Project description:Mapping of cohesion factor association sites in S. cerevisiae - Meiosis I chromosome segregation is established through regulation of microtubule-kinetochore interactions.
Project description:During meiosis, a single round of DNA replication is followed by two consecutive rounds of nuclear divisions called meiosis I and meiosis II. In meiosis I, homologous chromosomes segregate, while sister chromatids remain together. Determining how this unusual chromosome segregation behavior is established is central to understanding germ cell development. Here we show that preventing microtubule-kinetochore interactions during premeiotic S phase and prophase I is essential for establishing the meiosis I chromosome segregation pattern. Premature interactions of kinetochores with microtubules transform meiosis I into a mitosis-like division by disrupting two key meiosis I events: coorientation of sister kinetochores and protection of centromeric cohesin removal from chromosomes. Furthermore we find that restricting outer kinetochore assembly contributes to preventing premature engagement of microtubules with kinetochores. We propose that inhibition of microtubule-kinetochore interactions during premeiotic S phase and prophase I is central to establishing the unique meiosis I chromosome segregation pattern.
Project description:The recently proposed exozyme hypothesis posits that subunits of the RNA processing exosome assemble into structurally distinct protein complexes that function in disparate cellular compartments and RNA metabolic pathways. Here, in a genetic test of this hypothesis, we examine the role of Dis3 -- an essential polypeptide with endo- and 3' to 5' exo-ribonuclease activity -- in cell cycle progression. We present several lines of evidence that perturbation of DIS3 affects microtubule (MT) localization and structure in Saccharomyces cerevisiae. Cells with a DIS3 mutation: (i) accumulate anaphase and pre-anaphase mitotic spindles; (ii) exhibit spindles that are mis-oriented and displaced from the bud neck; (iii) harbor elongated spindle-associated astral MTs; (iv) have an increased G1 astral MT length and number; and (v) are hypersensitive to MT poisons. Mutations in the core exosome genes RRP4 and MTR3 and the exosome cofactor gene MTR4 -- but not other exosome subunit gene mutants -- also elicit MT phenotypes. RNA deep sequencing analysis (RNA-seq) shows broad changes in the levels of cell cycle- and microtubule-related transcripts in mutant strains. Collectively, the different mitotic phenotypes and distinct sets of mRNAs affected by the exosome subunit and cofactor mutants studied here suggest that Dis3 has a core exosome-independent role(s) in cell cycle progression. These observations are consistent with the predictions of the exozyme hypothesis and also suggest an evolutionarily conserved role for Dis3 in linking RNA metabolism, MTs, and mitotic progression.
