Progression and Spacing of Heterocyst Differentiation

异形囊分化的进展和间隔

• 批准号: 9723193
• 负责人: Coleman Wolk
• 金额: $ 33万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-09-01 至 2001-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9723193&HistoricalAwards=false
• 关键词: Progression; Spacing; Heterocyst; Differentiation

Wolk 9723193 Anabaena, a filamentous cyanobacterium, carries out oxygenic photosynthesis and aerobic N2-fixation in two types of cells, vegetative cells and heterocysts, respectively. Comprised wholly of vegetative cells in the presence of fixed nitrogen, filaments respond to nitrogen deprivation by having 5 to 10% of their cells, at semi-regular intervals, differentiate into heterocysts. This organism offers one of the few opportunities to study the ways in which a prokaryote regulates structural cellular differentiation, and a nearly unique opportunity to study prokaryotic formation of multicellular patterns. A number of developmental regulatory genes and genes involved in synthesis of heterocyst-specific structures have been identified, and certain of their interdependencies identified. However, the detailed mechanisms that regulate the progression of the differentiation process once that process has been initiated remain largely unknown, and no overall regulatory strategy has been discerned. hepA is a gene that is activated specifically in immature heterocysts starting several hours after nitrogen stepdown and whose activity is required for normal formation of a principal structural element of heterocysts, the outer, polysaccharide layer of their envelope. Aspects of the regulation of hepA will be investigated. Experimental evidence indicates that the pattern of spaced heterocysts results from an inhibition, by mature and developing heterocysts, of the differentiation of nearby cells into heterocysts, and suggests that the inhibition is mediated by the elaboration of some differentiation-inhibiting substance that moves outward along a filament. Because the differentiation of heterocysts is organized by inhibition, it appears appropriate for Anabaena to have genes whose products inhibit the initiation or progression of differentiation. However, a mutation in such a gene could lead all vegetative cells to start to differentiate into heterocysts, a result that might heretofore have been recog nized only as a lethal mutation. Analysis of a restricted class of conditional mutations will show whether there are such genes that control differentiation in Anabaena. Results obtained with these conditional mutations can elucidate mechanisms that underlie cellular differentiation and (or) multicellular pattern formation. The oxygen in the earth's atmosphere came initially from the growth of oxygen-producing cyanobacteria. This oxygen prevented the assimilation of nitrogen gas. Certain filamentous cyanobacteria overcame that impediment by inventing multicellular division of labor: spaced cells in a filament became heterocysts, cells unable to photosynthesize and grow, but able to fix nitrogen gas in an oxygen-containing environment. Thus arose what may have been the first multicellular pattern, and Anabaena, still an outstanding example of bacterial multicellularity. Heterocyst formation is being analyzed because it provides an example of bacterial differentiation that may be regulated in a unique fashion, and because of the important contribution of heterocysts to global nitrogen fixation. Analysis of the regulation of hepA and the use of conditional mutants represent approaches to understanding how differentiation progresses. Conditional mutation may also assist mechanistic analysis of pattern formation.

Anabaena是一种丝状蓝藻，它分别在营养细胞和异囊两种类型的细胞中进行含氧光合作用和需氧n2固定。在固定氮的存在下，细丝完全由营养细胞组成，对氮剥夺的反应是有5%到10%的细胞以半规则的间隔分化成异囊。这种生物为研究原核生物调节结构细胞分化的方式提供了为数不多的机会之一，并且为研究多细胞模式的原核形成提供了几乎独一无二的机会。已经确定了一些发育调节基因和参与异囊特异性结构合成的基因，并确定了它们之间的某些相互依赖性。然而，一旦分化过程开始，调控分化过程进展的详细机制在很大程度上仍然未知，也没有明确的总体调控策略。hepA是一种在未成熟的异囊中特异激活的基因，在氮降低数小时后开始激活，其活性对于异囊的主要结构元素，即包膜的外层多糖层的正常形成是必需的。将对hepA的监管方面进行调查。实验证据表明，间隔异囊的模式是由于成熟和发育中的异囊抑制附近细胞向异囊分化的结果，并表明这种抑制是由一些沿丝向外移动的分化抑制物质的细化所介导的。因为异囊的分化是通过抑制来组织的，所以对于鱼腥鱼来说，其产物抑制分化的开始或进展似乎是合适的。然而，这种基因的突变可能导致所有的营养细胞开始分化成异囊，这一结果可能迄今为止只被认为是一种致命的突变。对一类有限的条件突变的分析将显示是否有这样的基因控制水藻的分化。通过这些条件突变获得的结果可以阐明细胞分化和（或）多细胞模式形成的机制。地球大气中的氧气最初来自产氧蓝藻的生长。氧气阻止了氮气的同化。某些丝状蓝藻通过发明多细胞分工克服了这一障碍：在细丝中间隔的细胞变成了异囊，细胞不能进行光合作用和生长，但能够在含氧环境中固定氮气。由此产生了可能是第一个多细胞模式，以及水藻，它仍然是细菌多细胞的一个杰出例子。异囊体的形成之所以被分析，是因为它提供了一个可能以独特方式调节的细菌分化的例子，并且因为异囊体对全球固氮的重要贡献。对hepA调控的分析和条件突变体的使用代表了理解分化过程的方法。条件突变也有助于模式形成的机制分析。