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.
