ANALYSIS OF MEIOTIC CHROMOSOME SYNAPSIS IN YEAST

减数分裂是有性生殖生物体为了将生殖细胞中的染色体数目减少一半而经历的基本过程。 当减数分裂失败，染色体不平衡的配子的结果。 在哺乳动物中，这种染色体不平衡的配子受精产生的受精卵是不能存活的，并且是大量自然流产的原因。在产生可存活后代的情况下，观察到精神和形态缺陷，如21三体或特纳综合征（XO）所见。 了解减数分裂过程如何准确分离同源染色体，最终可能提供监测和防止这一过程失败所需的知识。同源物在减数分裂I中的正确分离要求它们首先通过形成称为联会复合体（SC）的多蛋白质结构而物理关联。SC是由复制的姐妹染色单体对沿着称为轴向元件（AE）的蛋白质核心沿着凝聚而成，然后通过插入中心区域而形成突触。 酵母中的遗传学研究已经证明，AE对于产生和包装交叉是重要的，以便它们确保适当的分离。 酵母AE的三个关键减数分裂特异性组分是HOP 1、RED 1和MEK 1。 遗传实验表明，Hop 1 p/Red 1 p复合物和Red 1 p同源寡聚体之间的平衡对AE功能很重要，并且这种化学计量由Mek 1 p激酶调节。 这项资助的重点是通过定义HOP 1，RED 1和MEK 1在减数分裂过程中的特定作用来了解AE在酵母中的功能。 为此，已经开发了一种新的筛选，其设计用于分离RED 1中功能突变体的分离。 该筛选已经成功地发现了与Hop 1 p结合特异性缺陷的RED 1等位基因。 这个突变体提供了一个有用的工具，以确定哪些减数分裂过程需要Red 1 p/Hop 1异源寡聚体。将在HOP 1中寻找类似的功能突变体分离，并进行补充实验。 Hop 1 p同源寡聚体在减数分裂双链断裂末端附近具有RED 1独立结合功能的假设将使用染色质免疫沉淀技术进行测试。为了了解AE组装是如何调节的，将使用遗传和生物化学方法来识别负责通过保守的苏氨酸磷酸化来激活Mek 1 p的激酶。

Meiosis is a fundamental process that sexually reproducing organisms undergo in order to reduce by half the chromosome number in germ cells. When meiosis fails, chromosomally imbalanced gametes result. In mammals the zygotes generated by fertilization of such chromosomally imbalanced gametes are inviable and account for a large number of spontaneous abortions. In cases where viable offspring are produced, mental and morphological defects such as those seen for Trisomy 21 or Turner syndrome (XO) are observed. Understanding how the meiotic process works to accurately segregate homologous chromosomes may ultimately provide the knowledge needed to monitor and prevent failures of this process. Proper segregation of homologs at Meiosis I requires that they first become physically associated by formation of a multi-protein structure called the synaptonemal complex (SC). The SC is formed by condensation of replicated pairs of sister chromatids along protein cores called axial elements (AEs) that are then synapsed by the insertion of a central region. Genetic studies in yeast have demonstrated that AEs are important for generating and packaging crossovers so that they ensure proper disjunction. Three key meiosis-specific components of yeast AEs are HOP1, RED1 and MEK1. Genetic experiments suggest that a balance between Hop1p/Red1p complexes and Red1p homo-oligomers is important for AE function and that this stoichiometry is regulated by the Mek1p kinase. The focus of this grant is to understand how AEs function in yeast by defining the specific roles of HOP1, RED1, and MEK1 during meiosis. Towards this end, a novel screen designed to isolate separation of function mutants in RED1 has been developed. This screen has already been successful in discovering an allele of RED1 that is specifically defective in binding to Hop1p. This mutant provides a useful tool to determine which meiotic processes require Red1p/Hop1 heterooligomers. Similar separation of function mutants will be sought in HOP1 and complementary experiments performed. The hypothesis that Hop1p homo-oligomers have a RED1-independent function in binding near the ends of meiotic double strand breaks will be tested using the chromatin immunoprecipitation technique. To understand how AE assembly is regulated, genetic and biochemical approaches will be used to identify the kinase responsible for activating Mek1p by phosphorylation of a conserved threonine.