Neurological defects and growth retardation in B-Raf–deficient mice. (A) Limb clasping reflex in P18 Mox2^cre/+;b-raf ^f/f and b-raf ^Δ/Δneu mice suspended by the tail. (B) Complete conversion of the b-raf ^f/f to b-raf ^Δ/Δ alleles in brain but not in other tissues of P18 b-raf ^Δ/Δneu mice. PCR analysis of: T, tail; B, brain; Liv, liver; L, lung; Sp, spleen; Th, thymus; H, heart; and K, kidney. N, negative control (H₂O); f/− and +/+, positive controls. (C) Immunoblots of brain lysates from P18 b-raf ^f/f (WT) and b-raf ^Δ/Δneu (KO) mice probed with antibodies against N- or C-terminal B-Raf epitopes demonstrate the complete absence of B-Raf protein. The position of the molecular weight markers is shown between the autoradiograms. The arrow indicates B-Raf. Actin immunoblot, loading control. (D) Immunoblot of brain and spinal cord lysates from P18 b-raf ^f/f (WT) and b-raf ^Δ/Δneu (KO) mice. MEK2 immunoblot, loading control.