QUANTITATIVE-ANALYSES OF NEUROEPITHELIAL CELL SHAPES DURING BENDING OF THE MOUSE NEURAL PLATE

Despite a wealth of information about cell behaviors contributing to n eurulation in chick embryos, similar behaviors in mouse embryos have y et to be well characterized. This study examines cell behaviors occurr ing during bending of the mouse neural plate, in particular, qualitati ve and quantitative changes in neuroepithelial cell shape. Our current results demonstrate that in mouse embryos 1) the median hinge point ( MHP), a localized region of neural plate that becomes anchored to the underlying prechordal plate mesoderm or notochord/notochordal plate an d forms a midline longitudinal furrow around which folding of the rema ining neural plate (i.e., the part of the neural plate not involved in MHP formation) occurs, develops during stages of neural fold elevatio n; 2) the MHP is enriched with wedge-shaped neuroepithelial cells but has significantly fewer spindle-shaped, inverted wedge-shaped, and glo bular neuroepithelial cells than do the adjacent paired lateral areas of the neuroepithelium (L); and 3) each L is enriched with spindle-sha ped, inverted wedge-shaped, and globular neuroepithelial cells but has significantly fewer wedge-shaped neuroepithelial cells than does the MHP. Thus wedging of neuroepithelial cells occurs during bending of th e mouse neural plate and is localized to the MHP during neural fold el evation. Similarly, previous studies in the chick have shown that neur oepithelial cells become wedge shaped during bending of the neural pla te and that such cell wedging is localized to the MHP during neural fo ld elevation. Such studies also have shed light on the roles of MHP fo rmation and localized wedging of neuroepithelial cells within the MHP in the chick; however, such roles have yet to be elucidated in the mou se. It is probable that the MHP in mouse embryos, like that in chick e mbryos, provides a locus for bending of the neural plate and that wedg ing of neuroepithelial cells within the MHP provides the force necessa ry to generate the longitudinal midline furrow around which subsequent folding of the neural plate (i.e., neural fold elevation) occurs. Fur ther studies are necessary to define these roles more precisely. (C) 1 994 Wiley-Liss, Inc.