Dicer1 Depletion in Male Germ Cells Leads to Infertility Due to Cumulative Meiotic and Spermiogenic Defects

Abstract

BackgroundSpermatogenesis 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 FindingsWe 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/SignificanceOur 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.

The role of epigenetics in idiopathic male infertility

“…Normozoospermic controls with normal P1/P2 ratio (10) • No significant quantitative differences between groups of patients with either an abnormally high or low P1/ P2 ratio compared to normal controls H19, MEST Normozoospermic controls (27) Oligozoospermic patients (96) • No aberration in MEST DNA methylation • Aberrant DNA methylation in H19 in oligozoospermic patients [62] cells and involved in proliferation, apoptosis, cell morphogenesis, and differentiation, abnormal expression of DDR1 in NOA patients may prevent primordial germ cell migration and development [48]. Table 1 gives a summary of the studies to date that analyze potential association of spermatozoal DNA methylation with male infertility.…”

“…miRNAs and endo-siRNAs are abundantly expressed in male germ cells throughout spermatogenesis, whereas piRNAs are only present in spermatocytes at the pachytene stage and in round spermatids [92,94]. The absolute requirement for miRNAs and endo-siRNAs for spermatogenesis has been shown by two initial studies where Dicer1 gene was knocked out in two different mouse models [95,96]. Germ-cell specific deletion of Dicer1 in these models has led to complete male infertility due to alterations in meiotic progression, increased spermatocyte apoptosis, and failure of haploid male germ cell differentiation.…”

“…Germ-cell specific deletion of Dicer1 in these models has led to complete male infertility due to alterations in meiotic progression, increased spermatocyte apoptosis, and failure of haploid male germ cell differentiation. Remarkably, Romero and colleagues also showed that Dicer1 is not required for spermatogonial stem cell renewal and mitotic proliferation, but is indispensible for meiotic and haploid stages of spermatogenesis [96]. To distinguish between the specific effects of miRNAs and endo-siRNAs, a following study has used Drosha and Dicer conditional knockout mouse models and reported that both knockout males were infertile due to impaired spermatogenesis characterized by depletion of spermatocytes and spermatids leading to oligoteratozoospermia or azoospermia [97].…”

A multi-faceted approach to understanding male infertility: gene mutations, molecular defects and assisted reproductive techniques (ART)

“…Of relevance to the function of DICER1and DROSHA in miRNAs biogenesis and spermatogenesis, it has also been demonstrated that mutations or single nucleotide polymorphisms (SNP) in Dicer1 and Drosha is associated with male infertility. A mutation in Dicer1 or Drosha may cause global alterations of miRNA expression and result in the upregulation of their target genes, which in turn could affect other interacting factors such as the miRNA 17-92 cluster, leading to apoptosis of spermatozoa and abnormal semen quality [195]. In a study by Qin et al, [196], they reported a significant association between Dicer1 and Drosha SNP with abnormal semen parameters and idiopathic male infertility.…”

Petits ARN non codants et spermatogenèse

“…Ces petits ARN, appelés piARN, s'associent avec les protéines PIWI pour former des complexes ribonucléoprotéiques impliqués notamment dans la répression des rétrotransposons au sein de la lignée germinale mâle. Concrètement, il existe deux souspopulations de piARN produites dans les cellules germinales mâles, [30,32] [25]. D'autres miARN tels que miR-322 et miR-323 ont été proposés comme favorisant la tumorigenèse des cellules germinales, se comportant donc comme des oncogènes potentiels [26].…”