A mutation in the Arsb gene; a mouse model that resembles MUCOPOLYSACCHARIDOSIS TYPE VI, MPS VI.

 

Authors: Michelle M. Curtain, Leah Rae Donahue

Source of support: NIH-NEI grant EY015073-05Z to Leah Rae Donahue

Mutation (allele) symbol: Arsbm1J

Mutation (allele) name: mutation 1 Jackson

Strain of origin:C57BL/6J

Current strain name: C57BL/6J-Arsbm1J/GrsrJ.

Stock #: 005598  (view JAX® Mice Data Sheet for additional information including Price and Supply Information)

Phenotype categories: craniofacial, skeletal, neurological, hearing

 

Abstract

We report here a new mutation in the arylsulfatase B gene (Arsb) which causes affected mice to have a phenotype that resembles Maroteaux-Lamy syndrome. ARSB deficiency is better known as the lysosomal storage disorder called MUCOPOLYSACCHARIDOSIS TYPE VI, MPS VI.  (see photo 1 and photo 2)

Origin and Description

Our Arsb mutation 1 Jackson arose in a C57BL/6J colony that was three generations descended from a male mouse that had been mutagenized with N-ethyl-N-nitrosourea (ENU) from the Neuroscience Mutagenesis Facility (NMF) at the Jackson Laboratory.

The m1J allele is recessive. These mutants have a combination of delayed muscle and nerve degeneration that affects their gait as they age. Mutants can still walk but appear less stable than controls. Mutants also have a skeletal phenotype consisting of a shortened snout, wide-set eyes, a thicker tail and digits and shortened limbs that become more noticeable with age.

Both male and female homozygotes are fertile. The colony is maintained by brother/sister matings with an m1J/m1J X +/m1J and the reciprocal. Mutants can be poor breeders with small litters, so +/m1J X +/m1J matings are done when necessary.

Genetic Analysis

An m1J/m1J male was crossed to a BALB/cByJ and obligate heterozygotes were then intercrossed to make F2 mutants that were utilized for linkage analysis . Spleen and tail tips from the affected F2 mutants were collected and stored at -80° C. Using our standard mapping protocol, the mutation was mapped to Chromosome 13. There was no recombination with D13Mit147 at 98.3 Mb (Ensembl release 54). Based on phenotype and map position similarities, Arsb located at 94.5 Mb (Ensembl release 54) was thought to be a good candidate gene.

Using the Primer3 design program, primers were designed to amplify the first four exons of the Arsb gene and were sequenced at The Jackson Laboratory core sequencing facility. A single base change from G to T was detected in exon 2 in the DNA sequence from three mutant mice. This base change modifies the amino acid Glutamic acid as the codon GAA is changed to TAA causing a premature stop codon. (see chromatogram)

Biological Characterization

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

Three-month-old male and female mutant and controls were collected and 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) (See protocol on the this website). Mutants were significantly smaller overall and had less body fat with more lean than controls; mutants also had significantly greater whole body BMD compared to heterozygotes. (See Table Two and Graph One and  Graph Two)

Craniofacial morphology of twelve-week-old mice:

Three-month-old male and female mutant and control skulls were collected and were prepared by incomplete maceration in potassium hydroxide, stained with alizarin red, and stored in undiluted glycerin (Green, 1952). Morphological measurements of the skull (See protocol this website) were made using digital calipers (Stoelting, Wood Dale, Ill) with previously established landmarks (Richtsmeier, 2000, see protocol this website). Skull BMD was significantly greater in male and female mutants and skull BMC was significantly greater in male mutants. Mutants from both sexes had significantly shorter noses and upper jaw lengths. (See Table One and Graph Three and Graph Four)

Pathology

A routine pathology screen on a two-and-a-half month old mutant showed clumped irregular cartilage in the growth plate of the knee and the spiral ganglion. An eight-month-old mutant revealed focal muscle degeneration and degeneration of peripheral nerves with macrophage infiltration. A 14-month-old male mutant had peripheral nerve degeneration along with spinal arthritis and strange looking vacuoles in the connective tissue around the spine; this mouse also had otitis media and a histologically normal heart but the aorta appeared larger than normal.

To confirm lysosomal storage, liver, kidney, lung and rear legs were stained with Mowry's colloidal iron stain. In a 26-week-old mutant, there were Kupffer cells in the liver that the littermate control did not show and there were some macrophages. In a 47-week-old mutant, Kupffer cells were in the bone marrow and the macrophages in the liver were larger. See slide 1, slide 2 ,  and slide 3)

The auditory brainstem response (ABR) was used to assess hearing in seven m1J/m1J and three +/m1J all 40 days of age or older. All mutants had severe hearing loss while their littermate controls had good hearing. The mucopolysaccaridoses are known to have associated hearing deficits, as do Arsbm1J mutant mice.

A clinical eye exam of two m1J/m1J and two +/m1J at three-and-a- half months old revealed no abnormalities except for one male m1J/m1J that had white in the cornea of one eye determined to be a developmental condition of C57BL/6 and not the result of the mutation.

Discussion

Maroteaux-Lamy syndrome in humans is characterized by short stature, stiff joints, dysmorphic facial features and cardiac abnormalities due to disruption in the arylsulfatase B gene. The C57BL/6J-Arsbm1J/GrsrJ mouse exhibits these symptoms phenotypically and the same gene responsible for Maroteaux-Lamy syndrome is disrupted in this mouse model.

Acknowledgements

The authors thank Coleen Kane for preparation of tissues for histological assessment; Rod Bronson, Ph.D. for pathological evaluation; Heping Yu and Chantal Longo-Guess for ABR analysis; Bo Chang, M.D. and Norm Hawes for eye examination and Patricia Ward-Bailey for assistance with manuscript preparation and web posting.