C57BL/6N-Gnb1^em5Frk/J

Stock number: 032865
Product name: Gnb1^K78R
Research areas: Neurobiology Research

Description

Gnb1^K78R knock-in mice carry a CRISPR/Cas9-generated K78R missense mutation in the mouse Gnb1 (guanine nucleotide binding protein (G protein), beta 1) gene that is homologous to a human mutation associated with GNB1 Encephalopathy. Heterozygous mice recapitulate many aspects of the disorder, including developmental delay, motor and cognitive deficits, and absence-like generalized seizures. Homozygotes are embryonic lethal.

Detailed description

Most G protein-coupled receptor (GPCR) signaling is transduced through a G protein heterotrimeric complex composed of three subunits: Gα, Gβ, and Gγ. Mutations in the human GNB1 gene, encoding G protein subunit beta 1, cause GNB1 Encephalopathy, a severe neurodevelopmental disorder characterized by global developmental delay, speech and ambulatory deficits, intellectual disability, and a variety of seizure types.

These Gnb1^K78R knock-in mice carry a CRISPR/Cas9-generated K78R missense mutation in the mouse Gnb1 gene that is homologous to the first mutation identified in a human patient (human NM_002074, mouse NM_008142, c.233 A>G; p.K78R). Normal protein levels are observed in the cortex of newborn mice, with high levels at the cellular membrane, and low levels in the cytosol. This mutation does not confer a null allele, and protein is properly targeted and localized in cells.

Homozygotes show embryonic lethality. Heterozygotes on a C57BL/6N (this Stock No. 032865) or a mixed genetic background (FVB, 129P2, C57BL/6NJ - see Stock No. 032895) show reduced viability, with low numbers of heterozygotes born.

Heterozygous mice recapitulate many of the aspects of the human disorder, including developmental delay, motor and cognitive deficits, absence-like generalized seizures, and frequent spike-wave discharges (SWD). Cortical neurons from heterozygous Gnb1^K78R mice cultured in vitro also display extended bursts of firing followed by extensive recovery periods. Both the in vivo and in vitro excitability phenotypes are effectively suppressed by the anti-epileptic drug ethosuximide (ETX). Evidence indicates that K78R is a gain-of-function mutation that causes G protein-coupled potassium channel (GIRK) activation that is potently inhibited by ETX.

Both male and female pups have a significantly reduced body weight at birth, compared to wildtype littermates. On a C57BL/6N background (Stock No. 032865), heterozygous pups remain significantly smaller as young adults at 6 weeks of age and exhibit deficits in the surface righting reflex and negative geotaxis tests. Pups on the mixed genetic background (Stock No. 032895) are generally bigger and healthier than pups on the C57BL/6N background, showing similar, albeit milder, developmental delays.

Development

A CRISPR/Cas9-generated K78R missense mutation was introduced to the mouse Gnb1 gene that is homologous to the first mutation identified in a human patient (human NM_002074, mouse NM_008142, c.233 A>G; p.K78R). The mutation was created in C57BL/6NCrl embryos. Resultant mice were backcrossed to C57BL/6NJ (Stock No. 005304) for at least 3 generations by the donating laboratory.