Characterization of the fertility of Kit haplodeficient male mice

Subfertility and Risk of Testicular Cancer in the EPSAM Case-Control Study

Background/objectives

It has been suggested that subfertility and testicular cancer share genetic and environmental risk factors. We studied both subfertility and the strongest known testicular cancer susceptibility gene, the c-KIT ligand (KITLG), whose pathway is involved in spermatogenesis.

Methods

The EPSAM case-control study is comprised of testicular cancer patients from the Province of Turin, Italy, diagnosed between 1997 and 2008. The present analysis included 245 cases and 436 controls from EPSAM, who were aged 20 years or older at diagnosis/recruitment. The EPSAM questionnaire collected information on factors such as number of children, age at first attempt to conceive, duration of attempt to conceive, use of assisted reproduction techniques, physician-assigned diagnosis of infertility, number of siblings, and self-reported cryptorchidism. Genotyping of the KITLG single nucleotide polymorphism (SNP) rs995030 was performed on the saliva samples of 202 cases and 329 controls.

Results

Testicular cancer was associated with the number of children fathered 5 years before diagnosis (odds ratio (OR) per additional child: 0.78, 95% confidence interval (CI): 0.58–1.04) and sibship size (OR per additional sibling: 0.76, 95% CI: 0.66–0.88). When considering the reproductive history until 1 year before diagnosis, attempting to conceive for at least 12 months or fathering a child using assisted reproduction techniques was not associated with the risk of testicular cancer, nor was age at first attempt to conceive or physician-assigned diagnosis of infertility. The SNP rs995030 was strongly associated with risk of testicular cancer (per allele OR: 1.83; 95%CI: 1.26–2.64), but it did not modify the association between number of children and the risk of testicular cancer.

Conclusion

This study supports the repeatedly reported inverse association between number of children and risk of testicular cancer, but it does not find evidence of an association for other indicators of subfertility.

Germ cell-specific targeting of DICER or DGCR8 reveals a novel role for endo-siRNAs in the progression of mammalian spermatogenesis and male fertility

Small non-coding RNAs act as critical regulators of gene expression and are essential for male germ cell development and spermatogenesis. Previously, we showed that germ cell-specific inactivation of Dicer1, an endonuclease essential for the biogenesis of micro-RNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs), led to complete male infertility due to alterations in meiotic progression, increased spermatocyte apoptosis and defects in the maturation of spermatozoa. To dissect the distinct physiological roles of miRNAs and endo-siRNAs in spermatogenesis, we compared the testicular phenotype of mice with Dicer1 or Dgcr8 depletion in male germ cells. Dgcr8 mutant mice, which have a defective miRNA pathway while retaining an intact endo-siRNA pathway, were also infertile and displayed similar defects, although less severe, to Dicer1 mutant mice. These included cumulative defects in meiotic and haploid phases of spermatogenesis, resulting in oligo-, terato-, and azoospermia. In addition, we found by RNA sequencing of purified spermatocytes that inactivation of Dicer1 and the resulting absence of miRNAs affected the fine tuning of protein-coding gene expression by increasing low level gene expression. Overall, these results emphasize the essential role of miRNAs in the progression of spermatogenesis, but also indicate a role for endo-siRNAs in this process.

Overlapping dose responses of spermatogenic and extragonadal testosterone actions jeopardize the principle of hormonal male contraception

Testosterone (T), alone or in combination with progestin, provides a promising approach to hormonal male contraception. Its principle relies on enhanced negative feedback of exogenous T to suppress gonadotropins, thereby blocking the testicular T production needed for spermatogenesis, while simultaneously maintaining the extragonadal androgen actions, such as potency and libido, to avoid hypogonadism. A serious drawback of the treatment is that a significant proportion of men do not reach azoospermia or severe oligozoospermia, commensurate with contraceptive efficacy. We tested here, using hypogonadal luteinizing hormone/choriongonadotropin receptor (LHCGR) knockout (LHR^−/−) mice, the basic principle of the T-based male contraceptive method, that a specific T dose could maintain extragonadal androgen actions without simultaneously activating spermatogenesis. LHR^−/− mice were treated with increasing T doses, and the responses of their spermatogenesis and extragonadal androgen actions (including gonadotropin suppression and sexual behavior) were assessed. Conspicuously, all dose responses to T were practically superimposable, and no dose of T could be defined that would maintain sexual function and suppress gonadotropins without simultaneously activating spermatogenesis. This finding, never addressed in clinical contraceptive trials, is not unexpected in light of the same androgen receptor mediating androgen actions in all organs. When extrapolated to humans, our findings may jeopardize the current approach to hormonal male contraception and call for more effective means of inhibiting intratesticular T production or action, to achieve consistent spermatogenic suppression.—Oduwole, O. O., Vydra, N., Wood, N. E. M., Samanta, L., Owen, L., Keevil, B., Donaldson, M., Naresh, K., Huhtaniemi, I. T. Overlapping dose responses of spermatogenic and extragonadal testosterone actions jeopardize the principle of hormonal male contraception.

SNPs in KIT and KITLG genes may be associated with oligospermia in Chinese population

KIT/KITLG signaling system is crucial for spermatogenesis, which suggests that KIT and KITLG genes may be involved in spermatogenesis impairment and male infertility. To explore the possible association of KIT and KITLG genes with male infertility having spermatogenesis impairment, polymorphism distributions of SNP rs3819392 in KIT gene as well as rs995030 and rs4474514 in KITLG gene were investigated in 372 patients with idiopathic azoospermia or oligospermia and 205 fertile controls. As a result, the significant differences in polymorphism distributions of SNP rs3819392 in KIT gene and rs4474514 in KITLG gene were observed between the patients with oligospermia and controls. The frequencies of allele G (94.2% versus 90.0% p = 0.022) and genotype GG (89.2% versus 82.0% p = 0.042) in patients with oligospermia were significantly higher than those in controls at rs3819392 locus in KIT gene. In addition, the genotype CC of rs4474514 in KITLG (8.2% versus 3.4%, p = 0.034) also significantly increased in oligospermic patients in comparison to controls. These findings indicated that SNP rs3819392 in KIT gene and rs4474514 in KITLG gene may be associated with oligospermia, suggesting that polymorphism of KIT and KITLG genes may play a role in oligospermia.

An essential role for insulin and IGF1 receptors in regulating sertoli cell proliferation, testis size, and FSH action in mice

Testis size and sperm production are directly correlated to the total number of adult Sertoli cells (SCs). Although the establishment of an adequate number of SCs is crucial for future male fertility, the identification and characterization of the factors regulating SC survival, proliferation, and maturation remain incomplete. To investigate whether the IGF system is required for germ cell (GC) and SC development and function, we inactivated the insulin receptor (Insr), the IGF1 receptor (Igf1r), or both receptors specifically in the GC lineage or in SCs. Whereas ablation of insulin/IGF signaling appears dispensable for GCs and spermatogenesis, adult testes of mice lacking both Insr and Igf1r in SCs (SC-Insr;Igf1r) displayed a 75% reduction in testis size and daily sperm production as a result of a reduced proliferation rate of immature SCs during the late fetal and early neonatal testicular period. In addition, in vivo analyses revealed that FSH requires the insulin/IGF signaling pathway to mediate its proliferative effects on immature SCs. Collectively, these results emphasize the essential role played by growth factors of the insulin family in regulating the final number of SCs, testis size, and daily sperm output. They also indicate that the insulin/IGF signaling pathway is required for FSH-mediated SC proliferation.

Dicer1 depletion in male germ cells leads to infertility due to cumulative meiotic and spermiogenic defects

BACKGROUND

Spermatogenesis is a complex biological process that requires a highly specialized control of gene expression. In the past decade, small non-coding RNAs have emerged as critical regulators of gene expression both at the transcriptional and post-transcriptional level. DICER1, an RNAse III endonuclease, is essential for the biogenesis of several classes of small RNAs, including microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs), but is also critical for the degradation of toxic transposable elements. In this study, we investigated to which extent DICER1 is required for germ cell development and the progress of spermatogenesis in mice.

PRINCIPAL FINDINGS

We show that the selective ablation of Dicer1 at the early onset of male germ cell development leads to infertility, due to multiple cumulative defects at the meiotic and post-meiotic stages culminating with the absence of functional spermatozoa. Alterations were observed in the first spermatogenic wave and include delayed progression of spermatocytes to prophase I and increased apoptosis, resulting in a reduced number of round spermatids. The transition from round to mature spermatozoa was also severely affected, since the few spermatozoa formed in mutant animals were immobile and misshapen, exhibiting morphological defects of the head and flagellum. We also found evidence that the expression of transposable elements of the SINE family is up-regulated in Dicer1-depleted spermatocytes.

CONCLUSIONS/SIGNIFICANCE

Our findings indicate that DICER1 is dispensable for spermatogonial stem cell renewal and mitotic proliferation, but is required for germ cell differentiation through the meiotic and haploid phases of spermatogenesis.

Dicer is required for haploid male germ cell differentiation in mice

Background

The RNase III endonuclease Dicer is an important regulator of gene expression that processes microRNAs (miRNAs) and small interfering RNAs (siRNAs). The best-characterized function of miRNAs is gene repression at the post-transcriptional level through the pairing with mRNAs of protein-encoding genes. Small RNAs can also act at the transcriptional level by controlling the epigenetic status of chromatin. Dicer and other mediators of small RNA pathways are present in mouse male germ cells, and several miRNAs and endogenous siRNAs are expressed in the testis, suggesting that Dicer-dependent small RNAs are involved in the control of the precisely timed and highly organised process of spermatogenesis.

Principal Findings

Being interested in the Dicer-mediated functions during spermatogenesis, we have analysed here a male germ cell-specific Dicer1 knockout mouse model, in which the deletion of Dicer1 takes place during early postnatal development in spermatogonia. We found that Dicer1 knockout testes were reduced in size and spermatogenesis within the seminiferous tubules was disrupted. Dicer1 knockout epididymides contained very low number of mature sperm with pronounced morphological abnormalities. Spermatogonial differentiation appeared unaffected. However, the number of haploid cells was decreased in knockout testes, and an increased number of apoptotic spermatocytes was observed. The most prominent defects were found during late haploid differentiation, and Dicer was demonstrated to be critical for the normal organization of chromatin and nuclear shaping of elongating spermatids.

Conclusions/Significance

We demonstrate that Dicer and Dicer-dependent small RNAs are imperative regulators of haploid spermatid differentiation and essential for male fertility.

Sertoli cell Dicer is essential for spermatogenesis in mice

Spermatogenesis requires intact, fully competent Sertoli cells. Here, we investigate the functions of Dicer, an RNaseIII endonuclease required for microRNA and small interfering RNA biogenesis, in mouse Sertoli cell function. We show that selective ablation of Dicer in Sertoli cells leads to infertility due to complete absence of spermatozoa and progressive testicular degeneration. The first morphological alterations appear already at postnatal day 5 and correlate with a severe impairment of the prepubertal spermatogenic wave, due to defective Sertoli cell maturation and incapacity to properly support meiosis and spermiogenesis. Importantly, we find several key genes known to be essential for Sertoli cell function to be significantly down-regulated in neonatal testes lacking Dicer in Sertoli cells. Overall, our results reveal novel essential roles played by the Dicer-dependent pathway in mammalian reproductive function, and thus pave the way for new insights into human infertility.

siRNA-mediated silencing of c-kit in mouse primary spermatogonial cells induces cell cycle arrest

Several genes/gene products are known to act in a concert to regulate the process of spermatogenesis. One such gene is c-kit, a transmembrane tyrosine kinase receptor which plays an indispensable role in the maturation and differentiation of spermatogonial germ cells (SGCs). In the present study, siRNA approach was used to assess the role of c-kit in survival and proliferation of murine primary SGCs. The effect of different concentrations of anti-c-kit siRNA-1 and siRNA-2 (0.15, 0.315, 0.625, 1.25, 2.50, 5, and 10 nM) on c-kit protein and mRNA expression at post-transfection time (0, 6, 12, 24, 48, and 72 hours) was assessed using an array of techniques such as flow cytometry, ELISA, Western blot, and RT-PCR. Transfection of cells with anti-c-kit siRNAs (0.15-10 nM) at various time points after (0-72 hours) showed significant knockdown c-kit mRNA and protein expression. MTT, Alamar blue assays, and RT-PCR were used to investigate the effects of c-kit silencing on survival, proliferation, distribution, and apoptosis of cells. Experiments were also conducted to determine the effects of c-kit knockdown on cell cycle distribution, DNA laddering, and apoptosis. The results indicated that the transfection with anti-c-kit siRNA induces DNA fragmentation and cell cycle arrest at G(2)/M phase leading to significant reduction in cell viability and proliferation. In addition, enhanced suppression of c-kit protein in P815 cells was observed after transfection as compared to ES-E14TG2alpha cells, suggesting early onset of c-kit protein repression in P815 cells leading to prolongation in cell doubling time. In conclusion, our data provide the first evidence of specific knockdown of c-kit expression in mouse primary SGCs, which emphasizes the critical role played by c-kit in germ cell survival, proliferation, and apoptosis.

Allelic heterogeneity at the equine KIT locus in dominant white (W) horses

White coat color has been a highly valued trait in horses for at least 2,000 years. Dominant white (W) is one of several known depigmentation phenotypes in horses. It shows considerable phenotypic variation, ranging from approximately 50% depigmented areas up to a completely white coat. In the horse, the four depigmentation phenotypes roan, sabino, tobiano, and dominant white were independently mapped to a chromosomal region on ECA 3 harboring the KIT gene. KIT plays an important role in melanoblast survival during embryonic development. We determined the sequence and genomic organization of the approximately 82 kb equine KIT gene. A mutation analysis of all 21 KIT exons in white Franches-Montagnes Horses revealed a nonsense mutation in exon 15 (c.2151C>G, p.Y717X). We analyzed the KIT exons in horses characterized as dominant white from other populations and found three additional candidate causative mutations. Three almost completely white Arabians carried a different nonsense mutation in exon 4 (c.706A>T, p.K236X). Six Camarillo White Horses had a missense mutation in exon 12 (c.1805C>T, p.A602V), and five white Thoroughbreds had yet another missense mutation in exon 13 (c.1960G>A, p.G654R). Our results indicate that the dominant white color in Franches-Montagnes Horses is caused by a nonsense mutation in the KIT gene and that multiple independent mutations within this gene appear to be responsible for dominant white in several other modern horse populations.

Association of genetic markers within the KIT and KITLG genes with human male infertility

BACKGROUND

There is much evidence involving the KIT tyrosine kinase receptor and its ligand KITLG in the survival and proliferation of germ cells. Animal models and functional studies in humans suggest that this signalling pathway plays a role in male infertility.

METHODS

We studied three and two single-nucleotide polymorphisms (SNPs) (rs3819392, rs3134885, rs2237012, rs10506957 and rs995030) located within the genomic region of the KIT and KITLG genes, respectively. A total of 167 idiopathic infertile men (sperm counts <5 million spz/ml) and 465 unrelated healthy controls from the same geographical region were genotyped for these SNPs.

RESULTS

We found a statistically significant association of the rs3819392 polymorphism, which is located within the KIT gene, with idiopathic male infertility. In addition, a deviation from the Hardy-Weinberg equilibrium (HWE) law was observed for rs10506957 polymorphism within the KITLG gene only in the infertile group.

CONCLUSIONS

Our data indicate that the KIT/KITLG system may be involved in a low sperm count trait in humans.

Infertility with defective spermiogenesis in mice lacking AF5q31, the target of chromosomal translocation in human infant leukemia

AF5q31 (also called MCEF) was identified by its involvement in chromosomal translocation with the gene MLL (mixed lineage leukemia), which is associated with infant acute lymphoblastic leukemia. Several potential roles have been proposed for AF5q31 and other family genes, but the specific requirements of AF5q31 during development remain unclear. Here, we show that AF5q31 is essential for spermatogenesis. Although most AF5q31-deficient mice died in utero and neonatally with impaired embryonic development and shrunken alveoli, respectively, 13% of AF5q31-deficient mice thrived as wild-type mice did. However, the male mice were sterile with azoospermia. Histological examinations revealed the arrest of germ cell development at the stage of spermiogenesis, and virtually no spermatozoa were seen in the epididymis. AF5q31 was found to be preferentially expressed in Sertoli cells. Furthermore, mutant mice displayed severely impaired expression of protamine 1, protamine 2, and transition protein 2, which are indispensable to compact the haploid genome within the sperm head, and an increase of apoptotic cells in seminiferous tubules. Thus, AF5q31 seems to function as a transcriptional regulator in testicular somatic cells and is essential for male germ cell differentiation and survival. These results may have clinical implications in the understanding of human male infertility.

Infertility with defective spermatogenesis and hypotestosteronemia in male mice lacking the androgen receptor in Sertoli cells

Androgens and the androgen receptor (AR) play important roles in male fertility, although the detailed mechanisms, particularly how androgen/AR influences spermatogenesis in particular cell types, remain unclear. Using a Cre-Lox conditional knockout strategy, we generated a tissue-specific knockout mouse with the AR gene deleted only in Sertoli cells (S-AR(-/y)). Phenotype analyses show the S-AR(-/y) mice were indistinguishable from WT AR mice (B6 AR(+/y)) with the exception of testes, which were significantly atrophied. S-AR(-/y) mice were infertile, with spermatogenic arrest predominately at the diplotene premeiotic stage and almost no sperm detected in the epididymides. S-AR(-/y) mice also have lower serum testosterone concentrations and higher serum leuteinizing hormone concentrations than B6 AR(+/y) mice. Further mechanistic studies demonstrated that S-AR(-/y) mice have defects in the expression of anti-Müllerian hormone, androgen-binding protein, cyclin A1, and sperm-1, which play important roles in the control of spermatogenesis and/or steroidogenesis. Together, our Sertoli cell-specific AR knockout mice provide in vivo evidence of the need for functional AR in Sertoli cells to maintain normal spermatogenesis and testosterone production, and ensure normal male fertility.

Cancer treatment with kinase inhibitors: what have we learnt from imatinib?

Over the past few years, a number of anticancer drugs have been developed that specifically target kinases known to be oncogenic. The leading drug in this area is imatinib mesylate, which targets ABL, KIT and PDGFR. It has been remarkably effective in the treatment of chronic myeloid leukaemia, although resistance remains a significant problem. From the imatinib experience in this setting, we present some principles of kinase inhibition that may have more general applicability in targeted anticancer therapy. It is clear that the identification of appropriate targets (activated kinases) and monitoring levels of response (to recognise emerging resistance) are essential to optimise clinical management.