03-P093 Tbx2 modulates proliferation and elongation of the mouse embryonic heart tube

In vertebrates, retinal progenitor cells (RPCs) are specified at the end of the gastrulation within the anterior neural plate (ANP) as a single domain called the eye field. From that single domain, positioned medially within the ANP, the RPCs give rise to two optic vesicles, positioned more laterally. How this dramatic morphogenetic remodelling occurs is not well understood. We will show that soon after their specification, RPCs do not present a classical neuroepithelial appearance, with apical and basal sides; instead, RPCs seem to be randomly oriented and present a more mesenchymal morphology. Less than an hour later, the RPCs have organised into a neuroepithelium with all their apical sides oriented towards the lumen of the eye field. This reorganisation is followed by the splitting of the eye field and the evagination of the optic vesicles. We will discuss the potential role of the Wnt/PCP pathway and the transcription factor Rx3 in these cellular rearrangements as well as the role of the morphogenetic movements of surrounding tissues (prospective telencephalon and hypothalamus) in the splitting of the eye field.