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Fig. 3. Cell-ECM adhesion molecules involved in gastrulation. Integrins form
heterodimers composed of an 
and a β subunit. The short
cytoplasmic domain of the β-subunit binds to the cytoskeletal protein
Talin. Integrins link to the actin cytoskeleton and to actin regulators, like
Rac1 and Ccd42, via Talin and other cytoplasmic proteins of the focal adhesion
complex, including focal adhesion kinase (FAK) or integrin-associated kinase
(ILK), the scaffold protein Paxillin, Vinculin, -actinin and others
(Zaidel-Bar et al., 2007).
HSPGs are categorized into the subfamilies of transmembrane syndecans,
GPI-anchored glypicans and extracellular proteoglycans
(Kirn-Safran et al., 2008).
Syndecans can bind to fibronectin (FN), possibly modulating cellular focal
adhesiveness (Morgan et al.,
2007), while interfering with growth factor distribution by
modifying the ECM. In reverse, FN might interfere with the growth factor
co-receptor function of HSPGs at the cell surface, for instance, modulating
signalling through the Wnt receptor Frizzled 7 (Fz7)
(Munoz et al., 2006).
Hyaluronan is a secreted linear polysaccharide of high molecular weight, but
without a polypeptide chain. During zebrafish gastrulation, it seems to act as
an autocrine signal, rather than as a migration substrate, activating Rac1 to
induce lamellipodia formation (Bakkers et
al., 2004). ECM, extracellular matrix; GPI, glycosyl
phosphatidylinositol; HSPGs, heparan sulfate proteoglycans.
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