Deciphering the developmental program in the ascidianCiona intestinalisjust prior to gastrulation

ABSTRACT The embryo of the ascidian Ciona intestinalis displays striking anatomical simplicity, with an invariant cleavage pattern during development. It has a monoploid genome like the model organisms Drosophila melanogaster and Caenorhabditis elegans , whereas vertebrates generally exhibit tetraploidy. In this study, I took advantage of these characteristics to investigate the development of the organism as one reverse-engineers an industrial product. First, the spatial expression of 211 genes was digitalized. Some genes showed variable expression patterns, which might reflect multiple snapshots of a single temporally dynamic expression at different times. Several developmental territories of the embryo were considered to be very similar to each other; however, this digitalization of gene expression patterns showed that differences occurred between individual blastomeres even within a single developmental territory. Furthermore, Ciona Brachyury ( Ci-Bra ) was expressed in those blastomeres in which both Fox (forkhead-box) A-a and Zic (zinc-finger) L were expressed, these proteins being upstream regulators of Ci-Bra. The approach described enables the developmental program to be studied in silico . SUMMARY STATEMENT A detailed expansion of our knowledge on an animal developmental program by using already published gene expression data with the aid of computers