Regulatory network for Ciona neural development. (A) Animal and vegetal views of 64-cell stage embryo showing the position of A (red), a (yellow), and b-line (green) neural lineages. (B) The Ciona CNS is subdivided into sensory vesicle, neck, visceral ganglion, and nerve cord along the A-P axis. The progeny of three neural lineages are colored according to the scheme in A. Five Hox genes exhibit partial spatial colinearity along the visceral ganglion and nerve cord (Ikuta et al. 2004). Additional homeodomain transcriptional factors like Otx, Pax2/5/8, and Dmbx are expressed in the anterior CNS (Takahashi and Holland 2004). Four FGF genes are expressed in partially overlapping domains along the CNS (Imai et al. 2002; Satou et al. 2002a). (C) Regulatory network for neural specification. The three Ciona neural lineages are specified by a combination of maternal and zygotic factors. Bold lines indicate that this interaction has been verified through the manipulation of binding sites within an enhancer. Asterisks indicate evidence for appropriate binding sites in the noncoding DNA upstream of the target genes. Dotted lines indicate tangential interaction indicated by embryological manipulations. Further details of the differentiation the neural lineages can be found in Supplement 2.
