The SYNGAP1fl floxed allele has loxP sites flanking exons 6-7 of the synaptic RasGAP (SynGAP) gene. Removal of the floxed sequence disrupts expression of full-length SynGAP and results in expression of a truncated/inactive SynGAP protein. These mice may be useful in Cre-lox studies of synapse development (specifically in dendritic spine), cognitive and behavioral maturation, intellectual disability and autism spectrum disorder.
Gavin Rumbaugh, The Scripps Research Institute
Mutations that cause intellectual disability (ID) and autism spectrum disorder (ASD) are commonly found in genes that encode for synaptic proteins. Syngap1 encodes a synaptic RasGAP (SynGAP) that is largely localized to dendritic spines in neocortical pyramidal neurons, where it suppresses signaling pathways linked to NMDA receptor (NMDAR)-mediated synaptic plasticity and AMPA receptor (AMPAR) membrane insertion. Syngap1 has alternative transcriptional start sites and several alternatively spliced C-terminal exons that result in many possible SynGAP isoforms. Human SYNGAP1 haploinsufficiency results from a truncation of the full-length protein. Exon 7 contains the first common methionine present in the shortest splice variant.
The SYNGAP1fl allele has loxP sites flanking exons 6-7 of the Syngap1 gene. Mice homozygous for the SYNGAP1fl allele are viable and fertile with no reported abnormalities. When bred to mice that express Cre recombinase, the resulting offspring may be useful in generating tissue-specific disruption of full-length SynGAP and expression of a truncated/inactive SynGAP protein.
For example, when SYNGAP1fl are bred to germline Cre-expressing mice, the resulting heterozygous offspring express a SynGAP protein truncated after exon 5 (known to be an inactivate SynGAP protein), as well as diminished levels of functional SynGAP (from the wildtype allele). Therefore, the heterozygous phenotype is the same as mice heterozygous for the global knockout allele, and both are a model of human SYNGAP1 haploinsufficiency - exhibiting normal synaptic transmission, modest defects in synaptic plasticity, enhanced synaptic function (accelerated rate of glutamatergic synapse maturation) during early neural development and profound cognitive and behavioral abnormalities. Specifically, heterozygous SynGAP-deficiency significantly disrupts excitatory/inhibitory (E/I) balance in the neural networks that support cognition and behavior. Abnormal behavioral phenotypes can be observing as early as 21 days of age with ~100% penetrance (although physiological abnormalities can be measured even earlier through other methods such as electrophysiological recordings). Furthermore, mice homozygous for the germline deletion of exons 6-7 are phenotypically the same as global knockout homozygotes - exhibiting complete postnatal lethality between 2-5 days of age.
In addition, to explore the behavioral contribution of in vivo Syngap1 dysfunction in distinct cellular populations, SYNGAP1fl mice may be bred to Emx1IRES cre mice (forebrain glutamatergic neurons and glia; Stock No. 005628), Gad2-IRES-Cre mice (developing GABAergic neurons; see Stock Nos. 010802 / 028867) and/or PV-Cre mice (parvalbumin-positive neurons; see Stock Nos. 008069 / 017320).
The conditional SYNGAP1 knockout mouse line (SYNGAP1fl) was constructed by genOway S.A. (France) as a pay-for-service on behalf of Dr. Gavin Rumbaugh (The Scripps Research Institute).
The targeting vector was designed to insert a loxP site upstream of exon 6, and a frt-flanked neo cassette followed by a second loxP site just downstream of exon 7 of the synaptic Ras GTPase activating protein 1 homolog (rat) locus (Syngap1) on chromosome 17.
The construct was electroporated into 129S2/SvPas-derived embryonic stem (ES) cells. Correctly targeted ES cells were identified and injected into recipient blastocysts. The donating investigator reports that chimeric males were bred Flp-deleter females (on a C57BL/6J genetic background) for germline deletion of the neo cassette; resulting in mice with the "Neo- SynGAP1 Flox" allele (SYNGAP1fl).
The SYNGAP1fl colony was maintained on this mixed genetic background for several generations (and the Flp-expressing allele was removed) prior to sending males (with black or agouti coat color) to The Jackson Laboratory Repository in 2012.
Upon arrival, males were used to cryopreserve sperm. To establish a living mouse colony, an aliquot of the frozen sperm may be used to fertilize oocytes from C57BL/6J inbred females (Stock No. 000664).
|Allele Name||targeted mutation 1.1, Genoway|
|Allele Type||Targeted (Conditional ready (e.g. floxed), No functional change)|
|Gene Symbol and Name||Syngap1, synaptic Ras GTPase activating protein 1 homolog (rat)|
|Strain of Origin||129S2/SvPas|
|Molecular Note||A loxP site was inserted usptream of exon 6. An FRT-flanked neo cassette with a 3' loxP site was inserted downstream of exon 7. Flp-mediated recombination removed the neo cassette and left exons 6 and 7 floxed.|
Mice homozygous for the floxed allele are viable and fertile with no reported abnormalities. When maintaining a live colony, heterozygous mice may be bred together, to wildtype mice from the colony or to C57BL/6J inbred mice (Stock No. 000664). Alternatively, homozygous mice may be bred together.
When using the SYNGAP1fl mouse strain in a publication, please cite the originating article(s) and include JAX stock #029303 in your Materials and Methods section.
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