Activation of meiotic recombination by nuclear import of the DNA break hotspot-determining complex in fission yeast

Abstract

Meiotic recombination forms crossovers important for proper chromosome segregation and offspring viability. This complex process involves many proteins acting at each of the multiple steps of recombination. Recombination initiates by formation of DNA double-strand breaks (DSBs), which in the several species examined occur with high frequency at special sites (DSB hotspots). In Schizosaccharomyces pombe DSB hotspots are bound with high specificity and strongly activated by linear element (LinE) proteins Rec25, Rec27, and Mug20, which form co-localized nuclear foci with Rec10, essential for all DSB formation and recombination. Here, we test the hypothesis that Rec10's nuclear localization signal (NLS) is crucial for coordinated nuclear entry after forming a complex with other LinE proteins. In NLS mutants, all LinEs were abundant in the cytoplasm, not the nucleus; DSB-formation and recombination were much reduced but not eliminated. Nuclear entry of limited amounts of Rec10, apparently small enough for passive nuclear entry, can account for residual recombination. LinEs are related to synaptonemal complex proteins of other species, suggesting that they also share an NLS, not yet identified, and protein complex-formation before nuclear entry.

Dynamic configurations of meiotic DNA-break hotspot determinant proteins

“…In addition, our results suggest that, unlike Rec10, the localizations of Rec25, Rec27 and Mug20 are interdependent with the other LinEs. These results support the model that the four LinE proteins form a multimeric LinE complex in the cytoplasm and are transported into the nucleus by the nuclear localization signal on Rec10, and that Rec10 alone can enter the nucleus but acts differently than the complete LinE complex; alternatively, the other LinE proteins may enter the nucleus on their own and form a complex with Rec10, and stay in the nucleus only if Rec10 is there (Wintrebert et al, 2021).…”

“…Rec10, Rec25, Rec27 and Mug20 form a LinE protein complex in the cytoplasm and are transported into the nucleus (Fig. 8A; Wintrebert et al, 2021). After DNA replication, LinE protein complexes bind to meiotic DSB hotspots (Fowler et al, 2013), form LinE clusters (Fowler et al, 2018), which appear as dotty foci in light microscopy of live cells (Fig.…”

Beyond microtubules: The cellular environment at the endoplasmic reticulum attracts proteins to the nucleus, enabling nuclear transport

“…Since physical interactions occur more frequently as the size of the molecules increases (Figure S1), larger proteins are more likely to accumulate at the perinucleus (Figures 2C and 2D). This provides insight for previous experimental observations: 1) proteins destined to reach the nucleus often form complexes before translocating to the nucleus 41,42 , 2) attaching specific moieties to anticancer drug particles, thereby increasing their size, facilitates targeting to the ER 43,44 , and 3) different types of particles, such as lipid nanoparticles and CaCO3, tend to accumulate in the perinuclear region based on their sizes 12-14 . While we focused on proteins with sizes comparable to the ER width (∼20 nm), cells also contain significantly larger particles (>>20nm) like vesicles and lysosomes 45,46 .…”

Beyond microtubules: The cellular environment at the endoplasmic reticulum attracts proteins to the nucleus, enabling nuclear transport

“…Since physical interactions occur more frequently as the size of the molecules increases ( Figure S1 ), larger proteins are more likely to accumulate at the perinucleus ( Figures 2 C and 2D). This provides insight for previous experimental observations: (1) proteins destined to reach the nucleus often form complexes before translocating to the nucleus, 44 , 45 (2) attaching specific moieties to anticancer drug particles, thereby increasing their size, facilitates targeting to the ER, 46 , 47 and (3) different types of particles, such as lipid and CaCO3 nanoparticles, whose sizes are larger than typical proteins, 22 tend to accumulate in the perinuclear region. 12 , 13 , 14 While we focused on proteins with sizes comparable to the ER width (∼20 ), cells also contain significantly larger particles (≫20 ) like vesicles and lysosomes.…”