Comparison of Cell Kinetics between the Boundary and the Interboundary Areas during Hindbrain Segmentation in the Chick Embryo.

Abstract

It has been proposed that a difference between the length of the cell cycle and the S−phase in cells in the rhombomere boundary and those in the center of each rhombomere (interboundary) produces a driving force for hindbrain segmentation. To assess the validity of this hypothesis, we examined the cell kinetics of rhombomeric cells in the chick embryo using two kinds of labeling procedures. Cumulative labeling indices with bromodeoxyuridine (BrdU) revealed that the ratio of the number of S−phase nuclei in the boundary tended to be greater than in the interboundary area, whereas the time intervals required for reaching the plateau phase of labeling indices were similar (6hr) in the two areas through all stages examined with the exception of r4 at stage 15. By employing a double labeling method using BrdU and iododeoxyuridine that enables the comparison of the length of the S−phase in cells in the boundary and interboundary areas, we demonstrated that the ratio of the number of double−labeled nuclei in the two areas was not significantly different at stage 15. The present studies have indicated that the cell kinetic parameters of the cell populations in the boundary are not significantly different from those in the interboundary during hindbrain segmentation and suggest that molecular and cellular interactions other than the differential growth rate may play more crucial roles in hindbrain segmentation.