title: Biased inheritance of the protein PatN frees vegetative cells to initiate patterned heterocyst differentiation.
abstract: Heterocysts, cells specialized for nitrogen fixation in certain filamentous cyanobacteria, appear singly in a nonrandom spacing pattern along the chain of vegetative cells. A two-stage, biased initiation and competitive resolution model has been proposed to explain the establishment of this spacing pattern. There is substantial evidence that competitive resolution of a subset of cells initiating differentiation occurs by interactions between a self-enhancing activator protein, HetR, and a diffusible pentapeptide inhibitor PatS-5 (RGSGR). Results presented here show that the absence of a unique membrane protein, PatN, in Nostoc punctiforme strain ATCC 29133 leads to a threefold increase in heterocyst frequency and a fourfold decrease in the vegetative cell interval between heterocysts. A PatN-GFP translational fusion shows a pattern of biased inheritance in daughter vegetative cells of ammonium-grown cultures. Inactivation of another heterocyst patterning gene, patA, is epistatic to inactivation of patN, and transcription of patA increases in a patN-deletion strain, implying that patN may function by modulating levels of patA. The presence of PatN is hypothesized to decrease the competency of a vegetative cell to initiate heterocyst differentiation, and the cellular concentration of PatN is dependent on cell division that results in cells transiently depleted of PatN. We suggest that biased inheritance of cell-fate determinants is a phylogenetic domain-spanning paradigm in the development of biological patterns.
authors.affiliation: Department of Microbiology, University of California, Davis, CA 95616, USA.
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Risser
authors.forename: Francis C Y
authors.initials: FC
authors.lastname: Wong
authors.forename: John C
authors.initials: JC
authors.lastname: Meeks
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002454:Cell Differentiation; D019070:Cell Lineage; D000458:Cyanobacteria / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004843:Epistasis, Genetic; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008856:Microscopy, Fluorescence / Q000379:methods; D009586:Nitrogen Fixation; D046937:Nostoc / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D016366:Open Reading Frames; D010641:Phenotype; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D049452:Green Fluorescent Proteins