B6;129S6-Lrp4^tm1Her/J

Stock number: 013157
Research areas: Cell Biology Research, Developmental Biology Research, Mouse/Human Gene Homologs, Neurobiology Research

Description

These Lrp4ECD mice harbor a hypomorphic allele of the low density lipoprotein receptor-related protein 4 locus that results in a truncated protein with loss of the transmembrane and intracellular domains of the LRP4 protein. The LRP4 extracellular domain (ECD) is expressed normally and secreted into the extracellular space; resulting in diminished, but not completely absent, LRP4 interactions with its extracellular ligands. These Lrp4ECD mice may be useful in studying the LRP4 extracellular domain in embryonic development (polysyndactyly, tooth, neuromuscular junction), as well as low-density lipoprotein (LDL) receptor family-, Shh-, Bmp-, and Wnt-signaling pathways.

Detailed description

The Lrp4 hypomorphic allele (Lrp4ECD, Lrp4 EC STOP, Lrp4^hypo, Megf7^-, Lrp4STOP1723) contains a premature stop codon within the exon immediately upstream of the transmembrane segment. Much of the targeted exon and 3' adjacent intron is absent. No functional full-length transcripts are detected in brain tissue. The transcript generated is out of frame beyond the sequences coding for the transmembrane segment, which results in a truncated protein with loss of the transmembrane and intracellular domains of the LRP4 protein. While the LRP4 extracellular domain (ECD) is expressed normally, the lack of a membrane anchor leads to shedding/secretion of the ECD into the extracellular space. This results in diminished, but not completely absent, LRP4 interactions with its extracellular ligands (i.e., hypomorphic phenotype). Mice homozygous for this Lrp4 hypomorphic allele are viable and fertile. Homozygous mice exhibit growth retardation, fully penetrant polysyndactyly with digit fusions, abnormal tooth development and changes in Shh- and Wnt-signaling. The tooth development abnormalities include supernumerary incisors/molars of reduced size and abnormal shape, and incisors with grooved enamel surfaces that exhibit the same molecular characteristics as the tips of molar cusps. Homozygous mice also have defects in neuromuscular junction development, and bone growth and turnover. These mutant mice may be useful in studying the LRP4 extracellular domain in embryonic development (polysyndactyly, tooth, neuromuscular junction), as well as low-density lipoprotein (LDL) receptor family-, Shh-, Bmp-, and Wnt-signaling pathways.

Development

A targeting vector was designed by site-specific mutation to insert a stop codon into exon 36 (codon 1723) of the Lrp4 (or Megf7) locus, as well as replace part of exon 36 and 2.1 kb of intron 36 with a PGKneobpA expression cassette (loxP::frt::PGK-neo^r cassette::loxP::frt followed by bovine growth hormone polyA signal). This results in deletion of the downstream portion of exon 36 including the transmembrane and intracellular domains of the Lrp4 protein. This was designed at the time to prevent production of a membrane-anchored receptor and eliminate residual functional activity (through alternative splicing of the extracellular domain or via the potential use of alternative promoters for transcription initiation). The construct was electroporated into 129S6/SvEvTac-derived SM1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts and chimeric males were bred with C57BL/6 females to establish the colony. Mice on a mixed C57BL/6;129S6/SvEv genetic background were sent to The Jackson Laboratory Repository. Upon arrival, mice were bred to C57BL/6J (Stock No. 000664) for at least one generation to establish the colony.

Allele

Symbol: Lrp4^tm1Her
Name: targeted mutation 1, Joachim Herz
MGI accession ID: MGI:3621893
Generation method: Targeted
Attributes: Null/Knockout
Marker symbol: Lrp4
Marker name: low density lipoprotein receptor-related protein 4
Chromosome: 2
Strain of origin: 129S6/SvEvTac
Molecular note: The locus was disrupted by the insertion of a stop codon just upstream of the transmembrane segment. Part of exon 36 and 2.1 kb of intron 36 were replaced with a neomycin resistance cassette. RT-PCR confirmed the complete lack of functional transcripts.