Intercellular Signaling Activity Encoded by hetN in the Cyanobacterium Anabaena sp. strain PCC 7120. Rivers, Orion S.
dc.contributor.department Microbiology 2019-05-28T20:15:14Z 2019-05-28T20:15:14Z 2017-08
dc.subject Anabaena
dc.subject intercellular signaling
dc.subject HetN
dc.subject cellular differentiation
dc.title Intercellular Signaling Activity Encoded by hetN in the Cyanobacterium Anabaena sp. strain PCC 7120.
dc.type Thesis
dcterms.abstract Developmental regulators coordinate cellular differentiation in many organisms. Regulators can be small molecules or proteins. Developmental regulators called morphogens are produced in source cell(s) that determine the developmental fate of cells adjacent to the source in a concentration dependent manner. The filamentous cyanobacterium Anabaena sp. Strain PCC 7120 is a model organism used to study cellular differentiation. When Anabaena filaments are supplied a source of fixed nitrogen a single cell type, vegetative cells, comprise the filaments. However, removal of fixed nitrogen from the medium induces differentiation of one in every 10- 15 cells into a heterocyst. Heterocysts are terminally differentiated cells that are the sites of atmospheric nitrogen fixation. Differentiation within Anabaena requires 24 hours and can be divided into four stages: induction, patterning, commitment, and morphogenesis. The periodic pattern of heterocyst is initially determined by the interplay of HetR, the primary activator of differentiation within Anabaena, and PatS, a diffusible inhibitor expressed during the patterning stage. The initial pattern of heterocysts in maintained during growth by a secondary inhibitor, HetN, which is expressed in mature heterocysts. The pentapeptide sequence RGSGR is conserved in the amino acid sequences of both inhibitors and has been shown to inhibit differentiation and induce HetR degradation when added to the medium, bind directly to HetR in vitro, and is required for the inhibitory function of PatS. In this work HetN was found to require the RGSGR sequence for inhibitory function and did not require predicted ketoacyl reductase activity. Full-length HetN was found to be confined to source cell(s) membranes, but a hetNdependent inhibitory signal was shown to move away from source heterocysts in a manner similar to a paracrine-type intercellular signal. The hetN-dependent inhibitory signal was found not to require the intercellular channel forming protein SepJ. However, mutation of sepJ reduced the signal range of the HetN-dependent inhibitory signal, suggesting its involvement in signal transport. Finally, evidence supporting the use of M119 of HetN as the developmentally regulated translational start site is presented. This work contributes to our knowledge of morphogen signals and supports the role of HetN as an inhibitory morphogen within Anabaena.
dcterms.description Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017.
dcterms.language eng
dcterms.publisher University of Hawaiʻi at Mānoa
dcterms.rights All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
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