Transition from a meiotic to a somatic-like DNA damage response during the pachytene stage in mouse meiosis
Fig 8
Pattern of 53BP1 at different stages of prophase-I by recovery time after irradiation.
SYCP3 (red), γH2AX (blue) and 53BP1 (green). (A-D) Control. 53BP1 is first detected at mid-pachytene (B) over the sex chromosomes and is maintained during late pachytene (C) and diplotene (D). During diplotene, the signal weakens, becoming no longer detectable by the end of this stage. The 53BP1 signal co-localizes with γH2AX over the sex chromosomes, X and Y. (E-H) 1 hour of recovery. From mid-pachytene (F) onwards, a large number of 53BP1 foci appear on the autosomes as diffuse clouds emerging from the SCs. The 53BP signal is similarly maintained in late pachytene (G) and diplotene (H) spermatocytes, although foci become smaller as prophase-I progresses. Arrows indicate the bivalents shown in details. These 53BP1 signals largely coincide those of γH2AX (red arrowheads), although γH2AX foci without 53BP1 are also present (blue arrowheads) (see detail in G). (I-L) 24 hours of recovery. A noticeable decrease in the number of 53BP1 and γH2AX foci occurs relative to the 1-hour time point. In some cases, these foci coincide with those of γH2AX (red arrowhead in left detail in K) and in others they do not (blue arrowhead right detail in K). (M-P) 72 hours of recovery. The number and distribution of 53BP1 and γH2AX foci are similar to those at 24 hours. The presence of two interstitial bridges between autosomal bivalents (arrows) can be more clearly seen in the enlarged details in (N). γH2AX is observed on one of the bridges (right), whereas both γH2AX and 53BP1 are co-localized on the other (left). (Q) Dotplot of the number of 53BP1 foci in spermatocytes grouped by recovery times. Three substages were considered (MP: mid pachytene; LP: late pachytene; ED: early diplotene). Increased numbers of foci are evident 1 hour after irradiation. ANOVA analysis showed statistical differences at this time between the three stages analyzed (p≤0.0001). Tukey's multiple comparisons test for individual comparisons between different stages showed no statistical differences between LP and ED cells. A reduction is observed in the number of foci in cells at all stages 24 hours after irradiation. An analogous situation is found 72 hours after irradiation. (R) Dotplot of the number of 53BP1 foci in spermatocytes grouped by stage. Cells at all stages return to control levels 72 hours after irradiation. ns: non-significant; *: p≤0.05; **: p≤0.01; ***: p≤0.001; ****: p≤0.0001.