Genetics of Heterocyst Differentiation and Patterning

从一组等同细胞发展分化细胞类型的模式是生物学中的基本范式。 在细菌中，一些蓝藻从营养细胞的细丝分化出固氮异形胞，这是在适当的环境条件下可以无限期维持的发育模式的少数例子之一。 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需的最小遗传元件集。鱼腥藻菌株PCC 7120是一种丝状蓝藻，可以被诱导从一系列未分化的营养细胞分化出一种固氮异形胞模式。 异形胞平均每隔10个细胞出现一次，是终末分化的，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确定与发育有关的遗传因素并确定其特征。 将使用鱼腥藻7120的基因工程菌株进行致突变方法，该菌株可以在不需要分化生长的条件下诱导形成接近100%的异形胞。 该项目的第二个目标是测试两个假设，涉及到抑制分化的基因hetN。 第三个目的是鉴定和表征hetN抑制分化所必需的其他基因。 这个项目是狭隘地集中在蓝藻异形胞分化的遗传学，但更广泛的生物学影响将在一般的分化和模式的形成。

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.