The deaf mouse mutant Jeff (Jf) is a single gene model of otitis media

Abstract

Otitis media is the most common cause of hearing impairment in children and is primarily characterized by inflammation of the middle ear mucosa. Yet nothing is known of the underlying genetic pathways predisposing to otitis media in the human population. Increasingly, large-scale mouse mutagenesis programs have undertaken systematic and genome-wide efforts to recover large numbers of novel mutations affecting a diverse array of phenotypic areas involved with genetic disease including deafness. As part of the UK mutagenesis program, we have identified a novel deaf mouse mutant, Jeff (Jf). Jeff maps to the distal region of mouse chromosome 17 and presents with fluid and pus in the middle ear cavity. Jeff mutants are 21% smaller than wild-type littermates, have a mild craniofacial abnormality, and have elevated hearing thresholds. Middle ear epithelia of Jeff mice show evidence of a chronic proliferative otitis media. The Jeff mutant should prove valuable in elucidating the underlying genetic pathways predisposing to otitis media.

Figure 1

The Jeff mouse mutant. A. Skeletal preparations of a Jf/+ and a control mouse. Shortened snout in adult Jf/+ mice is indicated by the arrow. B. Photograph of a Jf/+ mouse with its wild-type sibling indicating the smaller size of the mutant.

Figure 2

Physiology of the Jeff mouse mutant. Top. Thresholds for detection of a cochlear nerve compound action potential. Young mice were aged 34–37 days old, and old mice were 11–18 months old. Two mutants aged 28 months showed no responses up to the peak output of the sound system (indicated by open triangles), and only a few responses to high-intensity stimuli were detected among the remaining old group of mutants aged 11–18 months, indicated by black diamonds. Remaining lines represent mean ± SEM. Bottom. Endocochlear potentials are plotted, showing abnormally low measurements in several of the mutants in both young and old age groups.

Figure 3

Genetic mapping of the Jeff mutant. Speed backcrosses were utilized for the mapping of Jeff. Jf/+ sperm was used to fertilize C3H eggs, backcross progeny were phenotyped, and tail DNA from unaffected and affected individuals was prepared for genotyping (see Methods). Haplotypes of markers in the vicinity of Jeff are shown (filled boxes = BALB/c/C3H hybrids and Jeff mutants; open boxes = C3H homozygotes and wild-type mice at the Jeff locus). Marker and gene order is established by minimizing recombinants.Homology relationships to the human genome for distal mouse chromosome 17 are also shown. The gene Six2, which in human maps to 2p15–16 and lies within the conserved segment between mouse chromosome 17 and human 2p16–23, maps 1.96 ± 1.94 cM proximal to Jeff, indicating that the homolog of Jeff may map to human 2p. However, a single gene DUSP1 (mouse: Ptpn16), mapping to human 5q34, lies distal of six2 and disrupts this conserved segment.

Figure 4

Structure and histopathology of the Eustachian tube and middle ear cavity in wild-type mice and +/Jf mice. A,B. Parasaggital sections through the newborn Eustachian tube joining the middle ear cavity. Inserts show epithelium (asterisks) at increased magnification. Arrow indicates collapsed middle ear cavity (MEC). Scale bar = 100 µm; inserts = 10 µm. C,D. Comparison of middle ear cavity size in wild-type and adult Jf/+ mice (Jf/+ = 121 days old, +/+ = 127 days old). Scale bar = 1 mm. E,F. 3D reconstructions of the Eustachian tube (ET) and middle ear cavity (MEC) in newborn wild-type and Jf/+ mice. The Jf/+ Eustachian tube is narrowed at the orifice of the middle ear cavity (arrow). G,H. 3D reconstructions of the Eustachian tube and part of the middle ear cavity in wild-type and Jf/+ mice. The bend in the Jf/+ Eustachian tube is indicated (arrow). (Mice were siblings and both aged 50 days). I–L. Histopathology of the middle ear cavity demonstrating middle ear glue (I and J, arrows) and polypoid exophytic growths that project into the tympanic cavity (K. and L, arrows). Scale bar = 100 µm.

Figure 5

Ultrastructure of middle ear epithelium in Jeff mice. A–D. Scanning electron micrographs showing the middle ear epithelium in control mice (A,B) and Jf/+ mutants (C,D) aged 11–18 months. In low magnification A and C, the start of the Eustachian tube is indicated by the arrow. The boxes indicate the area from which the higher magnifications (B and D) are taken. (A,C) Scale bar = 100 µm; (B,D) scale bar = 5µm.

Figure 6

Cytokine staining of middle ear effusions in Jeff mice. Immunohistochemistry was carried out on Jf/+ and +/+ middle ear cavities with polyclonal antibodies raised to the cytokines TNFα, IL-1β, and IL-8 (all mice were 121 days old). Positively stained cells (indicated by arrows) were seen for all three cytokines: A. IL8, B. IL-1β, C. TNFα, D. Minus primary antibody control. Scale bars = 50 µM.