Brown algae evolved multicellularity independently of animals and higher plants, and so are of considerable interest to evolutionary and developmental biologists. The life cycle of the model brown alga Ectocarpus siliculosus consists of two independent, alternating multicellular forms(generations): sporophytes and gametophytes. This alternation of generations involves an alternating pattern of cell division in the `initial' cell:asymmetric initial-cell division occurs in gametophyte development and symmetric division in sporophyte development. Now Peters et al. (see ) provide a detailed account of the markedly different patterns of early development of these two generations, and correlate these differences with the mode of initial-cell division. Importantly, they also report a rare life cycle mutant,called imm, in which gametophyte characteristics develop in the sporophyte generation and in which genes normally expressed during the gametophyte stage are upregulated, while sporophyte-generation genes are downregulated. These insights into the development and genetic control of the E. siliculosus life cycle will enlighten future studies of this organism, the genome of which is currently being sequenced.
