MOLECULAR MECHANISMS OF DIFFERENTIATION

生物学中最具挑战性的问题是确定如何 同一基因组产生不同类型的细胞。作为一名 模型系统，以了解定向涉及的机制 真核生物中细胞的变化，我们已经开发了一个系统 在分裂酵母中交配型基因座的遗传开关， 裂殖酵母Pombe.P(正)和M(负)交配 类型的S.pombe通过一个 其中任何一个的拷贝的转置-取代反应 两个未表达的供体基因座mat2-P和mat3-M被传递 到表达的基因座，MAT 1。一个引人注目的观察是 在一对姐妹细胞内，多达92%的细胞分裂 这两个信元中只有一个在 下一代。我们最近已经表明，这种模式 细胞谱系的转换是由“流行遗传”染色体引起的 修饰，使某些染色体增强到 改变，而其他人则不是。此外，我们已经表明， 子代细胞之间的发育不对称是一种 遗传不等同亲本DNA链的后果。 我们的目标是定义“半可遗传”的分子本质 DNA“修饰”和后续事件所需的 正在切换。我们将直接测试限制-修改 我们提出的启动MAT 1切换事件的模型， 这是由特定部位的双链DNA断裂组成的。 更具体地说，我们将描述交换机的功能 (Swi)基因，我们已经建议这些基因是 修饰和DNA切割事件，使用基因 和分子技术。休息的性质和 修饰和DNA切割所需的序列如下 已定义。了解病毒的分子本质 细胞分化的发育程序。 可以预期庞贝具有普遍的生物学相关性，因为 所有的ercaryotes也被期望执行这样的程序。

A most challenging problem in biology is to detemine how different cell types are generated from the same genome. As a model system to understand the mechanisms involved in directed changes of cell in a eucaryote, we have exploited a system of heribale swithches of the mating type locus in the fission yeast, Schizosaccharomyces pombe. The P (plus) and M (minus) mating types of S. pombe interchange to the other cell type by a transposition-substitution reaction in which a copy of either one of two unexpressed donor loci, mat2-P and mat3-M, is transmitted to the expressed locus, mat 1. One striking observation is that within a pair of sister cells, in as many as 92% of cell divisions only one of the two cells generates a single switched cell in the next generation. We have recently shown that this pattern of switching in a cell lineage is due to an "epidgenetic" chromosomal modification such that some chromosomes are potentiated to switch whereas others are not. Furthermore, we have shown that the developmental asymmetry among daughter cells is a consequence of inheriting non-equivalent parental DNA chains. Our goal is to define the molecular nature of the "semi-heritable" DNA "modification" and the subsequent events required for switching. We will directly test the restriction-modification model we have proposed for initiating the mat 1 switching event, which is comprised of a site-specific double stranded DNA break. More specifically, we will characterize the function of the switch (swi) genes, which we have suggested to be required for the modification as well as DNA cleavage events, using both genetic and molecular techniques. The nature of the break and the sequences required for moditication and DNA cleavage will be defined. Understanding the molecular nature of the developmental program that leads to cellular differentiation in S. pombe can be expected to have general biological relevance since all ercaryotes are also expected to execute such programs.