Meiosis is a specialized cell division program that gives rise to gametes in sexually reproducing organisms. The first stage of meiosis, called meiosis I, uniquely involves the association, programmed recombination, and eventual segregation of homologous chromosomes. While this process is well understood from a genetic and cytological standpoint, our understanding of how the meiosis-specific cellular machinery is able to organize and manipulate meiotic chromosomes in 3D space to mediate their proper segregation remains a mystery. This area of study is significant, as errors in meiosis I chromosome segregation account for the vast majority of aneuploidies, extra or missing chromosomes in offspring, that occur in over half of human oocytes and 5-10% of clinically recognized pregnancies. As such, aneuploidy is the leading genetic cause of miscarriage and of mental retardation (e.g. Down syndrome, caused by trisomy of chromosome 21). The underlying causes of chromosome segregation errors in meiosis I are not well understood, and further progress toward identifying these causes will require a detailed understanding of the molecular mechanisms of meiosis-specific chromosome segregation machinery. Here, we propose to study three sets of meiotic chromosome-associated proteins that are critical for different aspects of chromosomes'organization and physical manipulation in meiosis I. Our approach combines in vitro reconstitution of purified proteins and complexes, 3D structural analysis of these complexes, and targeted genetic assays to test mutants designed to disrupt specific aspects of these proteins'structures and interactions. We will first study the S. cerevisiae monopolin complex, which binds chromosomes'kinetochores in meiosis I and modifies their attachments to spindle microtubules, to enable the proper orientation and segregation of homologous chromosomes. We will determine the architecture of the monopolin complex, and use engineered protein constructs in genetic assays to test whether it directly cross-links sister kinetochores to mediate their attachment to a single microtubule. Next, we will study the conserved chromosome-associated protein Hop1, a component of the proteinaceous "axis" about which each chromosome is organized. We will examine the roles of Hop1's conserved HORMA domain, a signaling domain shared with the spindle checkpoint protein Mad2, in regulating inter-homolog meiotic recombination, and in a meiosis-specific checkpoint monitoring recombination. Finally, we will study the synaptonemal complex, an essential polymeric assembly that links homologs together during meiotic recombination. As very little is known about the architecture of this complex or its functions, we will study the domain structure, protein-protein interactions, and self-assembly determinants of the key S. cerevisiae synaptonemal complex protein Zip1. Combined, this work will begin to provide a more accurate picture of the macromolecular structures and interactions underlying homologous chromosome recombination and segregation in meiosis I.

Public Health Relevance

The proposed project is highly relevant to public health, in that it investigates a process whose failure can result in infertility, miscarriage, and developmental disorders in children. Our work focuses on meiosis, the cell division program that gives rise to gametes in sexual reproduction, and particularly we concentrate on how cells segregate their chromosomes properly in meiosis to avoid aneuploidy. Aneuploidy, characterized by the gain or loss of one or more chromosomes in an embryo, occurs in 5-10% of clinically recognized pregnancies, and causes miscarriage or developmental disorders like Down syndrome. Our work to characterize the molecular mechanisms ensuring proper chromosome segregation during gamete formation could eventually enable therapies to reduce the prevalence of aneuploidy in embryos, and increase fertility in individuals with defects in the relevant cellular machinery.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM104141-02
Application #
8594255
Study Section
Molecular Genetics A Study Section (MGA)
Program Officer
Janes, Daniel E
Project Start
2012-12-10
Project End
2017-11-30
Budget Start
2013-12-01
Budget End
2014-11-30
Support Year
2
Fiscal Year
2014
Total Cost
$278,559
Indirect Cost
$107,559
Name
Ludwig Institute for Cancer Research Ltd
Department
Type
DUNS #
627922248
City
La Jolla
State
CA
Country
United States
Zip Code
92093
Kim, Yumi; Rosenberg, Scott C; Kugel, Christine L et al. (2014) The chromosome axis controls meiotic events through a hierarchical assembly of HORMA domain proteins. Dev Cell 31:487-502
Sarangapani, Krishna K; Duro, Eris; Deng, Yi et al. (2014) Sister kinetochores are mechanically fused during meiosis I in yeast. Science 346:248-51
Corbett, Kevin D; Desai, Arshad (2014) A new piece in the kinetochore jigsaw puzzle. J Cell Biol 206:457-9
Bhandari, Deepali; Zhang, Jinzhong; Menon, Shekar et al. (2013) Sit4p/PP6 regulates ER-to-Golgi traffic by controlling the dephosphorylation of COPII coat subunits. Mol Biol Cell 24:2727-38