Dissection of eukaryotic transmembrane signalling using Chlamydomonas.

Novel insights and surprises are often generated when investigators choose an organism that permits a new approach to a problem. For example, secretory and cell-cycle mutants in yeast have provided quantum leaps in elucidating these processes. Similarly, genetic systems are providing exciting new insights into signal transduction. The 'green yeast' Chlamydomonas has the potential to be a particularly rich organism for genetic analysis of signal transduction because, although unicellular, it has several interesting behaviours, which are discussed in this article by Lynne Quarmby and Criss Hartzell. Phototaxis results from the transduction of a light signal received by the eyespot to changes in flagellar beat. The mating reactions, which culminate in the fusion of gametes, are initiated in response to adhesion of flagellar proteins. Deflagellation, or flagellar shedding, is an acute response to a variety of stimuli. Molecular genetic analysis of behavioural mutants is providing new directions for understanding signal integration and segregation.