Perception of environmental conditions and the initiation of appropriate responses are critical for survival of an organism. At the cellular level, extracellula r signals that cause cells to change their behavior often require resetting the cell's program of gene transcription. In an increasing number of cases, it is po ssible to trace the route followed by a signal initiated at the cell surface to its transcription-factor targets. However, how a cell regulates the specificity of a response is less clear, given that the same signaling pathways can activate different sets of genes, and different signaling pathways can activate the same genes.

The flagellar regeneration system of the eukaryotic green alga Chlamydomonas reinhardtii is ideal for dissecting gene regulation in response to extracell ular signals. Chlamydomonas cells have a pair of flagella used for swimming in fresh water. Certain extracellular stimuli lead cells to detach their flagellar pair, begin reassembly of a new pair of fl agella, and also transiently to induce transcription of a large and specific set of RNA's encoding over 200 different flagellar proteins. The aim of research in my lab is to delineate the signaling pathways and me chanisms involved in the coordinate induction of flagellar RNA's of Chlamydomonas using cell biological, biochemical, microscopic, molecular, and genetic approaches.

Recent studies in the lab have implicated Ca²⁺ as a key common regulator of flagellar detachment, regrowth, and flagellar gene induction. Part of the current work in my lab is directed toward identifying elements of the intracellular Ca²⁺ signaling pathway leading to flagellar gene induction. Othe r work is directed toward defining DNA elements flanking the flagellar genes and the factors that interact with these elements, which regulate flagellar gene tr anscription.