Patterning of Cellular Differentiation by Lateral Inhibition in a Filamentous Cyanobacterium

丝状蓝藻中横向抑制的细胞分化模式

• 批准号: 1121346
• 负责人: Sean Callahan
• 金额: $ 29.54万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-01 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1121346&HistoricalAwards=false
• 关键词: Patterning; Cellular; Differentiation; Lateral; Inhibition

The development of a pattern of differentiated cell types from a group of equivalent cells is a fundamental phenomenon. 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. They allow the spatial separation of the two incompatible processes of photosynthesis and nitrogen fixation. Patterning of differentiation appears to be dependent on the interactions between several proteins. The first, HetR, is part of a regulatory circuit that shares the properties of biological switches, which turn graded input signals into a binary output: when the switch is "off",the cell remains undifferentiated, but when the switch is "turned on", the differentiation process begins and eventually becomes irreversible and self-sustaining. HetR acts to promote differentiation and is both necessary and sufficient to induce differentiation. PatS is a protein that prevents differentiation, apparently through interaction with HetR, and is responsible for determining the de novo patterning of heterocysts on a filament. HetN produces a signal involved in stabilization and maintenance of the pattern once it has formed. The premise is that the relative positions of cells is conveyed by concentration gradients of PatS and/or HetN extending from differentiating source cells. This phenomenon of "lateral inhibition" is implicated in governing the cellular differenitation and patterning in many developmental systems; but this has been experimentally demonstrated in relatively few systems. There is abundant preliminary evidence that HetN- and PatS-dependent signals move from cell to cell in filaments of Anabaena to create the periodic pattern of differentiated heterocysts and maintain it as the intervening heterocysts grow and divide. Only a pentapeptide, RGSGR, of HetN is required for its function as a patterning protein. This peptide is present also in PatS and is thought that these peptides are actively involved in the the suppresion of cellular differentiation. However, the functional form of HetN is unknown as is the route of intercellular movement within filaments of both inhibitors. Thus, the two specific aims of this project are to: 1. characterize the functional form of HetN that diffuses from cell to cell to maintain heterocyst patterning, and 2. determine the means of intercellular transfer of both HetN- and PatS-dependent inhibitory signals.This project is narrowly focused on the genetics of heterocyst differentiation in cyanobacteria, but the broader biological impact will be on the types of molecular mechanisms that control specification of cells for differentiation in many organisms. In addition, the project will promote teaching, training and learning by funding the research training of graduate students and undergraduate students, by enhancing sections of an undergraduate genetics laboratory course, by providing funded graduate students with teaching opportunities and by allowing their participation at national meetings. Mentoring of undergraduate students for research credit and as part of the Minority access to Research Careers (MARC) program will help to broaden participation of students of Pacific Islander descent in the biological sciences. In addition, cyanobacteria are beginning to be exploited for industrial purposes. It was hoped that existing genetically modified strains that produce extra heterocysts would have increased biohydrogen production, a byproduct of nitrogen fixation, by cyanobacteria. Unfortunately, these strains do not fix extra nitrogen nor produce extra hydrogen compared to the wild type strain because the extra heterocysts are clustered together for lack of bordered by vegetative cells. To engineer a strain with reduced spacing between individual heterocysts, one needs to understand how HetN and PatS determine the periodic pattern of heterocysts, which is the purpose of the work described in this proposal.

从一组等效细胞中分化细胞类型的模式的发展是一种基本现象。 Anabaena sp。 PCC 7120菌株是一种丝状蓝细菌，可诱导以区分氮固定杂环与未分化的营养细胞链。 杂环平均以10个细胞间隔发生终端分化，并且在形态，代谢和遗传上与营养细胞不同。 它们允许光合作用和氮固定的两个不兼容的过程的空间分离。 分化的模式似乎取决于几种蛋白质之间的相互作用。 第一个是HERTER，是具有生物开关的特性的监管电路的一部分，该电路将分级输入信号转换为二进制输出：当开关“关闭”时，单元格仍然不差异，但是当开关“打开”时，差异化过程开始并最终变得不可逆性和自我维护。 HETR的作用是促进分化的，既需要诱导分化的必要和足够。 PATS是一种蛋白质，显然是通过与HETR相互作用来阻止分化的蛋白质，并且负责确定丝状杂环的从头模式。一旦形成模式，HETN就会产生参与稳定和维护的信号。 前提是细胞的相对位置是通过PATS和/或HETN的浓度梯度从分化源细胞延伸的。 这种“横向抑制”现象与许多发育系统中的细胞分化和模式有关。但这在相对较少的系统中已经在实验中证明了这一点。 有大量的初步证据表明，HETN和PATS依赖性信号在Anabaena的细丝中从细胞转移到细胞，以创建分化的异囊肿的周期性模式，并随着中间的异质囊的生长和分裂而维持它。 HETN的功能是构图蛋白的功能，仅需要HETN的五肽RGSGR。这种肽也存在于PATS中，并认为这些肽积极参与细胞分化的抑制。然而，HETN的功能形式尚不清楚，在两个抑制剂的细丝中的细胞间运动途径也是如此。 Thus, the two specific aims of this project are to: 1. characterize the functional form of HetN that diffuses from cell to cell to maintain heterocyst patterning, and 2. determine the means of intercellular transfer of both HetN- and PatS-dependent inhibitory signals.This project is narrowly focused on the genetics of heterocyst differentiation in cyanobacteria, but the broader biological impact will be on the types of molecular控制细胞分化的许多生物体的机制。 此外，该项目将通过为研究生和本科生的研究培训提供资金来促进教学，培训和学习。 指导本科生研究学分，并作为少数群体获得研究职业的一部分（MARC）计划将有助于扩大太平洋岛民血统学生在生物科学中的参与。 此外，蓝细菌开始被利用是为了工业目的。 希望通过蓝细菌的现有产生额外杂囊的遗传改性菌株能够增加生物氢产生的产生，这是氮固定的副产品。 不幸的是，与野生型菌株相比，这些菌株不会固定额外的氮，也不会产生额外的氢，因为由于缺乏被营养细胞的边界，额外的杂环聚集在一起。 为了在单个杂环之间锻炼菌株的间距降低，需要了解HETN和PATS如何确定杂环的周期性模式，这是本提案中描述的工作的目的。