These Mybf/f floxed mutant mice possess loxP sites flanking exon 2 of the myeloblastosis oncogene (Myb) gene. This strain may be useful for studying the proliferation and differentiation of hematopoietic progenitor cells.
Klaus Rajewsky, Max Delbruck Centre for Molecular Medicine
Timothy P. Bender, University of Virginia
These Mybf/f floxed mutant mice possess loxP sites flanking exon 2 of the myeloblastosis oncogene (Myb) gene. MYB is a transcription factor involved in the regulation of hematopoiesis. Specifically, MYB is expressed throughout T cell development in the thymus, and is required for differentiation and survival of pro-B cells. Mice that are homozygous for this allele are viable and fertile. When these mutant mice are bred to mice that express Cre recombinase, resulting offspring will have exon 2 deleted in cre-expressing tissues.
For example, when crossed to Lck-cre mice expressing Cre recombinase in DP thymocytes (Stock No. 003802), resulting offspring have an 80% decrease of double-positive and CD4-positive T cells. Also, thymus cellularity is reduced by about 75%.
Stock No. 028881 is a similar strain with exon 6 floxed, targeting the c-Myb DNA binding domain, rather than exon 2. Due to a variety of c-Myb splice variants expressed from different promoters, deletion of exon 6 may still produce a truncated protein driven by a promoter that is still present upstream of exon 2. This includes 2 major variants that involve exons 9 and 9A. This Stock No. 035170, with loxP sites flanking exon 2, takes into account that splicing of nascent Myb mRNA between exon 1 and 2 occurs in the first reading frame, whereas all other known splices between coding exons are in the second and third reading frames. Thus, there are no known splicing events that could occur in frame down stream of exon 1 after Cre mediated deletion of exon 2. c-Myb proteins are not detected using antibodies that recognize epitopes in the N- or C-terminal ends after cre recombination in this line.
A targeting vector was designed to insert a single loxP site downstream of exon 1, and a loxP-flanked neomycin resistance (neo) cassette downstream of exon 2 of the myeloblastosis oncogene (Myb) gene. The construct was electroporated into 129P2/OlaHsd-derived IB10 embryonic stem (ES) cells. Correctly targeted ES cells were transiently transfected with a pIC-Cre expression plasmid to delete the neo cassette. Resulting ES cells contained multiple gene rearrangments; intact floxed-exon 2, intact floxed-neo cassette, or excision of both exon 2 and the neo cassette. Correctly targeted ES cells, containing only the floxed-exon 2, were injected into C57BL/6 blastocysts and resulting chimeric males were bred with C57BL/6 females. Resulting offspring were further backcrossed to C57BL/6J mice (Stock No. 000664) for at least 19 generations to produce a colony of Mybf/f mice. Upon arrival at The Jackson Laboratory, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6J oocytes.
|Allele Name||targeted mutation 1, University of Cologne|
|Allele Type||Targeted (Conditional ready (e.g. floxed), No functional change)|
|Gene Symbol and Name||Myb, myeloblastosis oncogene|
|Strain of Origin||129P2/OlaHsd|
|Molecular Note||Exon 2 remained floxed following the excision of a floxed neo via transient Cre-mediated expression. Southern blot confirmed recombination.|
When maintaining a live colony, homozygous mice may be bred together.
When using the Mybf mouse strain in a publication, please cite the originating article(s) and include JAX stock #035170 in your Materials and Methods section.