Kinetochore individualization for correct chromosome segregation in the oocyte

To divide the genetic material in mitosis cells must attach each sister chromatid with its attachment site called the kinetochore, to the opposite poles of the bipolar spindle. However, to generate haploid gametes, a diploid precursor cell must undergo two specific cell divisions, called meiosis I and II, without DNA replication. During the first meiotic division, whole chromosomes that have recombined are separated and during the second meiotic division, sister chromatids are separated such as in mitosis.

The LBD's MOM group investigated how oocytes "know" when they are supposed to separate chromosomes or sister chromatids. They found that an event they call “sister kinetochore individualization” takes place at the end of meiosis I, on co-oriented kinetochores, and allowing sister chromatid separation only in the immediately following meiosis II.

Overall, this work provides a better understanding of the fundamental mechanisms for the generation of fertilizable oocytes.

© Yulia Gryaznova and Katja Wassmann

Figure: A) Chromosome spreads of oocytes in metaphase and anaphase of meiosis I are used to determine whether sister kinetochores are fused or separated. Chromosomes are in blue (the DNA is stained with Hoechst), kinetochores in green, and Sgo2, a protein in the centromere region, magenta. Sister kinetochores are fused in metaphase and separated in anaphase. B) Explanatory scheme.


Team MOM - Mammalian Oocyte Meiosis

Kinetochore individualization in meiosis I is required for centromeric cohesin removal in meiosis II
Gryaznova Y, Keating L, Touati SA, Caldière D, El Yakoubi W, Buffin E and Wassmann K
The Embo Journal: 1er mars 2021.