Male Infertility: An Epigenetic Perspective
Besides known genetic and environmental factors, research over the last two decades has shed light on several epigenetic mechanisms and their association with male infertility. The male germ line undergoes extensive epigenetic remodeling throughout fetal
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Sweta Mohan, Sharvari Deshpande, and N.H. Balasinor
Abstract
Besides known genetic and environmental factors, research over the last two decades has shed light on several epigenetic mechanisms and their association with male infertility. The male germ line undergoes extensive epigenetic remodeling throughout fetal to adult life and is thus susceptible to environmental factors that can affect fertility. During fetal life, the primordial germ cells undergo removal of epigenetic marks (demethylation) followed by re-establishment of these marks according to the sex of the fetus, at the time of gonadal differentiation. Extensive programming of the epigenome occurs during the various phases of spermatogenesis, i.e., mitosis, meiosis, and spermiogenesis, leading to haploid-condensed spermatozoa with protamines as the major nucleoproteins. Shortly after fertilization, the sperm chromatin decondenses and the protamines are replaced by histones. The male pronucleus undergoes active demethylation. One such epigenetic phenomenon, genomic imprinting resulting in monoallelic expression of genes depending on the parent of origin, is involved in early embryogenesis. Aberrant methylation pattern of imprinting control region (ICR) of imprinted genes in the spermatozoa is associated with altered sperm morphology, count, and motility. This chapter provides a comprehensive overview of the epigenetic changes affecting spermatogenesis and male fertility. Keywords
Male infertility • Epigenetics • Genomic imprinting • Methylation • Demethylation Chromatin compaction
S. Mohan • S. Deshpande • N.H. Balasinor (*) Neuroendocrinology, National Institute for Research in Reproductive Health (ICMR), Parel, Mumbai 400012, India e-mail: [email protected]; [email protected] © Springer Nature Singapore Pte Ltd. 2017 R. Singh, K. Singh (eds.), Male Infertility: Understanding, Causes and Treatment, DOI 10.1007/978-981-10-4017-7_16
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Key Points • The male germ line undergoes extensive epigenetic remodeling throughout fetal to adult life. Thus, it is susceptible to adverse environmental changes affecting germ cell maturation and fertility. • Extensive epigenetic programming occurs during the various phases of spermatogenesis, i.e., mitosis, meiosis, and spermiogenesis, leading to haploid- condensed spermatozoa with protamines as the major nucleoproteins. • Aberrant methylation of imprinting control region (ICR) of imprinted genes in spermatozoa is associated with altered sperm count, motility, and morphology. • Inclusion of male epigenetic diagnostics in routine clinical investigations will be beneficial for infertility management and for selection of cases that will benefit from assisted reproductive technology (ART). • Extensive research is required to decide on the type of epigenetic tests/parameters that can be included in routine clinical investigations for spermatozoa.
16.1 Introduction Epigenetics is the study of heritable changes affecting gene expression that are not caused by changes in the underlyi
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