Wound healing in the primitive deep layer of the young chick blastoderm

Wound healing in the primitive deep layer of stage 4 chick blastoderms was studied in vitro by cinemicrophotography of living cultures and by photomicroscopy, scanning- and transmission electron microscopy after fixation. Experimental wounds with an average diameter of 0.3 mm healed completely within 2 to 4 h through migration of the cells at their rims. Healing occurred in mesenchyme-free areas, providing us with a purely epithelial reaction. The rim cells of the primitive deep layer formed extensions at their free flank, described as fila, filopodia, lamellae and lamellipodia. They were already present in blastoderms fixed at the earliest after the intervention. This reaction was ascribed to the elimination of a normal fellow cell at the side of the rim cell facing the defect. Movement of the rim cell ceased upon meeting another cell with the same polarity. At this moment lamellipodia disappeared as suddenly as they had formed, and the number of fila and filopodia decreased. We believe that the chick blastoderm's primitive deep layer might be appropriate for analysis of the factors governing primary epithelial wound healing.