Axial rotation in rat embryos: involvement of changes in the shapes and arrangement of cells.

Abstract

Rat embryos at the head-fold stage (9.5 days of gestation) were cultured for 32 hours in rat serum. Embryos rotated their axes (changing from the shape of a concave mid-region to that of a convex mid-region) during the last 5 hours of culture (from 27 h to 32 h in culture). Addition of 0.1 micrograms/ml cytochalasin D to the culture medium for this 5-hour period prevented axial rotation in the embryos and disturbed the appearance of microfilaments in the dermatome, the dorsal region of the trunk neural tube, and the dorsal epidermis. During the period of axial rotation, the dermatome and the dorsal epidermis extended and showed the arrangement of microfilaments along the cranio-caudal axis in the control embryos but not in the treated embryos. The dorsal region of the trunk neural tube in the control embryos consisted of a seam of neuroepithelial cells in which microfilaments were apparently arranged along the cranio-caudal axis but the region in the treated embryos was crowded with the neuroepithelial cells piled up randomly and microfilaments showed no arrangement. These results suggest that changes in the shapes and arrangement of the cells in the dermatome, the dorsal region of the trunk neural tube, and the dorsal epidermis cause extension of these tissues along the cranio-caudal axis and result in axial rotation. Microfilaments may play an essential role in changes in the shapes and arrangement of the cells in these tissues.