Upstream regulatory sequences required for specific gene expression in the ascidian neural tube.

The relatively simple structure of ascidians and the number of associated molecular resources that are available make ascidians an excellent experimental system for Investigating the molecular mechanisms underlying neural tube formation. The ascidian neural tube demonstrates the same basic morphology as that of vertebrates. We have described the expression of the neural tubespecific gene CiNut1, which is expressed within neural tube precursor cells from the gastrula stage, and along the entire length of the neural tube during its formation. In this study, we focused on the transcriptional mechanisms that regulate CiNut1 expression. We found that an approximately 1.0 kb upstream sequence was able to recapitulate endogenous CiNut1 expression. A deletion analysis showed that the 119 bp upstream fragment containing two ZicL-binding consensus sequences and one Fox core sequence could also drive the neural tube-specific expression. When mutations were Introduced into the distal ZicL binding site (ZicL1), the neural tube-specific expression almost disappeared. Although the Importance of the proximal ZicL site (ZicL2) and the Fox core sequence have yet to be elucidated, we hypothesize that ZicL regulates gene transcription in the entire neural tube of the ascidian.