SPATIOTEMPORAL CURVATURE PATTERN OF THE CAUDAL BODY AXIS FOR NON-MUTANT AND CURLY TAIL MOUSE EMBRYOS DURING THE PERIOD OF CAUDAL NEURAL-TUBE CLOSURE

During the period of early organogenesis the mouse embryo has a curved body shape, which is thought to interact with ongoing developmental p rocesses. Curly tail is a mouse mutant causing spina bifida, in which aberrant axial curvature is considered to be responsible for a delay i n the closure of the posterior neuropore (PNP). Since detailed descrip tions of axial curvature have never been made in either the normal or the mutant embryo, the onset and development of the aberrant axial cur vature in the curly tail embryo are unknown. In the present study, axi al curvature and segmental growth during closure of the PNP are descri bed using circle segments at each somite level in two non-mutant mouse strains. Using the radius and angle of the segments as parameters, CD -1 and Balb/c mouse embryos showed maxima of curvature at the levels o f the limb buds. Throughout development, a general axial unbending occ urred that was due to a level-specific combination of general outgrowt h and other factors. A marked additional decrease in the axial curvatu re was spatially and temporally related to the final closure of the PN P, indicating that this decrease of curvature facilitates the final cl osure of the PNP. In the curly tail embryo the segment parameter radiu s was used to relate the axial curvature to an aberrant neural tube cl osure pattern. These embryos exhibited an enhanced curvature over the entire neuropore region as soon as a delay in the PNP closure could be distinguished. A steep decrease in curvature during final closure of the PNP did also occur, but at a more caudal level. Both the axial lev el of straightening and the rate of curvature were normalized at advan ced developmental stages. The aberrant spatio-temporal curvature patte rn in the curly tail mouse embryo indicates that both the rate of curv ature and the axial level of unbending are important for a correct PNP closure.