Figure 3.

Genetic control of PAR recombination and pairing. A. Spo11 splice variants (see also fig. S4). i) Genomic organization and splicing. Spo11β includes exon 2, Spo11α excludes it. Y, catalytic tyrosine. ii–iii) Reverse transcriptase-PCR from flow-sorted meiocyte populations of adult mice. –RT, no reverse transcriptase; L/Z, leptonema/zygonema; P/D, pachynema/diplonema; S, spermatids. iv) SPO11 protein levels in adult testis extracts. Asterisk, a lower-mobility protein likely originating from the knock-out allele (fig. S5D). B. IF of SYCP1 and SYCP3 on pachytene nuclei (i) and of SYCP3 plus whole-chromosome FISH of early metaphase I spermatocyte nuclei (ii) from mice of the indicated genotypes. Inset in (i), schematic of X and Y chromosomes. Scale bars, 10 μm. (iii) Quantification of X-Y association; 57–65 nuclei scored/genotype. C. TUNEL-stained testis sections; apoptotic cells stain brown. Elongating spermatids (arrows) are rare in Spo11β-only mice. Inset shows a lagging chromosome (arrowhead) in a TUNEL-positive cell. D. RAD51/DMC1 focus counts in spermatocytes from control and Spo11β-only mice (bars = mean±SD). E. Nuclei (%) with PAR RAD51/DMC1 foci in mice of the indicated genotypes. 41–55 nuclei were scored per stage for each genotype. Asterisks indicate significant differences (P≤ 0.0002, two-tailed Mann-Whitney test). n.s., not significant, P=0.09.