Fig. 6. TNs and MLH1 foci in Sycp3^–/– oocytes. (A) An early prophase nucleus from a 15.5-day old foetus with 150 TNs (yellow) associated with SC-like structures (bright green) and 250 TNs (red) associated with unpaired cores (weak green). Immunostaining of RPA-TNs: core components SMC3, SYCP1, Rhodamine, red; centromeres, FITC, green. (B-D) Three pachytene oocytes nuclei from one ovary of a 17.5-day old foetus with different levels of synaptic defects. Chromosome cores were immunostained with rabbit anti-SMC3 (Rhodamine, weak red) and SC central elements with rabbit anti-SYCP1 (Rhodamine, bright red). The MLH1 foci are visualized by mouse anti-MLH1 and FITC-conjugated secondary antibody (green). (B) An oocyte nucleus with severe synaptic defects. Arrows mark some of the MLH1 foci that are not associated with brightly stained SYCP1 segments. (C) An oocyte nucleus with intermediate synaptic defects. There are more and longer SYCP1 segments and fewer free MLH1 foci (arrows). (D) A near-normal looking oocyte nucleus with well-developed SYCP1-defined SCs, few unsynapsed cores, and no free MLH1 foci.