FGF-dependent patterning of the Ciona intestinalis anterior neural plate

Tunicates are marine invertebrates belonging to the sister group to vertebrates. Their simple embryogenesis and compact genomes, along with the ease of experimental manipulation, make them well-suited for the study of cell-fate specification in chordates. Despite their extreme divergence, tunicate larvae possess a characteristic chordate body plan, and many developmental pathways have been shown to be conserved between tunicates and vertebrates. For example, FGF signaling is important for induction and patterning of neural tissue in both groups. Here, I demonstrate the role of FGF signaling in patterning the mid-gastrula neural plate and explore the transcriptional effectors functioning downstream of FGF signaling at this stage. I find distinct roles for two ETS family transcription factors in medial versus lateral cells of the neural plate. Furthermore, I provide evidence for a more posterior origin of photoreceptor cells than has been previously reported and show that photoreceptor specification does not depend on FGF signaling. I suggest that the cells previously identified as the photoreceptor progenitors in fact give rise to ependymal cells of the larval brain, and may be among the population of "stem-like" cells that differentiate into neurons in the adult brain