B6J.Cg-Sst^{tm3.1(flpo)Zjh}/AreckJ

Stock number: 031629
Product name: Sst-ires-Flp (C57BL/6J) , B6J.Sst-ires-Flp , SOM-IRES-FLPo (C57BL/6J) , B6J.SOM-IRES-FLPo
Research areas: Neurobiology Research, Research Tools

Description

Sst-ires-Flp knock-in mice (or SOM-IRES-FLPo) have FLPo recombinase expression in GABAergic neurons derived from the medial-ganglionic eminence (MGE) - as directed by the endogenous somatostatin promoter. These mice are useful for studying the fate of progenitor cells at the SST/CR intersection.
Stock No. 031629 is a C57BL/6J-congenic Sst-ires-Flp knock-in mouse line, called Sst-ires-Flp (C57BL/6J) or B6J.Sst-ires-Flp. Of note, the same Sst-IRES-Flp knock-in allele is also available on a STOCK genetic background as Stock No. 028579.

Detailed description

In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. The phenotype summarized below is for the parental line: Sst-ires-Flp knock-in mice on a C57BL/6;129S4 genetic background (Stock No. 028579). It should be noted that the phenotype of this C57BL/6J-congenic Sst-ires-Flp knock-in line (Stock No. 031629 ; Sst-ires-Flp (C57BL/6J) or B6J.Sst-ires-Flp) could vary from that of the parental line from which it was derived. The phenotype below describes the parental line (Stock No. 028579).

Sst-ires-Flp knock-in mice (or SOM-IRES-FLPo) express FLPo recombinase from the endogenous somatostatin (Sst) promoter/enhancer elements. SST expressing cells constitute half of the GABAergic neurons along the medial-ganglionic eminence and the preoptic areas (MGE-POA) and up to 30% all GABA neurons in many cortical areas. Homozygous mice are viable and fertile. FLPo is detected in somatostatin positive neurons across layer 2 to 6, including dendritic inhibitory interneurons such as Martinotti cells and Oriens-Lacunosum-Moleculare (O-LM) cells. As such, when Sst-ires-Flp mice are bred with mice containing frt-flanked sequence(s), Flp-mediated recombination will result in deletion of the flanked sequence(s) in the Sst-expressing cells of the offspring.

Sst-ires-Flp mice were bred to Ai65(RCFL-tdT)-neo mice (Stock No. 021875) (after removal of the loxP-flanked STOP codon by breeding with CR(calretinin)-ires-cre mice (Stock No. 010774) in order to study the fate of progenitor cells at the SST/CR intersection. tdTomato-labeled cells are enriched in layers 2 and 3 (L2/3), L5a, and L6 but are almost absent in L4. The L2/3 SST/CR cells have Martinotti cell morphology with an ascending axon that arborizes in L1 with fewer branches in L2/3. The L5 SST/CR neurons also have Martinotti cell morphology with ascending axons that invade layer 1. These neurons have adapting firing patterns.

Development

The Sst-ires-Flp knock-in allele (or SOM-IRES-FLPo) was designed by Dr. Z. Josh Huang (Cold Spring Harbor Laboratory). A targeting vector was designed to insert an internal ribosome entry site (IRES) fused to the FLPo recombinase gene (a codon-optimized FLPe gene modified for translation in mammalian cells and higher recombination efficiency in cells and in mice), followed by a loxP-flanked neo cassette, downstream of the stop codon of the somatostatin locus (Sst) on chromosome 16. This construct was electroporated into (C57BL/6 x 129S4/SvJae)F1-derived V6.5 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts. Chimeric animals were bred with B6.C-Tg(CMV-cre)1Cgn/J mice (Stock No. 006054) to generate the colony and remove the neo selection cassette. The resulting Sst-ires-Flp mice were bred to C57BL/6J mice to remove the Cre-expressing transgene, and then offspring were subsequently bred together to create a homozygous Sst-ires-Flp colony.
In January 2016, Sst-ires-Flp knock-in mice on a mixed genetic background (C57BL/6;129S4 ; animals showing either agouti or black coat color) were sent to The Jackson Laboratory Repository. Upon arrival, sperm was cryopreserved. An aliquot of that frozen sperm was used to fertilize C57BL/6J oocytes (Stock No. 000664) and rederive our live colony as Stock No. 028579, which was thereafter maintained by breeding mutant mice together.
In August 2016, Drs. Andrew K. Recknagel and Melissa R. Warden (Cornell University) purchased some Stock No. 028579 animals (total backcross generation N1 onto C57BL/6J). They further backcrossed them to C57BL/6J inbred mice for at least five additional generations - establishing their C57BL/6J-congenic Sst-ires-Flp knock-in mouse line, called Sst-ires-Flp (C57BL/6J) or B6J.Sst-ires-Flp. In 2018, they sent B6J.Sst-ires-Flp males with black coat color to The Jackson Laboratory Repository as Stock No. 031629. Upon arrival, males were bred to C57BL/6J females (Stock No. 000664) to rederive a live colony. Thereafter, B6J.Sst-ires-Flp females were bred to C57BL/6J males at least one generation (thus the Y chromosome of this congenic strain is of C57BL/6J origin).

Allele

Symbol: Sst^{tm3.1(flpo)Zjh}
Name: targeted mutation 3.1, Z Josh Huang
MGI accession ID: MGI:5700394
Generation method: Targeted
Attributes: Recombinase-expressing
Synonyms: somatostatin-Flp; Som-Flp; SOM-IRES-Flp; SST-Flp; SST-ires-Flpo
Marker symbol: Sst
Marker name: somatostatin
Marker synonyms: preprosomatostatin; Smst; SOM; SRIF; SS-14; SS-28; SST1
Chromosome: 16
Strain of origin: (C57BL/6 x 129S4/SvJae)F1
Expressed genes: FLP,FLP recombinase,Saccharomyces cerevisiae
Site of expression: FLP Recombinase is detected in somatostatin positive neurons.
Molecular note: The targeting vector is designed to insert an internal ribosome entry site (IRES) fused to flpo recombinase gene (a codon-optimized flpe gene modified for translation in mammalian cells and higher recombination efficiency in cells and in mice), followed by a loxP-flanked neo cassette, downstream of the stop codon of the gene. Cre-mediated recombination removed the floxed neo cassette.