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		DISCUSSION Genetic modification of mice embryos to produce mice deficient for Fgf10 lacked limb buds. This revealed that FGF10 is necessary for limb bud initiation. Treating embryos with SU5402 (final concentration 5 uM) did not inhibit limb bud outgrowth. This lead us to conclude that we did not completely inhibit FGF signaling and/or FGFR activity was restored some point after treatment before limb bud initiation. A possible way to remedy this result would be to reinject embros after the initial treatment or to treat the embryos at a time crucial to limb bud initiation. It has been demonstrated that mesodermal Fgf-10 initiates limb bud outgrowth and initiates the expression ofFgf8in the AER which subsequently upregulates Shhin the posterior margin or the developing limb bud. Subsequently, SHH upregulates Fgf4in the AER which in turn positively regulates Shh in the posterior limb. Furthermore, Sanz-Ezquerro and colleagues have demonstrated that SHH participates in an auto regulatory feedback loop in the limb bud (2000). When they ectopically expressed shh, they found that shhwas subsequently downregulated (Sanz-Ezquerro et al. 2000). As indicated by the high level of shh expression in the limb buds, we suspect that the FGF inhibition interfered with the autoregulatory mechanism of SHH (Figure 4). Previous research indicates that mutations in FGFR1, FGFR2, and FGFR 3 result in cranial malformations that involve multiple or all sutures (Wilkie 1997; as cited by