Fig. 3. Cellular functions regulated by Cdc42 in different polarized cell types. Most cell types can polarize under certain circumstances. This figure presents a few examples of polarized cells to highlight the multiplicity of aspects of cell polarity. Cell polarization results from the coordinate regulation of several cell functions. Most of these functions are under the control of Cdc42. (A) In migrating fibroblasts, the actin cytoskeleton promotes extension of the leading edge and retraction of the rear of the cell, the microtubule system associated with the centrosome aligns along the direction of migration and the Golgi apparatus faces the front of the cell and vesicular trafficking is oriented towards the leading edge. (B) During contact with a target cell, a cytotoxic T cell presents a polarized organization that allows the formation of a strong and stable cell-cell contact, and the orientation of the microtubule cytoskeleton and the secretory pathway in the direction of this contact. (C) In differentiated epithelial cells, the entire cell organization is polarized and allows the segregation of apical and baso-lateral proteins and membrane domains separated by tight junctions. The intracellular organization is also characterized by polarized cytoskeletal structures and polarized membrane traffic. (D) In the C. elegans zygote, the first division is asymmetric. The microtubule system is polarized, with asymmetric forces exerted on each pole of the embryo. This leads to an asymmetric positioning of the mitotic spindle. The protein distribution in the cytoplasm is also polarized, which will give rise to two non-equivalent daughter cells.