The role of Sgo1 in protection of centromeric cohesion, accurate segregation of chromosomes and maintaining genomic stability in mammalian meiosis

Projektinformationen

SGO1 IN MEIOSIS

ID Finanzhilfevereinbarung: 24429

Startdatum 1 Dezember 2005

Enddatum 30 November 2007

Finanziert unter

• Human resources and Mobility in the specific programme for research, technological development and demonstration "Structuring the European Research Area" under the Sixth Framework Programme 2002-2006

Gesamtkosten € 0,00

EU-Beitrag € 171 635,00

Koordiniert durch

THE CHANCELLOR, MASTERS AND SCHOLARS OF THE UNIVERSITY OF OXFORD
United Kingdom

Final Activity Report Summary - SGO1 IN MEIOSIS (The role of Sgo1 in protection of centromeric cohesion, accurate segregation of chromosomes and maintaining genomic stability in mammalian meiosis)

Sister chromatids are held together after DNA replication by protein complex called cohesin. This complex also plays crucial role in chromosome segregation later during cell division. For accurate segregation of chromosomes in meiosis, cohesin proteins must be removed sequentially. The cohesin located on chromosome arms, required for correct separation of homologues, is dissolved during the first meiotic division whereas centromeric cohesin is removed during the second division, coincident with separation of the sister chromatids. Using mouse oocytes, we have shown that this pattern of cohesin distribution previously observed in yeasts and other species also applies to mammalian meiosis. In yeast meiosis, cleavage of the Rec8 cohesin subunit along chromosome arms by the enzyme Separase is required for the resolution of chiasmata. Whether the same mechanism is also responsible for chiasmata resolution in animals was unclear. Instead, it has been suggested that the resolution of chiasmata is achieved by a Separase - independent mechanism related to prophase pathway.

To resolve this, we used a mouse strain in which Separase can be specifically deleted in oocytes by Cre recombinase expressed under the control of ZP3 promoter. Our results showed that Separase is required for chiasmata resolution, the removal of Rec8 from chromosome arms, and, unexpectedly, also for the extrusion of the first polar body. Separase is essential and females lacking this enzyme in oocytes are infertile. We have also shown that whereas the proteolytic activity of Separase is crucial for cohesin removal it is not required for its role in polar body extrusion.

Since Separase triggers both meiotic divisions, centromeric cohesin must somehow be resistant to Separase activity during meiosis I. It was recently shown in yeast that the proteins Sgo1 and phosphatase 2A (PP2A) are required for the protection of centromeric cohesion during the first meiotic division. However, it was unknown whether the same mechanism operates in mammalian meiosis. Since female meiosis in humans is prone to errors resulting in aneuploidy, it is very important to understand the processes underlying chromosome segregation. Therefore, we have studied the interaction of Sgo1 and PP2A in mammalian meiotic cells. Our results showed that mouse Sgo1 and PP2A interact both in vitro and in vivo in oocytes and that this interaction is required for the localisation of PP2A to the chromosomes. An Sgo1 mutation that blocks this interaction in vitro also prevented PP2A from binding to chromosomes in vivo.

Bub1 is an essential part of a regulatory network called the spindle checkpoint that monitors the attachment of chromosomes by the spindle apparatus. Since mouse oocytes can tolerate unattached kinetochores it was not clear whether the spindle checkpoint is active in those cells. We have used Bub1 - depleted oocytes and our results indicate that the timing of onset of anaphase I is indeed regulated by spindle checkpoint.