XB-ART-5124Dev Dyn July 1, 2003; 227 (3): 422-30.
Three-dimensional morphology of inner ear development in Xenopus laevis.
The three-dimensional morphology of the membranous labyrinth of Xenopus laevis is presented from embryonic through late tadpole development (stages 28 to 52, inclusive). This was accomplished by paint-filling the endolymphatic spaces of Xenopus ears at a series of stages, beginning with the embryonic otic vesicle and ending with the complex ear of the late tadpole. At stage 52, the inner ear has expanded approximately 23-fold in its anterior/posterior dimension compared with stage 28 and it is a miniature of the adult form. The paint-filling technique illustrates the dramatic changes required to convert a simple ear vesicle into the elaborate form of the adult, including semicircular canal formation and genesis of vestibular and auditory organs, and it can serve as a basis for phenotype identification in experimentally or genetically manipulated ears.
PubMed ID: 12815629
Article link: Dev Dyn
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|Figure 1. Structure of the inner ear in Xenopus laevis. A: Semi-diagrammatic medial view of a right inner ear based on a stage 52 paint-filled ear, with the location of the sensory organs indicated in black. The three semicircular canals and the utricle comprise the pars superior, whereas the pars inferior consists of the saccule, lagena, amphibian papilla, and basilar papilla. The endolymphatic duct is shown joining the pars inferior, but the extensive dorsal endolymphatic sac is not depicted. B: Whole-mounted medial view of a stage 60 right inner ear with the sensory epithelia labeled using an antiair cell antibody. Branches of the eighth nerve are still attached to the ear and also exhibit fluorescence. For Abbreviations, see list. Scale bar = 0.5 mm in B.|
|Figure 2. Paint-filled inner ears are shown in intact, fixed Xenopus laevis specimens at stage 28 (A) and stage 52 (B) to demonstrate the location and relative size of the developing ear. Images are lateral views. Inner ears were filled with paint to visualize the inner surface of the membranous labyrinth. The endolymphatic sac is visible in the stage 52 specimen (arrowhead), even though it did not fill with paint (see text). Total length of stage 52 specimen is 25 mm from tip of snout to tip of tail. Scale bar = 1.0 mm.|
|Figure 3. Atlas of the developing Xenopus laevis inner ear. The endolymph-filled spaces of the inner ear were injected with a solution of alkyd paint and imaged to present three-dimensional views of the inner surface of the ear as it develops from stage 28 to stage 52 (staging based on Nieuwkoop and Faber, 1994). All specimens are shown at the same magnification. For Abbreviations, see list. Scale bar = 1 mm.|
|Figure 4. Selected images enlarged from Figure 3. Lateral and medial aspects of ears at early stages reveal the emerging morphologic features of the developing otocyst. Ear images from stages 284 were approximately normalized to the stage 46 images; refer to Figure 3 for accurate size comparisons. For Abbreviations, see list.|
|Figure 5. Anatomic details of the Xenopus laevis inner ear. A: Otoconia in a stage 49 left inner ear, lateral perspective, in a methyl salicylate-cleared specimen that was not injected with paint. B: The location of the amphibian papilla (arrows) on the roof of its recess and the position of the endolymphatic duct are demonstrated in this dorsomedial view of a stage 51 paint-filled right inner ear. The endolymphatic sac is out of focus in the dorsal foreground and partially obscures the anterior and posterior semicircular canals. Axis serves both images. For Abbreviations, see list. Scale bars = 250 μm in A,B.|
|Figure 6. Mean length (tip of snout to tip of tail) of fixed, cleared Xenopus laevis specimens. Staging was based on Nieuwkoop and Faber, 1994 (see Experimental Procedures section), and sample size for each stage is given on the bar. E, early; L, late.|