Wound Healing in the Hindbrain of the Chick Embryo
Date
2003-01
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Publisher
University of Ghana
Abstract
The neural folds comprise two epithelial layers, namely, surface epithelium and neuroepithelium. In the fore and midbrain regions of the chick embryo, neural fold fusion in the dorsal midline involves a complete fusion of both layers. In the hindbrain region, however, fusion of the neuroepithelial portion of the neural folds does not occur. Rather, following apposition of the tips of the neural folds, many of the neuroepithelial cells that should participate in neural fold fusion undergo apoptosis. The rest of the neuroepithelial cells in the region of the dorsal midline undergo rearrangement and flattening to form a single-layered neuroepithelium of the hindbrain roof plate. It is not clear whether in the light of the above the hindbrain region may be a weakened portion of the neuraxis, and therefore, be predisposed to the development of neural tube defects (NTDs). The present study had a three-fold aim, namely, i) To ascertain whether the hindbrain roof plate at the time it is undergoing apoptosis possesses the ability to close when it is reopened through wounding, ii) to determine the mechanisms by which roof plate closure is achieved in the event of it occurring despite apoptosis iii) to determine whether wound healing in the hindbrain roof plate affects its morphogenetic thinning. Chick embryos at stages 11 and 12 of development were wounded in the dorsal midline of hindbrain rhombomeres rl/r2 and rl-r3, and reincubated for varying periods of time to allow healing to be effected. At zero hour, the wound was slit-like or gaped slightly, with the wound edges of the surface epithelium capping that of the neuroepithelium. Healing of both the surface epithelium and the neuroepithelium began from the ends of the wound within 30 minutes of reincubation. Healing of both layers then progressed in a zipper-like manner towards the middle portion of the wound. The sequence of healing was surface epithelium first, followed by neuroepithelium. Complete healing occurred in both rl/r2 and rl-r3 wounds, implying that the length of the wound did not affect the ability of the hindbrain roof plate to repair itself. Additionally, the longer rl-r3 wounds healed at a faster rate than the shorter rl/r2 wounds such that at any given time, the average length of wound healed for the two groups (i.e. rl/r2 and rl-r3) did not differ significantly. Acridine orange histochemistry revealed that apoptosis in the hindbrain occurred normally in the presence of wound healing leading to the normal morphogenetic thinning of the hindbrain roof plate. The implication is that the early embryo has reparative mechanisms in place to ensure that assaults to it are taken care of, thereby preventing the interference of normal morphogenesis. Healing of the neuroepithelium in the presence of massive apoptosis suggests that apoptosis may not likely predispose the hindbrain to the development of NTDs
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