CLONING AND EXPRESSION STUDIES OF CDNA FOR A NOVEL XENOPUS CADHERIN (XMN-CADHERIN), EXPRESSED MATERNALLY AND LATER NEURAL-SPECIFICALLY IN EMBRYOGENESIS

From a Xenopus tailbud cDNA library, we obtained the cDNA for a novel cadherin which was named as XmN-cadherin (Xenopus maternally expressed neural cadherin). The cDNA consisted of 3690 bp and encoded 922 amino acid residues. XmN-cadherin preserved five extracellular cadherin mot ifs, a single transmembrane domain, and a cytoplasmic domain, and was closely related by its sequence to R- and N-cadherin. In the adult fro g, XmN-cadherin mRNA was detected strongly in ovary, testis, brain, ey e, and kidney, and weakly in stomach, and intestine. In the egg, the m RNA occurred as a maternal mRNA at a relatively high level, and its le vel became very low by the neurula stage, then increased steadily ther eafter. Dissection experiments with 8-cell stage and neurula stage emb ryos revealed that the maternally inherited mRNA was relatively unifor mly distributed within the embryo. By a sharp contrast, whole mount in situ hybridization revealed that the zygotically expressed mRNA occur red almost exclusively in neural tissues such as brain, the anterior p art of spinal cord, and the optic and otic vesicles. Thus, XmN-cadheri n appears to have at least triple functions; it probably contributes i n early embryos to cell-type non-specific cell adhesion, but in post-n eurula embryos may be responsible for the development and/or maintenan ce of anterior neural tissues, and may be used in adult frog for the d evelopment and/or maintenance of neural, endodermal and reproductive o rgans.