Figure 5

Configurations of synapsed trivalents in pachytene nuclei of 2n = 32 spermatocytes (a–b) and ectopic associations between asynapsed trivalents and the XY bivalent (d–f). a–b.Trivalent configurations in a diagram (a) and in a well preserved nucleus (b). The synaptonemal complexes (green) and centromeres (red) were identified by immunochemistry, using, respectively, anti-SYCP3 and anti-CENPA antibodies. The trivalents present 3 points of attachment to the nuclear envelope, two of which correspond to the distal telomeres of the metacentric chromosomes synapsed with the long arms of the telocentric chromosomes (arrowheads), and the third to the attachment of the proximal telomeres of the telocentric chromosomes (arrow). The third point drags the pericentromeric heterochromatin of the 3 chromosomes involved in the trivalent towards the nuclear periphery. c–d. In nuclear spreads the chromosomal axes (red) and central element of the SC (green) were identified by immunochemistry, using, respectively, anti-SYCP3 and anti-SYCP1 antibodies. c) Two asynapsed trivalents are associated through both single axes from the two telocentric short arms (arrow). In both bonding zones, the protein SYCP1 was detected (yellow). The 6-remaning trivalents are totally synapsed. d) The single axis of an asynapsed trivalent is bound to the X chromosome single axis. At the end-to-end contact region, the SYCP1 protein was detected (arrowhead). e–f. γH2AX antibodies intensely labels the XY chromatin (blue), the chromatin surrounding asynapsed trivalent AEs, and is absent in the chromatin of synapsed bivalents. e) One asynapsed trivalent is associated to the XY bivalent only through chromatin where the modified histone γH2AX is detected (arrowhead). The 7-remaning trivalents are totally synapsed, not associated at all and without detection of γH2AX. f) Two asynapsed trivalents (arrows) and one asynapsed trivalent and the XY bivalent (arrowhead), are associated among them only through chromatin where the histone γH2AX is detected.