Fig. 2. Analysis of X chromosome synapsis in pachytene stage oocytes. (A) Pachytene stage oocyte from an XO female mouse immunostained with an antibody to SCP3 (green) to visualize the lateral elements of the SC, and hybridized with X-chromosome specific (purple) and telomere-specific (red) probes. The dispersed X chromosome signal (arrow) is due to the nature of the probe (DXWAS70 detects a multicopy sequence close to the centromere of the X chromosome) and the decondensed state of the chromatin at this stage. (B-F) Synaptic configurations of the univalent X chromosome during pachytene, (B) ‘asynapsed’ X chromosome showing a lateral element with telomeres present at both ends, (C) ‘fully self-synapsed’ X chromosome forming a hairpin structure with overlapping telomeres that appear as a single signal, (D) ‘partial self-synapsis including the centromere’ showing a portion of the lateral element synapsed with both telomeres overlapping and appearing as one, (E) ‘partial self-synapsis excluding the centromere’ showing a portion of the lateral element synapsed with two telomeres distinguishable, (F) ‘X/autosome association’ showing a triradial structure with three telomeres representing the X and an autosomal bivalent.
