Role of the Nodal Signaling pathway in amphioxus neural induction

Overview & Synopsis

Neural induction (NI) is the process through which pluripotent ectodermal cells are committed to a neural fate. In vertebrates, the dorsal organizer produces BMP antagonists, and other signals that induce neural cell fate. However, not much was known about NI in other chordates. Our team previously shown that the cephalochordate B. lanceolatum presents a functional organizer, and that the acquisition of epidermal fate relies on BMP activation. However, deprivation of BMP signals leads to an undifferentiated state of the ectoderm, indicating that BMP inhibition is not sufficient for NI. Moreover, FGF signal inhibition does not block NI, in the contrary to what is observed in several chordate lineages, suggesting that FGF is not the key signal to induce neural fate in amphioxus. Remarkably, activation of the Nodal/Activin pathway triggers NI and represent an instructive signal in this process in amphioxus. In this work, we have identified a group of putative non-exonic regulatory regions which are Activin-sensitive, through ATAC-seq, and searched for potential transcription factors binding sites. Our results suggest that Zinc Finger-related factors, as Klf1/2/4, might be playing crucial roles in neural development. We have also confirmed these results though comparative RNA-seq analyse at several developmental time points in embryo and ectodermal explants after Nodal activation.