Abstract
Abstract: :
Purpose: During development, neural stem cells of the central nervous system including the cerebral cortex and retina show pseudostratified structure, and enormously proliferate to produce a large number of neurons and glial cells. The neuroepithelial cells has long apical and basal processes, and the nucleus moves up and down within the cell according to the cell cycle (i.e., interkinetic nuclear migration); mitosis occurs at the apical (ventricular) surface, and the nucleus is located at the basal half in S phase. The molecular mechanism of this interkinetic nuclear migration is still unknown. Transcriptional factor Pax6 is strongly expressed in the neuroepithelial cells, and required for neurogenesis and neuronal specification. Pax6 deficient mice have cell kinetic abnormalities such as cell cycle elongation and mitotic mis–position in the cerebral cortex. To investigate a possibility that Pax6 is involved in interkinetic nuclear migration in the developing cerebral cortex, we examined the distribution of mitotic cells and recorded neuroepithelial cell behavior in the cerebral cortex of wild type Sprague–Dawley (SD) rat and Pax6 deficient rat embryos. Methods: Mitotic cells in the cortex primordium were detected with anti phosphorylated histone H3 antibody. Interkinetic nuclear migration was observed in live cortical slices. Cortex primordia were dissected out and neuroepithelial cells were labeled with fluorescent dye, DiI. The labeled cortex was cut into slices, which were embedded in collagen gel. Behavior of labeled cells was observed under a fluorescent microscope for 10 hours. Results: In the cortex primordium of Pax6 deficient rat, the number of cells dividing at the apical surface decreased and cells dividing at the basal side conversely increased compared with SD rat. Furthermore, abnormal interkinetic nuclear migration patterns such as premature descent of S–phase cells,unsteady ascent or descent of G2–phase cells, and ectopic cell dividion were observed in the Pax6 deficient rat. Conclusions: These results suggest that Pax6 is involved in interkinetic nucear migration in the cortex neuroepithelial cells. The images of cell behavior of the Pax6 deficient rat imply that the anchor apparatus at the apical side of the neuroepithelial cells becomes weakened. It is thus possible that transcriptional factor Pax6 may regulate expression of molecule(s) within the apical anchor.
Keywords: retinal development • transcription factors