Richard M. Losick

Harvard University

Primary Section: 22, Cellular and Developmental Biology
Secondary Section: 44, Microbial Biology
Membership Type: Member (elected 1992)

Research Interests

Our laboratory studies development in simple organisms that are accessible to genetic manipulation. The organisms we study are unicellular bacterium Bacillus subtilis and the filamentous bacterium Streptomyces coelicolor. These bacteria undergo elaborate cycles of cellular differentiation that culminate in the formation of a dormant cell, the spore. In B. subtilis this differentiation cycle involves the transformation of a vegetative cell into a two-compartment sporangium within which the spore is produced. The two compartments receive identical chromosomes yet have dissimilar developmental fates involving differential expression of distinct sets of genes. In contrast, S. coelicolor exhibits a mycelial fungus-like cycle of morphological differentiation involving the formation of upwardly projecting (aerial) hyphae that undergo septation into long chains of uninucleate cells, which, in turn metamorphose into pigmented spores. In B. subtilis we are focusing on the problems of how a progenitor cell (the vegetative bacterium) gives rise to dissimilar progeny (the cellular compartments of the sporangium) and how the two sporangial compartments communicate with each other so to coordinate developmental gene expression with the course of morphogenesis. In S. coelicolor we are investigating how aerial hyphae are erected and metamorphose into spores, and how morphological differentiation is governed by the exchange of chemical signals between cells. We are also studying the problem of chromosome segregation and cytokinesis in bacteria. A significant theme is our research is the use of cytological methods to visualize the subcellular location of individual proteins and chromosomal regions in living cells.

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