APICAL CELL ESCAPE FROM THE NEUROEPITHELIUM AND CELL-TRANSFORMATION DURING TERMINAL LIP FUSION IN THE HOUSE SHREW EMBRYO

The house shrew embryo has many cells in the ventricular lumen and on the luminal surface of the fusing terminal lip of the cephalic neural tube. The origin and fate of these cells were studied by means of ligh t and electron microscopy, and by DiI labeling in a whole-embryo cultu re system. The cells appeared at stage 11A and persisted until stage 1 2A. Most of the cells seemed to originate from the neuroepithelium, as shown by frequent observations of epithelial cell escape and DiI labe ling analysis. The cells on the luminal surface sometimes showed apopt otic features, but were not subjected to phagocytosis. Some of the esc aping cells seemed to migrate to the ventral part of the prosencephali c neuropore and insert themselves into it. Others separated from the l uminal surface and floated into the lumen. It seems likely that the fl oating cells either become autolyzed, or else change into macrophage-l ike cells, the latter alternative being supported by the results of Di I labeling. The macrophage-like cells actively phagocytosed the other degenerating cells and apoptotic bodies. These observations suggest th at the apical escape of cells may play an important role in the remode ling of the neural fold during the terminal lip fusion, and that early neuroepitheial cells may have the potential to become cells with vigo rous phagocytic activity, like macrophages.