Homologous recombination is a template-dependent DNA repair process that underpins DNA replication and genome stability, and is essential for chromosome segregation during meiosis. The fundamental recombination reaction is the formation of Joint Molecule (JM) intermediates via homologous pairing and DNA strand-exchange between a broken chromosome end and a homologous template. JMs are matured and resolved in distinct ways to produce products with or without an associated crossover. This proposal will investigate the in vivo roles of factors that regulate the formation and resolution of JMs during meiosis. The general hypothesis is that specialized JM processing factors are subject to distinct spatial and temporal regulation. Assigning in vivo functions to specific JM processing factors and understanding how they interact during recombination remain challenging issues, which are complicated by overlapping/compensatory activities and the need for specialized assays to monitor molecular phenotypes. DNA assays to monitor the chemical steps of recombination in vivo will form the cornerstone of this investigation. There are three distinct aims:
AIM1. To investigate the regulation of pro-crossover factors by post-translational modification. We have identified phosphorylation sites on three meiosis-specific factors that stabilize JMs and promote crossing-over. These factors are the DNA helicase, Mer3, the MutS? complex related to DNA mismatch repair factors, and a SUMO E3 ligase, Zip3. In this, aim our goal is to understand the functional consequences of these phosphorylations and identify the responsible kinases.
AIM2. To characterize factors that promote crossover-specific resolution of JMs. We have identified factors that promote biased resolution of JMs into crossovers. In this aim, we will further characterize these factors in order to: (i) identify activities and interactions required for crossng-over; (ii) demonstrate that specific factors act at the time of JM resolution; (iii) understand how polo-kinase, Cdc5, activates crossover-specific resolution.
AIM3. To understand how the Smc5/6 complex regulates processing of JMs during meiosis. We have shown that the SMC-family complex, Smc5/6 regulates both the formation and resolution of JMs. We will address the idea that smc5/6 mutants form pathological JM structures that cannot be processed by resolving enzymes. We will also investigate the general theme that the temporally distinct roles of the Smc5/6 complex in JM formation and JM resolution are mediated through regulation of distinct partner proteins, with a focus on the DNA helicases Mph1 and Sgs1. Results obtained from these studies will be broadly relevant for understanding meiotic recombination in all organisms and will be especially important for discerning meiotic processes that make crossing-over and homolog disjunction incredibly accurate processes.

Public Health Relevance

Chromosome pairing and homologous recombination are essential for sexual reproduction and DNA repair. Defects in these processes are linked to human infertility, pregnancy miscarriage and genetic diseases such as Down Syndrome and cancer. A greater understanding of their mechanisms and regulation will help us better understand and treat these diseases.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics A Study Section (MGA)
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Deatherage, James F
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University of California Davis
Anatomy/Cell Biology
Schools of Medicine
United States
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Owens, Shannon; Tang, Shangming; Hunter, Neil (2018) Monitoring Recombination During Meiosis in Budding Yeast. Methods Enzymol 601:275-307
Hunter, Neil (2015) Meiotic Recombination: The Essence of Heredity. Cold Spring Harb Perspect Biol 7:
Tang, Shangming; Wu, Michelle Ka Yan; Zhang, Ruoxi et al. (2015) Pervasive and essential roles of the Top3-Rmi1 decatenase orchestrate recombination and facilitate chromosome segregation in meiosis. Mol Cell 57:607-621
Lao, Jessica P; Cloud, Veronica; Huang, Chu-Chun et al. (2013) Meiotic crossover control by concerted action of Rad51-Dmc1 in homolog template bias and robust homeostatic regulation. PLoS Genet 9:e1003978
Copsey, Alice; Tang, Shangming; Jordan, Philip W et al. (2013) Smc5/6 coordinates formation and resolution of joint molecules with chromosome morphology to ensure meiotic divisions. PLoS Genet 9:e1004071
Sasanuma, Hiroyuki; Tawaramoto, Maki S; Lao, Jessica P et al. (2013) A new protein complex promoting the assembly of Rad51 filaments. Nat Commun 4:1676
Lao, Jessica P; Tang, Shangming; Hunter, Neil (2013) Native/Denaturing two-dimensional DNA electrophoresis and its application to the analysis of recombination intermediates. Methods Mol Biol 1054:105-20
Zakharyevich, Kseniya; Tang, Shangming; Ma, Yunmei et al. (2012) Delineation of joint molecule resolution pathways in meiosis identifies a crossover-specific resolvase. Cell 149:334-47
Lao, Jessica P; Hunter, Neil (2010) Trying to avoid your sister. PLoS Biol 8:e1000519
Zakharyevich, Kseniya; Ma, Yunmei; Tang, Shangming et al. (2010) Temporally and biochemically distinct activities of Exo1 during meiosis: double-strand break resection and resolution of double Holliday junctions. Mol Cell 40:1001-15

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