STOCK Tg(Camk2a-Grin2a/Grin2b)1Jzt/J

Stock number: 029151
Product name: Tg-GluN2A^2B(CT)
Research areas: Neurobiology Research, Research Tools

Description

Tg-GluN2A^2B(CT) mice have forebrain excitatory neuron over-expression of GluN2A^2B(CTR); a chimeric NMDA glutamate receptor composed of the Grin2a N-terminal and transmembrane domains fused to the Grin2b C-terminal intracellular domain. These mice are useful in studying synaptic plasticity, learning and memory.

Detailed description

The N-methyl-D-aspartate (NMDA) receptors are a class of ionotropic glutamate receptors involved in long-term potentiation, synaptic plasticity, learning and memory. NMDA receptor (NMDAR) channels are heteromers composed of two NMDAR1 (GluN1; Grin1) subunits and one or more of the four NMDAR2 subunits: NMDAR2A (GluN2A; Grin2a), NMDAR2B (GluN2B; Grin2b), NMDAR2C (GluN2C; Grin2c) and/or NMDAR2D (GluN2D; Grin2d).

The three lines listed below are part of a series of transgenic mice with forebrain excitatory neuron over-expression of GluN2A, GluN2B or GluN2D chimeric subunits in which the endogenous C-terminal intracellular domain of each was replaced with another subunit. All three lines exhibit transgene expression that is highly enriched in the cortex, striatum and hippocampus, but not in hindbrain regions such as the cerebellum. The donating investigator reports the overexpression levels were not quantified - in part because endogenous GluN2 subunit levels vary among brain areas, ages and individuals; complicating expression level analysis. When hemizygous for their respective transgene, all three lines are reported to be viable, fertile and indistinguishable from wildtype littermates in growth, body weight, locomotor activity and anxiety. To date (June 2016), the phenotype of homozygous mice has not been characterized.

Stock No. 029151: Tg-GluN2A^2B(CT) mice have forebrain excitatory neuron over-expression of GluN2A^2B(CTR); a chimeric NMDA glutamate receptor composed of the Grin2a N-terminal and transmembrane domains fused to the Grin2b C-terminal intracellular domain. These mice exhibit enhanced long-term potentiation, long-term recognition memory and contextual fear conditioning.

Stock No. 029152: Tg-GluN2B^2A(CT) mice have forebrain excitatory neuron over-expression of GluN2B^2A(CTR); a chimeric NMDA glutamate receptor composed of the Grin2b N-terminal and transmembrane domains fused to the Grin2a C-terminal intracellular domain. These mice exhibit significantly impaired long-term depression resulting in impaired short-term recognition memory and impaired long-term cued fear conditioning.

Development

The CaMKIIα-GluN2A^2B(CTR) transgene was designed in the laboratory of Dr. Joe Z. Tsien (Augusta University) to have ~8.5 kbp of the mouse Camk2a (CaMKIIα) promoter sequences placed upstream of a chimeric NMDA glutamate receptor (GluN2A^2B(CTR)) followed by an SV40 polyadenylation signal. Specifically, the GluN2A^2B(CTR) is encoded by the N-terminal and transmembrane domain sequences from the rat Grin2a locus (glutamate receptor, ionotropic, NMDA2A [epsilon 1]) fused with the C-terminal intracellular domain sequences from the rat Grin2b locus (glutamate receptor, ionotropic, NMDA2B [epsilon 2]). The 15.4 kbp transgene was used for pronuclear injection into C57BL/6J zygotes. Founder mice were bred with C57BL/6J mice for germline transmission. At some point, the transgenic line was bred to CB6F1 animals. The resulting Tg-GluN2A^2B(CT) (or Tg-NR2A^2B(CT)) mice from the founder line with the highest expression in forebrain regions (cortex and hippocampus) were propagated. The donating investigator reports that Southern blots indicate only one copy of the transgene was integrated into the genome, and there is no evidence of multiple copies. They reported the mice were bred with C57BL/6 wildtype mice for several years (~30 generations) prior to sending hemizygous males with black coat color to The Jackson Laboratory Repository in 2016 (see SNP results below). Upon arrival, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664).
Of note, it is not known if the Y chromosome has been fixed to the C57BL/6 background during backcrossing.

In 2016, a SNP (single nucleotide polymorphism) panel analysis, with markers covering all 19 chromosomes and the X chromosome was performed on the two transgenic males sent to The Jackson Laboratory Repository. This revealed ~71% of the polymorphic markers were homozygous for C57BL/6. Markers on 4 different chromosomes were not fixed for C57BL/6 allele-type: markers on chromosomes 11 and 16 were heterozygous for C57BL/6;BALB/c, while markers on chromosomes 2 and 3 were segregating for an allele-type other than C57BL/6 or BALB/c.
Regarding the live colony in 2017 - after one generation of breeding to C57BL/6J, three transgenic mice from our first generation rederived colony showed one animal remained heterozygous (C57BL/6;BALB/c) for the same chromosome 11 marker, while 2 animals remained segregating for an unknown allele-type on the same chromosome 2 marker.
Collectively, these data suggest that the mice sent to The Jackson Laboratory Repository were incompletely backcrossed onto C57BL/6, with at least two uncharacterized genetic background contributions. These data also suggest the segregating regions are not linked to the transgene.

Allele

Symbol: Tg(Camk2a-Grin2a/Grin2b)1Jzt
Name: transgene insertion 1, Joe Z Tsien
MGI accession ID: MGI:5780173
Generation method: Transgenic
Attributes: Inserted expressed sequence
Marker symbol: Tg(Camk2a-Grin2a/Grin2b)1Jzt
Marker name: transgene insertion 1, Joe Z Tsien
Chromosome: UN
Strain of origin: C57BL/6J
Expressed genes: Grin2a,glutamate ionotropic receptor NMDA type subunit 2A,rat; Grin2b,glutamate ionotropic receptor NMDA type subunit 2B,rat
Molecular note: The transgene is designed to have ~8.5 kbp of the mouse Camk2a promoter sequences placed upstream of a chimeric NMDA glutamate receptor followed by an SV40 polyadenylation signal. Specifically, the N-terminal and transmembrane domain sequences from the rat Grin2a locus are fused with the C-terminal intracellular domain sequences from the rat Grin2b locus. Mice from the founder line with the highest expression in forebrain regions (cortex and hippocampus) were propagated. The investigator reports that Southern blots indicate only one copy of the transgene was integrated into the genome, and there is no evidence of multiple copies.