Figure 6.

Paired X chromosomes in rec-8 mutants exhibit two stretches of SC. (A) Immunolocalization of HIM-8 (green) and SYP-1 (red) in early pachytene nuclei from rec-8(ok978) and wild-type. As some SCs from the top and bottom halves of the nuclei are superimposed in the full projections encompassing whole nuclei, partial projections showing half nuclei are shown. Colored dashed boxes indicate the enlarged regions of the HIM-8 focus and SC depicted in the smaller images below, with the color indicating paired (yellow) or unpaired (blue) HIM-8 foci. Bars, 5 µm. (B) Stacked bar plot showing the fraction of nuclei displaying paired (yellow) or unpaired (blue) HIM-8 foci. HIM-8 foci were considered paired if the distance between the foci was ≤ 0.7 µm (see Materials and Methods). All HIM-8 foci in wild-type are paired, and in rec-8(ok978) mutants 80% of the HIM-8 foci are paired. In wild-type, all of the paired HIM-8 foci are associated with one SC track (solid bar) indicating SCs between homologous chromosomes. However, within rec-8 mutant nuclei, we observed differences in the number of SC tracks associating with either the paired or unpaired HIM-8 focus/foci. Among the paired HIM-8 foci (yellow), the majority of the rec-8 mutant nuclei displayed HIM-8 foci associated with two SC tracks (dotted bar) suggesting SC assembly between sister chromatids. Paired HIM-8 foci were also observed to not be associated with SC tracks (vertical striped bar) or associated with one SC track (solid bar). Among the unpaired (blue) HIM-8 foci in rec-8 mutants, the majority of the nuclei displayed HIM-8 foci where each was associated with an SC track (horizontal striped bar), also suggesting that the SC is assembling between sister chromatids in this context. Unpaired HIM-8 foci were also observed where only one focus was associated with an SC track (diagonal striped bar). Number of early pachytene nuclei scored for HIM-8: wild-type, n = 90 and rec-8(ok798), n = 116. SC, synaptonemal complex.