Genetic Control of Pattern Formation in the Cyanobacterium Anabaena

水藻是一种丝状蓝藻，它对氮的缺乏作出反应，沿着丝状的半规则间隔的细胞被称为异囊，专门用于固定氮。响应氮减少而分化的细胞可能与最初感知氮剥夺的细胞相同；或者，如果后一种细胞通过启动从相邻细胞中清除氮的顺序过程来响应氮剥夺，则分化细胞可能位于远离首先感知氮剥夺的细胞的位置；或者如果分化仅仅表现出一种潜在的模式（尽管实验上可以操纵），那么分化的细胞可能与首先感知氮剥夺的细胞没有一致的空间关系。Wolk博士开发了一系列技术来研究发育中的丝中基因表达的空间和时间方面，以及基因对之间的依赖关系。该阵列包括使用转座子和定点插入，结合荧光素酶基因，沿丝逐个细胞报告单个启动子的活性。为了阐明杂种囊间隔形成的机制，他建议：1)鉴定控制杂种囊形成所需的基因、调控氮剥夺早期反应的基因以及它们之间的依赖关系；2)阐明氮素剥夺基因激活位点与杂种囊最终形成位置之间的空间关系；3)确定富氮细丝中可能存在的转录不均匀性与随后的分化是否存在空间关系；4)研究特定的实验操作如何影响分化和模式形成。

Anabaena is a filamentous cyanobacterium that responds to nitrogen deprivation by elaborating along the filaments semi- regularly spaced cells called heterocysts that are specialized for nitrogen fixation. The cells that differentiate in response to nitrogen step down may be the same as those that first sense nitrogen deprivation; or if the latter cells respond to nitrogen deprivation by initiating a sequential process of scavenging nitrogen form contiguous cell, the differentiating cells may be positioned distant from the cells that first sense nitrogen deprivation; or if differentiation merely makes manifest a latent (albeit experimentally manipulable) pattern, the differentiating cells may bear no consistent spatial relationship to the cells first sensing nitrogen deprivation. Dr. Wolk has developed an array of techniques to study spatial and temporal aspects of the expression of genes in the developing filament, and dependency relationships between pairs of genes. This array includes the use of transposons and site directed insertions that incorporate genes for luciferase to report on the activity of individual promoters cell by cell along a filament. To elucidate the mechanism of heterocyst spacing, he proposes to: 1) identify genes required for control of heterocyst formation, genes regulating early responses to nitrogen deprivation, and the dependency relationships among them; 2) elucidate the spatial relationship between the sites of activation of genes in response to nitrogen deprivation, ant the location of eventual heterocyst formation; 3) ascertain whether possible transcriptional inhomogeneities in nitrogen replete filaments bear any spatial relationship to subsequent differentiation; and 4) investigate how particular experimental manipulations affect differentiation and pattern formation.