Primary structure and developmental expression of a large cytoplasmic domain form of Xenopus laevis neural cell adhesion molecule (NCAM).

The neural cell adhesion molecule, (NCAM), is involved in cell-cell interactions during development of the vertebrate nervous system. NCAM exists in multiple protein forms and these are selectively expressed in different cells and at different times during development. Here we report the complete amino acid sequence of the large cytoplasmic form of Xenopus laevis NCAM, derived from a full-length cDNA clone. Using specific probes the expression of different NCAM transcripts during Xenopus embryogenesis has been examined. We find that transcripts encoding the large cytoplasmic domain form of NCAM exist in maternal RNA and that these are the only significant NCAM transcripts present until late gastrula when transcripts encoding the small cytoplasmic domain form of NCAM are first detected. No RNA encoding the small surface domain form of NCAM is detected during early development. These results indicate that the expression of NCAM sequences during early development of Xenopus differs from that described in other species.