Neuromuscular ataxia: a new spontaneous mutation in the mouse
Patricia F. Ward-Bailey,
Kenneth R. Johnson,
Rod T. Bronson,
Leah Rae Donahue,
Muriel T. Davisson
The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine 04609, USA
University of Maine at Orono, Orono, Maine 04473, USA
Received: 27 March 2000 / Accepted: 17 May 2000
Abstract. Neuromuscular ataxia, nma, is a new autosomal reces-
sive mutation that arose spontaneously in CBA/J inbred mice at
The Jackson Laboratory. The mutation, now maintained on the
hybrid background, when homozygous, causes small
size, uncoordinated gait, dysmetria, dystonia, general weakness,
and death shortly after weaning. No biochemical or morphological
abnormalities have been detected. We used an intercross between
mutant and CAST/Ei to map the nma mutation to
the proximal end of Chr 12. The most likely gene order places the
mutation between D12Mit270 and D12Mit54, non-recombinant
with D12Mit2 in 96 tested meioses.
Mouse mutants demonstrating neuromuscular deficiencies are im-
portant models for a variety of human neuromuscular diseases.
Such mutant animals are valuable tools for the study of pathology
contributing to neuromuscular dysfunction and can aid the mo-
lecular identification of responsible genes. Among the 190 neuro-
muscular and neurological genes and mutations listed in The
Mouse Genome Database (MGD 2000) are several mutants exhib-
iting many of the same behaviors as nma. Most mutants with this
type of behavior have obvious cerebellar defects; however, cer-
ebellar cytoarchitectural anomalies are not seen in the new muta-
The nma mutation is recessive and arose spontaneously in the
CBA/J inbred strain of mice at The Jackson Laboratory (Bar Har-
bor, Maine) in 1985. Homozygous mutant animals are recogniz-
able by 12 days of postnatal development by their small size,
uncoordinated gait, dysmetria, dystonia, and general weakness.
Mutant mice survive only a few days after weaning despite exten-
sive efforts to nurture them. Heterozygotes appear normal and
have a normal lifespan. The mutation was mapped to Chr 12.
Materials and methods
All the mouse stocks used in this study were reared under modified
barrier conditions at The Jackson Laboratory in the Mouse Mutant Re-
source (Davisson 1990). The nma mutation occurred in the CBA/J inbred
strain. It is maintained by alternately backcrossing B6C3FeF
hybrid) host females transplanted with nma/nma ovaries
males and then intercrossing the obligate nma/+ heterozy-
gous progeny to produce the next generation of nma/nma mice. The strain
is now at the 31st backcross generation. For linkage analysis, CAST/Ei
males were mated to host females with ovaries from B6C3Fe–nma/nma
hybrids from this initial cross were then intercrossed to produce
progeny. The F
progeny were scored visually when they were
between 14 and 21 days of age for phenotype, and spleens from 48 nma/
nma mutant animals were collected and stored at −70°C for subsequent
DNA typing to map the mutation.
x-rays. Radiographs were obtained from
two nma/nma and two control (+/?) 14-day-old mice by using a Hewlett-
Packard model 43855 Faxitron cabinet x-ray system.
Blood chemistries were performed at Tufts Univer-
sity School of Veterinary Medicine with an SMA Autoanalyzer. Glucose,
blood urea nitrogen (BUN), and alanine aminotransferase (ALT) were
measured in pooled plasma samples from nine nma/nma and eight +/?
animals at 2 weeks of age.
Tissues for histopathological examination
were prepared from 14-day-old nma/nma and +/? animals. Tissues were
fixed in situ in mice deeply anesthetized with tribomoethanol (Avertin) by
intracardiac perfusion with Bouin’s solution following a flush of physi-
ological saline. After demineralization, multiple cross-sections of thoracic
and lumbar vertebrae with spinal cord were prepared. Brains were sec-
tioned coronally from the cerebrum through the cerebellum. Cross and
longitudinal sections of lumbar muscles, fore- and hind limb muscles, and
samples of each of the somatic organs (liver, spleen, pancreas, stomach,
small intestine, colon, cecum, lungs, thymus, and heart) also were pre-
pared. For light microscopy, sections from all tissues were embedded in
paraffin, sectioned at 4–5 microns, and stained with hematoxylin and eosin
(H&E). Brain and spinal cord sections also were stained with Luxol fast
blue-cresylecht violet (LFB-CV) and Bodian’s stain.
Skeletons from two nma/nma and two control (+/?) 14-day-old mice
were prepared by partial maceration with 1% KOH, staining with alizarin
red S and alcian blue to reveal bone and cartilage, and then clearing in
glycerol (Green 1952).
For histological examination, inner ears from perfused mice were dis-
sected, demineralized in Bouin’s solution, and then embedded in paraffin
and sectioned. For gross morphological examination, cleared whole
mounts of inner ears from three nma/nma and three control mice were
prepared by fixation in neutral-buffered formalin, dehydration in ethanol,
and clearing overnight in methyl salicylate. Mice used for these analyses
were between 18 and 21 days of age.
Hearing was assessed by ABR threshold analysis
(Zheng et al. 1999) of six nma/nma and five +/? mice tested at 18–21 days
Intercrosses with linkage testing stocks and with
CAST/Ei were utilized to produce mutant mice. A genome scan was car-
ried out to determine the chromosomal location of the nma mutation (see
DNA was extracted from the frozen spleens of 48
mutant (homozygous) F
mice produced in the linkage cross by standard
phenol/chloroform extraction procedures.
Correspondence to: P. Ward-Bailey; E-mail: firstname.lastname@example.org
© Springer-Verlag New York Inc. 2000Mammalian Genome 11, 820–823 (2000).