Fig. 2. Discrete -H2AX foci are located over synapsed autosomal regions at pachytene. Three different pachytene spermatocytes after double immunolabelling of the cohesin subunit SMC3 (green) and the histone variant -H2AX (red). Merged images (SMC3 and -H2AX, fourth column) and DAPI stained nuclei (blue) are also shown. SMC3 staining indicates the absence of full synapsis (A,E,I). The number of -H2AX foci reveals the different pachytene substages. Early pachytene (A-D) with a large amount of -H2AX foci. The number of foci varies from seven to 12 in mid-pachytene (E-H), but foci are absent in late pachytene (I-L). Notice that the amount of synapsis is similar in all pachytene sub-stages. X indicates sex chromosome. Bar, 10 µm.