Isodicentric Y chromosomes and sex disorders as byproducts of homologous recombination that maintains palindromes.

Massive palindromes in the human Y chromosome harbor mirror-image gene pairs essential for spermatogenesis. During evolution, these gene pairs have been maintained by intrapalindrome, arm-to-arm recombination. The mechanism of intrapalindrome recombination and risk of harmful effects are unknown. We report 51 patients with isodicentric Y (idicY) chromosomes formed by homologous crossing over between opposing arms of palindromes on sister chromatids. These ectopic recombination events occur at nearly all Y-linked palindromes. Based on our findings, we propose that intrapalindrome sequence identity is maintained via noncrossover pathways of homologous recombination. DNA double-strand breaks that initiate these pathways can be alternatively resolved by crossing over between sister chromatids to form idicY chromosomes, with clinical consequences ranging from spermatogenic failure to sex reversal and Turner syndrome. Our observations imply that crossover and noncrossover pathways are active in nearly all Y-linked palindromes, exposing an Achilles' heel in the mechanism that preserves palindrome-borne genes.

Distinct prophase arrest mechanisms in human male meiosis.

To prevent chromosomal aberrations being transmitted to the offspring, strict meiotic checkpoints are in place to remove aberrant spermatocytes. However, in about 1% of males these checkpoints cause complete meiotic arrest leading to azoospermia and subsequent infertility. Here, we unravel two clearly distinct meiotic arrest mechanisms that occur during prophase of human male meiosis. Type I arrested spermatocytes display severe asynapsis of the homologous chromosomes, disturbed XY-body formation and increased expression of the Y chromosome-encoded gene ZFY and seem to activate a DNA damage pathway leading to induction of p63, possibly causing spermatocyte apoptosis. Type II arrested spermatocytes display normal chromosome synapsis, normal XY-body morphology and meiotic crossover formation but have a lowered expression of several cell cycle regulating genes and fail to silence the X chromosome-encoded gene ZFX Discovery and understanding of these meiotic arrest mechanisms increases our knowledge of how genomic stability is guarded during human germ cell development.

Strains matter: Success of murine in vitro spermatogenesis is dependent on genetic background.

The current strategy to preserve fertility of male prepubertal cancer patients consists of cryopreservation of a testicular tissue biopsy containing spermatogonial stem cells (SSCs). While in humans, fertility restoration strategies from prepubertal testicular tissues are still under investigation and have not yet resulted in complete germ cell differentiation, in mice various studies have described production of sperm and offspring through testicular organ culture and transplantation of in vitro propagated SSCs. Organ culture has shown to be successful in generating mature spermatozoa when using testicular fragments from various mouse strains, including CD1 and C57BL/6 J. Conversely, in vitro proliferation of SSCs from C57BL/6 J mice is highly inefficient when compared to other strains such as DBA2 or hybrid mice of C57BL/6 J and DBA2 with 75% C57BL/6 J background (B6D2F2). In this study, we investigated in vitro spermatogenesis by organ culture using testicular tissue from C57BL/6 J and B6D2F2 mice. Whereas spermatogenesis was initiated and completed in C57BL/6 J fragments, it could not be effectively supported in B6D2F2 testicular tissue. While maturation of Sertoli cells and Leydig cells functionality appeared to be identical between the two strains, in B6D2F2 tissue spermatogenesis did not proceed past the spermatocyte step, followed by a rapid decline of the number of all germ cells in the fragments. This suggests that the spermatogenic potential in vitro is dependent on specialized sites in the genome and therefore the organ culture conditions suboptimal for some strains of mice.

Comparison of DNA methylation patterns of parentally imprinted genes in placenta derived from IVF conceptions in two different culture media.

STUDY QUESTION: Is there a difference in DNA methylation status of imprinted genes in placentas derived from IVF conceptions where embryo culture was performed in human tubal fluid (HTF) versus G5 culture medium? SUMMARY ANSWER: We found no statistically significant differences in the mean DNA methylation status of differentially methylated regions (DMRs) associated with parentally imprinted genes in placentas derived from IVF conceptions cultured in HTF versus G5 culture medium. WHAT IS KNOWN ALREADY: Animal studies indicate that the embryo culture environment affects the DNA methylation status of the embryo. In humans, birthweight is known to be affected by the type of embryo culture medium used. The effect of embryo culture media on pregnancy, birth and child development may thus be mediated by differential methylation of parentally imprinted genes in the placenta. STUDY DESIGN, SIZE, DURATION: To identify differential DNA methylation of imprinted genes in human placenta derived from IVF conceptions exposed to HTF or G5 embryo culture medium, placenta samples (n = 43 for HTF, n = 54 for G5) were collected between 2010 and 2012 s as part of a multi-center randomized controlled trial in the Netherlands comparing these embryo culture media. Placenta samples from 69 naturally conceived (NC) live births were collected during 2008-2013 in the Netherlands as reference material. PARTICIPANTS/MATERIALS, SETTING, METHODS: To identify differential DNA methylation of imprinted genes, we opted for an amplicon-based sequencing strategy on an Illumina MiSeq sequencing platform. DNA was isolated and 34 DMRs associated with well-defined parentally imprinted genes were amplified in a two-step PCR before sequencing using MiSeq technology. Sequencing data were analyzed in a multivariate fashion to eliminate possible confounding effects. MAIN RESULTS AND THE ROLE OF CHANCE: We found no statistically significant differences in the mean DNA methylation status of any of the imprinted DMRs in placentas derived from IVF conceptions cultured in HTF or G5 culture medium. We also did not observe any differences in the mean methylation status per amplicon nor in the variance in methylation per amplicon between the two culture medium.groups. A separate surrogate variable analysis also demonstrated that the IVF culture medium was not associated with the DNA methylation status of these DMRs. The mean methylation level and variance per CpG was equal between HTF and G5 placenta. Additional comparison of DNA methylation status of NC placenta samples revealed no statistically significant differences in mean amplicon and CpG methylation between G5, HTF and NC placenta; however, the number of placenta samples exhibiting outlier methylation levels was higher in IVF placenta compared to NC (P < 0.00001). Also, we were able to identify 37 CpG sites that uniquely displayed outlier methylation in G5 placentas and 32 CpG sites that uniquely displayed outlier methylation in HTF. In 8/37 (G5) and 4/32 (HTF) unique outliers CpGs, a medium-specific unique outlier could be directly correlated to outlier methylation of the entire amplicon. LIMITATIONS, REASONS FOR CAUTION: Due to practical reasons, not all placentas were collected during the trial, and we collected the placentas from natural conceptions from a different cohort, potentially creating bias. We limited ourselves to the DNA methylation status of 34 imprinted DMRs, and we studied only the placenta and no other embryo-derived tissues. WIDER IMPLICATIONS OF THE FINDINGS: It has often been postulated, but has yet to be rigorously tested, that imprinting mediates the effects of embryo culture conditions on pregnancy, birth and child development in humans. Since we did not detect any statistically significant effects of embryo culture conditions on methylation status of imprinted genes in the placenta, this suggests that other unexplored mechanisms may underlie these effects. The biological and clinical relevance of detected outliers with respect to methylation levels of CpGs and DMR require additional analysis in a larger sample size as well. Given the importance and the growing number of children born through IVF, research into these molecular mechanisms is urgently needed. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the March of Dimes grant number #6-FY13-153. The authors have no conflicts of interest. TRIAL REGISTRATION NUMBER: Placental biopsies were obtained under Netherlands Trial Registry number 1979 and 1298.

ITGA6+ Human Testicular Cell Populations Acquire a Mesenchymal Rather than Germ Cell Transcriptional Signature during Long-Term Culture.

Autologous spermatogonial stem cell transplantation is an experimental technique aimed at restoring fertility in infertile men. Although effective in animal models, in vitro propagation of human spermatogonia prior to transplantation has proven to be difficult. A major limiting factor is endogenous somatic testicular cell overgrowth during long-term culture. This makes the culture both inefficient and necessitates highly specific cell sorting strategies in order to enrich cultured germ cell fractions prior to transplantation. Here, we employed RNA-Seq to determine cell type composition in sorted integrin alpha-6 (ITGA6+) primary human testicular cells (n = 4 donors) cultured for up to two months, using differential gene expression and cell deconvolution analyses. Our data and analyses reveal that long-term cultured ITGA6+ testicular cells are composed mainly of cells expressing markers of peritubular myoid cells, (progenitor) Leydig cells, fibroblasts and mesenchymal stromal cells and only a limited percentage of spermatogonial cells as compared to their uncultured counterparts. These findings provide valuable insights into the cell type composition of cultured human ITGA6+ testicular cells during in vitro propagation and may serve as a basis for optimizing future cell sorting strategies as well as optimizing the current human testicular cell culture system for clinical use.

Long-term health in recipients of transplanted in vitro propagated spermatogonial stem cells.

STUDY QUESTION: Is testicular transplantation of in vitro propagated spermatogonial stem cells associated with increased cancer incidence and decreased survival rates in recipient mice? SUMMARY ANSWER: Cancer incidence was not increased and long-term survival rate was not altered after transplantation of in vitro propagated murine spermatogonial stem cells (SSCs) in busulfan-treated recipients as compared to non-transplanted busulfan-treated controls. WHAT IS KNOWN ALREADY: Spermatogonial stem cell autotransplantation (SSCT) is a promising experimental reproductive technique currently under development to restore fertility in male childhood cancer survivors. Most preclinical studies have focused on the proof-of-principle of the functionality and efficiency of this technique. The long-term health of recipients of SSCT has not been studied systematically. STUDY DESIGN, SIZE, DURATION: This study was designed as a murine equivalent of a clinical prospective study design. Long-term follow-up was performed for mice who received a busulfan treatment followed by either an intratesticular transplantation of in vitro propagated enhanced green fluorescent protein (eGFP) positive SSCs (cases, n = 34) or no transplantation (control, n = 37). Using a power calculation, we estimated that 36 animals per group would be sufficient to provide an 80% power and with a 5% level of significance to demonstrate a 25% increase in cancer incidence in the transplanted group. The survival rate and cancer incidence was investigated until the age of 18 months. PARTICIPANTS/MATERIALS, SETTING, METHODS: Neonatal male B6D2F1 actin-eGFP transgenic mouse testis were used to initiate eGFP positive germline stem (GS) cell culture, which harbor SSCs. Six-week old male C57BL/6 J mice received a single dose busulfan treatment to deplete the testis from endogenous spermatogenesis. Half of these mice received a testicular transplantation of cultured eGFP positive GS cells, while the remainder of mice served as a control group. Mice were followed up until the age of 18 months (497-517 days post-busulfan) or sacrificed earlier due to severe discomfort or illness. Survival data were collected. To evaluate cancer incidence a necropsy was performed and tissues were collected. eGFP signal in transplanted testis and in benign and malignant lesions was assessed by standard PCR. MAIN RESULTS AND THE ROLE OF CHANCE: We found 9% (95% CI: 2-25%) malignancies in the transplanted busulfan-treated animals compared to 26% (95% CI: 14-45%) in the busulfan-treated control group, indicating no statistically significant difference in incidence of malignant lesions in transplanted and control mice (OR: 0.3, 95% CI: 0.1-1.1). Furthermore, none of the malignancies that arose in the transplanted animals contained eGFP signal, suggesting that they are not derived from the in vitro propagated transplanted SSCs. Mean survival time after busulfan treatment was found to be equal, with a mean survival time for transplanted animals of 478 days and 437 days for control animals (P = 0.076). LARGE SCALE DATA: NA. LIMITATIONS, REASONS FOR CAUTION: Although we attempted to mimic the future clinical application of SSCT in humans as close as possible, the mouse model that we used might not reflect all aspects of the future clinical setting. WIDER IMPLICATIONS OF THE FINDINGS: The absence of an increase in cancer incidence and a decrease in survival of mice that received a testicular transplantation of in vitro propagated SSCs is reassuring in light of the future clinical application of SSCT in humans. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by KiKa (Kika86) and ZonMw (TAS 116003002). The authors report no financial or other conflict of interest relevant to the subject of this article.

Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content.

The human Y chromosome began to evolve from an autosome hundreds of millions of years ago, acquiring a sex-determining function and undergoing a series of inversions that suppressed crossing over with the X chromosome. Little is known about the recent evolution of the Y chromosome because only the human Y chromosome has been fully sequenced. Prevailing theories hold that Y chromosomes evolve by gene loss, the pace of which slows over time, eventually leading to a paucity of genes, and stasis. These theories have been buttressed by partial sequence data from newly emergent plant and animal Y chromosomes, but they have not been tested in older, highly evolved Y chromosomes such as that of humans. Here we finished sequencing of the male-specific region of the Y chromosome (MSY) in our closest living relative, the chimpanzee, achieving levels of accuracy and completion previously reached for the human MSY. By comparing the MSYs of the two species we show that they differ radically in sequence structure and gene content, indicating rapid evolution during the past 6 million years. The chimpanzee MSY contains twice as many massive palindromes as the human MSY, yet it has lost large fractions of the MSY protein-coding genes and gene families present in the last common ancestor. We suggest that the extraordinary divergence of the chimpanzee and human MSYs was driven by four synergistic factors: the prominent role of the MSY in sperm production, 'genetic hitchhiking' effects in the absence of meiotic crossing over, frequent ectopic recombination within the MSY, and species differences in mating behaviour. Although genetic decay may be the principal dynamic in the evolution of newly emergent Y chromosomes, wholesale renovation is the paramount theme in the continuing evolution of chimpanzee, human and perhaps other older MSYs.

High mutation rates have driven extensive structural polymorphism among human Y chromosomes.

Although much structural polymorphism in the human genome has been catalogued, the kinetics of underlying change remain largely unexplored. Because human Y chromosomes are clonally inherited, it has been possible to capture their detailed relationships in a robust, worldwide genealogical tree. Examination of structural variation across this tree opens avenues for investigating rates of underlying mutations. We selected one Y chromosome from each of 47 branches of this tree and searched for large-scale variation. Four chromosomal regions showed extensive variation resulting from numerous large-scale mutations. Within the tree encompassed by the studied chromosomes, the distal-Yq heterochromatin changed length > or = 12 times, the TSPY gene array changed length > or = 23 times, the 3.6-Mb IR3/IR3 region changed orientation > or = 12 times and the AZFc region was rearranged > or = 20 times. After determining the total time spanned by all branches of this tree (approximately 1.3 million years or 52,000 generations), we converted these mutation counts to lower bounds on rates: > or = 2.3 x 10(-4), > or = 4.4 x 10(-4), > or = 2.3 x 10(-4) and > or = 3.8 x 10(-4) large-scale mutations per father-to-son Y transmission, respectively. Thus, high mutation rates have driven extensive structural polymorphism among human Y chromosomes. At the same time, we found limited variation in the copy number of Y-linked genes, which raises the possibility of selective constraints.

Intrachromosomal homologous recombination between inverted amplicons on opposing Y-chromosome arms.

Amplicons--large, nearly identical repeats in direct or inverted orientation--are abundant in the male-specific region of the human Y chromosome (MSY) and provide targets for intrachromosomal non-allelic homologous recombination (NAHR). Thus far, NAHR events resulting in deletions, duplications, inversions, or isodicentric chromosomes have been reported only for amplicon pairs located exclusively on the short arm (Yp) or the long arm (Yq). Here we report our finding of four men with Y chromosomes that evidently formed by intrachromosomal NAHR between inverted repeat pairs comprising one amplicon on Yp and one amplicon on Yq. In two men with spermatogenic failure, sister-chromatid crossing-over resulted in pseudoisoYp chromosome formation and loss of distal Yq. In two men with normal spermatogenesis, intrachromatid crossing-over generated pericentric inversions. These findings highlight the recombinogenic nature of the MSY, as intrachromosomal NAHR occurs for nearly all Y-chromosome amplicon pairs, even those located on opposing chromosome arms.

Gene copy number reduction in the azoospermia factor c (AZFc) region and its effect on total motile sperm count.

The azoospermia factor c (AZFc) region harbors multi-copy genes that are expressed in the testis. Deletions of the AZFc region lead to reduced copy numbers of these genes. Four (partial) AZFc deletions have been described of which the b2/b4 and gr/gr deletions affect semen quality. In most studies, (partial) AZFc deletions are identified and characterized using plus/minus sequence site tag (STS) polymerase chain reaction (PCR). However, secondary duplications increase the gene copy number without re-introducing the STS boundary marker. Consequently, the actual copy number of AZFc genes cannot be determined via STS PCR. In the current study, we first set out to determine by quantitative real-time PCR the actual copy number of all AZFc genes in men with (partial) AZFc deletions based on STS PCR. We then analyzed whether reduced gene copy numbers of each AZFc gene family were associated with reduced total motile sperm count (TMC), regardless of the type of deletion. We screened 840 men and identified 31 unrelated men with (partial) deletions of AZFc based on STS PCR. Of these 31 men, 6 men (19%) had one or more secondary duplications. For all AZFc genes, we found an association between a reduction in the copy number of each individual AZFc gene and reduced TMC. In gr/gr-deleted men, restoration of reduced gene copy numbers restored their TMC to normal values. Our findings suggest that the gene content of the AZFc region has been preserved throughout evolution through a dosage effect of the AZFc genes on TMC safeguarding male fertility.

Polymorphism for a 1.6-Mb deletion of the human Y chromosome persists through balance between recurrent mutation and haploid selection.

Many human Y-chromosomal deletions are thought to severely impair reproductive fitness, which precludes their transmission to the next generation and thus ensures their rarity in the population. Here we report a 1.6-Mb deletion that persists over generations and is sufficiently common to be considered a polymorphism. We hypothesized that this deletion might affect spermatogenesis because it removes almost half of the Y chromosome's AZFc region, a gene-rich segment that is critical for sperm production. An association study established that this deletion, called gr/gr, is a significant risk factor for spermatogenic failure. The gr/gr deletion has far lower penetrance with respect to spermatogenic failure than previously characterized Y-chromosomal deletions; it is often transmitted from father to son. By studying the distribution of gr/gr-deleted chromosomes across the branches of the Y chromosome's genealogical tree, we determined that this deletion arose independently at least 14 times in human history. We suggest that the existence of this deletion as a polymorphism reflects a balance between haploid selection, which culls gr/gr-deleted Y chromosomes from the population, and homologous recombination, which continues to generate new gr/gr deletions.

Sperm DNA methylation is predominantly stable in mice offspring born after transplantation of long-term cultured spermatogonial stem cells.

BACKGROUND: Spermatogonial stem cell transplantation (SSCT) is proposed as a fertility therapy for childhood cancer survivors. SSCT starts with cryopreserving a testicular biopsy prior to gonadotoxic treatments such as cancer treatments. When the childhood cancer survivor reaches adulthood and desires biological children, the biopsy is thawed and SSCs are propagated in vitro and subsequently auto-transplanted back into their testis. However, culturing stress during long-term propagation can result in epigenetic changes in the SSCs, such as DNA methylation alterations, and might be inherited by future generations born after SSCT. Therefore, SSCT requires a detailed preclinical epigenetic assessment of the derived offspring before this novel cell therapy is clinically implemented. With this aim, the DNA methylation status of sperm from SSCT-derived offspring, with in vitro propagated SSCs, was investigated in a multi-generational mouse model using reduced-representation bisulfite sequencing. RESULTS: Although there were some methylation differences, they represent less than 0.5% of the total CpGs and methylated regions, in all generations. Unsupervised clustering of all samples showed no distinct grouping based on their pattern of methylation differences. After selecting the few single genes that are significantly altered in multiple generations of SSCT offspring compared to control, we validated the results with quantitative Bisulfite Sanger sequencing and RT-qPCRin various organs. Differential methylation was confirmed only for Tal2, being hypomethylated in sperm of SSCT offspring and presenting higher gene expression in ovaries of SSCT F1 offspring compared to control F1. CONCLUSIONS: We found no major differences in DNA methylation between SSCT-derived offspring and control, both in F1 and F2 sperm. The reassuring outcomes from our study are a prerequisite for promising translation of SSCT to the human situation.

A comparative analysis of human adult testicular cells expressing stem Leydig cell markers in the interstitium, vasculature, and peritubular layer.

BACKGROUND: Origin of human adult Leydig cells (ALCs) is not well understood. This might be partly due to limited data available on the identification and location of human precursor and stem Leydig cells (SLCs) which hampers the study on the development of ALCs. OBJECTIVES: The aim of the present study was to investigate whether described human (PDGFRα, NGFR) and rodent (NES, PDGFRα, THY1, NR2F2) SLC markers are expressed by a common cell population within human adult testicular interstitial cells in vivo and before and after in vitro propagation. MATERIALS AND METHODS: Immunohistochemical analyses were used to identify localization of human adult testicular interstitial cells expressing described SLC markers. Next, interstitial cells were isolated and cultured. The percentage of cells expressing one or more SLC markers was determined before and after culture using flow cytometry. RESULTS: NR2F2 and PDGFRα were present in peritubular, perivascular, and Leydig cells, while THY1 was expressed in peritubular and perivascular cells. Although NES and NGFR were expressed in endothelial cells, co-localization with PDGFRα was found for both in vitro, although for NGFR only after culture. All marker positive cells were able to undergo propagation in vitro. DISCUSSION: The partly overlap in localization and overlap in expression in human testicular cells indicate that PDGFRα, NR2F2, and THY1 are expressed within the same ALC developmental lineage from SLCs. Based on the in vitro results, this is also true for NES and after in vitro propagation for NGFR. CONCLUSION: Our results that earlier described SLC markers are expressed in overlapping human interstitial cell population opens up further research strategies aiming for a better insight in the Leydig cell lineage and will be helpful for development of strategies to cure ALC dysfunction.

Propagation of human spermatogonial stem cells in vitro.

CONTEXT: Young boys treated with high-dose chemotherapy are often confronted with infertility once they reach adulthood. Cryopreserving testicular tissue before chemotherapy and autotransplantation of spermatogonial stem cells at a later stage could theoretically allow for restoration of fertility. OBJECTIVE: To establish in vitro propagation of human spermatogonial stem cells from small testicular biopsies to obtain an adequate number of cells for successful transplantation. DESIGN, SETTING, AND PARTICIPANTS: Study performed from April 2007 to July 2009 using testis material donated by 6 adult men who underwent orchidectomy as part of prostate cancer treatment. Testicular cells were isolated and cultured in supplemented StemPro medium; germline stem cell clusters that arose were subcultured on human placental laminin-coated dishes in the same medium. Presence of spermatogonia was determined by reverse transcriptase polymerase chain reaction and immunofluorescence for spermatogonial markers. To test for the presence of functional spermatogonial stem cells in culture, xenotransplantation to testes of immunodeficient mice was performed, and migrated human spermatogonial stem cells after transplantation were detected by COT-1 fluorescence in situ hybridization. The number of colonized spermatogonial stem cells transplanted at early and later points during culture were counted to determine propagation. MAIN OUTCOME MEASURES: Propagation of spermatogonial stem cells over time. RESULTS: Testicular cells could be cultured and propagated up to 15 weeks. Germline stem cell clusters arose in the testicular cell cultures from all 6 men and could be subcultured and propagated up to 28 weeks. Expression of spermatogonial markers on both the RNA and protein level was maintained throughout the entire culture period. In 4 of 6 men, xenotransplantation to mice demonstrated the presence of functional spermatogonial stem cells, even after prolonged in vitro culture. Spermatogonial stem cell numbers increased 53-fold within 19 days in the testicular cell culture and increased 18,450-fold within 64 days in the germline stem cell subculture. CONCLUSION: Long-term culture and propagation of human spermatogonial stem cells in vitro is achievable.

Characterization of Human Mesenchymal Stem Cells Isolated from the Testis.

Mesenchymal stem cells hold great promise for regenerative medicine as they can be easily isolated from different sources such as adipose tissue, bone marrow, and umbilical cord blood. Spontaneously arising pluripotent stem cells can be obtained in culture from murine spermatogonial stem cells (SSCs), while the pluripotency of the human counterpart remains a matter of debate. Recent gene expression profiling studies have demonstrated that embryonic stem cell- (ESC-) like cells obtained from the human testis are indeed closer to mesenchymal stem cells (MSCs) than to pluripotent stem cells. Here, we confirm that colonies derived from human testicular cultures, with our isolation protocol, are of mesenchymal origin and do not arise from spermatogonial stem cells (SSCs). The testis, thus, provides an important and accessible source of MSCs (tMSCs) that can be potentially used for nephrotoxicity testing in vitro. We further demonstrate, for the first time, that tMSCs are able to secrete microvesicles that could possibly be applied to the treatment of various chronic diseases, such as those affecting the kidney.

The influence of retinoic acid-induced differentiation on the radiation response of male germline stem cells.

Lifelong mammalian male fertility is maintained through an intricate balance between spermatogonial proliferation and differentiation. DNA damage in spermatogonia, for instance caused by chemo- or radiotherapy, can induce cell cycle arrest or germ cell apoptosis, possibly resulting in male infertility. Spermatogonia are generally more radiosensitive and prone to undergo apoptosis than somatic cells. Among spermatogonial subtypes the response to DNA damage is differentially modulated; undifferentiated spermatogonia, including the spermatogonial stem cells (SSCs), are relatively radio-resistant, whereas differentiating spermatogonia are very radiosensitive. To investigate the molecular mechanisms underlying this difference, we used an in vitro system consisting of mouse male germline stem (GS) cells that can be induced to differentiate. Using RNA-sequencing analysis, we analyzed the response of undifferentiated and differentiating GS cells to ionizing radiation (IR). At the RNA expression level, both undifferentiated and differentiating GS cells showed a very similar response to IR. Protein localization of several genes found to be involved in either spermatogonial differentiation or radiation response was investigated using mouse testis sections. For instance, we found that the transcription factor PDX1 was specifically expressed in undifferentiated spermatogonia and thus may be a novel marker for these cells. Interestingly, also at the protein level, undifferentiated GS cells showed a more pronounced upregulation of p53 in response to IR than differentiating GS cells. The higher p53 protein level in undifferentiated spermatogonia may preferentially induce cell cycle arrest, thereby giving these cells more time to repair inflicted DNA damage and increase their radio-resistance.

Prenatal undernutrition and leukocyte telomere length in late adulthood: the Dutch famine birth cohort study.

BACKGROUND: Energy restriction in prenatal life has detrimental effects on later life health and longevity. Studies in rats have shown that the shortening of telomeres in key tissues plays an important role in this association. OBJECTIVE: The aim of the current study was to investigate leukocyte telomere length in relation to prenatal famine exposure. DESIGN: The Dutch famine birth cohort consists of 2414 term singleton men and women who were born between 1943 and 1947 in Amsterdam around the time of the famine. At a mean age of 68 y, telomere length and the percentage of short telomeres was assessed in a subsample of 131 cohort members, of whom 45 were born before the famine (control), 41 were exposed to famine during early gestation, and 45 were conceived after the famine (control). Median telomere length was determined in peripheral blood leukocytes by a high-throughput quantitative fluorescent in situ hybridization-based technology. RESULTS: Leukocyte telomere length and the percentage of short telomeres did not differ between those exposed to famine during early gestation and those unexposed during gestation. A lower socioeconomic status at birth, frequent consumption of alcohol (specifically consumption of spirits), a history of cancer, and a lower self-reported health status were significantly associated with shorter leukocyte telomere length (all P ≤ 0.03). Currently having a job was significantly associated with a smaller percentage of short telomeres (P = 0.04). CONCLUSION: The results of the current study suggest that prenatal exposure to famine is not associated with the shortening of telomeres in peripheral blood leukocytes at age 68 y.

Clinical relevance of partial AZFc deletions.

To determine the number of DAZ gene clusters in the Y-bearing spermatozoa of patients who underwent intracytoplasmic sperm injection (ICSI) and to compare the outcome with the number of clusters found in the spermatozoa of normospermic men. Prospective study. Academic hospital.Forty-seven patients with impaired spermatogenesis who were attending our clinic for ICSI and 56 semen donors. Peripheral blood was drawn to obtain somatic DNA for polymerase chain reaction (PCR) analysis and leukocytes for karyotyping and FISH analysis. Three-color FISH was performed on the spermatozoa remaining after ICSI and on the spermatozoa of semen donors to determine the presence of the X and Y chromosome as well as the number of DAZ gene clusters. Number of DAZ gene clusters in Y-bearing spermatozoa. Five patients had only one DAZ gene cluster, one patient had a complete AZFc deletion, and one patient had three clusters on average. One of the semen donors also showed three DAZ gene clusters in his Y-bearing spermatozoa. None of the semen donors had only one DAZ gene cluster. Besides complete AZFc deletions, partial deletions are also associated with impaired spermatogenesis. As a result, these partial deletions that are not recognized by routine PCR are reintroduced into the population by the ICSI technique.

Genetic and epigenetic stability of human spermatogonial stem cells during long-term culture.

OBJECTIVE: To determine the genetic and epigenetic stability of human spermatogonial stem cells (SSCs) during long-term culture. DESIGN: Experimental basic science study. SETTING: Reproductive biology laboratory. PATIENT(S): Cryopreserved human testicular tissue from two prostate cancer patients with normal spermatogenesis. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Testicular cells before and 50 days after culturing were subjected to ITGA6 magnetic-activated cell sorting to enrich for SSCs. Individual spermatogonia were analyzed for aneuploidies with the use of single-cell 24-chromosome screening. Furthermore, the DNA methylation statuses of the paternally imprinted genes H19, H19-DMR (differentially methylated region), and MEG3 and the maternally imprinted genes KCNQ1OT1 and PEG3 were identified by means of bisulfite sequencing. RESULTS(S): Aneuploidy screening showed euploidy with no chromosomal abnormalities in all cultured and most noncultured spermatogonia from both patients. The methylation assays demonstrated demethylation of the paternally imprinted genes H19, H19-DMR, and MEG3 of 11%-28%, 43%-68%, and 18%-26%, respectively, and increased methylation of the maternally imprinted genes PEG 3 and KCNQ1OT of 13%-50% and 30%-38%, respectively, during culture. CONCLUSION(S): In the current culture system for human SSCs propagation, genomic stability is preserved, which is important for future clinical use. Whether the observed changes in methylation status have consequences on functionality of SSCs or health of offspring derived from transplanted SSCs requires further investigation.