Biology subjects

Hamamura, Y.

Publications and source records attributed to Hamamura, Y..

4 recordsLinked to original sources

bioRxiv2022

The cohesin subunit RAD21.2 functions as a recombination silencer of ribosomal DNA arrays

Introductory ParagraphIn many species, including Arabidopsis, heterochromatin often comprises repetitive DNA elements, such as arrays of ribosomal DNA (rDNA). Repetitive regions pose a risk in meiosis since recombination between them can lead to gross genomic rearrangements. However, meiotic recombination at rDNA arrays and other heterochromatic repeat regions is blocked by not well understood mechanisms. Here, we have identified RAD21.2, an -kleisin subunit of cohesin, as a repressor of meiotic recombination at the rDNA regions in Arabidopsis. We show that RAD21.2 co-localizes with heterochromatic factors and is specifically enriched at rDNA repeats, which are devoid of the meiosis specific -kleisin REC8, needed for recombination. Knocking down RAD21.2, we find that REC8 moves into the nucleolus organizing regions (NORs), where we see an increase of RAD51 recombinase foci numbers. Concomitantly, we find extensive rearrangements of the NORs and the offspring of these plants have large variation in rDNA copy numbers demonstrating that RAD21.2 is necessary for transgenerational genome stability. One-Sentence SummaryThe cohesin component RAD21.2 represses meiotic recombination and by that contributes to genome stability over generations.

cell biology↗

bioRxiv2022

Bipartite recruitment of PCH2 and COMET to the synaptonemal complex drives chromosome axis reconstruction leading to crossover restriction

Chromosome axis-associated HORMA domain proteins (HORMADs), e.g., ASY1 in Arabidopsis, are crucial for meiotic recombination. ASY1, as other HORMADs, is assembled on the axis at early meiosis and depleted when homologous chromosomes synapse. Puzzlingly, both processes are catalyzed by AAA+ ATPase PCH2 together with its cofactor COMET. Here, we show that the ASY1 remodeling complex is temporally and spatially differently assembled. While PCH2 and COMET appear to directly interact in the cytoplasm in early meiosis, PCH2 is recruited by the transverse filament protein ZYP1 and brought to the ASY1-bound COMET assuring the timely removal of ASY1 during chromosome synapsis. Since we found that the PCH2 homolog TRIP13 also binds to the ZYP1 homolog SYCP1 in mouse, we postulate that this mechanism is conserved among eukaryotes. Deleting the PCH2 binding site of ZYP1 led to a failure of ASY1 removal. Interestingly, the placement of one obligatory crossover per homologous chromosome pair, compromised by ZYP1 depletion, is largely restored in this engineered zyp1 allele suggesting that crossover assurance is promoted by synapsis. In contrast, the engineered zyp1 allele, similar to the zyp1 null mutant, showed elevated type I crossover numbers indicating that PCH2-mediated eviction of ASY1 from the axis restricts crossover formation.

cell biology↗

bioRxiv2020

Functional analysis of the chromosomal passenger complex in Arabidopsis

A key regulator of cell division in all eukaryotes is the kinase Aurora B, which is encoded by the Aurora 3 (AUR3) gene in Arabidopsis. Aurora B has at least two central functions during cell division. On the one hand, it is essential for the correct, i.e. balanced, segregation of chromosomes in mitosis and meiosis by controlling kinetochore function. On the other hand, Aurora B acts at the division plane, where it is necessary to complete cytokinesis. To accomplish these two spatially distinct functions, Aurora B in animals is guided to its sites of action by Borealin, INCENP, and Survivin that build together with Aurora B the chromosome passenger complex (CPC). However, besides Aurora homologs, only a candidate gene with restricted homology to INCENP has so far been described in Arabidopsis raising the question whether there exists a full complement of the CPC in plants and how Aurora homologs are targeted subcellularly. Here, we have identified and functionally characterized a Borealin homolog, BOREALIN RELATED (BORR), in Arabidopsis. This, together with detailed localization studies including the putative Arabidopsis INCENP homolog, supports the existence of a CPC in plants.

cell biology↗

bioRxiv2019

SWITCH 1/DYAD is a novel WINGS APART-LIKE antagonist that maintains sister chromatid cohesion in meiosis

Mitosis and meiosis both rely on cohesin, which embraces the sister chromatids and plays a crucial role for the faithful distribution of chromosomes to daughter cells. Prior to the cleavage by Separase at anaphase onset, cohesin is largely removed from chromosomes by the non-proteolytic action of WINGS APART-LIKE (WAPL), a mechanism referred to as the prophase pathway. To prevent the premature loss of sister chromatid cohesion, WAPL is inhibited in early mitosis by Sororin. However, Sororin homologs have only been found to function as WAPL inhibitors during mitosis in vertebrates and Drosophila. Here we show that SWITCH 1/DYAD defines a novel WAPL antagonist that acts in meiosis of Arabidopsis. Crucially, SWI1 becomes dispensable for sister chromatid cohesion in the absence of WAPL. Despite the lack of any sequence similarities, we found that SWI1 is regulated and functions in a similar manner as Sororin hence likely representing a case of convergent molecular evolution across the eukaryotic kingdom.

cell biology↗