These MitfMi mutant mice are characterized by small eyes, and lack of pigment in the eyes, inner ear, and skin, and early deafness. White spotting on the belly, head, and tail are common.Read More +
Mutations at the Mitf locus affect eye size, pigmentation, and the capacity for secondary bone resorption. Mice heterozygous for the MitfMi mutation have less iris pigment than wildtype and often have white spotting on the belly, head, and tail. Homozygous mutant mice have small eyes and are devoid of pigment in the eyes, inner ear, and skin. Homozygotes are deaf at an early age. There is a decrease of mast cells in the spleen and gut. Most homozygotes die around weaning but some may live for several months. There is a deficiency of secondary bone resorption (osteopetrosis) and the incisors fail to erupt. Immunological defects include decreased macrophage chemotactic responses, impaired proliferative responses to B cell and T cell mitogens, diminished responses in vitro to T-dependent and T-independent antigens and reduced NK cell activity.
The semi-dominant mutation microphthalmia (MitfMi) was found among descendants of an irradiated male by Hertwig before 1942. It was sent to Dr. E.S. Russell at The Jackson Laboratory from Dr. Hans Gruneberg in 1961. It was maintained with the dominant allele MitfMi-wh and crossed to C57BL/6J as MitfMi-wh/MitfMi each N generation until 1986 at N100. It was then backcrossed to C57BL/6J without MitfMi-wh to N105. A cross was then made of a host female bearing a C57BL/6J-MitfMi homozygous ovary to a C3HeB/FeJ-a/a male. The strain was then maintained by mating to the hybrid B6C3Fe-a/a each cross generation and mating the offspring each intercross generation.
|Gene Symbol and Name||a, nonagouti|
|Strain of Origin||old mutant of the mouse fancy|
|General Note||Insertion of the LV30 retrotransposon without the beta4 retrovirus sequence does not cause the nonagouti phenotype. J:278039|
|Molecular Note||Characterization of this allele shows an insertion of DNA comprised of a 5.5kb virus-like element, VL30, into the first intron of the agouti gene. The VL30 element itself contains an additional 5.5 kb sequence, flanked by 526 bp of direct repeats (beta4 retroviral sequence). The host integration site is the same as for at-2Gso and Aw-38J and includes a duplication of four nucleotides of host DNA and a deletion of 2 bp from the end of each repeat. Northern analysis of mRNA from skin of homozygotes shows a smaller agouti message and levels 8 fold lower than found in wild-type.|
|Allele Synonym(s)||m; mi|
|Gene Symbol and Name||Mitf, melanogenesis associated transcription factor|
|Strain of Origin||Not Specified|
|General Note||This mutation produces an osteopetrosis that resembles human osteopetrosis more than that produced by Ctsfop. MitfMi mutant mice have normal levels of M-CSF and its receptor. Osteoplasts are produced, but are unable to function normally in bone resorption (J:22788). |
Combination heterozygotes of MitfMi-wh/MitfMi show some interallelic complementation in that the heterozygote of the two alleles is more nearly normal than either homozygote (J:12967). MitfMi-Or/MitfMi mice resemble homozygous MitfMi-Or (J:15060).
|Molecular Note||This mutation was identified during an irradiation experiment, but it is not known whether it was induced in the treated male or spontaneously arose in an untreated mate. RT-PCR analysis identified a 3 nucleotide deletion in the transcript that results in a loss of one of four conserved arginine residues in the basic domain of the encoded protein. This mutation is predicted to affect the ability of the protein to bind DNA.|
When using the microphthalmia mouse strain in a publication, please cite the originating article(s) and include JAX stock #001573 in your Materials and Methods section.