Fig. 2.

Morphogenetic defects of three null mutant lines are shown. Fgf10 null mutants lack formation of any canals (A,B) but form a single undifferentiated pouch that carries the reduced and malformed anterior and horizontal cristae. These mutants lack a posterior crista entirely (B). Gata3 null mutants show arrest of ear formation at the level of the otocyst with barely recognizable initiation of sensory epithelia formation (D). Interestingly, the expression of Gata3 as revealed with the β-galactosidase marker shows disorganization suggestive of alterations of expression of Gata3 (C,D). Otx1 null mutants lack formation of the horizontal canal and show a fusion of the utricular and saccular epithelium across the enlarged utriculo-saccular foramen (E,F). The loss of a horizontal canal and fusion of the utriculo-saccular epithelium in the absence of Otx1 suggests that Otx1 expression in the ear was a crucial step in vertebrate ear evolution to segregate the common macula of cyclostomes into two gravistatic organs, the utricle and saccule. AC, anterior crista; HC, horizontal crista; PC, posterior crista; S, saccule; SN, sensory neurons; U, utricle. Bar indicates 100 μm. Modified after [44,68,109].