Both of these cell types originate from epithelial progenitors that become specified as prosensory precursors.
To elucidate the mechanism by which border cells become specified as neural crest cells, we established an explant assay of neural crest cell differentiation by culturing ectodermal explants of the neural plate border region of stage 4 chick embryos for 20 22 hr, corresponding in time to approximately stage 10 (Fig. 1B).
In the present study, we have analyzed when and by what mechanisms anterior neural cells become specified as eye-field cells and neural retina cells.
During embryogenesis a subset of cells become specified as primordial germ cells (PGCs), which will later produce eggs and sperm (Richardson and Lehmann, 2010).
Our findings link the requirement of the lens ectoderm for neural retina specification with the molecular mechanism by which cells in the forebrain become specified as neural retina by BMP activity.
In mice, SOX2 acts in conjunction with OCT 3/4 and its expression is maintained in primordial germ cells until they migrate, colonise the gonad, and become specified as pre-spermatogonia or oogonia, whereupon SOX2 is down regulated.
Together, these results suggest that the pPIm placode is a group of roughly eight neuroepithelial cells, each possessing the equivalent developmental potential to become specified as an IPC NB at the appropriate time.
In wild-type embryos, a single cell at the distal tip of each dorsal branch becomes specified as the terminal cell (TC) (Figure 4A).
Our studies demonstrate a novel role for Hairy in restriction of the terminal cell fate by limiting the domain of bnl expression in surrounding muscle cells such that only a single dorsal branch cell becomes specified as a terminal cell.
Our data support a model where Hairy in the somatic muscle, normally refines the spatial expression of bnl in the muscle cells that are in close proximity to the migrating tracheal branches, such that only a single cell at the tip of each dorsal branch becomes specified as the terminal cell.
