Figure 4. In situ hybridization - pool A transcripts.

Three pool A transcripts show a similar pattern of ectodermal expression orally. (A) A1 (apextrin). Shortly after closure of the blastopore expression is in discrete patches with none at the aboral end (1). As it gradually elongates, expression continues in the oral two-thirds of the planula (2–4), finally ending as a belt separating the oral and aboral ends as the planula rounds up at the time of settlement (5). (B) A5 (N-terminal nucleophile aminohydrolase). Initial expression, shortly after blastopore closure, is limited to the oral ectoderm (1,2), but by the time the planula has elongated (3) expression is found in the oral two-thirds of the planula, similar to that observed for apextrin; the ectoderm of the developing siphonoglyph is also staining (white asterisk). Expression then resolves to a region in the middle as the planula begins to metamorphose (4). A10 (unknown function) shows a similar expression pattern. All pre-settlement stages are oriented with aboral to the right, as that end leads when swimming, while post-settlement stages are oral side up. Where available, the virtual northern blots are reproduced in this figure.