The formation of an FGF signaling complex requires that both an FGF-family protein and its receptor interact with a heparan sulfate proteoglycan, but little was known about the function of heparan sulfate in this complex. The authors probed frozen tissue sections of mouse embryos with FGF-2 and FGF-4 to detect heparan sulfate expression patterns, and also examined the ability of two FGF receptor constructs to promote FGF signaling complex formation.

FGF-2 and FGF-4 bind to many of the same tissues, but FGF-4 does not recognize heparan sulfate in the heart or major blood vessels. One of the two FGF receptor constructs also demonstrated much less promiscuous complex-forming activity than the other. The results suggest that FGF-2, FGF-4, and FGF receptors recognize different forms of heparan sulfate that are expressed in a tissue-specific manner.The authors have now expanded their analysis to include five different FGFs and...

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