Asymmetric limb malformations in a new transgene insertional mutant, footless.

Six to eight copies of a transgene integrated into mouse chromosome 15 resulting in a new transgene insertional mutant, Footless, presenting with malformations of the limbs, kidney, and soft palate. Homozygotes possess a unique asymmetric pattern of limb truncations. Posterior structures from the autopod and zeugopod of the hindlimbs are missing with left usually more severely affected than right. In contrast, anterior structures are missing from the right forelimbs. The left forelimb is usually normal except for the absence of the distal telephalanges and nails. These structures are absent on all formed digits. In situ hybridization assays examined the expression of Shh, dHand, Msx2, Fgf8, En1, and Lmx1b in mutant limb buds and indicated normal establishment of the anterior/posterior and dorsal/ventral axes of the developing limbs. However, dysmorphology of the apical ectodermal ridge was observed in the mutant limb buds.