Genetics of Heterocyst Differentiation and Patterning

从一组等效细胞发展成分化细胞类型的模式是生物学的基本范式。在细菌中，一些蓝藻从营养细胞的细丝中分化出固氮异囊，这是少数几个在适当的环境条件下可以无限期维持的发育模式的例子之一。它代表了一个简单的模型系统，用于阐明生物体模式生成和维持所必需的最小遗传元素集。Anabaena sp.菌株PCC 7120是一种丝状蓝藻，可以诱导从一系列未分化的营养细胞分化成固氮异囊。异囊平均每隔10个细胞发生一次，终末分化，在形态、代谢和遗传上与营养细胞不同。该项目的第一个目标是鉴定和描述与发展有关的遗传因素。一种诱变方法将使用一种经过基因工程改造的Anabaena 7120菌株，该菌株可以在不需要分化的条件下诱导形成接近100%的异囊。该项目的第二个目标是测试与hetN基因抑制分化有关的两个假设。第三个目标是鉴定和表征抑制hetN分化所必需的其他基因。这个项目是狭隘地集中在蓝藻异囊分化的遗传学，但更广泛的生物学影响将是在一般的分化和模式形成。

The development of a pattern of differentiated cell types from a group of equivalent cells is a fundamental paradigm in biology. In bacteria, the differentiation of nitrogen-fixing heterocysts from a filament of vegetative cells by some cyanobacteria represents one of the few examples of a developmental pattern that can be maintained indefinitely given the appropriate environmental conditions. It represents a simple model system for elucidation of the minimal set of genetic elements that are necessary for pattern generation and maintenance by an organism. Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that can be induced to differentiate a pattern of nitrogen-fixing heterocysts from a chain of undifferentiated vegetative cells. Heterocysts occur, on average, at 10 cell intervals, are terminally differentiated, and differ from vegetative cells morphologically, metabolically, and genetically. The first objective of the project is the identification and characterization of genetic elements that are involved in development. A mutagenic approach will be pursued using a genetically engineered strain of Anabaena 7120 that can be induced to form close to 100% heterocysts under conditions that do not require differentiation for growth. The second objective of the project is to test two hypotheses that relate to inhibition of differentiation by the gene hetN. The third objective is the identification and characterization of additional genes that are necessary for inhibition of differentiation by hetN. This project is narrowly focused on the genetics of heterocyst differentiation in cyanobacteria, but the broader biological impact will be on differentiation and pattern formation in general.