In this strain exon 2 of the Mlh3, mutL homolog 3 (E coli), gene is disrupted. Homozygotes are infertile, exhibiting meiotic arrest during gametogenesis, and develop a higher frequency of gastrointestinal tumors when compared to controls. This mutant mouse strain may be useful in studies of microsatellite instability, DNA-damage response, and tumorigenesis.
Steven Lipkin, Weill Cornell Medical College
The Mlh3, mutL homolog 3 (E coli), gene encodes a DNA mismatch repair protein involved in mammalian meiotic recombination. These mice carry a targeted mutation of Mlh3 in which exon 2 has been replaced by sequence encoding lacZ and a floxed PGK-NEO cassette. Mice homozygous for this targeted mutation are viable but sterile, and exhibit increased microsatellite instability rate. Heterozygotes are viable and fertile.
Spermatocytes of homozygous males arrest at pachytene, diplonema and metaphase stages, resulting in azoospermia. Homozygous males exhibit small testis size when compared to wildtype controls. Oocytes of homozygous females fail to complete meiosis after fertilization. Gametes from homozygotes exhibit microsatellite instability and aneuploidy, in addition to meiotic arrest. No gene product (mRNA) is detected by Northern blot analysis of testes from homozygotes.
Homozygotes on the 129 Sv/Ev have a shortened life span, with a mean life span of 15.1 months.
An increased frequency of tumors of the gastrointestinal tract and other tissues is observed in homozygotes: more than 50% of homozygotes developed gastrointestinal tumors.
A targeting vector designed by Dr. Steven M. Lipkin (University of California, Irvine) containing sequence encoding lacZ and a floxed PGK-NEO cassette was used to disrupt exon 2. The construct was electroporated into unspecified 129S/SvEv derived embryonic stem (ES) cells. Correctly targeted ES cells were injected into blastocysts.
The resulting chimeric animals were crossed to C57BL/6 mice, and then backcrossed to C57BL/6 for 10 generations. Upon arrival at The Jackson Laboratory, the mice were crossed to C57BL/6J (Stock No. 000664) at least once to establish the colony.
|Expressed Gene||lacZ, beta-galactosidase, E. coli|
|Site of Expression|
|Allele Name||targeted mutation 1, Steven M Lipkin|
|Allele Type||Targeted (Reporter, Null/Knockout)|
|Gene Symbol and Name||Mlh3, mutL homolog 3|
|Expressed Gene||lacZ, beta-galactosidase, E. coli|
|Strain of Origin||129S/SvEv|
|Molecular Note||Exon 2 and downstream intronic sequence were replaced with a cassette containing lacZ and neo. Transcript was undetected by Nothern blot analysis of total testicular RNA. Immunofluorescence analysis of chromosomes during the meiosis I pachytene stage showed an absence of protein in homozygous mutant mice.|
When maintaining a live colony, these mice can be bred as heterozygotes. Homozygotes are viable but are not fertile.
When using the B6.129-Mlh3tm1Lpkn/J mouse strain in a publication, please cite the originating article(s) and include JAX stock #018845 in your Materials and Methods section.
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