Dale Kaiser, Ph.D.

Professor of Developmental Biology and of Biochemistry

How spatial patterns of differentiated cells arise is a central issue in development. Myxococcus xanthus and other myxobacteria differentiate spores in response to nutrient deprivation. While most bacteria sporulate individually, myxobacteria build large specifically shaped masses of spores, known as fruiting bodies. When their development is induced by starvation, a hundred thousand cells contribute to building a fruiting body. Cells that have entered into the fruiting body finally differentiate into environmentally resistant myxospores, which can survive years without nutrients. Our group studies how cells signal to each other and how cells move to build a fruiting body and to differentiate spores.

Recent work has emphasized the morphogenetic C-signal. The C-signal controls both the assembly of fruiting bodies and the differentiation of myxospores. Production of this signal, which is encoded by the csgA gene, is regulated by the act operon of 4 genes that are co-transcribed from the same start site. The actA and actB genes regulate the maximum level of the C-signal. By sequence homology, actB encodes a sigma-54 activator protein of the NTRC class. actA and actB are part of the same signal transduction pathway that responds to C-signal and regulates expression of CsgA protein, thus creating a positive feedback loop. The actC and actD genes regulate the time pattern of CsgA production withouut changing the maximum level. The act operon-regulated positive feedback loop explains how the C-signal rises continuously from early development to a peak at the time of sporulation so that it first induces aggregation then sporulation, and spores form only inside the fruiting body.