Developmental pattern formation controlled by patS in the cyanobacterium Anabaena sp. strain PCC 7120 /
How some cells within a uniform population acquire
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1998.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=732843831&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | How some cells within a uniform population acquire different fates and form a developmental pattern is a fundamental question in biology. We identified a small gene, patS, in the filamentous cyanobacterium Anabaena PCC 7120 that is critical for establishing a one- dimensional developmental pattern of single nitrogen- fixing heterocysts separated by approximately ten vegetative cells. Extra copies of patS, capable of encoding a 17 amino acid peptide, were found to block heterocyst differentiation. When patS expression was driven by a copper-inducible promoter [Ppetz], increased transcription of patS increased the degree of heterocyst inhibition. An in-frame patS-lacZ translational fusion showed two- to three-fold induction upon nitrogen stepdown, whereas an out-of- frame fusion showed background levels of [13]- galactosidase activity. Results of random hydroxylamine mutagenesis indicated that the last five amino acids of Pats are critical for its function. A synthetic pentapeptide corresponding to the five COOH- terminal residues of Pats blocked heterocyst development when added exogenously. The patS deletion strain AMC451 displayed increased initiation of heterocyst differentiation, leading to supernumerary heterocysts and abnormal spacing. The phenotype of AMC451 was rescued by re-introducing patS on a shuttle vector or by adding Pats pentapeptide exogenously. The AMC451 phenotype was also complemented by patS driven by an early heterocyst-specific promoter, Wept, suggesting that Pats functions cell nonautonomously. Pats also plays an important role in preventing adjacent cells from differentiating simultaneously in diazotrophically growing filaments. The expression pattern of a patS-gfp transcriptional fusion was analyzed in filaments. GFP fluorescence started to appear in some individual cells, two adjacent cells, and groups of cells at 6 hours after nitrogen stepdown. The groups of fluorescent cells resolved to individual cells with semi-regular intervals at 10 to 12 hours. At later times, GFP fluorescence was detected exclusively from proheterocysts. The fact that developing cells become committed to differentiation into heterocysts at 9 to 14 hours after nitrogen stepdown agrees with our model in which Pats is produced by differentiating cells to create a zone of inhibition that controls heterocyst pattern formation. |
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| Item Description: | Vita. In title, symbols are used. |
| Physical Description: | xi, 113 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references: pages 102-112. |