How are kinetochores remodelled for chromosome segregation during meiosis?

Kinetochores attach chromosomes to microtubules to mediate their segregation during mitosis and meiosis. During gamete formation by meiosis, kinetochores are adapted so that homologous chromosomes segregate in meiosis I and sister chromatids segregate in meiosis II. To achieve this, kinetochores take on specialized roles in homolog pairing, regulation of meiotic recombination and sister kinetochore co-orientation during meiosis I. Acquisition of these meiosis-specific properties of kinetochores is coupled to specialized kinetochore assembly and disassembly pathways. 1-3. The aim of this project is to understand how kinetochores are remodelled in meiosis to direct the segregation of chromosomes into gametes. To uncover conserved mechanisms of kinetochore remodelling in meiosis, two unrelated yeast species, Saccharomyces cerevisiae and Schizosaccharomyces pombe, will be used in two aims:

1. Determine how the inner kinetochore directs outer kinetochore assembly in early meiosis.
We discovered a kinetochore assembly pathway that is indispensable at the onset of meiosis, but not in mitosis. We hypothesise that specific recruitment of regulator factors (kinases, phosphatases) to the inner kinetochore triggers assembly or maintenance of the outer kinetochore in early meiosis. This idea will be tested using a combination of directed mutagenesis (using CRISPR-Cas9), immunoprecipitation/mass spectrometry, phosphoproteomics and live-cell microscopy.

2. Understand how kinetochore remodelling allows sister kinetochore fusion in meiosis I
The outer kinetochore disassembly at meiotic prophase and reassembly at prophase exit is hypothesised to help establish sister kinetochore co-orientation during meiosis I, the basis of Mendelian segregation. In S. cerevisiae, sister kinetochores are fused by a complex called monopolin and a protein known as Spo13 is also required for monoorientation. In S. pombe, monopolin is dispensable for monoorientation but the Moa1 protein, a functional homolog of Spo13 is required. Comparative biochemical and cell biological assays will be used to determine the relationship between monopolin and Spo13/Moa1-based co-orientation mechanisms.