Figure 3.

Mcmdc2^Gt/Gt spermatocytes are defective in homologous chromosomes synapsis and fail to progress through pachynema. Immunofluorescent images of meiotic chromosome spreads from Mcmdc2^Gt/+ and Mcmdc2^Gt/Gt spermatocytes were stained with the indicated antibodies. (A) Mcmdc2^Gt/Gt chromosomes fail to pair or synapse along their lengths. Only short patches of SC (marked by SYCP1 labeling) are present in adult spermatocytes. Note: spermatocytes from 19-day-old mice completely lacked such SYCP1 labeling. (B) Mcmdc2^Gt/Gt mutants fail to progress to midpachynema as evidenced by a lack of H1T staining and failure to undergo homologous chromosome pairing. The H1T signal exhibits bleed-through in the SYCP3 channel due to cross-reactivity between secondary antibodies. (C) Mcmdc2^Gt/Gt mutants have abnormally distributed γH2AX, which marks both asynapsed chromosomes and unrepaired DSBs. Unlike heterozygotes, the mutants lack a discrete XY body that is marked by intense γH2AX.