FIG. 6.

Increased frequency of meiotic recombination during pachytene in HR6B^−/− spermatocytes. (A) Meiotic spread preparations from wild-type (wt) and HR6B knockout (bb) mouse testes and from wild-type and HR6A knockout (aa) mouse fetal ovaries (E18) were stained with anti-SCP3 (SCP3, red signal) and anti-MLH1 (MLH1, green signal). In the HR6B knockout (bb), the number of MLH1 foci is increased (29 foci in this nucleus) compared to the wild type (23 foci). The average number of foci between wild-type and HR6A knockout oocytes does not differ (the number of foci for these two individual nuclei are 33 and 30, respectively). The SC structure of the knockout pachytene spermatocyte nucleus shown here has relatively few abnormalities. An increased number of MLH1 foci is found in bb nuclei that appear relatively normal and also in bb nuclei that show long and thin SC axes and/or loose SCP2/SCP3 beads (the latter is not shown). XY indicates the sex body. Scale bar, 20 μm. (B) The number of MLH1 foci per spermatocyte nucleus is indicated on the y axis. Please note that this axis starts at 21 foci. The gray squares indicate the average number of foci per nucleus per animal (N = the number of animals tested). For each animal at least 10 nuclei were counted. In black, the mean value and SEM are indicated (black square and error bars, respectively). MLH1 foci were counted in wild-type (wt), HR6A knockout (aY), and HR6B knockout (bb) spermatocytes. (C) Diakinesis/metaphase I spread preparations of wild-type (wt) and HR6B knockout (bb) spermatocyte nuclei. Bivalents showing two crossover events are indicated by and asterix. The bivalents containing the X and Y chromosome are indicated by XY. Note that the centromeric regions of the chromosomes are more heavily stained by DAPI. Scale bar, 10 μm.