Deletion Mapping of the Head Tilt (het) Gene in Mice: A Vestibular Mutation Causing Specific Absence of Otoliths

Corresponding author: John C. Schimenti, The Jackson Laboratory, 600 Main St., Bar Harbor, ME 04660., jcs{at}jax.org (E-mail).

Communicating editor: N. A. JENKINS

	ABSTRACT

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Head tilt (het) is a recessive mutation in mice causing vestibular dysfunction. Homozygotes display abnormal responses to position change and linear acceleration and cannot swim. However, they are not deaf. het was mapped to the proximal region of mouse chromosome 17, near the T locus. Here we report anatomical characterization of het mutants and high resolution mapping using a set of chromosome deletions. The defect in het mutants is limited to the utricle and saccule of the inner ear, which completely lack otoliths. The unique specificity of the het mutation provides an opportunity to better understand the development of the vestibular system. Complementation analyses with a collection of embryonic stem (ES)- and germ cell-induced deletions localized het to an interval near the centromere of chromosome 17 that was indivisible by recombination mapping. This approach demonstrates the utility of chromosome deletions as reagents for mapping and characterizing mutations, particularly in situations where recombinational mapping is inadequate.

LINKAGE mapping, with the goal of positional cloning, is a key strategy for the identification of genes underlying disease traits. In mice, simple recessive traits are mapped in backcross or intercross schemes, and several hundred or thousand meioses are often scored to narrow the gene-critical region to a size that is workable for physical identification through molecular cloning. This approach is largely unnecessary in Drosophila melanogaster due to the availability of deficiencies covering much of the genome. The locations of recessive mutations in this organism can be deciphered by crossing a single locus mutation to a set of deletions with nested breakpoints in the vicinity of the mutation. The advantage of this approach over recombinational mapping is that the result of the cross can be determined from the phenotype of a single, doubly heterozygous offspring.

Mice homozygous for the head tilt mutation (het/het) display behavior consistent with vestibular dysfunction (SWEET 1980 ). When held by the tail, they tend to flex ventrally and retract their limbs rather than the normal behavior of dorsal flexion with extended forelimbs. In response to linear downward acceleration (quickly lowering them by the tail), they generally fail to display the stereotypic protraction of forelimbs characteristic of normal animals. When dropped from a height of several inches, they have some difficulty righting themselves. They cannot swim due to an inability to sense correct orientation under water, but are not deaf (SWEET 1980 ). Before the present study, there were no data on potential dysmorphology in het/het mice. Anatomical studies of the inner ears of these mice were therefore performed, revealing a unique phenotype in which the utricle and saccule of the inner ear are specifically affected. The mutants are devoid of otoconia on the otolithic membrane. The otoconia, which are calcium carbonate crystals, are needed to transduce head movements for spatial perception.

het was mapped previously to within 1.77 cM of the T locus by linkage analysis, although the positions of the genes relative to the centromere were not determined. Here, we exploit a resource of chromosomal deletions that have breakpoints in the vicinity of T to further localize het. In complementation tests with several deletions, het was mapped to an interval associated with a single marker, D17Mit19, just proximal to the t complex region near the centromere of chromosome 17.

Aside from the utility of deletion complexes in the identification of novel genes (HOLDENER-KENNY et al. 1992 ; LYON et al. 1992 ; RINCHIK et al. 1994 ; RUSSELL et al. 1995 ; O'BRIEN et al. 1996 ), the present study demonstrates the value of nested deletions to rapidly map mutations to high resolution. The availability of deletion complexes around the genome will serve to complement traditional linkage analysis and provide powerful reagents for genetic analysis of atypical loci, such as quantitative trait loci (QTL), imprinted regions, or genes in locations (such as near a centromere) that may be difficult to map by recombination.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Inner ear preparations:
For whole mount preparations, mice between the ages of 8 and 12 wk were euthanized with carbon dioxide and promptly decapitated. Inner ears were dissected, and neutral-buffered Formalin was flushed through a hole made at the cochlear apex using a 26 G needle. They were then immersed in neutral-buffered Formalin, dehydrated in ethanol, and cleared in methyl salicylate. Samples can be stored indefinitely in this solution. For photography, samples were viewed with transmitted and polarized light on a dissection microscope.

For the histological sections in Figure 2A–D, inner ears were flushed as above with Bouin's fixative, immersed in same for 24–48 hr, and embedded in paraffin. Sections (5–10 µm) were cut, mounted on glass slides, and counterstained in hematoxylin/eosin (H&E). The sections in Figure 2 E and F, were prepared in a way that preserved the otoconia: mice were perfused with saline before dissection of inner ears, which were fixed in 2% paraformaldehyde, 2.5% glutaraldehyde, and then decalcified in 6.4% EDTA in 0.1 M phosphate buffer, pH 7.4, for 1 wk at 4°. They were then dehydrated at RT in 25–95% ethanol and infiltrated in 1:1 ethanol/JB4 resin overnight at 4°. The next day, fresh JB4 was added, and samples were infiltrated an additional 5 days at 4°. They were then put into fresh JB4 and prepared for sectioning. Sections were H&E stained.

View larger version (140K): In this window In a new window Download PPT slide   Figure 1. Absence of otoliths in the inner ears of head tilt mutants. (A) Whole mounts of inner ears from the indicated genotypes are shown. The utricular and saccular otoliths can clearly be seen in the phenotypically normal animals in the leftmost two panels, due to the refractile properties of otoconia. Their absence in the mutant ears (rightmost two panels) allows visualization of the oval window. (B) Higher magnification of normal (het/+) and mutant (D17Aus9df18J/het) inner ears reveals the pigmented cells of the utricle are retained in the mutants. Absence of otoliths in both the utricle and saccule are evident in the mutant. sc, semicircular canal; s, saccule; u, utricle; o, oval window; p, pigment cells.

View larger version (107K): In this window In a new window Download PPT slide   Figure 2. Histology of normal and head tilt inner ears. (A and B) Paraffin sections through the crista ampullaris of the horizontal semicircular canal of head tilt (D17Aus9df18J/het) and normal (+/het) mice. C, cupula; CA, crista; V, vestibular nerve. (C and D) Paraffin sections through the saccule of affected (het/het) and normal (het/+) inner ears reveal that the maculae (SM) of mutant mice are normal. The otolithic membranes (OM) are also present. (E and F) High magnification sections (x40) of utricular maculae, using fixation conditions that preserve the otoconia (see MATERIALS AND METHODS). g, gelatinous substance; O, otoconia; OM, otolithic membrane; M, macula.

Mice:
The deletions D17Aus9^{df2J, 4J, 5J, 18J, and 27J}, which were derived from F₁ hybrid embryonic stem (ES) cells, were generally crossed for one to two generations to C57BL/6J at the time of mating to het homozygotes. The latter were maintained at The Jackson Laboratory (TJL, Bar Harbor, ME). Although there was some variation in the expressivity, the head tilt phenotype was 100% penetrant. The head tilt stock in these crosses was maintained congenic on the C57BL/6J background, at TJL. Another set of deletions (T^{29H, 32H, and 33H}) was induced by treatment of (C3H x 101) F₁ males with X rays at the Mammalian Genetics Unit (Harwell, UK). T^34H arose spontaneously in a noninbred stock at Harwell. All were maintained by crossing to (C3H x 101) F₁ or to the inbred strain TFH/H. The radiation-induced T^22H deletion was reported previously (LYON 1992 ) as was the spontaneous deletion T^hp (DICKIE 1965 ). All complementation tests involved the identical het allele that arose at TJL. The T^hp complementation tests with het were performed both at Harwell and at TJL.

RFLPs and simple sequence repeat (SSR) variants:
Southern blotting of mouse DNA was performed by standard procedures, using alkaline transfer onto nylon membranes (MSI). The following probes were used: Cg100, a 1.5-kb EcoRI/BamHI fragment corresponding to the last exon of Tcp10 genes (SCHIMENTI et al. 1987 ); Tu48 and Tu119, corresponding to the D17Leh48 and D17Leh119 loci, respectively (FOX et al. 1985 ). DNA from the D17Aus9^{df2J, 4J, 5J, 18J, and 27J} deletions in trans to CAST/Ei was typed for a SSR polymorphism at the D17Tu1 locus using PCR primers as reported (HIMMELBAUER and SILVER 1993 ).

Auditory brain stem response test:
This was performed as described (NOBEN-TRAUTH et al. 1997 ).

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Head tilt mice completely lack otoliths:
Because the phenotype of the het mutants suggests an underlying vestibular dysfunction, the inner ears of het/het mice were examined. The cochlea, semicircular canals, oval window, and bones of the middle ear (stapes, incus, and malleus) were normal. However, there was a markedly abnormal appearance of the saccule and utricle as visualized under polarized light (Figure 1). These structures were nearly invisible in the mutants. Aside from the pigment-containing cells in the utricle, the lack of refracted light was due to complete absence of the otoconia. The otoconia are essentially calcium carbonate crystals that lie in the otolithic membrane that covers the sensory epithelia (maculae) in both the utricle and saccule. In all animals examined, otoliths were bilaterally absent. Histological sections of the inner ear confirmed that the utricle and saccule with their maculae were not missing in the mutant (Figure 2A), nor were there histologically detectable defects in the cristae ampullari of the semicircular canals (Figure 2B). To confirm previous observations that head tilt mutants are not deaf, and to test for the possibility of a more subtle hearing impairment, an auditory brain stem response (ABR) test was performed as previously described (NOBEN-TRAUTH et al. 1997 ). Four 1-month-old and seven 5-month-old het/het mutants exhibited normal evoked response, demonstrating no auditory dysfunction (data not shown).

Deletion mapping the het locus:
The het mutation was originally mapped near the T locus by standard linkage analysis, recombining in 1.77 ± 1.2% of progeny (SWEET 1980 ). To refine the map location of het, complementation tests were performed with several chromosomal deletions (described below) that remove the T locus (Figure 3). Heterozygosity for a mutation in the semidominant T gene results in a short tail (Brachyury, or "brachy") phenotype, enabling simple identification of mice that inherit T deletions. Thus, complementation tests were performed by crossing deletion-bearing mice to het/het homozygotes, and the brachy progeny (those bearing the deletion) were examined for the head tilt phenotype. The results of complementation tests performed in this manner are given in Table 1 and summarized in Figure 3. All short-tailed mice from noncomplementing deletions in trans to het had the head tilt phenotype, demonstrating that the penetrance of the mutation in these experiments was 100%. The phenotype of affected mice bearing a noncomplementing deletion in trans to the het mutation was identical to that of het/het mice, both in head-tilting behavior and inner ear morphology (Figure 1 and Figure 2; whole mounts of a representative of each tilting D17Aus9-series deletion in trans to het, plus T^22H, were performed), suggesting that the spontaneous het allele is a loss-of-function mutation.

View larger version (19K): In this window In a new window Download PPT slide   Figure 3. Deletion mapping of head tilt. The structure of the proximal region of chromosome 17 is shown at the top, with relevant loci shown (distances not to scale). Horizontal solid line, minimum amount of DNA removed in deletions (the locus above the very end of a solid line is deleted). Dashes at the ends of the solid lines, maximum amount of DNA that has been deleted (the locus above the very end of a dashed line is not deleted). Markers beginning "Mit" are abbreviated by removal of the prefix "D17." The markers 48 and 66D are abbreviated by removal of the prefix "D17Leh," and Aus9 is abbreviated by removal of the prefix "D17." The D17Leh119 (abbreviated as "119") and D17Leh66E (abbreviated as "66E") loci are actually present as a large inverted duplication spanning over 650 kb, having the following order of subloci: centromere-D17Leh119I - D17Leh66E - D17Leh66EII - D17Leh119II (HERRMANN et al. 1987 ). The probe used to detect the 66E loci was Cg100, corresponding to the Tcp10a gene present at the D17Leh66EII locus (BULLARD and SCHIMENTI 1990 ); thus, the breakpoint of T29H may lie within D17Leh66E. The proximal breakpoint of Thp was determined previously and lies between D17Leh66E and D17Leh66EII (BULLARD and SCHIMENTI 1990 ). Because the Tu119 probe used to detect the 119 loci hybridizes to both D17Leh119I and D17Leh119II, those deletions shown as removing "119" are actually missing both loci. The physical distances from D17Leh119I to T and from Tme to 66D are taken from HERRMANN et al. 1990 and SCHWEIFER et al. 1997 , respectively. The Yac clone shown to contain the Tu1, Aus9, and 48 loci, the size of which is currently unknown, is from our unpublished observations (A. PLANCHART and J. SCHIMENTI). The genetic distances between Brachyury (T), quaking (qk), and Tme are taken from Mouse Genome Database (http://www.informatics.jax.org/), and the distance between 48 and 119 was reported by HAMMER et al. 1989 . All the deletions shown to include Tme could not be transmitted through females (data not shown). Left, results of head tilt complementation tests. The het critical region is highlighted by gray vertical lines between D17Mit245 and D17Tu1.

The deletions used in these studies originated in three ways. One series of deletions was induced by irradiation of ES cells, and their breakpoints relative to microsatellite markers were characterized (YOU et al. 1997 ). These deletions are centered around the D17Aus9 locus, just centromeric to T (Figure 3). A new deletion in that series, D17Aus9^df27J, is included in the present study, and its breakpoints were characterized with the same set of markers. Additionally, these deletions were all scored for the presence or absence of the D17Tu1 locus (see MATERIALS AND METHODS).

A second set of four deletions was induced by germ cell mutagenesis at Harwell and they were recognized on the basis of their brachy phenotype. T^22H was analyzed in some detail by others (HOWARD et al. 1990 ), and we report further resolution of this deletion's breakpoints relative to microsatellite loci (Figure 3). The extent of the other three deletions—T^29H, T^32H, and T^33H—was determined by: (1) Complementation analysis with the quaking (qk) mutation; (2) assessment of transmissibility through females, the failure of which would indicate that the T maternal effect (Tme) locus was deleted; and (3) RFLP analysis with probes detecting the D17Leh48, D17Leh119, T66E, and T66D loci (Table 2). An additional Harwell deletion, T^34H, arose spontaneously and was characterized in the same fashion. The remaining deletion, T^hp, arose spontaneously (DICKIE 1965 ) and was characterized previously with respect to molecular analysis of breakpoints (BULLARD and SCHIMENTI 1990 ).

One conclusion that could be drawn from comparing the results of complementation tests to the positions of deletion breakpoints was that het must reside proximal to T. For example, the distal breakpoints of four deletions that do not remove head tilt—T^29H, T^32H, T^34H, and T^hp—extend further than the distal breakpoints of T^22H and D17Aus9^df27J, which are deleted for het (Figure 3).

Efforts were then concentrated on characterizing the deletion breakpoints centromeric to T, using a combination of polymorphic microsatellite markers and unique sequence hybridization probes in the region. The D17Leh48, D17Leh119, and D1766E loci were previously mapped in some detail through the use of recombinant t haplotypes (HERRMANN et al. 1987 ), but the order of markers proximal to D17Leh119 was deduced primarily by deletion mapping. Whereas D17Mit245 and D17Mit19 did not recombine in the F₂ mapping cross performed at MIT (DIETRICH et al. 1996 ), deletions with breakpoints between the two loci revealed that D17Mit245 is proximal to D17Mit19 (YOU et al. 1997 ). This conclusion is further supported by the present analysis of T^22H and D17Aus9^df27J (Figure 3). Similarly, deletion mapping indicated that D17Aus9 is proximal to D17Leh48 (BILINSKI et al. 1997 ). Finally, the observation that D17Aus9^df5J (and another deletion not presented here; R. BERGSTROM and J. SCHIMENTI, unpublished results) deletes D17Tu1 but not D17Mit19 , despite the lack of recombination between these markers in a backcross involving 374 progeny (HIMMELBAUER and SILVER 1993 ), establishes the order of markers: centromere-D17Mit245-D17Mit19-D17Tu1-D17Aus9-D17Leh48.

Given the order of markers near the chromosome 17 centromere, complementation analyses indicated that het resides between D17Mit245 and D17Tu1, in an interval marked by D17Mit19 (Figure 3). Those deletions whose breakpoints did not extend centromeric to D17Tu1 to delete D17Mit19—D17Aus9^df5J, T^hp, T^{29H, 32H, and 34H}—complemented het. However, all those that removed D17Mit19 (D17Aus9^{df2J, 4J, 18J, 27J} and T^22H) failed to complement. T^33H also failed to complement, but the breakpoint of this deletion as assayed by markers proximal to D17Leh48 was not determined. The combined data indicate that het lies in the interval between D17Mit245 and D17Tu1, in a position distal to the T^22H and D17Aus9^df27J breakpoints and proximal to the D17Aus9^df5J breakpoint.

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Head tilt has a specific vestibular defect:
A considerable collection of mutations affecting the inner ear in mice has been identified. These mutations usually cause behavioral abnormalities, such as circling or hyperactivity. Most inner ear mutants also exhibit deafness or other dysmorphologies besides vestibular problems and can be grouped into three categories of defects: morphogenetic, cochleosaccular, and neuroepithelial (STEEL and BROWN 1994 ; STEEL 1995 ). Morphogenetic mutants often have defects in the lateral semicircular canal, as in the twirler and fidget mutants (DEOL 1968 ). In some mutants of this class, the inner ear malformations are associated with neural tube defects (DEOL 1964A , DEOL 1964B ; STEEL 1995 ). Cochleosaccular defects are often associated with white spotting of the hair or skin. This is because such mutations affect migrating melanocytes, which form part of the stria vascularis of the cochlea. The stria is responsible for generating the endocochlear potential of the endolymph, necessary for the proper functioning of the sensory hair cells. Examples of mutations in this class are steel (Mgf^sl), dominant spotting (Kit^W), and splotch (Pax3^Sp). Mutants of the neuroepithelial class, including Snell's waltzer and shaker-1, display defects in sensory epithelia, such as the saccular maculae or the hair cells of the organ of Corti, respectively (DEOL and GREEN 1966 ; GIBSON et al. 1995 ). The head tilt mutation is unusual in its specificity, in that there are no apparent defects in the inner ears of these mice other than the absence of otoliths. Consistent with the normal cochlear morphology, het/het mice have no detectable hearing impairment as measured by ABR. The tilted head (thd) mutation also has a restricted otolith phenotype. The utricles of thd/thd mutants are usually devoid of otoliths, although the saccules contain a limited number of abnormally large otoconial crystals (ERWAY et al. 1971 ).

Genetic defects in otolith development were first observed in pallid (pa) mice, where the visually obvious phenotype is hypopigmentation of the coat due to defects in melanocyte development (LYON 1951 , LYON 1952 ). Affected (pa/pa) animals often showed phenotypes very similar to head tilt mice, due to unilateral or bilateral absence of utricular and/or saccular otoliths. Penetrance and expressivity of this particular trait was variable, and the otolith defects could be ameliorated by dietary supplementation of manganese during embryogenesis (ERWAY et al. 1966 ). Reduced pigmentation and absence of otoliths are also seen in muted (mu) mice (LYON and MEREDITH 1969 ).

While the otolith phenotype in pallid and head tilt mice are similar, the etiology of this specific effect in pallid appears directly related to the pigment-producing cells of the membranous labyrinths, implying that defective melanocyte function might be responsible for proper trace-element metabolism as it applies to formation of otoconia (ERWAY et al. 1971 ). Because het/het mice neither lack pigmentation granules in their inner ear (Figure 1), nor have any other obvious defects, it is likely that the failure of otolith formation lies in a different stage in the same developmental pathway.

Otoconia formation begins at day 14 or 15 during development and occurs very rapidly (LYON 1955 ; ANNIKO 1980 ). The otoconia lie in the otolithic membrane, an organic matrix that is secreted by and covers the macula, into which sensory hair bundles penetrate. Although the composition of the otoconia is dominated by calcium, the endolymph has very low levels of this element. This suggests that secretion of calcium by the sensory epithelium to the otoconial matrix is integral to formation of the otoconial crystals (ANNIKO 1980 ). Hence, it is reasonable to expect that the protein product of the het gene is required before day 14 of development and is possibly involved in calcium secretion by the neuroepithelial cells.

It was originally reported that head tilt mutants exhibited circling behavior (SWEET 1980 ). While this was apparent in the mice maintained at Harwell, circling was uncommon in the head tilt stocks used at TJL for the present study. It is likely that there are background influences on this aspect of the phenotype. While defects in semicircular canals are suggested by circling behavior, there were no indications of abnormalities from the whole mounts (Figure 1) or paraffin sections through the sensory organ (crista ampullaris; Figure 2A). Perhaps there are subtle defects that went undetected.

Utility of induced deletion complexes in mapping and genome analysis:
Using a set of spontaneous and radiation-induced deletions as reagents to map both molecular and phenotypic markers, het was determined to lie proximal to the T locus, to an interval associated with D17Mit19 and flanked by D17Mit245 and D17Tu1. Available data indicate this is a very small region. We are aware of two mapping crosses that assayed recombination between these markers, neither of which produced a recombinant between D17Mit245 and D17Mit19. These are the MIT F₁ (C57BL/6J-Ob x CAST) intercross consisting of 92 meioses (DIETRICH et al. 1996 ) and an interspecific (C57BL/6J x CAST) F₁ x C57BL/6J backcross that scored 374 progeny (HIMMELBAUER and SILVER 1993 ).

The maximal size of the critical region is currently defined by the breakpoints of T^22H and D17Aus9^df27J on the centromeric side and D17Aus9^df5J on the distal (Figure 3). We possess four other deletions with breakpoints in this interval that have yet to be complementation tested (YOU et al. 1997 ; R. BERGSTROM and J. SCHIMENTI, unpublished results), for a total of seven breakpoints in the het critical region. Considering the absence of recombinants in 466 meioses discussed above, a standard mapping cross might require the generation of several thousand progeny to produce a similar number of breakpoints. Hence, in situations where deletions are available, their use as mapping reagents in positional cloning projects can be a valuable resource.

Deletions may be particularly useful as mapping tools in special situations, where standard recombinational mapping is impossible or not efficient. These include complicated genetic systems such as t haplotypes (SILVER 1985 ), which are refractory to standard genetic analysis due to inversions that block recombination with wild-type chromosomes, imprinted regions, QTL, genes located near centromeres, or traits such as T-associated sex reversal (Tas), which is defined exclusively on the basis of haploinsufficiency of proximal chromosome 17 (WASHBURN et al. 1990 ). The ability to generate deletion complexes at will around the genome (YOU et al. 1997 ) makes these applications more widely available.

	FOOTNOTES

¹ Present address: Oak Ridge National Laboratory, Life Sciences Division, Oak Ridge, TN 37831.

	ACKNOWLEDGMENTS

The authors thank Verity Letts for help with inner ear preparations, review of the manuscript, and initially pointing out the potential defects in het. We thank Rod Bronson for helpful discussions on the inner ear, Leona Gagnon and Linda Washburn for providing het mice, Deb Lane for histology, Joyce Worcester for aid in producing figures, and Pat Cherry for secretarial assistance. Additionally, we thank Ken Johnson and Yin Zheng for the ABR test data and also for reviewing (Dr. Johnson) the manuscript. This work was supported by National Institutes of Health (NIH) grant HD-24374 to J.S. and a Cancer Center core grant (CA34196) to The Jackson Laboratory. The animal studies at Harwell were carried out under the guidance issued by the Medical Research Council in "Responsibility in the Use of Animals for Medical Research" (July 1993) and Home Office project license 30/00875. M.F.L. is partly supported by European Union contract no. CHRX-CT93-0181. Y.Y. is the recipient of a National Research Service Award fellowship (HD08015). ABR tests were performed under a contract (N01-DC62108) from the National Institute on Deafness and Other Communication Disorders with The Jackson Laboratory that supports screening of inbred and mutant strains of mice for hearing impairment. Finally, the C57BL/6J het colony was developed and maintained with support from NIH grant RR-01183 to Muriel T. Davisson and Eva M. Eicher.

Manuscript received April 3, 1998; Accepted for publication June 26, 1998.

	LITERATURE CITED

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

ANNIKO, M., 1980  Development of otoconia. Am. J. Otolaryn. 1:400-410.

BILINSKI, P., J. SCHIMENTI, and A. GOSSLER, 1997  A new spontaneous deletion on chromosome 17 including brachyury. Mamm. Genome 12:932-933.

BULLARD, D. and J. SCHIMENTI, 1990  Molecular cloning and genetic mapping of the t complex responder candidate gene family. Genetics 124:957-966[Abstract].

DEOL, M. S., 1964a  The abnormalities of the inner ear in kreisler mice. J. Embryol. Exp. Morphol. 12:475-490.

DEOL, M. S., 1964b  The origin of the abnormalities of the inner ear in dreher mice. J. Embryol. Exp. Morphol. 12:727-733.

DEOL, M. S., 1968  Inherited diseases of the inner ear in man in the light of studies on the mouse. J. Med. Genet. 5:137-158[Free Full Text].

DEOL, M. S. and M. C. GREEN, 1966  Snell's waltzer, a new mutation affecting behaviour and the inner ear in the mouse. Genet. Res. 8:339-345[Medline].

DICKIE, M. M., 1965 Mouse News Lett. 32: 43–44.

DIETRICH, W. F., J. MILLER, R. STEEN, M. A. MERCHANT, and D. DAMRON BOLES et al., 1996  A comprehensive genetic map of the mouse genome. Nature 380:149-152[Medline].

ERWAY, L. C., L. S. HURLEY, and A. FRASER, 1966  Neurological defect: manganese in phenocopy and prevention of a genetic abnormality of inner ear. Science 152:1766-1768[Abstract/Free Full Text].

ERWAY, L. C., A. S. FRASER, and L. S. HURLEY, 1971  Prevention of congenital otolith defect in pallid mutant mice by manganese supplementation. Genetics 67:97-108[Free Full Text].

FOX, H., G. MARTIN, M. F. LYON, B. HERRMAN, and A.-M. FRISCHAUF et al., 1985  Molecular probes define different regions of the mouse t complex. Cell 40:63-69[Medline].

GIBSON, F., J. WALSH, P. MBURU, A. VARELA, and K. A. BROWN et al., 1995  A type VII myosin encoded by the mouse deafness gene shaker-1. Nature 374:62-64[Medline].

HAMMER, M. H., J. C. SCHIMENTI, and L. M. SILVER, 1989  On the origins of t complex inversions. Proc. Nat. Acad. Sci. USA 86:3261-3265[Abstract/Free Full Text].

HERRMANN, B. G., D. P. BARLOW, and H. LEHRACH, 1987  A large inverted duplication allows homologous recombination between chromosomes heterozygous for the proximal t complex inversion. Cell 48:813-825[Medline].

HERRMANN, B. G., S. LABEIT, A. POUSTKA, T. R. KING, and H. LEHRACH, 1990  Cloning of the T gene required in mesoderm formation in the mouse. Nature 343:617-622[Medline].

HIMMELBAUER, H. and L. SILVER, 1993  High-resolution comparative mapping of mouse chromosome 17. Genomics 17:110-120[Medline].

HOLDENER-KENNY, B., S. K. SHARAN, and T. MAGNUSON, 1992  Mouse albino-deletions: from genetics to genes in development. BioEssays 14:831-839[Medline].

HOWARD, C., G. GUMMERE, M. LYON, D. BENNETT, and K. ARTZT, 1990  Genetic and molecular analysis of the proximal region of the mouse t-complex using new molecular probes and partial t-haplotypes. Genetics 126:1103-1114[Abstract].

LYON, M., 1992  Deletion of mouse t-complex distorter-1 produces an effect like that of the t-form of the distorter. Genet. Res. Camb. 59:27-33[Medline].

LYON, M. and R. MEREDITH, 1969  Muted, a new mutant affecting coat colour and otoliths of the mouse, and its position in linkage group XIV. Genet. Res. 14:163-166[Medline].

LYON, M. F., 1951  Hereditary absence of otoliths in the house mouse. J. Physiol. 114:410-418.

LYON, M. F., 1952  Absence of otoliths in the mouse: an effect of the pallid mutant. J. Genet. 51:638-650.

LYON, M. F., 1955  The development of the otoliths of the mouse. J. Embryol. Exp. Morph. 3:213-229.

LYON, M. F., T. R. KING, Y. GONDO, J. M. GARDNER, and Y. NAKATSU et al., 1992  Genetic and molecular analysis of recessive alleles at the pink-eyed dilution (p) locus of the mouse. Proc. Nat. Acad. Sci. USA 89:6968-6972[Abstract/Free Full Text].

NOBEN-TRAUTH, K., Q. Y. ZHENG, K. R. JOHNSON, and P. M. NISHINA, 1997  mdfw: a deafness susceptibility locus that interacts with deaf waddler (dfw^2J). Genomics 44:266-272[Medline].

O'BRIEN, T., D. METALLINOS, H. CHEN, M. SHIN, and S. TILGHMAN, 1996  Complementation mapping of skeletal and central nervous system abnormalities in mice of the piebald deletion complex. Genetics 143:447-461[Abstract].

RINCHIK, E., J. BELL, P. HUNSICKER, J. FRIEDMAN, and I. JACKSON et al., 1994  Molecular genetics of the brown (b)-locus region of mouse chromosome 4: origin and molecular mapping of radiation and chemical induced lethal brown deletions. Genetics 137:845-854[Abstract].

RUSSELL, L. B., C. S. MONTGOMERY, N. L. CACHEIRO, and D. K. JOHNSON, 1995  Complementation analyses for 45 mutations encompassing the pink-eyed dilution (p) locus of the mouse. Genetics 141:1547-1562[Abstract].

SCHIMENTI, J., L. VOLD, D. SOCOLOW, and L. M. SILVER, 1987  An unstable family of large DNA elements in the center of mouse t haplotypes. J. Mol. Biol. 194:583-594[Medline].

SCHWEIFER, N., P. J. VALK, R. DELWEL, R. COX, and F. FRANCIS et al., 1997  Characterization of the C3 YAC contig from proximal mouse chromosome 17 and analysis of allelic expression of genes flanking the imprinted Igf2r gene. Genomics 43:285-297[Medline].

SILVER, L. M., 1985  Mouse t haplotypes. Annu. Rev. Genet. 19:179-208[Medline].

STEEL, K., 1995  Inherited hearing defects in mice. Annu. Rev. Genet. 29:675-701[Medline].

STEEL, K. P. and S. D. BROWN, 1994  Genes and deafness. Trends Genet. 10:428-435[Medline].

SWEET, H., 1980  Head tilt. Mouse News Lett. 63:19.

WASHBURN, L. L., B. K. LEE, and E. M. EICHER, 1990  Inheritance of T-associated sex reversal in mice. Genet. Res. 56:185-191[Medline].

YOU, Y., R. BERGSTROM, M. KLEMM, B. LEDERMAN, and H. NELSON et al., 1997  Chromosomal deletion complexes in mice by radiation of embryonic stem cells. Nature Genet. 15:285-288[Medline].

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