Figure 6.

HEI10 behavior compared to ASY1 and ZYP1 dynamics during prophase I. The images (A₁-A₄) show enlarged regions delimited by dashed boxes. Chromatin was counterstained with DAPI. (A) Throughout prophase I until late diplotene, HEI10 foci follow the dynamics of ZYP1. At zygotene, HEI10 foci are present at the central region of the SC marked by ZYP1. At the end of synapsis during pachytene single HEI10 foci become more prominent. At diplotene, the progression of SC disassembly causes the fragmentation of the SC, and HEI10 can be detected either as numerous low-intensity foci organized along the central element, or as a few prominent foci most likely corresponding to crossover- fated recombination sites. At late diakinesis, ASY1 and ZYP1 disappear, but HEI10 proteins remain as distinct spots at the potential recombination sites. Bars = 5 μm. (A₁) At zygotene, HEI10 foci occur exclusively in SCs marked by ZYP1. Bar = 1 μm. (A₂) At pachytene, individual HEI10 foci become more pronounced and clearly distinguishable (arrows). Bar = 1 μm. (A₃) Low-intensity HEI10 foci along the residual central region of the SC exist in parallel to a pronounced HEI10 focus (arrow) indicating a recombination site at late diplotene. ASY1 threads coil up at this position. Bar = 1 μm. (A₄) An A chromosome ring bivalent at late diakinesis with two HEI10 spots marking the potential sites of crossovers. ASY1 and ZYP1 signals are no longer detectable. Bar = 1 μm. (B) Two A chromosome ring bivalents accompanied by a single B chromosome (arrow) at diplotene. Similar as on the A chromosomes HEI10 threads are evident on the self-paired B chromosome. Bar = 2 μm. (C) Typical twisted SC structures marked by ASY1, ZYP1, and HEI10 on an A bivalent at diplotene. (C₁) The enlarged view of (C) shows the co-localization of the three proteins at the fragmented SC and indicates the ongoing desynapsis. Bar = 2 μm. (C₂,C₃) Besides weak HEI10 foci along ZYP1, two pronounced HEI10 spots are visible at higher magnification. The localization of such foci toward the bivalent connection sites at late diakinesis (A₄,D) suggests the staining of crossovers. Note, the HEI10 spot in (C₂) is localized slightly apart from the central element of the SC marked by ZYP1. Bar = 2 μm. (D,D₁) Distinct HEI10 spots (arrowheads) on an A chromosome ring bivalent at late diplotene. Both spots are not located on SC residues and likely correspond to the HEI10 signals exclusively evident at late diakinesis (A₄). Bar = 2 μm. (E) Three A bivalents at late diakinesis show two HEI10 foci each. Instead, the single B chromosome (arrow) does not contain any HEI10 spots. Bar = 2 μm.