Use of in situ expression patterns to identify candidate genes. (A) In 32-cell stage Ciona embryos, Otx is expressed in the neural lineage a6.5 and b6.5 blastomeres (photo taken from the Ghost database). (B) Diagram of a 32-cell stage embryo illustrating that at this stage FGF9/16/20 is the only Ciona FGF zygotically expressed in cells (blue) neighboring Otx expressing cells (red) (Bertrand el al. 2003). Multiplex in situ hybridization techniques (B. Davidson, W. Shi, and M. Levine, in prep.) that permit visualization of multiple genes simultaneously will greatly enhance the ability to identify potential regulatory cascades based on comparative expression patterns.