How Cell-Cell Adhesion Contributes to Early Embryonic Development
Cell-cell adhesion is a crucial process during embryonic development from earliest stages on. Keeping cells together during morphological changes in tissue composition is essential for the integrity of the developing organism and different cell-cell adhesion molecules including cadherins, immunoglobulins, and integrins contribute to this tissue cohesion. Cadherins dominate in early Xenopus development and for this reason the review will focus on this group. Cadherins are transmembrane glycoproteins mediating a calcium-dependent cell-cell adhesion. They consist of an intracellular and a transmembrane domain together with an extracellular domain with several repeats specific for the different cadherin types. The first described cadherins had five extracellular repeats with four calcium-binding sites each for three calcium ions as a common structure (Fig. 13.1, see type I). Typically, they possess an HAV tripeptide localized to function as binding site for homophilic trans dimerization. They were named classical cadherins or type I cadherins. In other cadherins, which were identified later, the HAV tripeptide is replaced mostly by a QAV tripeptide. Still there are striking similarities in gene structure justifying the term “cadherin” for these molecules as well. Therefore, the subfamily of type II or atypical cadherins (Fig. 13.1, type II) was created for them.
KeywordsXenopus Laevis Early Embryonic Development Xenopus Embryo Blastula Stage Cranial Neural Crest
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