These mice carry point mutations (Tyr630Ala, Leu633Leu-Ala634Gln, and Tyr638Ala) in the KIX transcription factor-binding region of the mouse Ep300 gene. They may be useful in studies of hematopoiesis.
Paul K. Brindle, St. Jude Children's Research Hospital
Ep300 (E1A binding protein p300) is a histone acetylase that is required for normal development. It interacts with a significant percentage of mammalian transcriptional regulatory proteins and mutations in the gene have been found in hematopoietic and epithelial tumors.
This strain, on a C57BL/6 background, carries point mutations in the protein-binding KIX domain of the mouse Ep300 gene that were designed to disrupt the binding surface for transcription factors c-Myb (Myb) and CREB (Creb1). The homozygous viability and phenotype of C57BL/6-backcrossed animals have not been characterized.
On a mixed C57BL/6 and 129 genetic background (B6/129), multilineage defects occur in hematopoiesis, including anemia, B-cell deficiency, thymic hypoplasia, megakaryocytosis, amd thrombosis.
Homozygous p300KIX/KIX mice on a mixed B6/129 background are generally viable, but some loss due to undefined causes before 3 weeks of age may be seen. Surviving 4-week-old homozygotes are on average 50-70% of the size of wildtype or heterozygous littermates. They have a marked reduction in thymocyte numbers (~5% of wildtype) and have severe anemia (hematocrit 20.2 +/- 5.3 versus 42.3 +/- 1.4% for wildtype) and thrombosis ((5.0 +/- 1.1) x 109 versus (1.2 +/- 0.2) x 109 platelets per ml for wildtype). B6/129 homozygotes show increased variation in erythrocyte size and the presence of megathrombocytes. Megakaryocytic hyperplasia with a corresponding decrease in other bone marrow elements is also seen. Thymuses from B6/129 homozygous animals have a decreased number of cells, but the distribution of single- and double-positive CD4 and CD8 thymocytes is normal. Peripheral populations of single-positive T cells are in the normal range. In contrast, there is a deficit of B220-positive, IgM-positive, IgD-positive mature B cells. B6/129 heterozygous animals are essentially normal with the exception of a small increase in platelets.
Homozygous mice on a C57BL/6J x 129S2/SvPasCrl F1 background (generated by crossing this C57BL/6 background line with 129S2 background line Stock No. 025528) are much healthier than the B6/129 random mixed background counterparts with less severe runting. The F1 mice retain all of the hematopoietic phenotypes seen in the B6/129 mixed animals.
Tyr630Ala (TAT->GCT), Leu633Leu Ala634Gln (CTA GCC->CTG CAG, producing a PstI restriction site), and Tyr638Ala (TAT->GCT) mutations were introduced to the KIX domain and a loxP-flanked neomycin cassette was placed in an upstream intron through homologous recombination in 129P2/OlaHsd-derived E14 embryonic stem (ES) cells. Transient expression of cre recombinase in the ES cells was done to excise the neomycin cassette. This strain was backcrossed to C57BL/6 for 32 generations by the donating laboratory.
|Allele Name||targeted mutation 1, Paul K Brindle|
|Allele Type||Targeted (Hypomorph)|
|Gene Symbol and Name||Ep300, E1A binding protein p300|
|Strain of Origin||129P2/OlaHsd|
|Molecular Note||A floxed neomycin selection cassette was inserted upstream of the exon encoding the KIX domain and the KIX containing exon itself was mutated so that the tyrosine at amino acid residue 630 became alanine, the alanine at residue 634 became glutamine and the tyrosine at residue 638 became alanine (Y630A, A634Q and Y638A). Transient cre expression then excised the selection cassette. Expression and stability of the mutated product were normal.|
Heterozygotes are viable and fertile. Homozygotes have not been characterized.
When using the p300 kix mouse strain in a publication, please cite the originating article(s) and include JAX stock #025170 in your Materials and Methods section.