Sexual reproduction depends on meiosis, the specialized cell division that gives rise to gametes. During meiosis, two consecutive rounds of chromosome segregation follow one round of DNA replication to yield four haploid gametes from one diploid progenitor. In meiosis I, homologous chromosomes segregate and in meiosis 11, sister chromatids split. Much of the same cell cycle machinery controls mitosis and meiosis. However, segregation of homologous chromosomes in meiosis I and progression into meiosis 11 directly after meiosis I necessitate several modifications to the basic cell cycle machinery. In this thesis, I have investigated how cell cycle regulators function during gametogenesis. First, I show that the mitotic exit network, which is a signaling pathway essential for mitotic exit, is dispensable for the meiotic divisions, and in fact signals via a mechanism distinct from mitosis. Second, I present data that the Polo kinase Cdc5, which activates mitotic exit in budding yeast, has gained additional roles during meiosis 1. I show that CDC5 is required for the removal of cohesin from chromosome arms in meiosis I, which is a prerequisite for meiosis I segregation. Despite the central role of CDC5 in regulating meiosis I, CDC5 is dispensable during meiosis 11. In sum, understanding how cell cycle regulators control the specialized meiotic divisions has improved our understanding of how different cell division types are established.

The diversity of RNAs inside living cells is amazing. We have known of the more “classic” RNA species: mRNA, tRNA, rRNA, snRNA and snoRNA for some time now, but in a steady stream new types of molecules are being described as it is becoming clear that most of the genomic information of cells ends up in RNA. To deal with the enormous load of resulting RNA processing and degradation reactions, cells need adequate and efficient molecular machines. The RNA exosome is arising as a major facilitator to this effect. Structural and functional data gathered over the last decade have illustrated the biochemical importance of this multimeric complex and its many co-factors, revealing its enormous regulatory power. By gathering some of the most prominent researchers in the exosome field, it is the aim of this volume to introduce this fascinating protein complex as well as to give a timely and rich account of its many functions. The exosome was discovered more than a decade ago by Phil Mitchell and David Tollervey by its ability to trim the 3’end of yeast, S. cerevisiae, 5. 8S rRNA. In a historic account they laid out the events surrounding this identification and the subsequent birth of the research field. In the chapter by Kurt Januszyk and Christopher Lima the structural organization of eukaryotic exosomes and their evolutionary counterparts in bacteria and archaea are discussed in large part through presentation of structures.

In recent years, the study of the plant cell cycle has become of major interest, not only to scientists working on cell division sensu strictu , but also to scientists dealing with plant hormones, development and environmental effects on growth. The book The Plant Cell Cycle is a very timely contribution to this exploding field. Outstanding contributors reviewed, not only knowledge on the most important classes of cell cycle regulators, but also summarized the various processes in which cell cycle control plays a pivotal role. The central role of the cell cycle makes this book an absolute must for plant molecular biologists.

A look into the phenomena of sex and reproduction in all organisms, taking an innovative, unified and comprehensive approach.

The Cell Cycle: Principles of Control provides an engaging insight into the process of cell division, bringing to the student a much-needed synthesis of a subject entering a period of unprecedented growth as an understanding of the molecular mechanisms underlying cell division are revealed.