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Preliminary characterization of the craniofacial morphology of the B6C3Fea/a-din/+ mouse strain
Dense incisors (din) is an autosomal recessive mutation
mapped to Chr 16 near the pituitary transcription factor gene Pit1,
but not a mutation in Pit1. Complete incisor eruption past the gingiva
does not occur in homozygous (din/din) mice. Continued dentin
formation gradually occludes the pulp chambers creating a dense
incisor (H.O. Sweet et al. 1996. J Hered. 87, 162-7).
Homozygous (din/din) and control (+/?) B6C3Fea/a-din
/+ mice were collected in groups (n=2-8) of age 4, 8, 12, and 16
weeks. Bone mineral density (BMD) scans (PIXImus, LUNAR, Madison,
WI) were completed of skulls and bodies separately. The skulls were
prepared by incomplete maceration in KOH, alizarin red stained,
and stored in glycerin. Seven measurements of the skull along with
ear pinnae length were then taken with digital calipers (Stoelting,
Wood Dale, Ill). The skull measurements are as follows: total skull
length, (tip of the nasal bone to back of the occipital bone) nose
length, (nasal bone to coronal suture) skull height, (lowest point
of the angular process of lower jaw to frontal bone) skull width,
(measured at the widest points of the parietal bone) inner canthal
distance, and length of both jaws.
Most skull measurements and overall body mass proved to be significantly
dependent on genotype. However, the data showed no genotypic effect
on any of the following allometric comparisons at any age; skull
length/nose length, skull height/skull length, skull length/skull
width, skull height/skull width. This indicates the din mutation
effects growth in all areas of the skull equally.
The following graphs show the effect of genotype at different ages
on the percent fat, skull BMD, whole body BMD (g/cm2) and the ratio
of skull BMD to whole body BMD. The percent fat measurements indicate
a reduction in body fat in the din/din homozygotes. This
could be explained as the effect of incomplete incisor eruption
on consumption. Stomach contents inspected during necropsy indicate
that the homozygotes do continue to eat. However their total caloric
intake may be reduced. The skull BMD and whole body BMD of the din/din
homozygotes are significantly less at 8 and 12 weeks of age. The
ratios of skull BMD to whole body BMD indicate that the mineralization
defect caused by the din mutation is not specific to the
skull.
Author: Joiel D. Bauschatz
Date: February 16,
2001
Last Updated:
6/27/02
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