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.