Tissue Distribution of Connexins
There are more than 20 known connexin proteins identified in the human and mice genome. However, not all the 20 connexins are expressed in all the cells. The expression of connexins has been shown to vary between tissues. Some of the connexins, for example, Cx43, show wide tissue distribution and while others are restricted to a particular cell type or tissue. The tissue distribution of connexins demonstrates their relevance in executing tissue-specific functions. Although connexins show similar, topological features, there exists appreciable amount of variability among different connexins. The variability involved in connexins allows for a great deal of diversity in gap junction formation. Each gap junction appears to confer some specificity for what type of molecules pass through it, based on either the charge or size of the molecule. Based on that specificity, it seems likely that even small amounts of a particular gap junction with a unique composition of connexins could be important for the movement of a particular metabolite or set of metabolites. Identifying what connexins are present in a particular tissue, even if only in small amounts, could thus be crucial for understanding their roles in cell communication as well as cell adhesion. These subtle variations in connexins and hence gap junctions are crucial for performing specialized function of different cell types and tissues. In the following paragraphs, the tissue distribution and tissue-specific function of connexins will be discussed.