The Losick laboratory studies differentiation, morphogenesis and multicellularity in the spore-forming bacterium Bacillus subtilis. We investigate 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. We study the regulatory mechanisms that govern sporulation gene expression and novel pathways of intercellular signaling. We also investigate how the morphological features of the developing spore assemble and how they do so at the right time and in the right place. We are elucidating the cues that govern protein subcellular localization and assembly of macromolecular complexes. Finally, and taking advantage of the discovery that “wild” strains of B. subtilis form architecturally complex communities of cells in which spore formation takes place preferentially in fruiting body-like aerial structures, we are investigating the circuitry that governs multicellularity and mechanisms that link spore formation to multicellularity.