Cataracts and Retarded Hair Growth in rhg
Authors:Michelle Curtain, Leah Rae Donahue and Patricia F. Ward-Bailey
Source of Support: NIH-NEI grant EY015073 to Leah Rae Donahue and was supported by NIH/NCRR grant RR01183 to the Mouse Mutant Resources (M.T.Davisson,PI) and Cancer Center Core Grant CA34196.
Mutation (allele) name: retarded hair growth
Mutation (allele) symbol: rhg
Strain of Origin: AKR/J
Current Stain Name: B6Ei;AKR-rhg/J
Stock Number: 003544 (view JAX® Mice Data Sheet for additional information including Price and Supply Information)
Phenotype Category: hair, eye, size
Origin and Description
The retarded hair growth (rhg)mutation originally arose on the AKR/J strain background (Fox et al.1978) but due to AKR leukemia, the mutation was tansfered onto a C57BL/6JEi background . This autosomal recessive mutation is characterized by smaller mice that have delayed fur development. At birth mutants are the same size as littermates, and at one-week of age mutants are smaller and appear hairless compared to controls. (See Photo) At two weeks of age mutants have no hair compared to littermates who now have a full coat. At three weeks of age mutants are still smaller but are starting to get fur and at four weeks of age fur usually grows in and they begin to catch up in size. After one month, mutants can be identified by the ruffled appearance of their fur due to the different directions it has grown instead of uniform and in one direction. Mutants later can be identified by the white at the tips of their hair.
This strain is maintained by mating heterozygous female to a homzygous male or the reciprocal as both males and females are fertile. From these matings, mutants comprise 41% of the progeny or just under the 50% expected ratio.
Tissues for histopathological examination were prepared and an rhg/rhg female and male exhibited follicular dysplasia. (See Photo) A 13-day-old mutant also had hematoposis in the liver and the pancreas looked underdeveloped. However, it looks to be an isolated case, as it could not be seen in other mutants. A ten-month-old female rhg/rhg had an atrophic thymus. Serum from two-week-old male and female rhg/rhg and +/rhg were analyzed and mutants had significantly lower levels of abumin, alkaline, phosphatase, amylase and thyroid hormone (T4) levels.
A clinical eye exam using an ophthalmoscope revealed that rhg/rhg mice had cataracts and their +/rhg littermates did not. Overall, five rhg/rhg and six +/rhg mice were examined and ages were 2 months and three-and-half months old.
Auditory Brain Stem Response (ABR) was analyzed in 1 female and male +/rhg and 1 female and male rhg/rhg littermates at one month of age. They all had normal hearing.
Genetic Analysis
For linkage analysis, an AKR/J mutant was crossed to a C57BL/6JEi control. F1 heterozygotes were intercrossed and 33 mutant F2s were collected. Additionally, a B6Ei;AKR-rhg/J mutant was crossed to C3H/HeJ for mapping and 31 mutant F2s were collected and analyzed. rhg maps between markers D7Mit206 at 132 Mb and D7Mit105 at 135.7 Mb. Based on map position Sult1a1 at 133.8 Mb was a candidate gene. The PCR -amplified DNA products were sequenced, but no differences were found between mutants and controls.
Biological Characterization
DEXA Analysis of Whole Body BMD and Body Composition
Six female rhg/rhg and six female +/rhg were collected and assessed by PIXImus densitometry (GE LUNAR, Madison, WI) at 12 weeks of age. (http://www.jax.org/cranio/standard_protocols.html) Differences in whole Body BMD, BMC and Lean measurements were all statistically significant with values of rhg/rhg females having less than those of +/rhg females. Skull BMD and BMC measurements were significantly lower in the mutants. (Graph 1 and Graph 2 and Table 1)
Craniofacial Morphology
These same six female mutants and control 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 were also made using digital calipers (Stoelting, Wood Dale, Ill) with previously established landmarks (Richtsmeier, 2000). During this collection process, right ear pinnae was measured. Skull height and ear pinna length were statistically significant with mutants being less. Also, the skull to nose length ratio was significant. (Graph 2 and Table 2)
Discussion
Retarded hair growth mutants have follicular dysplasia, delayed overall growth, bone and craniofacial abnormalities and develop cataracts.
References
Fox S et al.,(1978) "Retarded hair growth (rhg)." Mouse News Lett 58():47
Green, M.C. (1952) A rapid method for clearing and staining specimens for the demonstration of bone. The Ohio Journal of Science 52(1):31-33. January 1952
Richtsmeier JT, Baxter, LL, Reeves, RH. (2000) Parallels of craniofacial maldevelopment in Down syndrome and Ts65Dn mice. Dev. Dyn. Feb;217(2):137-45.
Acknowledgements
We would like to thank the following for their expertise:
Mapping the Mutation: Dr. Eva Eicher’s lab
Phenotypic Characterization and Sequencing: Victoria DeMambro
Clinical Eye Evaluation: Norm Hawes
ABR analysis: Chantal Longo-Guess
Pathology: Coleen Kane
Pathology Evaluation: Rod Bronson, Ph.D
Colony Management: Louise Dionne
