Fig. 3. RAD51 foci appear over cohesin axes. Early meiotic stages of male meiosis after double immunololabelling of the cohesin subunit SMC3 (green in first column) and the recombinase RAD51 (red in second column). Merged images (SMC3 and -H2AX) are in the forth column and DAPI stained nuclei (blue) are observed in the third one. Several focal planes were merged to obtain each image. Early leptotene (A-D) is characterised by the presence of threads of cohesin axes in a polarised nuclear region (A). Notice that RAD51 foci (B) are located over SMC3 threads (D). Mid-leptotene (E-H). Progressive maturation of cohesin axes (E). The number of RAD51 foci rapidly increase (F) and remain associated to the cohesin axes (H). The characteristic bouquet-like arrangement can be identified in zygotene spermatocytes (I-L). Both SMC3 paired-axes (I) and RAD51 foci (J) are polarised in a discrete region of the nucleus. It is evident that the localisation of RAD51 foci is strictly restricted to paired cohesin axes (L). RAD51 foci are restricted to thick, synapsed, cohesin axes at early pachytene (M-P). Mid-pachytene (Q-T) shows a lower amount of RAD51 foci (R). Notice that, in all cases RAD51 signals are located over synapsed regions (D,H,L,P,T). X indicates sex chromosome. Bars, 10 µm.