Expression of M-cadherin protein in myogenic cells during prenatal mouse development and differentiation of embryonic stem cells in culture.

Molecules regulating morphogenesis by cell-cell interactions are the cadherins, a class of calcium-dependent adhesion molecules. One of its members, M-cadherin, has been isolated from a myoblast cell line (Donalies et al. [1991] Proc. Natl. Acad. Sci. U.S.A. 88:8024-8028). In mouse development, expression of M-cadherin mRNA first appears at day 8.5 of gestation (E8.5) in somites and has been postulated to be down-regulated in developing muscle masses (Moore and Walsh [1993] Development 117:1409-1420). Affinity-purified polyclonal M-cadherin antibodies, detecting a protein of approximately 120 kDa, were used to study the cell expression pattern of M-cadherin protein. It was first visualized in somites at E10 1/3 and could be confined to desmin positive, myotomal cells. At all subsequent prenatal stages, M-cadherin was only found in myogenic cells of somitic origin. The detection of the protein at E10 1/3 suggests a translational delay of M-cadherin mRNA of 1 to 2 days (E8.5 vs. E10 1/3). This was further supported by the finding that during differentiation of ES cell line BLC6 into skeletal muscle cells in culture, expression of M-cadherin mRNA can be detected 2 days prior to M-cadherin protein. During prenatal development, the pattern of M-cadherin expression changes: In E10 1/3 embryos and also in myotomal cells of later stages, M-cadherin is evenly distributed on the cell surface. In developing muscle masses (tested at E16 to E18), however, M-cadherin protein becomes clustered most likely at sites of cell-cell contact as indicated by double-labelling experiments: M-cadherin-staining is the positive image of laminin negative areas excluding the presence of a basal lamina at M-cadherin positive sites. Furthermore, M-cadherin is coexpressed with the neuronal cell adhesion molecule N-CAM which has been shown to mediate cell-cell contact in myogenic cells. In summary, our results are in line with the idea that M-cadherin might play a central role in myogenic morphogenesis.