A EUKARYOTIC TISSUE DENSITY SENSOR

该建议涉及真核生物质量效应子：细胞外 这些分子可以让组织内的单个细胞感受到 整个组织的质量。 这样的分子会集中在 在创伤发育过程中参与生长调节 愈合和组织再生。 质量感知中断 机制可能导致肿瘤形成。 作为模型系统，我们 将使用条件培养基因子（CMF）分泌的发展 盘基网柄藻细胞。 在浸没单层培养中， 网骨藻细胞在高细胞密度下分化， 在低密度下;然而，在低密度下的细胞将分化 在预先使高密度细胞饥饿的培养基中 （条件培养基）。 对这一现象的解释是， 在发育过程中，网骨细胞需要能够感知 无论它们是否远离聚合中心，因此需要 继续表达聚集特异性基因，或者它们是否 因此需要继续 表达聚集特异性基因，或者它们是否处于或 因此可以开始表达 分化特异性基因。 由于发展网骨藻 细胞不分裂，CMF是一种质量效应物，而不是促分裂剂 或生长因子。 在高等真核生物中， 不同的效应器和受体的机制， 细胞可以感知其他肝细胞的数量，胰腺， 其他胰腺细胞的数量等。 条件培养基显示， 分化的细胞与70 kD蛋白质共纯化， 一个约5 kD的分子;有趣的是，这两个分子都有 相同的活动，不需要组合， 分化 5 kD CMF及其是否相关 和/或一个是否从另一个导出。 编码70的基因 将分离kD CMF并测序，以与其他CMF进行比较。 已知蛋白质 如果5kD CMF是多肽，则其基因将 类似的特点。 CMF的生理作用将是 通过描述其时间调节的特征来检查 分泌，哪些细胞类型分泌它，可能的因素， 调节其分泌及其与细胞相互作用的程度。 cAMP介导的趋化机制。 长期 我们的目标是在分子基础上了解整个转导过程， 细胞感知是否存在 大量的其他细胞

This proposal concerns eucaryotic mass effectors: extracellular molecules that allow individual cells within a tissue to sense the mass of the entire tissue. Such molecules would be centrally involved in the regulation of growth during development wound healing and tissue regeneration. Disruption of the masssensing mechanism could lead to tumor formation. As a model system, we will use the conditioned medium factor (CMF) secreted by developing Dictyostelium discoideum cells. In submerged monolayer culture, Dictyostelium cells differentiate at high cell densities but not at low densities; cells at low densities will however differentiate in medium in which a high density of cells was previously starved (a conditioned medium). An explanation this phenomenon is that during development, Dictyostelium cells need to be able to sense whether they are far from an aggregation center and thus need to continue expressing aggregation specific genes, or whether they are at or near an aggregation center and thus need to be continue expressing aggregation specific genes, or whether they are at or near an aggregation center and thus can begin expressing differentiation- specific genes. Since developing Dictyostelium cells do not divide, CMF is a mass effector rather than a mitogen or growth factor. In higher eucaryotes, one could envision similar mechanisms with different effectors and receptors so that liver cell could sense the number of other liver cells, pancreas the number of other pancreas cells, etc. Fractionation of the conditioned medium shows that the activity that allows low density cells to differentiate copurifies with a 70 kD protein as well as with a ~5 kD molecule; interestingly, the two molecules both have the same activity and do not need to be combined to allow differentiation. The 5 kD CMF's and whether they are related and/or if one is derived from the other. The gene encoding the 70 kD CMF will be isolated and sequenced for comparison with other known proteins. If the 5 kD CMF is a polypeptide, its gene will similarly be characterized. The physiological role of CMF will be examined by characterizing the temporal regulation of its secretion, which cell types secrete it, possible factors that might regulate its secretion and the extent of its interaction with the Dictyostelium cAMP mediated chemotaxis mechanism. The long term goal is to understand on a molecular basis the entire transduction mechanism whereby cells sense whether they are in the presence of a large mass of other cells.