Sufu, A Repressor Of Signaling,involves In The Limb Bud Patterning And Digit Number Determination

Anterior-posterior(A-P) patterning and outgrowth of the vertebrate limb bud are coordinated by two critical centers during limb bud development : the zone of polarizing activity(ZPA) in the posterior mesenchyme and the apical ectodermal ridge(AER) in the distal ectoderm. Sonic hedgehog(Shh), the secreted signal molecule, is expressed in the ZPA and is sufficient for the determination of polarizing activity. Absence or ectopic expression of Shh results in abnormal digits formation. Suppressor of fused(Sufu), a repressor of Shh signaling pathway, primarily interact with Gli transcription factor to regulate the activity of Shh signaling. However, the roles of Sufu in limb development are still unknown. Therefore, we constructed conditional Sufu knockout mouse model. We found the conditional deletion of Sufu in mesoderm-derived mesenchymal cells with Dermo1-Cre transgenic mouse could lead to preaxial polydactyly. This phenotype is associated with late ectopic anterior expression of Shh. The downstream genes,such as ptched1、Gli1 express ectopicly at E11.5.The FGF signal molecules in AER including fgf4 and fgf8 are expanded towards the anterior limb bud at E10.5,E11.5. The gene of BMP antagonist Gremlin1(GREM1) shows intense ectopic expression at the anterior of limb bud at E10.5. The Hoxds gene family that has important role in limb outgrowth and digit patterning express ectopicly at E11.5.The repressor form of Gli2 and Gli3 decrease markedly at protein level.It implies that the absence of Sufu in mesenchymal cells results in the abnormity of self-regulatory feedback loops of Shh/Grem1/Fgf, Sufu is a critical regulator of controlling the mouse digit mumber and limb patterning.