MuSC, a novel member of the immunoglobulin superfamily, is expressed in neurons of a subset of cranial sensory ganglia in the mouse embryo

In contrast to the spinal sensory ganglia which reiterate a basic organizational and functional unit, each cranial ganglion mediates a distinct sensory modality and exhibits a characteristic pattern of peripheral and central neuronal connectivity. Molecules responsible for establishment and maintenance of the cranial ganglion‐specific networks are not known. Our hamster monoclonal antibody 802C11 strongly stained neurons and their processes of the VIIIth cranial ganglion (hearing and equilibrium), but not of the Vth cranial (somatosensory) or spinal ganglia in the mouse embryo. The cellular staining pattern of positive neurons suggested that the antigen was associated with the cell membrane, and biochemical analyses of the antigen from adult mouse brain showed the antigen to be a glycosylated intrinsic membrane protein of ≈100 kDa. The antigen was purified, and based on the partial amino acid sequences, its entire cDNA was cloned. A bacterially expressed polypeptide encoded by the cDNA was recognized by the antibody. The deduced amino acid sequence revealed that the antigen belongs to the immunoglobulin superfamily with a significant homology (73.5% identity) to chicken SC1 protein. Chicken SC1 has been shown to be a cell–cell adhesion molecule in vitro with a proposed role in neurite extension of spinal motor neurons. These results suggest that our murine SC1‐related protein (MuSC) is involved in the pathfinding and/or fasciculation of specific cranial sensory nerve fibres.