Fate of Cranial Placode Progenitors Induced by Zic1 and Retinoic Acid Signaling

Objectives: Cranial placodes are thickenings of the embryonic head ectoderm that contribute to the paired sense organs (nose, ear and eye) and to the cephalic peripheral nervous system (cranial ganglia). We have previously shown that the transcription factor Zic1 is sufficient to activate a cranial placode developmental program when expressed in Xenopus ectoderm explants. Zic1 mediates its activity non-cell autonomously by regulating retinoic acid (RA) production.
Methods: To determine whether the placode progenitors generated by Zic1 can give rise to placodes with distinct identities we analyzed the fate of these cells by RT-qPCR and in situ hybridization, at different time points in culture, focusing on genes specifically expressed in the adenohypohyseal (Pitx3 and Lhx3), olfactory (Dmrt4 and Ebf2), lens (Pax6 and Lens1), trigeminal (Pax3 and Tbx2) and otic (Pax8 and Sox9) placodes.
Results: The results of these experiments will be presented and discussed in the context of current models of cranial placodes specification.
Conclusions: These studies are expected to provide novel insights into the regulatory cascade controlling cranial placodes formation.