Figure 7. Synaptic initiation complexes (SCISs) in zygotene meiocytes.

(A) Representative zygotene spermatocyte (left), with antibodies against SYCP3 (detecting the axial/lateral elements of the SC) in red and CREST antiserum-positive signals (recognizing centromeric regions) in blue. Intense red signals indicate points where the axial/lateral elements have merged, consistent with full synapsis (i.e., SCISs). SCISs are located at, or near the telomeres, an arrangement typical for human males. The center panel shows a blow-up of a partially-synapsed bivalent (circled) and the right panel provides a schematic of the bivalent, with the synapsed regions at the ends of the arms and the proximal regions (including the centromeres) asynapsed. (B, C) Representative images of zygotene stage oocytes (left), with the axial/lateral element protein SYCP3 in red, the transverse element protein SYCP1 in green and centromere-associated CREST in blue; merged SYCP3/SYCP1 signals (yellow) indicate regions of synapsis (i.e., SCISs). Center panels provide blow-ups of partially synapsed bivalents (circled) and the right panel schematics, demonstrating the presence of multiple SCISs per chromosomes and in (C), co-localization of the centromere and one of the SCISs.