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Dynamics of radiation induced γH2AX foci in chromatin subcompartments of mouse pachytene spermatocytes and round spermatids
Author(s) -
Singh Priti,
Raman Mercy J.
Publication year - 2014
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.22314
Subject(s) - heterochromatin , euchromatin , biology , chromatin , histone , nucleoplasm , constitutive heterochromatin , microbiology and biotechnology , dna , genetics , nucleus , nucleolus
SUMMARY Chromatin compaction is thought to influence the severity of radiation‐induced DNA damage. We assessed how chromatin state affects DNA double‐strand break repair within eu‐/heterochromatin domains in male germ cells by profiling the spatiotemporal dynamics of γ‐radiation‐induced γH2AX foci in confocal images of mouse pachytene spermatocytes and round spermatids (5 min to16 hr post‐irradiation, in vivo). In unirradiated cells, all DNA‐dense heterochromatin domains showed compaction by anti‐H3K9me3‐staining, except for peripheral areas. Following irradiation, this signal was lost within 5 min, but regained later (8–16 hr); these two events coincided with the appearance and loss of γH2AX foci, respectively. While euchromatin showed a large number of bright foci in both cell types, heterochromatin had few foci. In spermatids, a few small, faint foci appeared within chromocenters. Pachytene‐stage, on the other hand, lacked foci within heterochromatin, although a few were closely associated with the heterochromatin periphery. The number of euchromatin foci in spermatids showed a dose‐dependent enhancement following irradiation (0.5–4 Gy), although no significant increase was seen in the quantity of heterochromatin foci. While all foci in pachytene‐stage cells were resolved, spermatids showed large residual foci—especially from heterochromatin foci, which remained faint for up to 4 hr, then increased in size between 8–16 hr, expanding at the chromocenter periphery and eventually protruding into euchromatin at H3K9me3‐signal‐free areas. Thus, this study identified scant foci formation and poor repair within heterochromatin, with distinctly different dynamics in meiotic and post‐meiotic stages of spermatogenesis, and provides direct evidence for heterochromatin decompaction following DNA damage, which facilitates repair/repositioning of foci towards euchromatin domains. It is the first demonstration of spatiotemporal mobilization of double‐strand breaks with respect to chromatin subdomains in male germ cells. Mol. Reprod. Dev. 81: 484–496, 2014. © 2014 Wiley Periodicals, Inc .