In Vivo Analysis of the Mesenchymal-to-Epithelial Transition During Chick Secondary Neurulation.

The neural tube in amniotic embryos forms as a result of two consecutive events along the anteroposterior axis, referred to as primary and secondary neurulation (PN and SN). While PN involves the invagination of a sheet of epithelial cells, SN shapes the caudal neural tube through the mesenchymal-to-epithelial transition (MET) of neuromesodermal progenitors, followed by cavitation of the medullary cord. The technical difficulties in studying SN mainly involve the challenge of labeling and manipulating SN cells in vivo. Here we describe a new method to follow MET during SN in the chick embryo, combining early in ovo chick electroporation with in vivo time-lapse imaging. This procedure allows the cells undergoing SN to be manipulated in order to investigate the MET process, permitting their cell dynamics to be followed in vivo.