Epithelium and mesenchyme represent two extremes in the organization of groups of cells. Epithelial cells array themselves into flat sheets or rolled tubes, while mesenchymal cells appear less coordinated in their structure-forming activities and form fewer and looser connections with other cells. These tissue-level differences are reflected at the level of the individual cell as well. Under the microscope, mesenchymal cells are amorphous and lack the distinct apical-basal polarity that characterizes their epithelial counterparts. Both types of cells contribute to the body's function in distinct ways, with epithelium being the essential structural and physiological component of organs and tissues such as the kidney and the lining of the gut, and mesenchyme forming all migratory cells, including metastatic cancer cells, as well providing support for the epithelium in various contexts. Despite (or perhaps because of) these differences, our anatomy contains countless examples of interaction between epithelial and mesenchymal cells. Indeed, nearly every one of the body's structures, from internal organs to limbs to teeth, is made up of a mesenchymal and an epithelial component.

Developmental biologists are particularly interested in the ability of each of these cell types to be converted into its counterpart, epithelial cells become mesenchymal, while in other situations the reverse transformation occurs. Now, Yoshiko Takahashi (Team Leader, RIKEN CDB Laboratory for Body Patterning; Kobe, Japan) and colleagues report a heretofore unknown mechanism by which mesenchymal-epithelial transitions (METs) are regulated in the embryogenesis of the chicken. The article, published in the September 14 issue of Developmental Cell, describes how a pair of intracellular molecules affects the ability of mesenchymal cells to convert into epithelial cells during the formation of somites early in embryogenesis. Somites are transitory structures that appear in a head-down direct
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Contact: Doug Sipp
sipp@cdb.riken.jp
RIKEN Center for Developmental Biology
13-Sep-2004

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