Brachyury downstream notochord differentiation in the ascidian embryo

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Abstract
The ascidian tadpole represents the most simplified chordate body plan. It contains a notochord composed of just 40 cells, but as in vertebrates Brachyury is essential for notochord differentiation. Here, we show that the misexpression of theBrachyury gene (Ci-Bra) of Ciona intestinalisis sufficient to transform endoderm into notochord. Subtractive hybridization screens were conducted to identify potentialBrachyury target genes that are induced upon Ci-Bramisexpression. Of 501 independent cDNA clones that were surveyed, 38 were specifically expressed in notochord cells. These potentialCi-Bra downstream genes appear to encode a broad spectrum of divergent proteins associated with notochord formation.