This Mesd knockout exhibits an embryonic lethal phenotype and may be useful in studies of primitive streak formation, epiblast differentiation, visceral endoderm function, Wnt signaling, low-density lipoprotein receptor family mediated endocytosis and signaling.
Bernadette C. Holdener, Stony Brook University
Mutant homozygotes display an embryonic lethal phenotype, failing to develop past embryonic day 9.5. At embryonic day 7.5, homozygous embryos lack a primitive streak and mesodermal derivatives with a smaller epiblast surrounded by an expanded parietal endoderm. Mice homozygous for this targeted mutation exhibit a phenotype similar to homozygotes carrying the mesd deletion (Holdener et al., Development. 1994;120(5):1335-46. Hsieh, J-C et al Cell 2003; 112(3): 355-367). Wnt signaling is blocked in homozygous embryos (aged embryonic day 7.5) as assessed by crossing with B6.Cg-Tg(BAT-lacZ)3Picc/J (STOCK No. 5317) mice that express beta-galactosidase in the presence of activated beta-catenin. Expression of the pluripotency molecular markers, Oct4, Nanog, and Sox2, continues in the epiblast of homozygous embryos (day 8.5). LRP2, low density lipoprotein receptor-related protein 2, or Megalin, protein is not localized to the apical membrane of the visceral endoderm and is diffusely distributed in the cytoplasm. Ultrastructural analysis reveals a reduction in size and number of organelles in visceral endoderm cells. Lysosome number and size is also reduced and endocytosis function is defective in the visceral endoderm cells of mutant embryos. During backcrossing, the Y chromosome may not have been fixed to the C57BL/6J genetic background. Mice heterozygous for this targeted mutation are viable, fertile, normal in size.
A targeting vector containing a PGK-Neo cassette was used to disrupt most of exon 1 and all of exons 2 and 3. The construct was electroporated into 129 derived embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts. The resulting chimeric animals were tested for germline transmission. The mice were backcrossed to C57BL/6J for 8 generations. During backcrossing, the Y chromosome may not have been fixed to the C57BL/6J genetic background. Upon arrival at The Jackson Laboratory, the mice were crossed to C57BL/6J (Stock No. 000664) at least once to establish the colony.
|Allele Name||targeted mutation 1, Bernadette C Holdener|
|Allele Type||Targeted (Null/Knockout)|
|Allele Synonym(s)||Mesdtm1bch; Mesdc2tm1Bch|
|Gene Symbol and Name||Mesd, mesoderm development LRP chaperone|
|Strain of Origin||129|
|Molecular Note||Exon 2 and 3 were replaced with a neo cassette.|
When maintaining a live colony, these mice can be bred as heterozygotes. Homozygotes have an embryonic lethal phenotype, failing to develop past embryonic day 9.5.
When using the B6.129-Mesdtm1Bch/J mouse strain in a publication, please cite the originating article(s) and include JAX stock #013577 in your Materials and Methods section.