In human sperm, about 85 to 90% of the genome is associated ...

created [InstanceEdit:9822197] May, Bruce, 2022-12-21
dbId 9822230
displayName In human sperm, about 85 to 90% of the genome is associated ...
modified [InstanceEdit:9841053] May, Bruce, 2023-08-07
schemaClass Summation
text In human sperm, about 85 to 90% of the genome is associated with protamines rather than histones (reviewed in Torres-Flores and Hernández-Hernández 2020, Ribas-Maynou et al. 2022). Protamines provide a much higher packing density of DNA in the nucleus but there are few reports of epigenetic marks on protamines (Brunner et al. 2014). After fertilization, protamines in the male pronucleus are replaced with histones provided by the oocyte cytoplasm (reviewed in Yang et al. 2015, Okada and Yamaguchi 2017). The result is a decondensation of sperm chromatin that produces a chromatin state that is permissive for transcription.
Dissociation of protamines from DNA appears to be controlled by phosphorylation of the protamines PRM1 and PRM2 (inferred from mouse homologs in Gou et al. 2020). The kinase SRPK1 phosphorylates both PRM1 and PRM2, which recruit the histone chaperones Nucleoplasmin 2 (NPM2) and HIRA (inferred from mouse homologs in Gou et al. 2020). NPM2 then dissociates the phosphorylated PRM1 from DNA. By inference NPM1 and NPM3, which are also present in the zygote, may also dissociate PRM1 and PRM2 from DNA (Okuwaki et al. 2012).
Nucleosomes in the zygote are characterized by H3.3 and H2AX (H2A.X) (reviewed in Martire and Banaszynski 2020). HIRA chaperones histone H3.3 and acts together with NPM proteins to assemble nucleosomes from individual histone proteins. Asymmetric dimethylation of H3.3 arginine-17 catalyzed by METTL23 is required for assembly of H3.3 into chromatin in the male pronucleus (inferred from mouse homologs in Hatanaka et al. 2017) . The oocyte-specific histone H1, H1FOO (H1.8, H1-8), is also deposited on the newly formed chromatin at this time and persists until the 8-cell stage (McGraw et al. 2006). In mouse embryos, H1foo is not required for development (Sánchez-Sáez et al. 2022).
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