NEW CELL-SURFACE MARKER OF THE RAT FLOOR PLATE AND NOTOCHORD

Regionally expressed cell surface molecules are thought to mediate con tact-dependent interactions that regulate pattern formation and axon p athfinding in the developing vertebrate central nervous system (CNS), We recently isolated monoclonal antibody (mAb) CARO 2 through a screen for positional markers in the developing rat CNS, Between embryonic d ay (E)11.5 and E13, mAb CARO 2 specifically labels both the floor plat e and notochord in the developing spinal cord, In contrast to the dist ribution of several well-characterized ventral midline markers, mAb CA RO 2 labeling is restricted to the apical portion of the floor plate a nd the outer surface of the notochord, The anterior limit of mAb CARO 2 immunoreactivity corresponds to the midbrain/hindbrain border, Floor plate labeling persists throughout embryogenesis, whereas notochord l abeling is not detectable after E13, During later stages of embryonic development (E16-E20) apically restricted floor plate labeling is pres ent only in the rostral spinal cord, In postnatal rats, mAb CARO immun oreactivity is not present in any region of the CNS, Immunoblot analys es show that mAb CARO 2 recognizes an epitope on a 28-kD protein that is enriched in the floor plate, transiently expressed during embryogen esis, and membrane-associated, Consistent with the latter result, mAb CARO 2 labels the surfaces of floor plate cells, These findings sugges t that the CARO 2 antigen is a new cell surface marker of the floor pl ate and notochord which may participate in neural cell patterning and/ or axon guidance in the developing rat spinal cord. (C) 1998 Wiley-Lis s, Inc.