A short face mutation on chromosome 11

Michelle M. Curtain, Leah Rae Donahue

Source of Support: NIH-NEI grant EY015073 to Leah Rae Donahue

Mutation (allele) symbol: Sofa

Mutation (allele) name: short face

Strain of Origin: C57BL/6J-ApcMin/+

Current Strain Name: B6(AKR)-Sofa/J

Stock Number: 004235 (view JAX® Mice Data Sheet for additional information including Price and Supply Information)

Phenotype Category: Craniofacial

Abstract

We report a new spontaneous mutation with a short nose.

Origin and description

The dominant  Sofa mutation arose spontaneously in the C57BL/6J-ApcMin/+ (stock #002020) production colony of The Jackson Laboratory in 2000. The ApcMin strain arose from an AKR XC57BL/6J mating and was subsequently backcrossed for 47 generations to C57BL/6J when the Sofa mutation arose in the ApcMin colony. The ApcMin mutation is no longer in the Sofa colony as was confirmed by genotyping breeders in the Sofa strain two separate times for ApcMin; all typed as wild types.

The Sofa mutation affects skull shape and is characterized by a short nose, domed skull and wide set eyes. (See Photo) Both males and females are affected and have normal fertility. The mutation has varied penetrance ranging from an obvious to a subtler short nose phenotype. For this reason, mice that are phenotypically categorized as controls may occasionally be low penetrance carriers of the Sofa mutation. The strain is maintained by mating a +/+ to a +/Sofa sibling.

Genetic analysis

Using our standard mapping protocol, Sofa was mapped by mating a female from the A/J inbred strain to a male Sofa heterozygous mutant. Affected  mice were then backcrossed to normal A/J mice to produce N2 offspring. Spleen and tail tips were collected from the affected N2 mice and stored at -70 degrees C. DNA was extracted from either spleen or tail tips using standard phenol extraction methods. PCR was done with MIT or Research Genetics primer pairs (MapPairs, from Research Genetics, Huntsville, Ala., or from Integrated DNA Technologies, Coralville, Ia.) According to scoring of 180 meiosis, Sofa maps to Chromosome 11 with flanking markers of D11MIT4 (1/180) and D11MIT364 (1/180), or from 68.4 Mb to 72.0 Mb. There is no recombination at D11MIT298 (69.3 Mb) or D11MIT29 (69.6 Mb).

Homozygotes are lethal. Outcrossing an A/J inbred to a +/Sofa and scoring F2s at the Sofa critical region, homozygotes were not observed in embryos at stages ranging from E 18.5 down to E 7.5. Thirty seven percent (15 out of 41 embryos) were wild type and 63% (26/41) were heterozygote.

Biological characterization

Craniofacial morphology of twelve-week-old mice:

Skulls were prepared by incomplete maceration in potassium hydroxide, stained with alizarin red, and stored in undiluted glycerin (Green, 1952). Morphological measurements of the skull (Table 1-See protocol on this website.) were made using digital calipers (Stoelting, Wood Dale, Ill) with previously established landmarks (Richtsmeier, 2000, see protocol this website). Statistical differences between mutants and controls within both sexes are seen. For skull length, nose length and lower jaw length, mutants are less. Significantly different ratios within male and female mutants and controls are upper to lower jaw length, skull to nose length, skull height to skull length, and skull length to skull width.  (See graph 3, graph 4 and graph 5). Overall, skull shape seems to be the primary characteristic of the Sofa mutation affecting equally male and female mutants. Furthermore, the face of the Sofa skull is more affected than the back of the skull.

DEXA analysis of whole body aBMD and body composition of twelve-week-old mice:

Whole body, areal bone mineral density (aBMD), bone mineral content (BMC) and body composition (lean, fat and % fat mass) was assessed by PIXImus densitometry (GE LUNAR, Madison, WI) (Table 2-See protocol on this website). Significant differences varied between sexes. Most notable is whole body fat and percent fat that is significantly reduced in heterozgote males compared to wildtype males. Between females, controls have significantly higher whole body BMD, body lean, total mass and skull BMC compared to mutants. (See graph 1 and graph 2) Overall, mutants may be smaller than controls and the results vary depending on male or female data.

Using our standard pathological screen no lesions were found in four, six and nine-week-old mutant mice. Hearing was assessed by auditory brainstem response (ABR). Mutants and controls were examined at two, three and six months of age and no hearing loss were reported. Several sporadic cases of otitis media were found but did not appear to segregate with the mutation. A clinical eye exam of mutants and controls ranging from 1 to 2 months old revealed no abnormalities.

Acknowledgements

We wish to thank: Coleen Marden for preparation of tissues for histological assessment; Rod Bronson, Ph.D, pathological evaluation; Stephen Murray, Ph.D, with instruction for embryo collection; Heping Yu for ABR analysis, Qing Yin Zheng for the Otitis Media screen, Norm Hawes for clinical eye evaluation, and Pat Ward-Bailey for assistance with manuscript preparation and web posting.