We are investigating mechanisms that generate pattern in developing embryos. Specifically, we study somitogenesis, the process by which repeated tissue blocks, or somites (segments), are formed from the growing vertebrate tailbud. Somites form in a precise temporal and spatial manner, with a new somite pair forming every 30 minutes in a zebrafish embryo, the model organism we study. Somitic cells later form axial skeleton, dermis, and most body musculature. It has been proposed that somitogenesis is controlled by an intrinsic "segmentation clock", and that one molecular output of the clock is the oscillating expression of several mRNAs in the presomitic mesoderm. However, the molecular nature of the clock itself is unknown. We are pursuing genetic and genomic approaches to isolate components upstream and downstream of oscillating genes in order to understand how vertebrate embryos make body segments. Our studies will address how cells assess their position within an embryo, how cells respond to positional signals or gradients, and how cells communicate positional information locally to their neighbors.