EUKARYOTIC TISSUE DENSITY SENSOR

这项提议涉及到真核质量效应器：细胞外 允许组织中的单个细胞感觉到 整个组织的质量。这样的分子将集中在 在发育创伤中参与生长的调节 愈合和组织再生。质量感觉的中断 机制可能导致肿瘤的形成。作为一个模范系统，我们 将使用由开发人员分泌的条件培养因子(CMF) 盘基网眼菌细胞。在水下单层培养中， 网柄苔藓细胞在高细胞密度下分化，但不 在低密度下；然而，低密度下的细胞将分化 在先前高密度细胞饥饿的培养液中 (条件培养液)。对这一现象的解释是 在发育过程中，网柄基细胞需要能够感知 他们是否远离聚合中心，因此需要 继续表达聚集特异性基因，或者无论它们是 位于聚合中心或其附近，因此需要继续 表达聚集特异性基因，或者它们是在还是 在聚集中心附近，因此可以开始表达 分化特异性基因。自发育至今，网柄苔藓 细胞不分裂，CMF是质量效应器而不是有丝分裂原 或者是生长因子。在高等真核生物中，人们可以想象类似的情况 作用机制不同的效应物和受体使肝脏 细胞可以感觉到其他肝细胞的数量，胰腺 其他胰腺细胞的数量等。 条件培养液显示，允许低密度的活性 细胞分化为70kD的蛋白质以及 有一个~5kD的分子；有趣的是，这两个分子都有 相同的活动，并且不需要组合以允许 差异化。5个KD CMF及其是否相关 和/或如果一个是从另一个派生的。编码70的基因 KD CMF将被分离并测序，以便与其他 已知的蛋白质。如果5kD的CMF是一种多肽，它的基因将 同样，也要表现出自己的特点。CMF的生理作用将是 通过表征ITS的时间调节来检验 分泌，哪些细胞类型分泌它，可能的因素可能 调节其分泌及其与细胞的相互作用程度 网柄苔藓cAMP介导的趋化机制。从长远来看 目标是在分子的基础上理解整个转导 细胞感知它们是否存在于 一大堆其他细胞。

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.