplaced or excess cells. Precise control of this process is essential to maintain the continuity and integrity of the germline, and to prevent germ cells from colonizing locations other than the gonads. Through careful analyses of primordial germ cell distribution in developing Drosophila melanogaster embryos, we show that normal germ cell development involves extensive programmed cell death during stages 10-12 of embryogenesis. This germ cell death is mediated by Drosophila p53 (p53). Mutations in p53 result in excess primordial germ cells that are ectopic to the gonads. Initial movements of the germ cells appear normal, and wild-type numbers of germ cells populate the gonads, indicating that p53 is required for germ cell death, but not migration. To our knowledge, this is the first report of a loss-of-function phenotype for Drosophila p53 in a non-sensitized background. The p53 phenotype is remarkably similar to that of outsiders (out) mutants. Here, we show that the out gene encodes a putative monocarboxylate transporter. Mutations in p53 and out show nonallelic noncomplementation. Interestingly, overexpression of p53 in primordial germ cells of out mutant embryos partially suppresses the out germ cell death phenotype, suggesting that p53 functions in germ cells either downstream of out or in a closely linked pathway. These findings inform models in which signaling between p53 and cellular metabolism are integrated to regulate programmed cell death decisions.

Deletion of genes implicated in protecting the integrity of male germ cells has differential effects on the incidence of DNA breaks and germ cell loss

Background

Infertility affects ∼20% of couples in Europe and in 50% of cases the problem lies with the male partner. The impact of damaged DNA originating in the male germ line on infertility is poorly understood but may increase miscarriage. Mouse models allow us to investigate how deficiencies in DNA repair/damage response pathways impact on formation and function of male germ cells. We have investigated mice with deletions of ERCC1 (excision repair cross-complementing gene 1), MSH2 (MutS homolog 2, involved in mismatch repair pathway), and p53 (tumour suppressor gene implicated in elimination of germ cells with DNA damage).

Principal Findings

We demonstrate for the first time that depletion of ERCC1 or p53 from germ cells results in an increased incidence of unrepaired DNA breaks in pachytene spermatocytes and increased numbers of caspase-3 positive (apoptotic) germ cells. Sertoli cell-only tubules were detected in testes from mice lacking expression of ERCC1 or MSH2 but not p53. The number of sperm recovered from epididymes was significantly reduced in mice lacking testicular ERCC1 and 40% of sperm contained DNA breaks whereas the numbers of sperm were not different to controls in adult Msh2 −/− or p53 −/− mice nor did they have significantly compromised DNA.

Conclusions

These data have demonstrated that deletion of Ercc1, Msh2 and p53 can have differential but overlapping affects on germ cell function and sperm production. These findings increase our understanding of the ways in which gene mutations can have an impact on male fertility.

P53 expression between 13-27 weeks old human male fetus gonads

P53 is a tumor suppressor gene and a critical component of cellular mechanisms that respond to genotoxic stresses. During normal fetal development, some of these cells lose their genomic stability because of intensive cell proliferation. They arrest cell cycle progression and repair genomic stability by p53 induction or die via apoptosis. If p53 is overexpressed, some structures may have different abnormalities. This study was conducted to investigate normal p53 expression in human male gonads during second trimester. Twenty one normal human male fetuses' testes in 2nd trimester were processed and immunohistochemistry was applied. The spermatogonia with nuclear and perinuclear staining, were accepted as p53 (+). The number of p53 (+) spermatogonia was counted in randomly 10 different seminiferous tubules. The results suggest that p53 expression in gonads of human male fetuses significantly increases in the 20th week.

Epigenetic control of MAGE gene expression by the KIT tyrosine kinase

The Class I MAGE proteins include the MAGE-A, MAGE-B, and MAGE-C antigens, which are normally expressed only in male germ cells but may be aberrantly expressed in melanomas and other tumors. It is known that MAGE gene expression is epigenetically repressed by promoter region methylation in most cells but factors controlling MAGE gene promoter methylation have not been identified. Using transcript microarray analysis and immunoblotting we found that MAGE-A and MAGE-C mRNA and protein are selectively downregulated by pharmacologic inhibition of KIT in KIT-dependent mast cell lines. Methylation-specific polymerase chain reaction studies showed that the MAGE-A3 and MAGE-C2 gene promoter regions were de-methylated in the presence of activated KIT but became methylated on inhibition of KIT, consistent with the downregulation of mRNA and protein. This is early evidence of a tyrosine kinase affecting MAGE gene promoter region methylation and expression, and represents early evidence of a tyrosine kinase in the epigenetic control of gene expression. MAGE proteins suppress apoptosis and promote tumor survival, and are novel targets for functional manipulation and immunotherapy. Understanding the factors controlling MAGE gene expression may allow more effective therapeutic strategies targeting MAGE antigens.

Ddb2 is a haploinsufficient tumor suppressor and controls spontaneous germ cell apoptosis

Damage-specific DNA-binding (DDB) protein heterodimer has been extensively studied in the context of nucleotide excision repair. However, the smaller subunit, DDB2, is also implicated in tumor suppressor p53-mediated processes, although the precise details of the DDB2 - p53 interactions are unknown. Here, we report that Ddb2(-/-) and Ddb2(+/-) mice have shortened lifespans and increased frequency and spectrum of spontaneous tumors. Notably, Ddb2 deficiency enhances lung and mammary adenocarcinomas. Ddb2(-/-) mice are smaller than normal. Whereas weights of kidneys and livers are reduced proportionately, spleens from Ddb2(-/-) mice gradually enlarge with age due to lymphoid proliferation. Ddb2(-/-) mice also have larger testes, and the testicular germ cells show significantly decreased spontaneous apoptosis. These changes parallel reduced levels of p53 and its serine 15 phosphorylation in testicular germ cells. Since tumors that appeared in heterozygous Ddb2(+/-) mice conserve the wild-type Ddb2 allele, Ddb2 RNA expression and Ddb2 exon sequence, Ddb2 heterozygosity can facilitate tumor development as a haploinsufficient tumor suppressor. These results demonstrate that in whole animals as in cultured cells Ddb2 can regulate apoptosis and tumor incidence.

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.

Testicular Germ Cell Tumors: A Paradigm for the Successful Treatment of Solid Tumor Stem Cells

Treatment of testicular germ cell tumors (TGCTs) has been a success primarily due to the exquisite responsiveness of this solid tumor to cisplatin-based therapy. Despite the promise of cure for the majority of TGCT patients, the effectiveness of therapy for some patients is limited by toxicity and the problem of resistance. There is compelling rationale to further understand the biology of TGCTs in order to better treat other solid tumors and to address the shortcomings of present TGCT therapies. TGCTs contain undifferentiated pluripotent stem cells, known as embryonal carcinoma, that share many properties with human embryonic stem cells. The importance of cancer stem cells in the initiation, progression and treatment of solid tumors is beginning to emerge. We discuss TGCTs in the context of solid tumor curability and targeted cancer stem cell therapy.

Apoptosis during the seasonal spermatogenic cycle of Rana catesbeiana

In the bullfrog Rana catesbeiana, testicular weight is constant throughout the year, but the volume densities of germinative and interstitial compartments undergo inverse changes from winter (non-breeding) to summer (breeding). The occurrence of apoptosis in the seminiferous lobules of bullfrogs was investigated in these two periods using sections stained with haematoxylin and eosin (H&E), the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling) method and transmission electron microscopy. TUNEL-positive cells were observed in the seminiferous lobules, and ultrastructural morphological details confirmed the occurrence of cell death by apoptosis. In summer, the occurrence of several spermatogenic processes (in addition to spermiogenesis and spermiation), and then the overconsumption of Sertoli cell-derived pro-survival factors, could be responsible for the increased density of apoptotic cells. Alternatively, the low apoptotic frequency in winter could be related to the constant homeostasis in the germinative compartment given that most lobules are filled with primary spermatocytes. As volume densities of interstitial and germinative compartments undergo inverse seasonal variations through the year, the incidence of apoptosis (in summer) could play a part in controlling the spermatogenic process, maintaining the lobular size when interstitial tissue is maximally developed. In winter, the low apoptotic cell density leads to spermatogenic recrudescence and, thereby, the production of an adequate quantity of spermatozoa for the next breeding period. Thus, apoptosis may participate not only in the maintenance of spermatogenic homeostasis, but also in the cyclical control of the different spermatogenic processes according to seasonal changes of the testicular compartments as a whole.

Effect of low-level radiation on the death of male germ cells

Hormetic and adaptive responses induced by low-level radiation in hematopoietic and immune systems have been observed, as shown by stimulatory effects on cell growth and resistance to subsequent radiation-induced cytogenetic damage. However, in terms of cell death by apoptosis, the effects of low-level radiation are controversial: Some studies showed decreased apoptosis in response to low-level radiation while others showed increased apoptosis. This controversy may be related to the radiation doses or dose rates and also, more importantly, to the cell types. Testes are one of the most radiosensitive organs. The loss of male germ cells after exposure to ionizing radiation has been attributed to apoptosis. In the present study, the effects of low-level radiation at doses up to 200 mGy on mouse male germ cells in terms of apoptosis and the expression of apoptosis-related proteins were examined at different times after whole-body exposure of mice to low-level radiation. In addition, the effect of pre-exposure to low-level radiation on subsequent cell death induced by high doses of radiation was examined to explore the possibility of low-level radiation-induced adaptive response. The results showed that low-level radiation in the dose range of 25-200 mGy induced significant increases in apoptosis in both spermatogonia and spermatocytes, with the maximal effect at 75 mGy. The increased apoptosis is most likely associated with Trp53 protein expression. Furthermore, 75 mGy low-level radiation given pre-irradiation led to an adaptive response of seminiferous germ cells to subsequent high-level radiation-induced apoptosis. These results suggest that low-level radiation induces increased apoptosis in male germ cells but also induces a significant adaptive response that decreases cell death after a subsequent high-dose irradiation.

Application of transcriptional and biological network analyses in mouse germ-cell transcriptomes

Serial analysis of gene expression (SAGE) provides a global analysis platform for profiling mRNA populations present in cells of interest without the constraint of gene selection and the ambiguous nature of data obtained. However, most of the reports on SAGE and germ cell development are limited to descriptive analyses. Here, we report a series of bioinformatic analyses using recently published SAGE data on the transcriptome of mouse type A spermatogonia (Spga), pachytene spermatocytes (Spcy), and round spermatids (Sptd). Tags with a total count of > or =20 in three SAGE libraries were examined. Our aim was to identify and discover potential transcriptional regulators and pathways involved at different stages of spermatogenesis. Unsupervised hierarchical clustering based on tag expression and Gene Ontology analysis were applied to identify genes and biological processes overrepresented at a particular stage of development. The 5' cis-regulatory elements were examined for common regulators in different functional clusters. Potential biological networks were also constructed to reveal the link between the gene candidates. Biological pathways related to the three germ cell stages were constructed. A number of known transcription regulators in spermatogenesis, including NF-kappaB, SP1, AP-1, and EGR, were identified. Novel promoter elements such as the E box in Spga-specific genes, GATA in Spcy-specific genes, and GKLF in Sptd-specific genes were also observed. Taken together, our approach is reliable and provides a foundation for the generation of novel biological hypotheses for studying spermatogenesis.

P53 levels determine outcome during beta-catenin tumor initiation and metastasis in the mammary gland and male germ cells

beta-Catenin, an oncogene, and P53, a tumor suppressor, are common targets of mutation in human cancers. It has been observed that P53 is often inactivated in tumors involving beta-catenin activation. In an attempt to model this situation in vivo, we crossed the previously characterized MMTV-DeltaN-beta-catenin mouse with the P53 knockout mouse. Female multiparous mice that carry the MMTV-DeltaN-beta-catenin transgene and that are heterozygous for P53 (Tg(DeltaN-betaCat)/+, P53+/-) display an increased tumor burden (2.05 vs 1.31 tumors/animal), with a generally more advanced pathology, and increased metastatic rate (39 vs 0%) relative to transgenic female mice that are wild type for P53 (Tg(DeltaN-betaCat)/+, P53+/+). These differences were not due to complete loss of P53 as only one of 21 tumors demonstrated loss of heterozygosity at the P53 locus. Furthermore, no mutations were present in tumors retaining a single wild-type allele. Tg(DeltaN-betaCat)/+, P53-/- male mice developed testicular teratomas and survived an average of 65 days, whereas non-Tg(DeltaN-betaCat), P53-/- males survived an average of 84 days. Sixty-two percent of Tg(DeltaN-betaCat), P53-/- mice developed testicular teratomas, whereas only 10% of the non-Tg(DeltaN-betaCat), P53-/- mice developed these tumors. These results indicate that the level of P53 and the tissue of origin are important factors in determining outcome of cancer caused by oncogene activation.

Impairment of spermatogenesis and enhancement of testicular germ cell apoptosis induced by exogenous all-Trans-retinoic acid in adult lizardPodarcis sicula

In mammals, retinoic acid is involved in the regulation of testicular function by interaction with two families of nuclear receptors, retinoic acid receptor (RAR) and retinoid X receptor (RXR). Among RAR isoforms, the testicular cells of the lizard were found to express only RARalpha (3.7 kb) and RARbeta (3.4 kb) mRNAs, as reported here. In this study, the effects of exogenous all-trans-retinoic acid (atRA) on spermatogenesis of a non-mammalian seasonal reproducer were investigated. Daily intraperitoneal injections of atRA or atRA plus testosterone (atRA+T) were given for 2 weeks to adult males of the lizard Podarcis sicula. In animals treated with atRA, the seminiferous tubules were markedly reduced in cross-area. The seminiferous epithelium collapse was responsible for a sensible reduction in the number of germ cells and disruption in normal epithelial organization. In comparison, in atRA+T-treated lizards the loss of germinal cells was significantly less. The loss of germ cells observed in both experimental groups results from an induction of apoptotic process, as revealed by TUNEL analysis. Although low in number, apoptotic germ cells were also observed in the control groups (saline- and T-treated lizard), where the main germ cells undergoing apoptosis are primary spermatocytes (most frequently) and some spermatogonia. In conclusion, it is shown here that retinoic acid has deleterious effects on lizard spermatogenesis, causing a severe depletion of seminiferous epithelium, probably via induction of apoptotic processes. These effects are not completely inhibited by simultaneous administration of testosterone, although this hormone, once injected, is able to stimulate spermatogenesis and protect germinal cells from apoptotic cell death.

Spermatocyte-specific expression of constitutively active heat shock factor 1 induces HSP70i-resistant apoptosis in male germ cells

Spermatocytes, the most sensitive male germ cells to heat-induced apoptosis, do not respond to hyperthermia by inducing heat shock proteins (HSPs), including HSP70i, which has been previously shown to confer resistance to apoptosis in somatic cells. To dissect the mechanism of heat-induced apoptosis and to determine if we could protect spermatocytes by expressing HSP70i, we engineered transgenic mice that express in spermatocytes constitutively active heat shock transcription factor (HSF)1. Such HSF1 expression did not lead to transcription of inducible Hsp70 genes, but instead induced caspase-dependent apoptosis that mimicked heat shock-induced death of spermatogenic cells. Both mitochondria-dependent and death receptor-dependent pathways appear to be involved in such HSF1-induced apoptosis: the levels of Bcl-2 family proteins became increased, p53 protein accumulated and expression levels of caspase-8 and death-receptor-interacting proteins (including Fas-associated death domain protein and TNF receptor associated death domain protein) became elevated. Surprisingly, the constitutive spermatocyte-specific expression of HSP70i in double-transgenic males did not protect against such HSF1-induced apoptosis.

Role of oxidative stress in ethanol induced germ cell apoptosis - An experimental study in rats

The study was undertaken to evaluate the possible involvement of oxidative stress in the pathogenesis of ethanol induced testicular atrophy in rats. Adult male rats were orally administered ethanol at a dose of 1.6 g/kg body weight/day for four weeks. Twenty-four hours after the last treatment the rats were sacrificed using anesthetic ether. Testes were removed and weighed. Apoptosis was studied by using the Feulgen reaction on 5 μ thin paraffin sections of testis. Testicular homogenate was prepared and centrifuged. The supernatant was used for the estimation of extent of lipid peroxidation and antioxidant defense status. There was significant reduction in body weight: and in testicular weight and diameter in ethanol treated rats. Extent of germ cell apoptosis was significantly high in ethanol treated rats. Ethanol treated rats showed significantly high tissue TBARS level and glutathione S-transferase activity; and low tissue ascorbic acid, reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activities. Chronic ethanol administration resulted in high oxidative stress in the testes either due to increased extent of lipid peroxidation or due to decreased antioxidant defenses, and thereby induces germ cell apoptosis leading to testicular atrophy.

The testicular fatty acid binding protein PERF15 regulates the fate of germ cells in PERF15 transgenic mice

The quality control of sperm is critical for efficient reproduction. In germ cells, cell death involves different processes to those in somatic cells, and in many cases, the trigger to induce cell death in deficient germ cells is still unclear. It is known that the fatty acid composition of sperm is related to fertility. Composition of the fatty acid of germ cells changes dynamically during spermatogenesis, and fatty acid binding protein (FABP) may be involved in these changes. In this study, we developed transgenic mice with a testicular germ-cell-specific FABP (PERF15) transgene, whose expression was controlled by the Cre-LoxP site-specific recombination system. We also developed transgenic mice with the Cre gene under the control of the spermatocyte specific Pgk2 promoter. In double transgenic mice, following Cre-mediated recombination of the PERF15 containing transgene, PERF15 was strongly overexpressed. Its overexpression induced multinucleate symplasts to form, indicating programmed germ cell death occurred at the elongated spermatid stage. As a result, sperm harboring the transgene were significantly decreased, but the surviving sperm demonstrated higher fertility than natural sperm. Therefore, we conclude that PERF15 associate with the direction of germ cell fates and preserve the quality of sperm.

Programmed cell death in the germline

In many organisms, programmed cell death of germ cells is required for normal development. This often occurs through highly conserved events including the transfer of vital cellular material to the growing gametes following death of neighboring cells. Germline cell death also plays a role in such diverse processes as removal of abnormal or superfluous cells at certain checkpoints, establishment of caste differentiation, and individualization of gametes. This review focuses on the cell death events that occur during gametogenesis in both vertebrates and invertebrates. It also examines the signals and machinery that initiate and carry out these germ cell deaths.

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.

Cryopreservation and Thawing Is Associated with Varying Extent of Activation of Apoptotic Machinery in Subsets of Ejaculated Human Spermatozoa1

We investigated the impact of cryopreservation and thawing on levels of caspases-3, -8, and -9 activity, intact mitochondrial membrane potential (Deltapsim), and DNA fragmentation in human spermatozoa. Eleven pools of cryopreserved and eight pools of fresh semen samples were examined. Mature and immature fractions were separated on a two-layer density gradient (47% and 90%) and further subdivided based on the externalization of phosphatidylserine and its binding to annexin V-labeled superparamagnetic microbeads (ANMB). Levels of activated caspases were assessed using fluorescein-labeled inhibitors of caspases (FLICA), Deltapsim using a lipophilic cationic dye, and DNA fragmentation by the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay. Cryopreservation was significantly associated with activation of caspases-3, -8, and -9, as well as disruption of the mitochondrial membrane potential but no significant changes were observed in DNA fragmentation. In mature sperm, caspase activation was only detected in the ANMB+ fraction, whereas in immature sperm, both ANMB+ and ANMB- fractions showed activated caspase levels. In ANMB+ immature sperm, apoptosis seemed to be triggered by a surface ligand-receptor mechanism as well as by disruption of mitochondria, whereas in ANMB- immature sperm, apoptosis was induced by activation of caspase-9 following loss of intact Deltapsim. These results demonstrate that selection of annexin V-negative mature spermatozoa might be of clinical relevance for fertility preservation, as this sperm fraction shows no activated apoptosis during the cryopreservation process.

Spontaneous mutagenesis is enhanced in Apex heterozygous mice

Germ line DNA directs the development of the next generation and, as such, is profoundly different from somatic cell DNA. Spermatogenic cells obtained from young adult lacI transgenic mice display a lower spontaneous mutant frequency and greater in vitro base excision repair activity than somatic cells and tissues obtained from the same mice. However, spermatogenic cells from old lacI mice display a 10-fold higher mutant frequency. This increased spontaneous mutant frequency occurs coincidentally with decreased in vitro base excision repair activity for germ cell and testicular extracts that in turn corresponds to a decreased abundance of AP endonuclease. To directly test whether a genetic diminution of AP endonuclease results in increased spontaneous mutant frequencies in spermatogenic cell types, AP endonuclease heterozygous (Apex(+/-)) knockout mice were crossed with lacI transgenic mice. Spontaneous mutant frequencies were significantly elevated (approximately twofold) for liver and spleen obtained from 3-month-old Apex(+/-) lacI(+) mice compared to frequencies from Apex(+/+) lacI(+) littermates and were additionally elevated for somatic tissues from 9-month-old mice. Spermatogenic cells from 9-month-old Apex(+/-) lacI(+) mice were significantly elevated twofold compared to levels for 9-month-old Apex(+/+) lacI(+) control mice. These data indicate that diminution of AP endonuclease has a significant effect on spontaneous mutagenesis in somatic and germ line cells.

The A-type cyclins and the meiotic cell cycle in mammalian male germ cells

There are two mammalian A-type cyclins, cyclin Al and A2. While cyclin A1 is limited to male germ cells, cyclin A2 is widely expressed. Cyclin A2 promotes both Gl/S and G2/M transitions in somatic cells and cyclin A2-deficient mice are early embryonic lethal. We have shown that cyclin Al is essential for passage of spermatocytes into meiosis I (MI) by generating mice null for the cyclin A1 gene Ccna1. Both Ccna1(-/-) males and females were healthy but the males were sterile because of a cell cycle arrest before MI. This arrest was associated with desynapsis abnormalities, low M-phase promoting factor activity, and apoptosis. We have now determined that human cyclin A1 is expressed in similar stages of spermatogenesis and are exploring its role in human male infertility and whether it may be a novel target for new approaches for male contraception.

Heat shock transcription factor 1 is involved in quality-control mechanisms in male germ cells

Quality-control mechanisms in spermatogenesis are important to eliminate injured or abnormal cells, thereby protecting the organism from abnormal development in the next generation. The processes of spermatogenesis are highly sensitive to high temperatures; however, the mechanisms by which injured germ cells are eliminated remain unclear. Here, we found that heat shock proteins are not induced in male germ cells in response to thermal stress, although heat shock transcription factor 1 (HSF1) is activated. Using HSF1-null mice, we showed that apoptosis of pachytene spermatocytes was markedly inhibited in testes with a single exposure to heat and in the cryptorchid testes, indicating that HSF1 promotes apoptotic cell death of pachytene spermatocytes exposed to thermal stress. In marked contrast, HSF1 acts as a cell-survival factor of more immature germ cells, probably including spermatogonia, in testes exposed to high temperatures. These results demonstrate that HSF1 has two opposite roles in male germ cells independent of the activation of heat shock genes.

Developmental Expression of p63 in the Mouse Testis

p63 is a member of the p53 gene family and have structural similarities with p53. p63 encodes for multiple isotypes either with N-terminal transactivation domain (TAp63) or without it (DeltaNp63). In the mammalian testis, it has been shown that p53 plays important roles in the regulation of germ cell apoptosis and meiosis. However, little is known for the physiological function of p63 in the mammalian spermatogenesis. To investigate the potential roles of p63 in the developing mouse testis, we examined the expression pattern of p63 in the mouse testis from birth to adulthood. In addition to the TAp63 mRNA which was continuously expressed in the developing testis, transcripts encoding DeltaNp63 was detected at specific stages of testicular development by RT-PCR, from postnatal day 1 to day 7 and from 3 weeks to 4 weeks after birth. Western blot analysis of whole testis lysates with anti-p63 antibody revealed an approximately 68 kD band throughout development and a less abundant protein at 60 kD in the earlier period of postnatal development. Immunopositive reactions for p63 were observed as early as 10 days after birth and p63 protein was localized to the nuclei of spermatocytes and round spermatids. These findings strongly suggest that p63 might be involved in the regulation of proliferation and differentiation of spermatogenic cells in the developing mouse testis.

Effects of age on DNA double-strand breaks and apoptosis in human sperm

OBJECTIVE

This study was designed to explore the relationship between men's age and DNA damage and apoptosis in human spermatozoa.

DESIGN

Semen samples were collected from men between the ages of 20 and 57 years. Sperm DNA double-strand breaks were assessed using the neutral microgel electrophoresis (comet) assay, and apoptosis was estimated using the DNA diffusion assay.

SETTING

Academic medical center.

PATIENT(S)

Sixty-six men aged 20 to 57 years were recruited from infertility laboratory and general populations and consented to donate a semen sample. Recruitment was determined by time and day of analysis; the only exclusions were for azoospermia, prostatitis, or prior cancer therapy.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

DNA damage and apoptosis in human sperm.

RESULT(S)

Age correlated with an increasing percentage of sperm with highly damaged DNA (range: 0-83%) and tended to inversely correlate with percentage of apoptotic sperm (range: 0.3%-23%). For example, percentage of sperm with highly damaged DNA, comet extent, DNA break number, and other comet measures was statistically significantly higher in men aged 36-57 years than in those aged 20-35 years, but percentage apoptosis was statistically significantly lower in the older group. Semen analysis showed percentage motility to be significantly higher in younger age groups.

CONCLUSION(S)

This study clearly demonstrates an increase in sperm double-stranded DNA breaks with age. Our findings also suggest for the first time an age-related decrease in human sperm apoptosis. These novel findings may indicate deterioration of healthy sperm cell selection process with age.

Determinants of retroviral-mediated gene delivery to mouse spermatogonia

Spermatogonia represent a new route to transgenesis in mice and potentially in some commercially important domesticated animals. In addition, these cells are also a potential target for viral integration in patients receiving somatic cell gene therapy. But the factors influencing retroviral transduction into spermatogonia are not well understood. Because retroviral transduction is affected in part by the proliferative status of the host cell, we developed an improved cell culture system in which spermatogonia survive and proliferate for several days. We used this system to test the ability of a variety of murine and avian retroviruses to infect spermatogonia. We investigated the factors influencing retroviral transduction of spermatogonia, including the proliferative status of the infected cell, the type of viral envelope, the type of retroviral long terminal repeat, and the method of viral delivery. Here we show that many of the widely used retroviral vector systems can be used to successfully transduce spermatogonia at high efficiency. Moreover, we show that retroviral delivery of MDM2, the major downregulator of p53, promotes spermatogonial survival in culture, suggesting that p53 plays a role in regulating spermatogonial apoptosis induced by growth factor deprivation. These results further demonstrate the usefulness of this novel system of targeting substances of interest to the testis. These data have important implications for improving animal transgenesis and for understanding the risks associated with somatic cell gene therapy.

Diethylstilbestrol induces rat spermatogenic cell apoptosis in vivo through increased expression of spermatogenic cell Fas/FasL system

The significant role that estrogens play in spermatogenesis has opened up an exciting area of research in male reproductive biology. The realization that estrogens are essential for proper maintenance of spermatogenesis, as well as growing evidence pointing to the deleterious effects of estrogen-like chemicals on male reproductive health, has made it imperative to dissect the role estrogens play in the male. Using a model estrogen, diethylstilbestrol (DES), to induce spermatogenic cell apoptosis in vivo in the male rat, we provide a new insight into an estrogen-dependent regulation of the Fas-FasL system specifically in spermatogenic cells. We show a distinct increase in Fas-FasL expression in spermatogenic cells upon exposure to diethylstilbestrol. This increase is confined to the spermatid population, which correlates with increased apoptosis seen in the haploid cells. Testosterone supplementation is able to prevent DES-induced Fas-FasL up-regulation and apoptosis in the spermatogenic cells. DES-induced germ cell apoptosis does not occur in Fas-deficient lpr mice. One other important finding is that spermatogenic cells are type II cells, as the increase in Fas-FasL expression in the spermatogenic cells is followed by the cleavage of caspase-8 to its active form, following which Bax translocates to the mitochondria and precipitates the release of cytochrome c that is accompanied by a drop in mitochondrial potential. Subsequent to this, activation of caspase-9 occurs that in turn activates caspase-3 leading to the cleavage of poly(ADP-ribose) polymerase. Taken together, the data indicate that estrogen-like chemicals can precipitate apoptotic death in spermatogenic cells by increasing the expression of spermatogenic cell Fas-FasL, thus initiating apoptosis in the same lineage of cells through the activation of the apoptotic pathway chosen by type II cells.

Apoptosis and proliferation during seasonal testis regression in the brown hare (Lepus europaeus L.)

Testes samples of 52 brown hares (Lepus europaeus L.), sacrificed between July and January, were subjected to immuno histochemical analysis. The terminal deoxynucleotidyl transferase-mediated d'UTP nick end labelling (TUNEL) method was applied to detect apoptosis; and antibodies to proliferating cell nuclear antigen (PCNA) were used to evaluate cell proliferation in the testes. In the seminiferous epithelium, the apoptotic processes were evident from August to early November with maximal values in September. Cell death in germ cells occurs predominantly during the prophase of the first meiotic division. In July, and from mid-November onwards, only the occasional TUNEL-positive cells can be seen. The proliferation of germ cells continues during the testis regression phase. The average number of PCNA-positive cells decreases slightly from September onwards and rises again in mid-November.

The mammalian SIR2alpha protein has a role in embryogenesis and gametogenesis

The yeast Sir2p protein has an essential role in maintaining telomeric and mating type genes in their transcriptionally inactive state. Mammalian cells have a very large proportion of their genome inactive and also contain seven genes that have regions of homology with the yeast sir2 gene. One of these mammalian genes, sir2alpha, is the presumptive mammalian homologue of the yeast sir2 gene. We set out to determine if sir2alpha plays a role in mammalian gene silencing by creating a strain of mice carrying a null allele of sir2alpha. Animals carrying two null alleles of sir2alpha were smaller than normal at birth, and most died during the early postnatal period. In an outbred background, the sir2alpha null animals often survived to adulthood, but both sexes were sterile. We found no evidence for failure of gene silencing in sir2alpha null animals, suggesting that either SIR2alpha has a different role in mammals than it does in Saccharomyces cerevisiae or that its role in gene silencing in confined to a small subset of mammalian genes. The phenotype of the sir2alpha null animals suggests that the SIR2alpha protein is essential for normal embryogenesis and for normal reproduction in both sexes.

Regulated expression and ultrastructural localization of galectin-1, a proapoptotic beta-galactoside-binding lectin, during spermatogenesis in rat testis

Galectin-1, a highly conserved beta-galactoside-binding protein, induces apoptosis of activated T cells and suppresses the development of autoimmunity and chronic inflammation. To gain insight regarding the potential role of galectin-1 as a novel mechanism of immune privilege, we investigated expression and ultrastructural localization of galectin-1 in rat testis. Galectin-1 expression was assessed by Western blot analysis and immunocytochemical localization in testes obtained from rats aged from 9 to 60 days. Expression of this carbohydrate-binding protein was developmentally regulated, and its immunolabeling exhibited a stage-specific pattern throughout the spermatogenic process. Immunogold staining using the anti-galectin-1 antibody revealed the typical Sertoli cell profile in the seminiferous epithelium, mainly at stages X-II. During spermiation (stages VI-VIII), a strong labeling was observed at the luminal pole of seminiferous epithelium, localized on apical stalks of Sertoli cells, on heads of mature spermatids, and on bodies of residual cytoplasm. Moreover, spermatozoa released into the lumen showed a strong immunostaining. Following spermiation (stage VIII), galectin-1 expression was restored at the basal portion of Sertoli cells and progressively spread out through the whole cells as differentiation of germinal cells proceeded. Immunoelectron microscopy confirmed distribution of galectin-1 in nuclei and cytoplasmic projections of Sertoli cells and on heads and tails of late spermatids and residual bodies. Surface localization of galectin-1 was evidenced in spermatozoa from caput epididymis. Thus, the regulated expression of galectin-1 during the spermatogenic cycle suggests a novel role for this immunosuppressive lectin in reproductive biology.

Absence of p53 and FasL has sexually dimorphic effects on both development and reproduction

Reproduction and development are highly dependent on apoptosis to balance the proliferation that necessarily occurs during these processes. How the absence of two apoptotic factors in mice would affect reproduction and development was examined. Given previous reports of increased neural tube defects in p53-/- female fetuses, decreased fertility in gld female mice, and altered spermatogenesis in both p53 and gld male mice, the possibility that these phenotypes might be enhanced by the elimination of a second apoptotic factor was investigated. The reproductive vigor and the health of offspring were monitored during the production of the new double-deficient strain (FasL-/-p53-/-) for any changes from the reported phenotypes. Thus, any unusual phenotypes that could lead to new models for studying mechanisms of health and disease would be identified. Double-deficient male offspring appeared healthy and occurred at expected frequencies. Additionally, spermatogenesis and male fertility were unaffected by the gene deficiencies. On the other hand, FasL+/+p53-/- and FasL-/-p53-/- female mice were susceptible to increased malformations and post-natal death. These abnormalities were consistent with previous reports of neural tube defects in p53-/- female mice. Fertility rates were also significantly decreased in p53-/- female mice that lived to be adults, an observation not previously reported. Finally, the absence of both FasL and p53 led to dystocia in pregnant female mice, suggesting that the two genes play complementary roles in parturition. Therefore, although male mouse development and reproduction remained unaffected by p53 and FasL deficiencies, female mouse development was adversely affected by the absence of p53, and no live litters were born to female mice with the combined absence of both FasL and p53. In this report, we suggest a potential mechanism involving corpora luteal regression to explain this defect in parturition in FasL-/-p53-/- female mice.

Sperm apoptosis in fresh and cryopreserved bull semen detected by flow cytometry and its relationship with fertility

The present study was conducted to detect sperm apoptosis in fresh and frozen semen and to determine its relationship with bull fertility. Three ejaculates were collected from five breeding bulls with different fertility levels and were cryopreserved using standard methods. Two flow cytometric methods were employed to measure apoptosis: an assay for phosphatidylserine (PS) translocation across the plasma membranes using fluorescein-labeled Annexin V and propidium iodide (PI), and an assay for nicked DNA using bromodeoxyuridine (BrdU), terminal deoxynucleotidyl transferase, and fluorescein-labeled anti-BrdU monoclonal antibody. Both assays showed that fresh sperm contained 10%-20% apoptotic sperm. Significant differences in the percentage of apoptotic sperm were observed among the bulls. Cryopreservation induced translocation of PS to the outer leaflet of the plasma membrane and caused most of the necrotic cells in fresh sperm to disintegrate. Bull fertility was significantly related to the percentage of necrotic or viable sperm in fresh semen as detected by the Annexin V/PI assay, to the number of apoptotic sperm in fresh semen as detected by the TUNEL assay, and to the level of chromatin or DNA condensation as detected by PI staining. The present study suggests that the presence of apoptotic spermatozoa in fresh semen could be one of the reasons for poor fertility in breeding bulls.

The C. elegans homolog of the p53 tumor suppressor is required for DNA damage-induced apoptosis

In mammals, one of the key regulators necessary for responding to genotoxic stress is the p53 transcription factor. p53 is the single most commonly mutated tumor suppressor gene in human cancers. Here we report the identification of a C. elegans homolog of mammalian p53. Using RNAi and DNA cosuppression technology, we show that C. elegans p53 (cep-1) is required for DNA damage-induced apoptosis in the C. elegans germline. However,cep-1 RNAi does not affect programmed cell death occurring during worm development and physiological (radiation-independent) germ cell death. The DNA binding domain of CEP-1 is related to vertebrate p53 members and possesses the conserved residues most frequently mutated in human tumors. Consistent with this, CEP-1 acts as a transcription factor and is able to activate a transcriptional reporter containing consensus human p53 binding sites. Our data support the notion that p53-mediated transcriptional regulation is part of an ancestral pathway mediating DNA damage-induced apoptosis and reveals C. elegans as a genetically tractable model organism for studying the p53 apoptotic pathway.

A putative, ubiquitin-dependent mechanism for the recognition and elimination of defective spermatozoa in the mammalian epididymis

The normal structure and function of sperm are prerequisites for successful fertilization and embryonic development, but little is known about how defective sperm are eliminated during mammalian spermatogenesis. Here, we describe a ubiquitin-dependent, sperm quality control mechanism that resides in the mammalian epididymis, the site of sperm maturation and storage. We used immunofluorescence, electron microscopy, western blotting and pulse-chase experiments to show that ubiquitin is secreted by the epididymal epithelium and binds to the surface of defective sperm. Most of the ubiquitinated sperm are subsequently phagocytosed by the epididymal epithelial cells. A portion of defective sperm escapes phagocytosis and can be found in the ejaculate. Cultured epididymal cells maintain their ability to produce ubiquitin and phagocytose the defective sperm, as well as the ubiquitin-coated microspheres, in vitro. The surprising phenomenon of cell-surface ubiquitination in defective sperm provides a possible mechanism for sperm quality control in mammals and a new marker of semen abnormalities in men and animals.

Adenovirus-mediated p53 gene transfer to rat testis impairs spermatogenesis

The tumor suppressor protein p53 participates in normal cell differentiation as well as induction of programmed cell death. The authors investigated the effect of p53 overexpression on spermatogenesis by transferring p53 gene into the rat testes. Replication-deficient recombinant adenovirus vectors were constructed to include cytomegalovirus (CMV) promoter driving wild-type p53 (Ad-CMV-p53) or beta-galactosidase (Ad-CMV-beta-gal). Virus was delivered to cells of the tubules by slow retrograde injection through the rete testis. At 0, 4, 7, and 14 days, testes were removed, weighed, and analyzed histopathologically, including immunohistochemistry for p53, Bcl-2, Bax, and interleukin-1beta converting enzyme (ICE). Testicular weight was decreased in Ad-CMV-p53 group at 14 days after injection, while no change occurred in phosphate-buffered saline-injected controls or Ad-CMV-beta-gal-infected testes. Beyond 4 days, cell degradation in tubules interfered with immunohistochemical observation in the Ad-CMV-p53 group. At 4 days, p53 was expressed mostly in spermatocytes. Bax showed greater expression in the p53 group than in the control or Ad-CMV-beta-gal group. ICE, expressed mostly in spermatids, was more abundant in the p53 group than in controls. Overall, p53 overexpression in the testis impaired spermatogenesis.

Role of epithelial cells and programmed cell death in Hydra spermatogenesis

Spermatogenesis in higher animals is a tightly regulated process, in which survival and death of sperm precursor cells depends on the presence of somatic cells in gonads. In the basal metazoan Hydra spermatogenesis takes place in anatomically simple testes and in the absence of accessory structures. Hydra sperm precursors are derived from interstitial stem cells. Here we show that large numbers of sperm precursors in testes of Hydra vulgaris undergo programmed cell death (apoptosis) and that ectodermal epithelial cells phagocytose the apoptotic sperm precursors. This is surprising since so far no evidence has been reported that epithelial cells are directly involved in germ cell differentiation in Hydra. We propose that, similar to Sertoli cells in mammals, in Hydra epithelial cells support and perhaps even control spermatogenesis.

Role of Sertoli cells in injury-associated testicular germ cell apoptosis

This review examines experimental models of Sertoli cell injury resulting in germ cell apoptosis. Since germ cells exist in an environment created by Sertoli cells, paracrine signaling between these intimately associated cells must regulate the process of germ cell death. Germ cell apoptosis may be signaled by a decrease in Sertoli cell pro-survival factors, an increase in Sertoli cell pro-apoptotic factors, or both. The different models of Sertoli cell injury indicate that spermatogenesis is susceptible to disruption, and that targeting critical Sertoli cell functions can lead to rapid and massive germ cell death.

Immature germ cell conception-in vitro germ cell manipulation

Experimental studies in laboratory animals have shown that successful conception can be achieved by fertilizing oocytes with immature male germ cells. This gave rise to the concept that immature germ cells recovered from the testes of azoospermic men with maturation arrest may be used for assisted reproduction. However, in contrast to using germ cells recovered from healthy animals, clinical application to the treatment of male sterility is burdened by inherent defects in germ cells attributable to underlying testicular pathology. The recent introduction of in vitro germ cell culture/manipulation techniques makes it possible, in some cases, to overcome the in vivo maturation arrest by allowing an additional meiotic and post-meiotic differentiation and the selective harvesting of cells devoid of apoptosis-related nuclear and cytoplasmic damage. These techniques enabled the first births of normal infants fathered by azoospermic men with maturation arrest at the primary spermatocyte stage and improved the efficacy of assisted reproduction in men with maturation arrest at the round spermatid stage.

Apoptosis of fetal testicular cells is regulated by both p53-dependent and independent mechanisms

A portion of fetal germ cells undergoes apoptosis in the physiological context, but the molecular mechanisms of their apoptosis are largely unknown. Because p53 tumor suppressor gene product promotes apoptosis in various types of cells, we have investigated the expression of p53 in fetal gonads and examined the influence of loss of p53 function in fetal gonad cells using mice deficient in the p53 gene. We found that the expression of p53 protein in fetal testis was induced after 15.5 dpc (days post coitum), while the expression was not detected in fetal ovary. The number of apoptotic cells found in the seminiferous tubules of fetal testes was not significantly different between p53-deficient and wild-type mice until 16.5 dpc. At 17.5 dpc, however, more apoptotic cells were observed in wild-type testes than in the p53-deficient mice. In contrast, a similar number of apoptotic cells was found in fetal ovaries throughout these developmental stages. These observations indicate that p53 promotes apoptosis of fetal testicular cells after 16.5 dpc.

Drosophila p53 is a structural and functional homolog of the tumor suppressor p53

The importance of p53 in carcinogenesis stems from its central role in inducing cell cycle arrest or apoptosis in response to cellular stresses. We have identified a Drosophila homolog of p53 ("Dmp53"). Like mammalian p53, Dmp53 binds specifically to human p53 binding sites, and overexpression of Dmp53 induces apoptosis. Importantly, inhibition of Dmp53 function renders cells resistant to X ray-induced apoptosis, suggesting that Dmp53 is required for the apoptotic response to DNA damage. Unlike mammalian p53, Dmp53 appears unable to induce a G1 cell cycle block when overexpressed, and inhibition of Dmp53 activity does not affect X ray-induced cell cycle arrest. These data reveal an ancestral proapoptotic function for p53 and identify Drosophila as an ideal model system for elucidating the p53 apoptotic pathway(s) induced by DNA damage.

Infertility associated with incomplete spermatogenic arrest and oligozoospermia in Egr4-deficient mice

Male fertility is complex and depends upon endocrine/paracrine regulatory mechanisms and morphogenetic processes occurring during testicular development, spermatogenesis (mitosis and meiosis) and spermiogenesis (spermatid maturation). Egr4 (NGFI-C, pAT133), a member of the Egr family of zinc-finger transcription factors, is thought to be involved in cellular growth and differentiation, but its specific function has been previously unknown. We derived Egr4 null mice through targeted mutagenesis and found that they were phenotypically normal with the exception that males, but not females, were infertile. Egr4 is expressed at low levels within male germ cells during meiosis and is critical for germ cell maturation during the early-mid pachytene stage. While most Egr4 null male germ cells undergo apoptosis during early-mid pachytene, some are capable of maturing beyond an apparent Egr4-dependent developmental restriction point. Consequently, a limited degree of spermiogenesis occurs but this is accompanied by markedly abnormal spermatozoon morphology and severe oligozoospermia. Egr4 appears to regulate critical genes involved in early stages of meiosis and has a singularly important role in male murine fertility. These data raise the possibility that Egr4 may contribute to some forms of human idiopathic male infertility.

An Mn2+-stimulated neutral-sphingomyelinase in seminiferous tubules of immature Wistar rats

Mammalian sphingomyelinases have been implicated in many important physiological and pathophysiological processes. The seminiferous tubules of immature (19 day-old) Wistar rats have at least three types of sphingomyelinases, a lysosomal one and two microsomal ones. One of the microsomal sphingomyelinases is active at pH 6.5 and is stimulated by Mn2+ > Co2+ > Mg2+, and the other is active at pH 7.4 and is stimulated by Mn2+ > Mg2+ and inhibited by Co2+. The two microsomal enzymes are only slightly inhibited by EDTA and at pH 7.4 the stimulatory effects of Mn2+ and Mg2+ are additive. These data characterize the existence of two different membrane-bound sphingomyelinases in the seminiferous tubules of the rat.

Deficiency of Trp53 rescues the male fertility defects of Kit(W-v) mice but has no effect on the survival of melanocytes and mast cells

Mutations of the receptor tyrosine kinase, Kit, or its ligand, mast growth factor (Mgf), affect three unrelated cell populations: melanocytes, germ cells, and mast cells. Kit signaling is required initially to prevent cell death in these lineages both in vitro and in vivo. Mgf appears to play a role in the survival of some hematopoietic cells in vitro by modulating the activity of p53. Signaling by Mgf inhibits p53-induced apoptosis of erythroleukemia cell lines and suppresses p53-dependent radiation-induced apoptosis of bone marrow cells. We tested the hypothesis that cell survival in Kit mutant mice would be enhanced by p53 deficiency in vivo. Double-mutant mice, which have greatly reduced Kit receptor tyrosine kinase activity and also lack Trp53, were generated and the affected cell lineages examined. Mast cell, melanoblast, and melanocyte survival in the double Kit(W-v/W-v):Trp53(-/-) mutants was not increased compared to the single Kit(W-v/W-v):Trp53(+/+) mutants. However, double-mutant males showed an increase in sperm viability and could father litters, in contrast to their homozygous Kit mutant, wild-type p53 littermates. This germ cell rescue appears to be male specific, as female ovaries were similar in mice homozygous for the Kit mutant allele with or without p53. We conclude that defective Kit signaling in vivo results in apoptosis by a p53-independent pathway in melanocyte and mast cell lineages but that in male germ cells apoptosis in the absence of Kit is p53-dependent.

The role of apoptosis in normal and abnormal embryonic development

Programmed cell death or apoptosis is a widespread biological phenomenon. Apoptosis is characterized by typical cell features such as membrane blebbing, chromatin condensation, and DNA fragmentation. It involves a number of membrane receptors (e.g., Fas, TNFR) and a cascade of signal transduction steps resulting in the activation of a number of cysteine proteases known as caspases. Disordered apoptosis may lead to carcinogenesis and participates in the pathogenesis of Alzheimer disease, Parkinson disease, or AIDS. Programmed cell death plays an important role in the processes of gamete maturation as well as in embryo development, contributing to the appropriate formation of various organs and structures. Apoptosis is one of the mechanisms of action of various cytotoxic agents and teratogens. Teratogen-induced excessive death of embryonic cells is undoubtedly one of the most important events preceding the occurrence of structural abnormalities, regardless of their nature. Therefore understanding the mechanisms involved in physiological as well as in disturbed or dysregulated apoptosis may lead to the development of new methods of preventive treatment of various developmental abnormalities. The present review summarizes data on the mechanisms of programmed cell death and concentrates on apoptosis involved in normal or disturbed gametogenesis and in normal and abnormal embryonic development.