1. Epigenetics of the male gamete
Douglas T. Carrell, Ph.D., H.C.L.D. 
Fertility and Sterility 
Volume 97, Issue 2, Pages (February 2012)
DOI: /j.fertnstert
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2. Figure 1
Chromatin remodeling and epigenetic modifications in human sperm. DNA methylation is the first line of epigenetic modification of chromatin through methylation of position of cytosines found in CpG dinucleotides. An intermediate step in demethylation is the formation of 5-hydroxymethylcytosine residues, which are also observed in mature sperm. DNA is bound to histone octamers with unique modifications that present a second level of regulation of gene transcription. Most histones are removed from the elongating spermatid and replaced with protamines that result in a higher order of DNA packaging and silence gene expression. Retained histones are interspersed between protamine toroids and may be bound to matrix attachment regions, which facilitates replication of loop domains in the embryo.
Fertility and Sterility  , DOI: ( /j.fertnstert )
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3. Figure 2
Summary of critical chromatin and DNA methylation modification in sperm, the embryo, and primordial germ cells. Key chromatin changes are demonstrated by the protamination of sperm during spermiogenesis, followed by replacement of protamines with histones at the pronuclear stage of embryogenesis. The active demethylation of sperm DNA after fertilization is contrasted with passive demethylation of maternally derived DNA. Resetting of imprinting occurs in the primordial germ cells and tissue-specific methylation changes occur throughout development.
Fertility and Sterility  , DOI: ( /j.fertnstert )
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