Toward Systems Biology

May 30 - 31, June 1, 2011


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Forcing Unicellular Organisms to Form Multicellular Organized Structures

Formation of multicellular organs and determination of their 3 dimensional shapes are known to be controlled by specific genetic programs. Microorganisms such as yeast and bacteria are unicellular organisms that commonly do not form complex multicellular structures. Colonies formed by laboratory strains when grown on solid surfaces are concentric and simple, not manifesting obvious differentiation signs. Indeed, in response to environmental conditions wild strains may show remarkable patterns of colony organization deviated from the common concentric shape, but these patterns are two dimensional, formed on the surface. Here I show that yeast could be forced to form 3 dimensional structures, composed of millions of cells that are organized to a stalk shapes that can reach a height of 3.0 centimeters and a width of 0.5 cm in diameter. Anatomical analysis of the stalks reveals spatial organization and cell specialization. The suggested mechanism of stalk formation and cell organization is purely mechanical environmental processes, with no direct involvement of genetic/biochemical control. We propose that the capability of forming semi-differentiated stalks is a general property of microorganisms. We further argue that mechanical environmental forces may be fundamentally crucial for development and organization of organs of higher organisms too, sometime overruling genetic programs.

David Engelberg, The Hebrew University of Jerusalem.

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