ANNEXIN-IV IS A MARKER OF ROOF AND FLOOR PLATE DEVELOPMENT IN THE MURINE CNS

Midline structures, such as the notochord and floor plate, are crucial to the developing central nervous system (CNS). Previously, we demons trated that annexin IV is an excellent marker of midline structures. I n the present study, we explore the possible role of annexin IV in dev elopment of the CNS midline. Using immunocytochemistry with an antibod y to annexin IV, we have elucidated the temporal and spatial expressio n of this molecule. Annexin IV is present in the notochord at embryoni c day (E) 8.5, prior to its expression in any structures within the ne ural tube. Subsequently, annexin IV is expressed by floor plate cells at E9.5. Annexin IV is also expressed in the roof plate, but not until E10.5. To determine if normal morphogenesis of these midline structur es is essential for annexin TV expression, we analyzed two strains of mutant mice that have defective formation of either the floor or the r oof plate. In Danforth's short-tail mice, the floor plate is absent fr om the caudal spinal cord, and annexin TV immunopositivity disappears at the level where the floor plate is missing. In curly tail mutant mi ce, there can be a failure of the neural tube to close, and in these r egions there is no annexin IV expression in presumptive roof plate cel ls. Finally, annexin IV immunolabeling is present from the caudal spin al cord, through the brainstem up to the diencephalon and lamina termi nalis. Thus, annexin IV is an excellent marker for differentiated midl ine cells, is temporally and spatially correlated with development of the floor and roof plates, and is expressed in a rostral-caudal manner that supports the hypothesis that the floor plate extends the full le ngth of the original neural tube. (C) 1996 Wiley-Liss, Inc.