Adenine nucleotide translocase 4 deficiency leads to early meiotic arrest of murine male germ cells

The adenine nucleotide translocase family underlies cardiac ischemia-reperfusion injury through the mitochondrial permeability pore independently of cyclophilin D

The mitochondrial permeability transition pore (mPTP) is implicated in cardiac ischemia-reperfusion (I/R) injury. During I/R, elevated mitochondrial Ca2+ triggers mPTP opening, leading to necrotic cell death. Although nonessential regulators of this pore are characterized, the molecular identity of the pore-forming component remains elusive. Two of these genetically verified regulators are cyclophilin D (CypD) and the adenine nucleotide translocase (ANT) family. We investigated the ANT/CypD relationship in mPTP dynamics and I/R injury. Despite lacking all ANT isoforms, Ca2+-dependent mPTP opening persisted in cardiac mitochondria but was desensitized. This desensitization conferred resistance to I/R injury in ANT-deficient mice. CypD is hypothesized to trigger mPTP opening through isomerization of ANTs at proline-62. To test this, we generated mice that expressed a P62A mutated version of ANT1. These mice showed similar mPTP dynamics and I/R sensitivity as the wild type, indicating that P62 is dispensable for CypD regulation. Together, these data indicate that the ANT family contributes to mPTP opening independently of CypD.

The essential role of adenine nucleotide translocase 4 on male reproductive function in mice

Adenine nucleotide translocator 4 (Ant4), an ATP/ADP transporter expressed in the early phases of spermatogenesis, plays a crucial role in male fertility. While Ant4 loss causes early arrest of meiosis and increased apoptosis of spermatogenic cells in male mice, its other potential functions in male fertility remain unexplored. Here, we utilized Ant4 knockout mice to delineate the effects of Ant4-deficiency on male reproduction. Our observations demonstrated that Ant4-deficiency led to infertility and impaired testicular development, which was further investigated by evaluating testicular oxidative stress, autophagy, and inflammation. Specifically, the loss of Ant4 led to an imbalance of oxidation and antioxidants. Significant ultrastructural alterations were identified in the testicular tissues of Ant4-deficient mice, including swelling of mitochondria, loss of cristae, and accumulation of autophagosomes. Our results also showed that autophagic flux and AKT-AMPK-mTOR signaling pathway were affected in Ant4-deficient mice. Moreover, Ant4 loss increased the expression of pro-inflammatory factors. Overall, our findings underscored the importance of Ant4 in regulating oxidative stress, autophagy, and inflammation in testicular tissues. Taken together, these insights provided a nuanced understanding of the significance of Ant4 in testicular development.

Renal Mitochondrial ATP Transporter Ablation Ameliorates Obesity-Induced CKD

SIGNIFICANCE STATEMENT

This study sheds light on the central role of adenine nucleotide translocase 2 (ANT2) in the pathogenesis of obesity-induced CKD. Our data demonstrate that ANT2 depletion in renal proximal tubule cells (RPTCs) leads to a shift in their primary metabolic program from fatty acid oxidation to aerobic glycolysis, resulting in mitochondrial protection, cellular survival, and preservation of renal function. These findings provide new insights into the underlying mechanisms of obesity-induced CKD and have the potential to be translated toward the development of targeted therapeutic strategies for this debilitating condition.

BACKGROUND

The impairment in ATP production and transport in RPTCs has been linked to the pathogenesis of obesity-induced CKD. This condition is characterized by kidney dysfunction, inflammation, lipotoxicity, and fibrosis. In this study, we investigated the role of ANT2, which serves as the primary regulator of cellular ATP content in RPTCs, in the development of obesity-induced CKD.

METHODS

We generated RPTC-specific ANT2 knockout ( RPTC-ANT2-/- ) mice, which were then subjected to a 24-week high-fat diet-feeding regimen. We conducted comprehensive assessment of renal morphology, function, and metabolic alterations of these mice. In addition, we used large-scale transcriptomics, proteomics, and metabolomics analyses to gain insights into the role of ANT2 in regulating mitochondrial function, RPTC physiology, and overall renal health.

RESULTS

Our findings revealed that obese RPTC-ANT2-/- mice displayed preserved renal morphology and function, along with a notable absence of kidney lipotoxicity and fibrosis. The depletion of Ant2 in RPTCs led to a fundamental rewiring of their primary metabolic program. Specifically, these cells shifted from oxidizing fatty acids as their primary energy source to favoring aerobic glycolysis, a phenomenon mediated by the testis-selective Ant4.

CONCLUSIONS

We propose a significant role for RPTC-Ant2 in the development of obesity-induced CKD. The nullification of RPTC-Ant2 triggers a cascade of cellular mechanisms, including mitochondrial protection, enhanced RPTC survival, and ultimately the preservation of kidney function. These findings shed new light on the complex metabolic pathways contributing to CKD development and suggest potential therapeutic targets for this condition.

The mitochondrial protease PARL is required for spermatogenesis

Mitochondrial function plays an important role in the maintenance of male fertility. However, the mechanisms underlying mitochondrial defect-related infertility remain mostly unclear. Here we show that a deficiency of PARL (Parl-/-), a mitochondrial protease, causes complete arrest of spermatogenesis during meiosis I. PARL deficiency led to severe downregulation of proteins of respiratory chain complex IV in testes that did not occur in other tested organs, causing a deficit in complex IV activity and ATP production. Furthermore, Parl-/- testes showed an almost complete loss of HSD17B3, a protein of the sER responsible for the last step in testosterone synthesis. While testosterone production appeared to be restored by overexpression of HSD17B12, loss of the canonical testosterone synthesis led to an upregulation of luteinizing hormone (LH) and of LH-regulated responses. These results suggest an important impact of the downstream regulation of mitochondrial defects that manifest in a cell-type-specific manner and extend beyond mitochondria.

Mitochondrial defects caused by PARL deficiency lead to arrested spermatogenesis and ferroptosis

Impaired spermatogenesis and male infertility are common manifestations associated with mitochondrial diseases, yet the underlying mechanisms linking these conditions remain elusive. In this study, we demonstrate that mice deficient for the mitochondrial intra-membrane rhomboid protease PARL, a recently reported model of the mitochondrial encephalopathy Leigh syndrome, develop early testicular atrophy caused by a complete arrest of spermatogenesis during meiotic prophase I, followed by degeneration and death of arrested spermatocytes. This process is independent of neurodegeneration. Interestingly, genetic modifications of PINK1, PGAM5, and TTC19 - three major substrates of PARL with important roles in mitochondrial homeostasis - fail to reproduce or modify this severe phenotype, indicating that the spermatogenic arrest arises from distinct molecular pathways. We further observed severe abnormalities in mitochondrial ultrastructure in PARL-deficient spermatocytes, along with prominent electron transfer chain defects, disrupted coenzyme Q (CoQ) biosynthesis, and metabolic rewiring. These mitochondrial defects are associated with a germ cell-specific decrease in GPX4 expression leading arrested spermatocytes to ferroptosis - a regulated cell death modality characterized by uncontrolled lipid peroxidation. Our results suggest that mitochondrial defects induced by PARL depletion act as an initiating trigger for ferroptosis in primary spermatocytes through simultaneous effects on GPX4 and CoQ - two major inhibitors of ferroptosis. These findings shed new light on the potential role of ferroptosis in the pathogenesis of mitochondrial diseases and male infertility warranting further investigation.

Mitochondria Quality Control and Male Fertility

Mitochondria are pivotal to cellular homeostasis, performing vital functions such as bioenergetics, biosynthesis, and cell signalling. Proper maintenance of these processes is crucial to prevent disease development and ensure optimal cell function. Mitochondrial dynamics, including fission, fusion, biogenesis, mitophagy, and apoptosis, maintain mitochondrial quality control, which is essential for overall cell health. In male reproduction, mitochondria play a pivotal role in germ cell development and any defects in mitochondrial quality can have serious consequences on male fertility. Reactive oxygen species (ROS) also play a crucial role in sperm capacitation, but excessive ROS levels can trigger oxidative damage. Any imbalance between ROS and sperm quality control, caused by non-communicable diseases or environmental factors, can lead to an increase in oxidative stress, cell damage, and apoptosis, which in turn affect sperm concentration, quality, and motility. Therefore, assessing mitochondrial functionality and quality control is essential to gain valuable insights into male infertility. In sum, proper mitochondrial functionality is essential for overall health, and particularly important for male fertility. The assessment of mitochondrial functionality and quality control can provide crucial information for the study and management of male infertility and may lead to the development of new strategies for its management.

Mitochondrial regulation during male germ cell development

Mitochondria tailor their morphology to execute their specialized functions in different cell types and/or different environments. During spermatogenesis, mitochondria undergo continuous morphological and distributional changes with germ cell development. Deficiencies in these processes lead to mitochondrial dysfunction and abnormal spermatogenesis, thereby causing male infertility. In recent years, mitochondria have attracted considerable attention because of their unique role in the regulation of piRNA biogenesis in male germ cells. In this review, we describe the varied characters of mitochondria and focus on key mitochondrial factors that play pivotal roles in the regulation of spermatogenesis, from primordial germ cells to spermatozoa, especially concerning metabolic shift, stemness and reprogramming, mitochondrial transformation and rearrangement, and mitochondrial defects in human sperm. Further, we discuss the molecular mechanisms underlying these processes.

Fertility Relevance Probability Analysis Shortlists Genetic Markers for Male Fertility Impairment

Impairment of male fertility is one of the major public health issues worldwide. Nevertheless, genetic causes of male sub- and infertility can often only be suspected due to the lack of reliable and easy-to-use routine tests. Yet, the development of a marker panel is complicated by the large quantity of potentially predictive markers. Actually, hundreds or even thousands of genes could have fertility relevance. Thus, a systematic method enabling a selection of the most predictive markers out of the many candidates is required. As a criterion for marker selection, we derived a gene-specific score, which we refer to as fertility relevance probability (FRP). For this purpose, we first categorized 2,753 testis-expressed genes as either candidate markers or non-candidates, according to phenotypes in male knockout mice. In a parallel approach, 2,502 genes were classified as candidate markers or non-candidates based on phenotypes in men. Subsequently, we conducted logistic regression analyses with evolutionary rates of genes (dN/dS), transcription levels in testis relative to other organs, and connectivity of the encoded proteins in a protein-protein interaction network as covariates. In confirmation of the procedure, FRP values showed the expected pattern, thus being overall higher in genes with known relevance for fertility than in their counterparts without corresponding evidence. In addition, higher FRP values corresponded with an increased dysregulation of protein abundance in spermatozoa of 37 men with normal and 38 men with impaired fertility. Present analyses resulted in a ranking of genes according to their probable predictive power as candidate markers for male fertility impairment. Thus, AKAP4, TNP1, DAZL, BRDT, DMRT1, SPO11, ZPBP, HORMAD1, and SMC1B are prime candidates toward a marker panel for male fertility impairment. Additional candidate markers are DDX4, SHCBP1L, CCDC155, ODF1, DMRTB1, ASZ1, BOLL, FKBP6, SLC25A31, PRSS21, and RNF17. FRP inference additionally provides clues for potential new markers, thereunder TEX37 and POU4F2. The results of our logistic regression analyses are freely available at the PreFer Genes website (https://prefer-genes.uni-mainz.de/).

Mitochondrial dynamics during spermatogenesis

Mitochondrial fusion and fission (mitochondrial dynamics) are homeostatic processes that safeguard normal cellular function. This relationship is especially strong in tissues with constitutively high energy demands, such as brain, heart and skeletal muscle. Less is known about the role of mitochondrial dynamics in developmental systems that involve changes in metabolic function. One such system is spermatogenesis. The first mitochondrial dynamics gene, Fuzzy onions (Fzo), was discovered in 1997 to mediate mitochondrial fusion during Drosophila spermatogenesis. In mammals, however, the role of mitochondrial fusion during spermatogenesis remained unknown for nearly two decades after discovery of Fzo Mammalian spermatogenesis is one of the most complex and lengthy differentiation processes in biology, transforming spermatogonial stem cells into highly specialized sperm cells over a 5-week period. This elaborate differentiation process requires several developmentally regulated mitochondrial and metabolic transitions, making it an attractive model system for studying mitochondrial dynamics in vivo We review the emerging role of mitochondrial biology, and especially its dynamics, during the development of the male germ line.

MiRNAs Expression Profiling of Bovine (Bos taurus) Testes and Effect of bta-miR-146b on Proliferation and Apoptosis in Bovine Male Germline Stem Cells

Spermatogenesis is a complex biological process regulated by well-coordinated gene regulation, including MicroRNAs (miRNAs). miRNAs are endogenous non-coding ribonucleic acids (ncRNAs) that mainly regulate the gene expression at post-transcriptional levels. Several studies have reported miRNAs expression in bull sperm and the process of spermatogenic arrest in cattle and yak. However, studies for the identification of differential miRNA expression and its mechanisms during the developmental stages of testis still remain uncertain. In the current study, we comprehensively analyzed the expression of miRNA in bovine testes at neonatal (3 days after birth, n = 3) and mature (13 months, n = 3) stages by RNA-seq. Moreover, the role of bta-miR-146b was also investigated in regulating the proliferation and apoptosis of bovine male germline stem cells (mGSCs) followed by a series of experiments. A total of 652 miRNAs (566 known and 86 novel miRNAs) were identified, whereas 223 miRNAs were differentially expressed between the two stages. Moreover, an elevated expression level of bta-miR-146b was found in bovine testis among nine tissues, and the functional studies indicated that the overexpression of bta-miR-146b inhibited the proliferation of bovine mGSCs and promoted apoptosis. Conversely, regulation of bta-miR-146b inhibitor promoted bovine mGSCs proliferation. This study provides a basis for understanding the regulation roles of miRNAs in bovine testis development and spermatogenesis.

A 20/20 view of ANT function in mitochondrial biology and necrotic cell death

The adenosine nucleotide translocase (ANT) family of proteins are inner mitochondrial membrane proteins involved in energy homeostasis and cell death. The primary function of ANT proteins is to exchange cytosolic ADP with matrix ATP, facilitating the export of newly synthesized ATP to the cell while providing new ADP substrate to the mitochondria. As such, the ANT proteins are central to maintaining energy homeostasis in all eukaryotic cells. Evidence also suggests that the ANTs constitute a pore-forming component of the mitochondrial permeability transition pore (MPTP), a structure that forms in the inner mitochondrial membrane that is thought to underlie regulated necrotic cell death. Additionally, emerging studies suggest that ANT proteins are also critical for mitochondrial uncoupling and for promoting mitophagy. Thus, the ANTs are multifunctional proteins that are poised to participate in several aspects of mitochondrial biology and the greater regulation of cell death, which will be discussed here.

Mitochondrial fusion is required for spermatogonial differentiation and meiosis

Differentiating cells tailor their metabolism to fulfill their specialized functions. We examined whether mitochondrial fusion is important for metabolic tailoring during spermatogenesis. Acutely after depletion of mitofusins Mfn1 and Mfn2, spermatogenesis arrests due to failure to accomplish a metabolic shift during meiosis. This metabolic shift includes increased mitochondrial content, mitochondrial elongation, and upregulation of oxidative phosphorylation (OXPHOS). With long-term mitofusin loss, all differentiating germ cell types are depleted, but proliferation of stem-like undifferentiated spermatogonia remains unaffected. Thus, compared with undifferentiated spermatogonia, differentiating spermatogonia and meiotic spermatocytes have cell physiologies that require high levels of mitochondrial fusion. Proteomics in fibroblasts reveals that mitofusin-null cells downregulate respiratory chain complexes and mitochondrial ribosomal subunits. Similarly, mitofusin depletion in immortalized spermatocytes or germ cells in vivo results in reduced OXPHOS subunits and activity. We reveal that by promoting OXPHOS, mitofusins enable spermatogonial differentiation and a metabolic shift during meiosis.

Inhibition of mitochondrial permeability transition by deletion of the ANT family and CypD

The mitochondrial permeability transition pore (MPTP) has resisted molecular identification. The original model of the MPTP that proposed the adenine nucleotide translocator (ANT) as the inner membrane pore-forming component was challenged when mitochondria from Ant1/2 double null mouse liver still had MPTP activity. Because mice express three Ant genes, we reinvestigated whether the ANTs comprise the MPTP. Liver mitochondria from Ant1, Ant2, and Ant4 deficient mice were highly refractory to Ca2+-induced MPTP formation, and when also given cyclosporine A (CsA), the MPTP was completely inhibited. Moreover, liver mitochondria from mice with quadruple deletion of Ant1, Ant2, Ant4, and Ppif (cyclophilin D, target of CsA) lacked Ca2+-induced MPTP formation. Inner-membrane patch clamping in mitochondria from Ant1, Ant2, and Ant4 triple null mouse embryonic fibroblasts showed a loss of MPTP activity. Our findings suggest a model for the MPTP consisting of two distinct molecular components: The ANTs and an unknown species requiring CypD.

Extramitochondrial cardiolipin suggests a novel function of mitochondria in spermatogenesis

The acrosome is a protease-rich organelle in sperm essential for fertilization but little is known about acrosome biogenesis. Ren et al. find that the mitochondrial lipid cardiolipin and some mitochondrial proteins translocate to the acrosome during spermatogenesis, suggesting that mitochondria directly contribute to the assembly of this sperm-specific organelle.

Mitochondria contain cardiolipin (CL), an organelle-specific phospholipid that carries four fatty acids with a strong preference for unsaturated chains. Unsaturation is essential for the stability and for the function of mitochondrial CL. Surprisingly, we found tetrapalmitoyl-CL (TPCL), a fully saturated species, in the testes of humans and mice. TPCL was absent from other mouse tissues but was the most abundant CL species in testicular germ cells. Most intriguingly, TPCL was not localized in mitochondria but was in other cellular membranes even though mitochondrial CL was the substrate from which TPCL was synthesized. During spermiogenesis, TPCL became associated with the acrosome, a sperm-specific organelle, along with a subset of authentic mitochondrial proteins, including Ant4, Suox, and Spata18. Our data suggest that mitochondria-derived membranes are assembled into the acrosome, challenging the concept that this organelle is strictly derived from the Golgi apparatus and revealing a novel function of mitochondria.

Launaea taraxacifolia (Willd.) Amin ex C. Jeffrey inhibits oxidative damage and econucleotidase followed by increased cellular ATP in testicular cells of rats exposed to metropolitan polluted river water

BACKGROUND

Humans are directly/indirectly exposed to hazardous chemicals from the aquatic environment. We investigated the protection of the Launea taraxacifolia methanolic extract (LTME) on the hydroxyl steroid dehydrogenases [(∆5-3β-hydroxyl steroid dehydrogenase (∆5-3β-HSD) and the ∆5-17β-hydroxyl steroid dehydrogenase (∆5-17β-HSD), testicular 5'-nucleotidase and lactate dehydrogenase (LDH)] activities as well as the key indicators of oxidative stress in germinal epithelial cells of rats induced with surulere polluted river water (SPRW).

METHODS

The animals were divided into six groups (n=8). Group I was given 1 mL of distilled water only, Group II received 1 mL of SPRW only, Group III received 200 mg/kg LTME before+1 mL of SPRW after, Group IV received 200 mg/kg LTME+1 mL of SPRW, Group V received 1 mL of SPRW before+200 mg/kg LTME after and Group VI received 200 mg/kg LTME only. The treatment was done via oral administration for 28 days.

RESULTS

The HPLC results showed the abundance of quercetin and quercitrin. The SPRW increased 5'-nucleotidase with the concomitant decrease of ∆5-3β-HSD, ∆5-17β-HSD and LDH activities in rats exposed in relation to the control. Similarly, the administration of the SPRW caused a systemic oxidative damage along with adverse histopathological changes in germinal epithelial cells.

CONCLUSIONS

Interestingly, these alterations were differentially reversed by LTME via the elevation of steroidogenic enzymes and cellular ATP.

GeneGini: Assessment via the Gini Coefficient of Reference "Housekeeping" Genes and Diverse Human Transporter Expression Profiles

The expression levels of SLC or ABC membrane transporter transcripts typically differ 100- to 10,000-fold between different tissues. The Gini coefficient characterizes such inequalities and here is used to describe the distribution of the expression of each transporter among different human tissues and cell lines. Many transporters exhibit extremely high Gini coefficients even for common substrates, indicating considerable specialization consistent with divergent evolution. The expression profiles of SLC transporters in different cell lines behave similarly, although Gini coefficients for ABC transporters tend to be larger in cell lines than in tissues, implying selection. Transporter genes are significantly more heterogeneously expressed than the members of most non-transporter gene classes. Transcripts with the stablest expression have a low Gini index and often differ significantly from the "housekeeping" genes commonly used for normalization in transcriptomics/qPCR studies. PCBP1 has a low Gini coefficient, is reasonably expressed, and is an excellent novel reference gene. The approach, referred to as GeneGini, provides rapid and simple characterization of expression-profile distributions and improved normalization of genome-wide expression-profiling data.

A Testis-Specific Long Non-Coding RNA, lncRNA-Tcam1, Regulates Immune-Related Genes in Mouse Male Germ Cells

Spermatogenesis is precisely controlled by hormones from the hypothalamus-pituitary-gonadal axis and testis-specific genes, but the regulatory mechanism is not fully understood. Recently, a large number of long non-coding RNAs (lncRNAs) are found to be transcribed at each stage of meiosis of male germ cells, and their functions in spermatogenesis have yet to be fully investigated. lncRNA-testicular cell adhesion molecule 1 (lncRNA-Tcam1) is a nuclear lncRNA which is specifically expressed in mouse male germ cells and presumed to play a role in gene regulation during meiosis. Here, we present the identification of potential target genes of lncRNA-Tcam1 using spermatocyte-derived GC-2spd(ts) cells. Initially, 55 target gene candidates were detected by RNA-sequencing of two GC-2spd(ts) cell clones that were stably transfected with transgenes to express lncRNA-Tcam1 at different levels. Expression of 21 genes of the candidates was found to be correlated with lncRNA-Tcam1 at 7-14 postnatal days, when lncRNA-Tcam1 expression was elevated. Subsequently, we examined expression levels of the 21 genes in other two GC-2spd(ts) clones, and 11 genes exhibited the correlation with lncRNA-Tcam1. Induction of lncRNA-Tcam1 transcription using the Tet-off system verified that six genes, Trim30a, Ifit3, Tgtp2, Ifi47, Oas1g, and Gbp3, were upregulated in GC-2spd(ts) cells, indicating that lncRNA-Tcam1 is responsible for the regulation of gene expression of the six genes. In addition, five of the six genes, namely, Ifit3, Tgtp2, Ifi47, Oas1g, and Gbp3, are immune response genes, and Trim30a is a negative regulator of immune response. Altogether, the present study suggests that lncRNA-Tcam1 is responsible for gene regulation for the immune response during spermatogenesis.

Characterization of two adenine nucleotide translocase paralogues in the stink bug, Plautia stali

Adenine nucleotide translocase (ANT) is a nuclear-coded mitochondrial protein that exchanges ATP for ADP across the mitochondrial inner membrane. Most organisms possess several ANT paralogues, and functional differences among these paralogues remain largely unknown. In the present study, we identified ANT paralogue genes in hemipteran species: the stink bug, bean bug, pea aphid, and Japanese mealybug. The ANT paralogues of the stink bug, Plautia stali, are encoded by two genes, PsANTI1 and PsANTI2. PsANTI1 was constantly expressed at all developmental stages and in all tissues analyzed. In contrast, the expression levels of PsANTI2 were undetectable in first instar nymphs and adult antennae. Gene silencing of each paralogue in P. stali revealed that PsANTI1 plays an important role in homeostasis, whereas the depletion of PsANTI2 failed to result in lethality. Thus, we concluded that PsANTI1 is a good target gene for developing novel pesticides.

Discoveries, metabolic roles and diseases of mitochondrial carriers: A review

Mitochondrial carriers (MCs) are a superfamily of nuclear-encoded proteins that are mostly localized in the inner mitochondrial membrane and transport numerous metabolites, nucleotides, cofactors and inorganic anions. Their unique sequence features, i.e., a tripartite structure, six transmembrane α-helices and a three-fold repeated signature motif, allow MCs to be easily recognized. This review describes how the functions of MCs from Saccharomyces cerevisiae, Homo sapiens and Arabidopsis thaliana (listed in the first table) were discovered after the genome sequence of S. cerevisiae was determined in 1996. In the genomic era, more than 50 previously unknown MCs from these organisms have been identified and characterized biochemically using a method consisting of gene expression, purification of the recombinant proteins, their reconstitution into liposomes and transport assays (EPRA). Information derived from studies with intact mitochondria, genetic and metabolic evidence, sequence similarity, phylogenetic analysis and complementation of knockout phenotypes have guided the choice of substrates that were tested in the transport assays. In addition, the diseases associated to defects of human MCs have been briefly reviewed. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

The epigenetic processes of meiosis in male mice are broadly affected by the widely used herbicide atrazine

BACKGROUND

Environmental factors such as pesticides can cause phenotypic changes in various organisms, including mammals. We studied the effects of the widely used herbicide atrazine (ATZ) on meiosis, a key step of gametogenesis, in male mice.

METHODS

Gene expression pattern was analysed by Gene-Chip array. Genome-wide mapping of H3K4me3 marks distribution was done by ChIP-sequencing of testis tissue using Illumina technologies. RT-qPCR was used to validate differentially expressed genes or differential peaks.

RESULTS

We demonstrate that exposure to ATZ reduces testosterone levels and the number of spermatozoa in the epididymis and delays meiosis. Using Gene-Chip and ChIP-Seq analysis of H3K4me3 marks, we found that a broad range of cellular functions, including GTPase activity, mitochondrial function and steroid-hormone metabolism, are affected by ATZ. Furthermore, treated mice display enriched histone H3K4me3 marks in regions of strong recombination (double-strand break sites), within very large genes and reduced marks in the pseudoautosomal region of X chromosome.

CONCLUSIONS

Our data demonstrate that atrazine exposure interferes with normal meiosis, which affects spermatozoa production.

Incomplete meiotic sex chromosome inactivation in the domestic dog

BACKGROUND

In mammalian meiotic prophase, homologous chromosome recognition is aided by formation and repair of programmed DNA double-strand breaks (DSBs). Subsequently, stable associations form through homologous chromosome synapsis. In male mouse meiosis, the largely heterologous X and Y chromosomes synapse only in their short pseudoautosomal regions (PARs), and DSBs persist along the unsynapsed non-homologous arms of these sex chromosomes. Asynapsis of these arms and the persistent DSBs then trigger transcriptional silencing through meiotic sex chromosome inactivation (MSCI), resulting in formation of the XY body. This inactive state is partially maintained in post-meiotic haploid spermatids (postmeiotic sex chromatin repression, PSCR). For the human, establishment of MSCI and PSCR have also been reported, but X-linked gene silencing appears to be more variable compared to mouse. To gain more insight into the regulation and significance of MSCI and PSCR among different eutherian species, we have performed a global analysis of XY pairing dynamics, DSB repair, MSCI and PSCR in the domestic dog (Canis lupus familiaris), for which the complete genome sequence has recently become available, allowing a thorough comparative analyses.

RESULTS

In addition to PAR synapsis between X and Y, we observed extensive self-synapsis of part of the dog X chromosome, and rapid loss of known markers of DSB repair from that part of the X. Sequencing of RNA from purified spermatocytes and spermatids revealed establishment of MSCI. However, the self-synapsing region of the X displayed higher X-linked gene expression compared to the unsynapsed area in spermatocytes, and was post-meiotically reactivated in spermatids. In contrast, genes in the PAR, which are expected to escape MSCI, were expressed at very low levels in both spermatocytes and spermatids. Our comparative analysis was then used to identify two X-linked genes that may escape MSCI in spermatocytes, and 21 that are specifically re-activated in spermatids of human, mouse and dog.

CONCLUSIONS

Our data indicate that MSCI is incomplete in the dog. This may be partially explained by extensive, but transient, self-synapsis of the X chromosome, in association with rapid completion of meiotic DSB repair. In addition, our comparative analysis identifies novel candidate male fertility genes.

Two adenine nucleotide translocase paralogues involved in cell proliferation and spermatogenesis in the silkworm Bombyx mori

Mitochondrial adenine nucleotide translocase (ANT) specifically acts in ADP/ATP exchange through the mitochondrial inner membrane. This transporter protein thereby plays a significant role in energy metabolism in eukaryotic cells. Most mammals have four paralogous ANT genes (ANT1-4) and utilize these paralogues in different types of cells. The fourth paralogue of ANT (ANT4) is present only in mammals and reptiles and is exclusively expressed in testicular germ cells where it is required for meiotic progression in the spermatocytes. Here, we report that silkworms harbor two ANT paralogues, the homeostatic paralogue (BmANTI1) and the testis-specific paralogue (BmANTI2). The BmANTI2 protein has an N-terminal extension in which the positions of lysine residues in the amino acid sequence are distributed as in human ANT4. An expression analysis showed that BmANTI2 transcripts were restricted to the testis, suggesting the protein has a role in the progression of spermatogenesis. By contrast, BmANTI1 was expressed in all tissues tested, suggesting it has an important role in homeostasis. We also observed that cultured silkworm cells required BmANTI1 for proliferation. The ANTI1 protein of the lepidopteran Plutella xylostella (PxANTI1), but not those of other insect species (or PxANTI2), restored cell proliferation in BmANTI1-knockdown cells suggesting that ANTI1 has similar energy metabolism functions across the Lepidoptera. Our results suggest that BmANTI2 is evolutionarily divergent from BmANTI1 and has developed a specific role in spermatogenesis similar to that of mammalian ANT4.

Mitochondrial ATP transporter Ant2 depletion impairs erythropoiesis and B lymphopoiesis

Adenine nucleotide translocases (ANTs) transport ADP and ATP through mitochondrial inner membrane, thus playing an essential role for energy metabolism of eukaryotic cells. Mice have three ANT paralogs, Ant1 (Slc25a4), Ant2 (Slc25a5) and Ant4 (Slc25a31), which are expressed in a tissue-dependent manner. While knockout mice have been characterized with Ant1 and Ant4 genes, which resulted in exercise intolerance and male infertility, respectively, the role of the ubiquitously expressed Ant2 gene in animal development has not been fully demonstrated. Here, we generated Ant2 hypomorphic mice by targeted disruption of the gene, in which Ant2 expression is largely depleted. The mice showed apparently normal embryonic development except pale phenotype along with a reduced birth rate. However, postnatal growth was severely retarded with macrocytic anemia, B lymphocytopenia, lactic acidosis and bloated stomach, and died within 4 weeks. Ant2 depletion caused anemia in a cell-autonomous manner by maturation arrest of erythroid precursors with increased reactive oxygen species and premature deaths. B-lymphocyte development was similarly affected by Ant2 depletion, and splenocytes showed a reduction in maximal respiration capacity and cellular ATP levels as well as an increase in cell death accompanying mitochondrial permeability transition pore opening. In contrast, myeloid, megakaryocyte and T-lymphocyte lineages remained apparently intact. Erythroid and B-cell development may be particularly vulnerable to Ant2 depletion-mediated mitochondrial dysfunction and oxidative stress.

Testicular niche required for human spermatogonial stem cell expansion

Prepubertal boys treated with high-dose chemotherapy do not have an established means of fertility preservation because no established in vitro technique exists to expand and mature purified spermatogonial stem cells (SSCs) to functional sperm in humans. In this study, we define and characterize the unique testicular cellular niche required for SSC expansion using testicular tissues from men with normal spermatogenesis. Highly purified SSCs and testicular somatic cells were isolated by fluorescence-activated cell sorting using SSEA-4 and THY1 as markers of SSCs and somatic cells. Cells were cultured on various established niches to assess their role in SSC expansion in a defined somatic cellular niche. Of all the niches examined, cells in the SSEA-4 population exclusively bound to adult testicular stromal cells, established colonies, and expanded. Further characterization of these testicular stromal cells revealed distinct mesenchymal markers and the ability to undergo differentiation along the mesenchymal lineage, supporting a testicular multipotent stromal cell origin. In vitro human SSC expansion requires a unique niche provided exclusively by testicular multipotent stromal cells with mesenchymal properties. These findings provide an important foundation for developing methods of inducing SSC growth and maturation in prepubertal testicular tissue, essential to enabling fertility preservation for these boys.

Adenine nucleotide translocase 4 is expressed within embryonic ovaries and dispensable during oogenesis

Adenine nucleotide translocase (Ant) facilitates the exchange of adenosine triphosphate across the mitochondrial inner membrane and plays a critical role for bioenergetics in eukaryotes. Mice have 3 Ant paralogs, Ant1 (Slc25a4), Ant2 (Slc25a5), and Ant4 (Slc25a31), which are expressed in a tissue-dependent manner. We previously identified that Ant4 was expressed exclusively in testicular germ cells in adult mice and essential for spermatogenesis and subsequently male fertility. Further investigation into the process of spermatogenesis revealed that Ant4 was particularly highly expressed during meiotic prophase I and indispensable for normal progression of leptotene spermatocytes to the stages thereafter. In contrast, the expression and roles of Ant4 in female germ cells have not previously been elucidated. Here, we demonstrate that the Ant4 gene is expressed during embryonic ovarian development during which meiotic prophase I occurs. We confirmed embryonic ovary-specific Ant4 expression using a bacterial artificial chromosome transgene. In contrast to male, however, Ant4 null female mice were fertile although the litter size was slightly decreased. They showed apparently normal ovarian development which was morphologically indistinguishable from the control animals. These data indicate that Ant4 is a meiosis-specific gene expressed during both male and female gametogenesis however indispensable only during spermatogenesis and not oogenesis. The differential effects of Ant4 depletion within the processes of male and female gametogenesis may be explained by meiosis-specific inactivation of the X-linked Ant2 gene in male, a somatic paralog of the Ant4 gene.

Male contraception: another Holy Grail

The idea that men should participate in family planning by playing an active role in contraception has become more acceptable in recent years. Up to the present the condom and vasectomy have been the main methods of male contraception. There have been and continue to be efforts to develop an acceptable hormonal contraceptive involving testosterone (T) suppression. However the off target affects, delivery of the analogs and the need for T replacement have proven difficult obstacles to this technology. Research into the development of non-hormonal contraception for men is progressing in several laboratories and this will be the subject of the present review. A number of promising targets for the male pill are being investigated. These involve disruption of spermatogenesis by compromising the integrity of the germinal epithelium, interfering with sperm production at the level of meiosis, attacking specific sperm proteins to disrupt fertilizing ability, or interfering with the assembly of seminal fluid components required by ejaculated sperm for acquisition of motility. Blocking contractility of the vas deferens smooth muscle vasculature to prevent ejaculation is a unique approach that prevents sperm from reaching the egg. We shall note the lack of interest by big pharma with most of the support for male contraception provided by the NIH.

Mitochondria and mammalian reproduction

Mitochondria are cellular organelles with crucial roles in ATP synthesis, metabolic integration, reactive oxygen species (ROS) synthesis and management, the regulation of apoptosis (namely via the intrinsic pathway), among many others. Additionally, mitochondria in different organs or cell types may have distinct properties that can decisively influence functional analysis. In terms of the importance of mitochondria in mammalian reproduction, and although there are species-specific differences, these aspects involve both energetic considerations for gametogenesis and fertilization, control of apoptosis to ensure the proper production of viable gametes, and ROS signaling, as well as other emerging aspects. Crucially, mitochondria are the starting point for steroid hormone biosynthesis, given that the conversion of cholesterol to pregnenolone (a common precursor for all steroid hormones) takes place via the activity of the cytochrome P450 side-chain cleavage enzyme (P450scc) on the inner mitochondrial membrane. Furthermore, mitochondrial activity in reproduction has to be considered in accordance with the very distinct strategies for gamete production in the male and female. These include distinct gonad morpho-physiologies, different types of steroids that are more prevalent (testosterone, estrogens, progesterone), and, importantly, the very particular timings of gametogenesis. While spermatogenesis is complete and continuous since puberty, producing a seemingly inexhaustible pool of gametes in a fixed environment; oogenesis involves the episodic production of very few gametes in an environment that changes cyclically. These aspects have always to be taken into account when considering the roles of any common element in mammalian reproduction.

Effects of exposure to extremely low frequency magnetic fields on spermatogenesis in adult rats

The constant exposure of modern society to extremely low frequency magnetic fields (ELF-MF) has raised considerable concerns about the potential risks to male reproduction. However, the epidemiological and experimental data remain contradictory and inconclusive. In the present study, we investigated the effects of 50 Hz ELF-MF of 500 µT applied 4 h/day, 7 days/week for 4 and 8 weeks on male reproduction, focusing on changes in spermatogenesis. Several biological endpoints related to testicular function and spermatogenesis were measured, including the following: body mass, masses of testes and epididymis, sperm count and abnormal sperm ratio in the caudal epididymis, serum testosterone level, testicular histology, frequency of 14 stages of the cycle of the seminiferous epithelium and of four stages of meiosis I, germ cell apoptosis and testicular oxidative status. No significant differences were found in the biological endpoints between the sham control and the exposed rats in either the 4- or 8-week exposure period. These negative results may result from the lack of change in serum testosterone. In conclusion, our study indicates that exposure to low intensity ELF-MF may have no adverse effects on spermatogenesis.

The mitochondrial ADP/ATP carrier (SLC25 family): pathological implications of its dysfunction

In aerobic eukaryotic cells, the high energy metabolite ATP is generated mainly within the mitochondria following the process of oxidative phosphorylation. The mitochondrial ATP is exported to the cytoplasm using a specialized transport protein, the ADP/ATP carrier, to provide energy to the cell. Any deficiency or dysfunction of this membrane protein leads to serious consequences on cell metabolism and can cause various diseases such as muscular dystrophy. Described as a decisive player in the programmed cell death, it was recently shown to play a role in cancer. The objective of this review is to summarize the current knowledge of the involvement of the ADP/ATP carrier, encoded by the SLC25A4, SLC25A5, SLC25A6 and SLC25A31 genes, in human diseases and of the efforts made at designing different model systems to study this carrier and the associated pathologies through biochemical, genetic, and structural approaches.

Identification of adenine nucleotide translocase 4 inhibitors by molecular docking

The protein adenine nucleotide translocase (ANT) is localized in the mitochondrial inner membrane and plays an essential role in transporting ADP into the mitochondrial matrix and ATP out from the matrix for cell utilization. In mammals there are four paralogous ANT genes, of which ANT4 is exclusively expressed in meiotic germ cells. Since ANT4 has been shown essential for spermatogenesis and male fertility in mice, inhibition of ANT4 appears to be a reasonable target for male contraceptive development. Further, in contrast to ANT1, ANT2 and ANT3 that are highly homologous to each other, ANT4 has a distinguishable amino acid sequence, which serves as a basis to develop a selective ANT4 inhibitor. In this study, we aimed to identify candidate compounds that can selectively inhibit ANT4 activity over the other ANTs. We used a structure-based method in which ANT4 was modeled then utilized as the basis for selection of compounds that interact with sites unique to ANT4. A large chemical library (>100,000 small molecules) was screened by molecular docking and effects of these compounds on ADP/ATP exchange through ANT4 were examined using yeast mitochondria expressing human ANT4. Through this, we identified one particular candidate compound, [2,2'-methanediylbis(4-nitrophenol)], which inhibits ANT4 activity with a lower IC50 than the other ANTs (5.8 μM, 4.1 μM, 5.1 μM and 1.4 μM for ANT1, 2, 3 and 4, respectively). This newly identified active lead compound and its chemical structure are expected to provide new opportunities to optimize selective ANT4 inhibitors for contraceptive purposes.

Exposure to bisphenol A disrupts meiotic progression during spermatogenesis in adult rats through estrogen-like activity

The effect of bisphenol A (BPA) on the reproductive system is highly debated but has been associated with meiotic abnormalities. However, evidence is lacking with regard to the mechanisms involved. In order to explore the underlying mechanisms of BPA-induced meiotic abnormalities in adult male rats, we exposed 9-week-old male Wistar rats to BPA by gavage at 0, 2, 20 or 200 μg/kg body weight (bw)/day for 60 consecutive days. 17β-Estradiol (E2) was administered at 10 μg/kg bw/day as the estrogenic positive control. Treatments with 200 μg/kg bw/day of BPA and E2 significantly decreased sperm counts and inhibited spermiation, characterized by an increase in stage VII and decrease in stage VIII in the seminiferous epithelium. This was concomitant with a disruption in the progression of meiosis I and the persistence of meiotic DNA strand breaks in pachytene spermatocytes,and the ataxia-telangiectasia-mutated and checkpoint kinase 2 signal pathway was also activated; Eventually, germ cell apoptosis was triggered as evaluated by terminal dUTP nick-end labeling assay and western blot for caspase 3. Using the estrogen receptor (ER) antagonist ICI 182780, we determined that ER signaling mediated BPA-induced meiotic disruption and reproductive impairment. Our results suggest that ER signaling-mediated meiotic disruption may be a major contributor to the molecular events leading to BPA-related male reproductive disorders. These rodent data support the growing association between BPA exposure and the rapid increase in the incidence of male reproductive disorders.

The mitochondrial transporter family SLC25: identification, properties and physiopathology

SLC25 is a large family of nuclear-encoded transporters embedded in the inner mitochondrial membrane and in a few cases other organelle membranes. The members of this superfamily are widespread in eukaryotes and involved in numerous metabolic pathways and cell functions. They can be easily recognized by their striking sequence features, i.e., a tripartite structure, six transmembrane α-helices and a 3-fold repeated signature motifs. SLC25 members vary greatly in the nature and size of their transported substrates, modes of transport (i.e., uniport, symport or antiport) and driving forces, although the molecular mechanism of substrate translocation may be basically the same. Based on substrate specificity, 24 subfamilies, well conserved throughout evolution, have been functionally characterized mainly by transport assays upon heterologous gene expression, purification and reconstitution into liposomes. Several other SLC25 family members remain to be characterized. In recent years mutations in the SLC25 genes have been shown to be responsible for 11 diseases, highlighting the important role of SLC25 in metabolism.

SCaMC-1Like a member of the mitochondrial carrier (MC) family preferentially expressed in testis and localized in mitochondria and chromatoid body

Mitochondrial carriers (MC) form a highly conserved family involved in solute transport across the inner mitochondrial membrane in eukaryotes. In mammals, ATP-Mg/Pi carriers, SCaMCs, form the most complex subgroup with four paralogs, SCaMC-1, -2, -3 and -3L, and several splicing variants. Here, we report the tissue distribution and subcellular localization of a mammalian-specific SCaMC paralog, 4930443G12Rik/SCaMC-1Like (SCaMC-1L), which displays unanticipated new features. SCaMC-1L proteins show higher amino acid substitution rates than its closest paralog SCaMC-1. In mouse, SCaMC-1L expression is restricted to male germ cells and regulated during spermatogenesis but unexpectedly its localization is not limited to mitochondrial structures. In mature spermatids SCaMC-1L is detected in the mitochondrial sheath but in previous differentiation stages appears associated to cytosolic granules which colocalize with specific markers of the chromatoid body (CB) in post-meiotic round spermatids and inter-mitochondrial cement (IMC) in spermatocytes. The origin of this atypical distribution was further investigated by transient expression in cell lines. Similarly to male germ cells, in addition to mitochondrial and cytosolic distribution, a fraction of SCaMC-1L-expressing COS-7 cells display cytosolic SCaMC-1L-aggregates which exhibit aggresomal-like features as the CB. Our results indicate that different regions of SCaMC-1L hinder its import into mitochondria and this apparently favours the formation of cytosolic aggregates in COS-7 cells. This mechanism could be also operational in male germ cells and explain the incorporation of SCaMC-1L into germinal granules.

Evolutionary genomics implies a specific function of Ant4 in mammalian and anole lizard male germ cells

Most vertebrates have three paralogous genes with identical intron-exon structures and a high degree of sequence identity that encode mitochondrial adenine nucleotide translocase (Ant) proteins, Ant1 (Slc25a4), Ant2 (Slc25a5) and Ant3 (Slc25a6). Recently, we and others identified a fourth mammalian Ant paralog, Ant4 (Slc25a31), with a distinct intron-exon structure and a lower degree of sequence identity. Ant4 was expressed selectively in testis and sperm in adult mammals and was indeed essential for mouse spermatogenesis, but it was absent in birds, fish and frogs. Since Ant2 is X-linked in mammalian genomes, we hypothesized that the autosomal Ant4 gene may compensate for the loss of Ant2 gene expression during male meiosis in mammals. Here we report that the Ant4 ortholog is conserved in green anole lizard (Anolis carolinensis) and demonstrate that it is expressed in the anole testis. Further, a degenerate DNA fragment of putative Ant4 gene was identified in syntenic regions of avian genomes, indicating that Ant4 was present in the common amniote ancestor. Phylogenetic analyses suggest an even more ancient origin of the Ant4 gene. Although anole lizards are presumed male (XY) heterogametic, like mammals, copy numbers of the Ant2 as well as its neighboring gene were similar between male and female anole genomes, indicating that the anole Ant2 gene is either autosomal or located in the pseudoautosomal region of the sex chromosomes, in contrast to the case to mammals. These results imply the conservation of Ant4 is not likely simply driven by the sex chromosomal localization of the Ant2 gene and its subsequent inactivation during male meiosis. Taken together with the fact that Ant4 protein has a uniquely conserved structure when compared to other somatic Ant1, 2 and 3, there may be a specific advantage for mammals and lizards to express Ant4 in their male germ cells.

Computational analysis of the transcriptional regulation of the adenine nucleotide translocator isoform 4 gene and its role in spermatozoid glycolytic metabolism

Computational phylogenetic analysis coupled to promoter sequence alignment was used to understand mechanisms of transcriptional regulation and to identify potentially coregulated genes. Our strategy was validated on the human ANT4 gene which encodes the fourth isoform of the mitochondrial adenine nucleotide translocator specifically expressed during spermatogenesis. The movement of sperm flagella is driven mainly by ATP generated by glycolytic pathways, and the specific induction of the mitochondrial ANT4 protein presented an interesting puzzle. We analysed the sequences of the promoters, introns and exons of 30 mammalian ANT4 genes and constructed regulatory models. The whole human genome and promoter database were screened for genes that were potentially regulated by the generated models. 80% of the identified co-regulated genes encoded proteins with specific roles in spermatogenesis and with functions linked to male reproduction. Our in silico study enabled us to precise the specific role of the ANT4 isoform in spermatozoid bioenergetics.

Lactate dehydrogenase C and energy metabolism in mouse sperm

We demonstrated previously that disruption of the germ cell-specific lactate dehydrogenase C gene (Ldhc) led to male infertility due to defects in sperm function, including a rapid decline in sperm ATP levels, a decrease in progressive motility, and a failure to develop hyperactivated motility. We hypothesized that lack of LDHC disrupts glycolysis by feedback inhibition, either by causing a defect in renewal of the NAD(+) cofactor essential for activity of glyceraldehyde 3-phosphate dehydrogenase, sperm (GAPDHS), or an accumulation of pyruvate. To test these hypotheses, nuclear magnetic resonance analysis was used to follow the utilization of labeled substrates in real time. We found that in sperm lacking LDHC, glucose consumption was disrupted, but the NAD:NADH ratio and pyruvate levels were unchanged, and pyruvate was rapidly metabolized to lactate. Moreover, the metabolic disorder induced by treatment with the lactate dehydrogenase (LDH) inhibitor sodium oxamate was different from that caused by lack of LDHC. This supported our earlier conclusion that LDHA, an LDH isozyme present in the principal piece of the flagellum, is responsible for the residual LDH activity in sperm lacking LDHC, but suggested that LDHC has an additional role in the maintenance of energy metabolism in sperm. By coimmunoprecipitation coupled with mass spectrometry, we identified 27 proteins associated with LDHC. A majority of these proteins are implicated in ATP synthesis, utilization, transport, and/or sequestration. This led us to hypothesize that in addition to its role in glycolysis, LDHC is part of a complex involved in ATP homeostasis that is disrupted in sperm lacking LDHC.

Functional expression of human adenine nucleotide translocase 4 in Saccharomyces cerevisiae

The adenine nucleotide translocase (ANT) mediates the exchange of ADP and ATP across the inner mitochondrial membrane. The human genome encodes multiple ANT isoforms that are expressed in a tissue-specific manner. Recently a novel germ cell-specific member of the ANT family, ANT4 (SLC25A31) was identified. Although it is known that targeted depletion of ANT4 in mice resulted in male infertility, the functional biochemical differences between ANT4 and other somatic ANT isoforms remain undetermined. To gain insight into ANT4, we expressed human ANT4 (hANT4) in yeast mitochondria. Unlike the somatic ANT proteins, expression of hANT4 failed to complement an AAC-deficient yeast strain for growth on media requiring mitochondrial respiration. Moreover, overexpression of hANT4 from a multi-copy plasmid interfered with optimal yeast growth. However, mutation of specific amino acids of hANT4 improved yeast mitochondrial expression and supported growth of the AAC-deficient yeast on non-fermentable carbon sources. The mutations affected amino acids predicted to interact with phospholipids, suggesting the importance of lipid interactions for function of this protein. Each mutant hANT4 and the somatic hANTs exhibited similar ADP/ATP exchange kinetics. These data define common and distinct biochemical characteristics of ANT4 in comparison to ANT1, 2 and 3 providing a basis for study of its unique adaptation to germ cells.

Drug transporters, the blood-testis barrier, and spermatogenesis

The blood-testis barrier (BTB), which is created by adjacent Sertoli cells near the basement membrane, serves as a 'gatekeeper' to prohibit harmful substances from reaching developing germ cells, most notably postmeiotic spermatids. The BTB also divides the seminiferous epithelium into the basal and adluminal (apical) compartment so that postmeiotic spermatid development, namely spermiogenesis, can take place in a specialized microenvironment in the apical compartment behind the BTB. The BTB also contributes, at least in part, to the immune privilege status of the testis, so that anti-sperm antibodies are not developed against antigens that are expressed transiently during spermatogenesis. Recent studies have shown that numerous drug transporters are expressed by Sertoli cells. However, many of these same drug transporters are also expressed by spermatogonia, spermatocytes, round spermatids, elongating spermatids, and elongated spermatids, suggesting that the developing germ cells are also able to selectively pump drugs 'in' and/or 'out' via influx or efflux pumps. We review herein the latest developments regarding the role of drug transporters in spermatogenesis. We also propose a model utilized by the testis to protect germ cell development from 'harmful' environmental toxicants and xenobiotics and/or from 'therapeutic' substances (e.g. anticancer drugs). We also discuss how drug transporters that are supposed to protect spermatogenesis can work against the testis in some instances. For example, when drugs (e.g. male contraceptives) that can perturb germ cell adhesion and/or maturation are actively pumped out of the testis or are prevented from entering the apical compartment, such as by efflux pumps.

Adenine nucleotide translocase family: four isoforms for apoptosis modulation in cancer

Mitochondria have important functions in mammalian cells as the energy powerhouse and integrators of the mitochondrial pathway of apoptosis. The adenine nucleotide translocase (ANT) is a family of proteins involved in cell death pathways that perform distinctly opposite functions to regulate cell fate decisions. On the one hand, ANT catalyzes the adenosine triphosphate export from the mitochondrial matrix to the intermembrane space with the concomitant import of ADP from the intermembrane space to the matrix. On the other hand, during periods of stress, ANT could function as a lethal pore and trigger the process of mitochondrial membrane permeabilization, which leads irreversibly to cell death. In human, ANT is encoded by four homologous genes, whose expression is not only tissue specific, but also varies according to the pathophysiological state of the cell. Recent evidence revealed a differential role of the ANT isoforms in apoptosis and a deregulation of their expression in cancer. In this review, we introduce the current knowledge of ANT in apoptosis and cancer cells and propose a novel classification of ANT isoforms.

Dnmt3b recruitment through E2F6 transcriptional repressor mediates germ-line gene silencing in murine somatic tissues

Methylation of cytosine residues within the CpG dinucleotide in mammalian cells is an important mediator of gene expression, genome stability, X-chromosome inactivation, genomic imprinting, chromatin structure, and embryonic development. The majority of CpG sites in mammalian cells is methylated in a nonrandom fashion, raising the question of how DNA methylation is distributed along the genome. Here, we focused on the functions of DNA methyltransferase-3b (Dnmt3b), of which deregulated activity is linked to several human pathologies. We generated Dnmt3b hypomorphic mutant mice with reduced catalytic activity, which first revealed a deregulation of Hox genes expression, consistent with the observed homeotic transformations of the posterior axis. In addition, analysis of deregulated expression programs in Dnmt3b mutant embryos, using DNA microarrays, highlighted illegitimate activation of several germ-line genes in somatic tissues that appeared to be linked directly to their hypomethylation in mutant embryos. We provide evidence that these genes are direct targets of Dnmt3b. Moreover, the recruitment of Dnmt3b to their proximal promoter is dependant on the binding of the E2F6 transcriptional repressor, which emerges as a common hallmark in the promoters of genes found to be up-regulated as a consequence of impaired Dnmt3b activity. Therefore, our results unraveled a coordinated regulation of genes involved in meiosis, through E2F6-dependant methylation and transcriptional silencing in somatic tissues.