Abstract
During meiosis, homologous chromosomes pair at close proximity to form the synaptonemal complex (SC). This association is mediated by transverse filament proteins that hold the axes of homologous chromosomes together along their entire length. Transverse filament proteins are highly aggregative and can form an aberrant aggregate called the polycomplex that is unassociated with chromosomes. Here, we show that the Ecm11-Gmc2 complex is a novel SC component, functioning to facilitate assembly of the yeast transverse filament protein, Zip1. Ecm11 and Gmc2 initially localize to the synapsis initiation sites, then throughout the synapsed regions of paired homologous chromosomes. The absence of either Ecm11 or Gmc2 substantially compromises the chromosomal assembly of Zip1 as well as polycomplex formation, indicating that the complex is required for extensive Zip1 polymerization. We also show that Ecm11 is SUMOylated in a Gmc2-dependent manner. Remarkably, in the unSUMOylatable ecm11 mutant, assembly of chromosomal Zip1 remained compromised while polycomplex formation became frequent. We propose that the Ecm11-Gmc2 complex facilitates the assembly of Zip1 and that SUMOylation of Ecm11 is critical for ensuring chromosomal assembly of Zip1, thus suppressing polycomplex formation.
Highlights
Meiosis is a special type of cell cycle necessary for sexual reproduction [1]
The first round of division is unique to meiosis in that homologous chromosomes are segregated to opposite poles
We demonstrate that post-translational modification of Ecm11 with small ubiquitin-related modifier (SUMO) is critical for ensuring the chromosomal loading of transverse filaments
Summary
Meiosis is a special type of cell cycle necessary for sexual reproduction [1]. A diploid cell undergoes one round of DNA replication followed by two rounds of successive nuclear segregation, meiosis I and meiosis II respectively. At meiosis I, homologous chromosomes are segregated to opposite poles whereas at meiosis II, sister chromatids separate. Four haploid gametes form from one diploid progenitor cell. Homologous recombination plays two critical roles in ensuring the faithful segregation of homologous chromosomes at meiosis I [2]. In early prophase I, homologous recombination provides a means for chromosomes to find their homologous partners, facilitating pairing of homologous chromosomes. Crossover recombination events provide a physical connection that maintains homologous associations until chromosomes are properly aligned on the metaphase I spindle
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