Fig. 4.

Malformations of the stapes observed inBrn4 null mice. The stapes of the mutant animals demonstrate several malformations, particularly in the stapedial footplate. A, C, E, Wild-type stapes are depicted. B, D,F, Mutant stapes are depicted. A,B, The footplate of the stapes (arrow inA) in mutant embryos (B) is flatter in comparison with that in wild-type stapes (A). C, D, A lateral view of the stapes demonstrates that the crus from which the stapedial ligament is attached is thinner in the mutant animals (D) than in the wild-type animals (C). E, F, Examination of the sole of the stapes footplate illustrates the slightly eccentric ovoid shape of the wild-type footplate (E). The mutant footplate adopts a more polygonal shape with an acutely angled tip on one end of the footplate (arrow in F). Stapes (n = 10) isolated from six mutant male animals were examined. Wild-type stapes (n = 15) were examined from eight male animals, including six wild-type littermates, two males from the inbred strain 129/SvJ, and two CBA/2J male animals.