Control of homologous chromosome division in the mammalian oocyte

Homologous chromosomes are segregated during the first meiotic division (meiosis I). Unfortunately, human oocytes are particularly susceptible to mis-segregation errors, so generating aneuploid, often non-viable, embryos. Here we review the cell biology of meiosis I and how homolog disjunction is regulated for mammalian oocytes. We focus on the activity of the anaphase-promoting complex/cyclosome (APC/C), which is responsible for timely degradation of the cohesin component, REC8 and the cyclin B regulatory subunit of maturation-promoting factor, both essential steps for meiosis I completion. In particular, we examine the role played by the spindle assembly checkpoint in controlling the APC/C activity, and in so doing ensuring accurate disjunction of homologs.