Figure 5.

Pairing/synapsis defects in three mer2 nonnull mutants. (A–H,O,R,S) 3D-SIM pictures of Spo76-GFP and Hei10-GFP costaining. The seven bivalents are distinguishable by their lengths and colors (e.g., the two longest are red and yellow, and the smallest is blue). (A,B) Coalignment (A) and synapsis (B) of wild-type homologs are always synchronous, even when two are entangled (arrow in A). (C,D) Pairing/synapsis is either completely defective (C) or partially defective (D) in mer2-19 and mer2-del2. Nevertheless, Hei10 foci form in the few synapsed segments (arrows in D). More nuclei are shown in Supplemental Figure S3, H–L. (E,F) All mer2-17 zygotene nuclei exhibit a mixture of partially aligned (yellow, green, and purple pairs in F) and partially synapsed (red, blue, and orange pairs) homologs, the latter with Hei10 foci (red arrows in E). (G,H) Interlocking in mer2-17: The purple bivalent is entrapped in the yellow pair (arrow). Red arrows point to Hei10 foci. (I–K) Mer3 foci form normally in the three mutants (here mer2-del2) and, like in wild type (I), occur in matching pairs in the segments where coalignment occurs (arrows in J). (K) Corresponding DAPI. (L–N) Note the difference in number and spacing of Msh4 foci in wild type (L) and mer2-19 (M). (N) Corresponding DAPI. (O–R) mer2-17 exhibits complete SC formation with at least one Hei10 focus per bivalent (O,P; red arrows point to close foci) and seven chiasmate bivalents (Q) at diplotene. (R) Example of one bivalent (right) with close Hei10 foci (top and bottom) and another bivalent (left) with close foci adjacent to an open space due to an interlocking (red arrows). (S) At pachytene, mer2-19 remains mostly asynaptic except for few synapsed segments where Hei10 foci accumulate (red arrows). Bars, 2 µm.