Meiotic control of the APC/C: similarities & differences from mitosis

The proper segregation of chromosomes at meiosis I and II is essential for producing gametes with the correct haploid genome (Figure 1). During oogenesis, meiotic progression is arrested at the first or second division during development. Maturation of the oocytes or fertilization is required to relieve these blocks, respectively. Spermatogenesis is a continuous process that occurs throughout most of the life of the male. Yeast sporulation possesses the hallmarks of mammalian meiosis and is similar to spermatogenesis in that the process does not exhibit programmed arrest points. In Saccharomyces cerevisiae, entry into the meiotic program is dependent upon cell-type and environmental clues [1]. Following induction, premeiotic DNA replication occurs followed by a lengthy prophase in which homologous chromosomes synapse and undergo a high level of genetic recombination prior to meiosis I ([2] & Figure 1). This genetic exchange is essential for chromosomes to correctly align at metaphase I. It is during meiosis I, the reductional division, that the sister chromatids remain paired, attach to only one spindle, and segregate together. This centromeric cohesion is lost during the second meiotic division, which resembles mitosis, where the replicated sisters make bipolar attachments and separate to opposite poles [3]. The resulting four haploid nuclei are each encased in a multi-layered structure called a spore that remains dormant until induced to reenter mitotic cell division by growth signals [1]. Thus, the monopolar attachment of replicated sister chromatids at meiosis I and the execution of two nuclear divisions without an intervening S phase represent two major differences between meiotic and mitotic divisions.The basic cell cycle machinery driving mitotic cell division (e.g., DNA polymerases, cyclin dependent kinases, ubiquitin ligases) is also required to execute meiosis. However, meiosis presents several challenges that are not found during mitosis such as maintaini