Spatial control of cell differentiation in Myxococcus xanthus

Myxococcus xanthus develops species-specific multicellular fruiting bodies. Starting from a uniform mat of cells, some cells enter into nascent fruiti ng body aggregates, whereas other cells remain outside. The cells within th e fruiting body differentiate from rods into spherical, heat-resistant spor es, whereas the cells outside the aggregates, called peripheral cells, rema in rod-shaped. Early developmentally regulated genes are expressed in perip heral cells as well as by cells in the fruiting bodies. By contrast, late d evelopmental genes are only expressed by cells within the nascent fruiting bodies. The data show that peripheral cells begin to develop, but are unabl e to express genes that are switched on later than about 6 h after the star t of development. All of the genes whose expression is limited to the fruit ing body are dependent on C-signaling either directly or indirectly, wherea s the genes that are equally expressed in peripheral rods and in fruiting b ody cells are not. One of the C-signal-dependent and spatially patterned op erons is called dev, and the dev operon has been implicated in the process of sporulation. It is proposed that expression of certain genes, including those of the dev operon, is limited to the nascent fruiting body because fr uiting body cells engage in a high level of C-signaling. Peripheral cells d o less C-signaling than fruiting body cells, because they have a different spatial arrangement and are at lower density. As a consequence, peripheral cells fail to express the late genes necessary for spore differentiation.