B6;129S-Grin2b^{tm1.1(Grin2a)Bjha}/J

Stock number: 023538
Product name: GluN2B to GluN2A replacement
Research areas: Developmental Biology Research, Neurobiology Research

Description

The GluN2B-to-GluN2A (2B->2A) allele replaces the GluN2B (Grin2b) gene with a full-length GluN2A (Grin2a) sequence; this abolishes GluN2B gene function and expresses GluN2A from the endogenous mouse GluN2B promoter/enhancer elements. These 2B->2A mice may be useful in studying the N-methyl-D-aspartate receptor (NMDAR) and its downstream signaling molecules/pathways (including alpha-CaMKII and mTOR), synaptic plasticity (learning and memory), social behavior and the NR2B-NR2A developmental switch.

Detailed description

The N-methyl-D-aspartate receptor (NMDAR) is a specific type of ionotropic glutamate receptor and the predominant molecular device for controlling synaptic plasticity. The NMDAR is a heterotetramer composed of two GluN1 subunits and combinations of GluN2 subunits (N2A, N2B, N2C, N2D) or GluN3 subunits (N3A, N3B). Whereas NR2B is predominant in early postnatal brain development, the number of NR2A subunits grows after birth, and eventually NR2A subunits outnumber NR2B. This is called NR2B-NR2A developmental switch. GluN2B is a critical regulator of synaptic plasticity and social behavior. GluN2B is also affected by Tau phosphorylation and beta-amyloid.

In this targeted mutation strain, full-length rat GluN2A (Grin2a) cDNA replaces most of the first coding exon (exon 4) of the mouse GluN2B (Grin2b) gene, including the initial ATG site. This both abolishes endogenous GluN2B expression and directs rat GluN2A expression from the endogenous mouse GluN2B promoter/enhancer elements. Compared to wildtype, the 2B->2A allele has earlier onset of GluN2A expression (the same time as that of GluN2B). Homozygous mice are GluN2B-null with early postnatal glutamatergic cortical synapses composed only of GluN2A-containing N-methyl D-aspartate receptors (NMDARs), rather than the GluN2B-containing NMDARs normally present at this developmental timepoint. Homozygous mice display a high rate of perinatal lethality (~8% survive past birth) and surviving homozygotes have diminished feeding/fitness. Homozygous mice also exhibit depressed social exploratory behavior. Heterozygous mice are viable and fertile.

Development

The 2B->2A targeting vector was designed to insert a full-length rat ionotropic glutamate receptor NMDA2A (Grin2a; GluN2A or NR2A) cDNA sequence and a loxP-flanked PGK-neo selection cassette into the first coding exon (exon 4) of the ionotropic glutamate receptor NMDA2B locus (Grin2b; GluN2B or NR2B) on chromosome 6. This removed most of Grin2b exon 4 (including the ATG site); resulting in a nonsense transcript downstream of the GluN2A cDNA sequence. The targeting vector was electroporated into MC1 129S6/SvEvTac-derived embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts. Chimeric males were bred with C57BL/6 females. Mutant mice were then bred to 129-background animals expressing Cre recombinase in the male germline (Prm-Cre; Stock No. 003328) to delete the floxed PGK-neo cassette. The resulting GluN2B-to-GluN2A replacement (2B->2A) mice were maintained on a mixed C57BL/6-129 genetic background by the donating laboratory. The Prm-Cre transgene was bred out of the line. Upon arrival, males were used to cryopreserve sperm. To establish the living 2B->2A mouse colony, an aliquot of the frozen sperm was used to fertilize oocytes from C57BL/6J inbred females (Stock No. 000664).

Allele

Symbol: Grin2b^{tm1.1(Grin2a)Bjha}
Name: targeted mutation 1.1, Benjamin J Hall
MGI accession ID: MGI:5307054
Generation method: Targeted
Attributes: Null/Knockout; Inserted expressed sequence
Marker symbol: Grin2b
Marker name: glutamate receptor, ionotropic, NMDA2B (epsilon 2)
Chromosome: 6
Strain of origin: 129S6/SvEvTac
Expressed genes: Grin2a,glutamate ionotropic receptor NMDA type subunit 2A,rat
Molecular note: Exon 4, the first coding exon, was replaced with the a cDNA encoding for rat Grin2a and a loxP site flanked neomycin resistance gene cassette via homologous recombination. Cre mediated recombination removed the neo cassette. Western blot analysis indicates premature expression of Grin2a and absence of expression of Grin2b in homozygous mice.