DNA methylation in spermatogenesis and male infertility

Abstract

Abstract. Infertility is a significant problem for human reproduction, with males and females equally affected. However, the molecular mechanisms underlying male infertility remain unclear. Spermatogenesis is a highly complex process involving mitotic cell division, meiosis cell division and spermiogenesis; during this period, unique and extensive chromatin and epigenetic modifications occur to bring about specific epigenetic profiles in spermatozoa. It has recently been suggested that the dysregulation of epigenetic modifications, in particular the methylation of sperm genomic DNA, may serve an important role in the development of numerous diseases. The present study is a comprehensive review on the topic of male infertility, aiming to elucidate the association between sperm genomic DNA methylation and poor semen quality in male infertility. In addition, the current status of the genetic and epigenetic determinants of spermatogenesis in humans is discussed. Contents1. Introduction 2. DNA methylation 3. DNA methylation and spermatogenesis 4. DNA methylation and genomic imprinting 5. DNA methylation and male infertility 6. Conclusion IntroductionEpigenetics is the study of genomic structural modifications that affect gene expression without altering the underlying nucleotide sequence (1-3). Epigenetic mechanisms involved in the regulation of gene expression include the regulation of non-coding RNA, chromatin remodeling, DNA methylation and histone modifications (4,5). Of these mechanisms, DNA methylation has been implicated in numerous biological functions, such as the development of spermatozoa and early embryos, and the repression of endogenous retrotransposons, while it also has a wide range of effects in gene expression (2,3,6). The dysregulation of DNA methylation has previously been associated with various human disorders, and has been shown to increase the risk of fertilization failure, dysfunction in embryogenesis, perinatal mortality, congenital abnormalities, preterm birth and low birth weight (7-11). The present review assesses the significance of DNA methylation in spermatogenesis in order to elucidate the association between the dysregulation of DNA methylation and male infertility. This may provide a basis for the prevention and treatment of male infertility, as well as permit the evaluation of the epigenetic quality of sperm in order to reduce the risk of epigenetic diseases in cases where conception is performed by assisted reproductive technology (ART). DNA methylationEpigenetic mechanisms are critical regulators of gene expression during spermatogenesis that may influence male fertility (12-14). Cytosine, a key DNA base, is methylated at the position, typically in the context of CpG dinucleotides. The methylation of constitutive heterochromatic and promoter regions is generally associated with reduced gene transcription (Fig. 1A) (15-18). Therefore, DNA methylation is a type of epigenetic modification that can effectively promote gene silencing (Fig. 1B). The methyl group for this chemical modif...

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