CONTROL OF GENOME SIZE

这个项目的目标是表征的机制，由倍性在酿酒酵母是有限的。具有高达6n倍性的酵母很容易产生，然而，使用低分辨率技术不可能产生具有高于6n（大于6n）倍性的活酵母。多倍体的局限性在其他真核细胞中也以细胞类型特异性的方式出现。许多肝细胞为4n倍体，但达到8n倍体的数量有限。此外，大鼠肝癌细胞的增殖活性与其倍性成反比。相比之下，巨核细胞可高达64n。本研究计划的具体目的如下：(1)准确地确定酵母多倍体增加的限制。利用互补标记从大量亲本细胞杂交中选择有活力的8n多倍体。将确定8n多倍体出现的频率（如果这些菌株可能出现8n多倍体）。将仔细检查分离的8n酵母的表型。(2)鉴定参与限制多倍体的基因。已知有17个基因具有倍性调控表达。通过过表达多倍体中被抑制的多倍体和破坏诱导的多倍体来分析每一种表达的改变在预防存活大于6n株中可能起的作用。(3)通过比较n × n和多倍体杂交，确定杂交过程中基因表达模式的差异。全基因组mRNA表达微阵列将用于分析n × n、2n × 2n和4n × 4n杂交中的酵母。这些杂交之间差异表达的基因将被识别并进一步检查。

The goals of this project are to characterize the mechanisms by which ploidy is limited in Saccharomyces cerevisiae. Yeast with ploidies as high as 6n have been easily generated, however, it has not been possible using low-resolution techniques to generate viable yeast with a ploidy above 6n (greater than 6n). Limitations in polyploidy are also seen in other eukarytoic cells in a cell-type specific manner. Many liver hepatocytes are 4n, but, the number that achieve a ploidy of 8n are limited. In addition, the proliferative activity of rat liver carcinoma cells decreases in an inverse proportion to their ploidy. In contrast, megakaryocytes can reach as high as 64n. The specific aims of this research proposal are the following: (1) Accurately identify the limits on increasing polyploidy in yeast. Complementary markers will be used to select for viable 8n polyploids from crosses using large numbers of parental cells. The frequency with which 8n polyploids arise (if 8n polyploidy is possible in these strains) will be determined. The phenotypes of isolated 8n yeast will be carefully examined. (2) Identify genes that are involved in limiting polyploidy. Seventeen genes are known to have ploidy-regulated expression. The role that the altered expression of each may play in the prevention of viable greater than 6n strains will be analyzed by overexpressing those that are repressed in polyploids and disrupting those that are induced. (3) Identify differences in the patterns of genes expressed during conjugation when comparing n x n and polyploid crosses. Whole genome mRNA expression microarrays will be used to analyze yeast in n x n, 2n x 2n, and 4n x 4n crosses. Genes that are differentially expressed between these crosses will be identified and examined further.