Pattern of γH2AX after irradiation in early prophase mouse spermatocytes.

SYCP3 (green) and γH2AX (red) at different stages of prophase I by recovery time after irradiation. (A-E) Control. (A) Early leptotene. γH2AX localizes as small scattered foci over the short threads of forming AEs. (B) Mid-late leptotene. AEs are more extended and now a massive γH2AX signal covers the nucleus. This pattern is also found in early zygotene (C), when AEs are completely formed and homologues start to synapse. (D) Late zygotene. Homologous chromosomes have nearly completed synapsis. γH2AX signal still occupies large chromatin regions, mostly on the unsynapsed autosomes and the X chromosome (X). The Y chromosome (Y) is devoid of massive γH2AX labeling. (E). Early pachytene. Autosomes are completely synapsed, whereas sex chromosomes show a variable degree of synapsis. γH2AX extends over both sex chromosomes (X and Y) and regions of chromatin around some autosomes (arrows). (F-J) 1 hour of recovery. Increased γH2AX signal is observed in the nucleus of spermatocytes from early leptotene to early pachytene. The signal covers the entire nucleus at all the stages, contrasting with the pattern of control cells. (K-O) 24 hours of recovery. There is an evident decrease in the amount of γH2AX in early leptotene, late zygotene and early pachytene spermatocytes, comparable to the controls. γH2AX localizes around the sex chromosomes, and some foci present in autosomes (arrows). (P-T) 72 hours of recovery. A pattern analogous to that at 24 hours is found. Chromosomal connections involving SYCP3 are observed between some bivalents (arrowhead).