SWITCH1 (SWI1): a novel protein required for the establishment of sister chromatid cohesion and for bivalent formation at meiosis

Abstract

We have characterized a new gene, SWI1, involved in sister chromatid cohesion during both male and female meiosis in Arabidopsis thaliana. A first allele, swi1.1, was obtained as a T-DNA tagged mutant and was described previously as abnormal exclusively in female meiosis. We have isolated a new allele, swi1.2, which is defective for both male and female meiosis. In swi1.2 male meiosis, the classical steps of prophase were not observed, especially because homologs do not synapse. Chromatid arms and centromeres lost their cohesion in a stepwise manner before metaphase I, and 20 chromatids instead of five bivalents were seen at the metaphase plate, which was followed by an aberrant segregation. In contrast, swi1.2 female meiocytes performed a mitotic-like division instead of meiosis, indicating a distinct role for SWI1 or a different effect of the loss of SWI1 function in both processes. The SWI1 gene was cloned; the putative SWI1 protein did not show strong similarity to any known protein. Plants transformed with a SWI1-GFP fusion indicated that SWI1 protein is present in meiocyte nuclei, before meiosis and at a very early stage of prophase. Thus, SWI1 appears to be a novel protein involved in chromatid cohesion establishment and in chromosome structure during meiosis, but with clear differences between male and female meiosis.

OsREC8 Is Essential for Chromatid Cohesion and Metaphase I Monopolar Orientation in Rice Meiosis

“…However, we could not observe the complete loss of cohe- sion during late prophase I as observed in Arabidopsis switch1 mutants (Mercier et al, 2001) or C. elegans rec8/ spo11 double mutants (Pasierbek et al, 2001). In Osrec8-1 meiocytes, a pair of sister chromatids of each univalent aligned on the equatorial plate, attached by microtubules emanating from the opposite pole at metaphase I.…”

ASY1 mediates AtDMC1-dependent interhomolog recombination during meiosis in Arabidopsis

“…How axis morphogenesis and recombination initiation are coordinated remains to be resolved. One potential candidate is the SWITCH1 (SWI1) protein (Mercier et al 2001(Mercier et al , 2003. Mutants lacking SWI1 fail to initiate recombination, do not form axial elements, and ASY1 localiza-tion does not progress beyond the stage of chromatinassociated foci, implying that these may be interdependent processes.…”

OsAM1 is required for leptotene-zygotene transition in rice

“…Four swi1 alleles [20,21,43,44] and six am1 alleles [22][23][24] have been reported. The two proteins, SWI1 and AM1 have similar functions in the early phases of meiosis, such as regulation of chromosome structure and control of homologous recombination.…”

“…In swi1-2 mutant male meiocytes, chromatid arms and centromeres lose their cohesion, resulting in the formation of 20 chromatids instead of 5 bivalents; however, female meiocytes retain centric/whole-arm cohesion, but lack synapsis and undergo a mitosis-like division in lieu of a reductional meiosis I [20,21]. In the am1-1 (ameiotic1-1) mutant allele of maize, both male and female meiocytes fail to enter meiosis; instead, they proceed with several mitotic divisions and then degrade.…”