In vertebrate embryos, several major cadherin types have been identified. For example, E-cadherin is expressed on all early mammalian embryonic cells, even at the zygote stage. In the zebrafish embryo, E-cadherin is needed for the formation and migration of the epiblast as a sheet of cells during gastrulation. Loss of E-cadherin in the half-baked zebrafish mutant results in a failure of deep epiblast cells to move radially into the more superficial epiblast layer, an in vivo cell sorting process known as radial intercalation that helps power epiboly (spreading) of the epiblast during gastrulation (Figure 4.1; see also Chapter 11 and Kane et al. 2005). Later in development, this E-cadherin is restricted to epithelial tissues of embryos and adults.
In mammals, P-cadherin is found predominantly on the placenta, where it helps the placenta stick to the uterus (Nose and Takeichi 1986; Kadokawa et al. 1989). N-cadherin becomes highly expressed on the cells of the developing central nervous system (Hatta and Takeichi 1986), while R-cadherin is critical in retina formation (Babb et al. 2005). A class of cadherins called protocadherins (Sano et al. 1993) lacks the attachment to the actin cytoskeleton through catenins. Expressing similar protocadherins is an important means of keeping migrating epithelial cells together, and expressing dissimilar protocadherins is an important way of separating tissues (as when the axial mesoderm forming the notochord separates from the surrounding paraxial mesoderm that will form somites; see Chapter 17).
Babb, S. G., S. M. Kotradi, B. Shah, C. Chiappini-Williamson, L. N. Bell, G. Schmeiser, E. Chen, Q. Liu and J. A. Marrs. 2005. Zebrafish R-cadherin (Cdh4) controls visual system development and differentiation. Dev. Dyn. 233: 930–945.
Hatta, K. and M. Takeichi. 1986. Expression of N-cadherin adhesion molecules associated with early morphogenetic events in chick development. Nature 320: 447–449.
Kadokawa, Y., I. Fuketa, A. Nose, M. Takeichi and N. Nakatsuji. 1989. Expression of E- and P-cadherin in mouse embryos and uteri during the periimplantation period. Dev. Growth Diff. 31: 23–30.
Kane, D. A., K. N. McFarland and R. M. Warga. 2005. Mutations in half baked/E-cadherin block cell behaviors that are necessary for teleost epiboly. Development 132: 1105–1116.
Nose, A. and M. Takeichi. 1986. A novel cadherin adhesion molecule: Its expression patterns associated with implantation and organogenesis of mouse embryos. J. Cell Biol. 103: 2649–2658.
Sano, K., H. Tanihara, R. L. Heimark, S. Obata, M. Davidson, T. St John, S. Taketani and S. Suzuki. 1993. Protocadherins: A family of cadherin-related molecules in central nervous system. EMBO J. 12: 2249–2256.
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