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#protamines

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Fertilization in mammals-l

Protamines in sperm primarily:

Sperm DNA packaging diverges from somatic chromatin organization to ensure hydrodynamic shape and protection during transit. Histones replaced by protamines PRM1 and PRM2 small basic proteins rich in arginine and cysteine forming disulfide bonds. Protamines coil DNA into donut-shaped toroids, reducing nuclear volume tenfold, silencing transcription and conferring resistance to nucleases and oxidative stress. Correct protamine ratio critical; excess PRM1 or PRM2 leads to incomplete condensation, DNA fragmentation and infertility. Compact protamine-based chromatin safeguards paternal genome en route to oocyte and ensures epigenetic delivery, embryonic integrity and genome stability post-fertilization.

Ref: Balhorn, Genome Biology 2007: Protamine structure, DNA toroids and paternal chromatin condensation in sperm.

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Fertilization in mammals-ll

Protamines primarily function to:

During spermiogenesis histones are sequentially replaced first by transition proteins then by small arginine-rich protamines PRM1 and PRM2. This exchange packages DNA into highly condensed toroidal structures, reducing nuclear volume, transcriptionally silencing genome and shielding paternal chromosomes from oxidative and nucleolytic damage during transit through male and female tracts. Disulfide crosslinking between protamines stabilizes compaction giving characteristic hydrodynamic sperm head shape. Balanced PRM1 to PRM2 ratio is critical; imbalance correlates with DNA fragmentation, male infertility, poor embryo development due to faulty chromatin packaging, genome instability and epigenetic dysregulation.

Ref: Gilbert, Developmental Biology, 11th ed., Chapter 19: Protamines and sperm chromatin compaction during spermiogenesis.

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