B6J.Cg-Sst^{tm2.1(cre)Zjh}/MwarJ

Stock number: 028864
Product name: Sst-IRES-Cre knock-in (C57BL/6J)
Research areas: Neurobiology Research, Research Tools

Description

Sst-IRES-Cre knock-in mice express Cre recombinase in somatostatin-expressing neurons. These mice may be useful in studying dendritic inhibitory interneurons such as Martinotti cells and Oriens-Lacunosum-Moleculare cells.

While Sst-IRES-Cre was designed as a 3' knock-in allele, additional characterization indicates it has significantly diminished endogenous Sst expression - see details below. As such, researchers should consider using heterozygous Sst-IRES-Cre mice and wildtype littermate controls in all their studies.

Of note, the same Sst-IRES-Cre knock-in allele is also available on a C57BL/6N genetic background as Stock No. 018973 and a STOCK background as Stock No. 013044.

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-Cre knock-in mice on a mostly C57BL/6;129S4 genetic background (Stock No. 013044). It should be noted that the phenotype of this C57BL/6J-congenic line (Stock No. 028864 Sst-IRES-Cre knock-in (C57BL/6J)) could vary from that of the parental line from which it was derived. The phenotype below describes the parental line (Stock No. 013044).

The Sst-IRES-Cre knock-in allele (or SOM-IRES-Cre) has an internal ribosome entry site and Cre recombinase in the 3' UTR of the somatostatin locus (Sst). As such, the endogenous Sst promoter/enhancer elements direct cre expression to somatostatin-expressing neurons. While Sst-IRES-Cre was designed as a 3' knock-in allele, additional characterization indicates it has significantly diminished endogenous Sst expression - see details below. As such, researchers should consider using heterozygous Sst-IRES-Cre mice and wildtype littermate controls in all their studies.
When Sst-IRES-Cre mice are bred with mice containing loxP-flanked sequences, Cre-mediated recombination will result in deletion of the floxed sequences in the Sst-expressing cells in the offspring.

In 2010, the donating investigator of Stock No. 013044 reported Cre recombinase activity is specific and efficient; largely recapitulating the endogenous somatostatin expression pattern with efficient recombination. They reported Cre recombinase activity is observed in somatostatin positive neurons (including dendritic inhibitory interneurons such as Martinotti cells and Oriens-Lacunosum-Moleculare (O-LM) cells). The donating investigator did not examine cre expression in tissues other than brain. Sst expression from the Sst-IRES-Cre allele was not evaluated. They also reported that homozygous mice were viable, fertile and normal in size, with no gross physical abnormalities or behavioral abnormalities.

Although Sst-IRES-Cre was designed as a 3' knock-in allele, additional characterization indicates it has significantly diminished endogenous Sst expression. Specifically, in 2016, unpublished research using Stock No. 013044 reported the Sst-IRES-Cre allele had diminished Sst RNA expression, and homozygous mice had abnormal locomotor activity (reduced in males during circadian cycle active phase, increased in females by the end of circadian cycle active phase). Heterozygous mice had partial recovery of Sst expression and normal behavioral responses. Furthermore, the findings of another group confirmed Sst-IRES-Cre imparts an allele dosage-dependent knock-down of endogenous Sst expression [Viollet et al. 2017 Front Endocrinol (Lausanne) 8:131 (PMID:28674519)]. Researchers should consider using heterozygous Sst-IRES-Cre mice and wildtype littermate controls in their studies.

For characterization information of the Sst-IRES-Cre knock-in allele, see images at the Allen Institute for Brain Science website (Sst-IRES-Cre images).

If the recombinase activity pattern of this allele is further characterized by the Genetic Resource Science group at The Jackson Laboratory, such findings will be reported on the Mouse Genome Informatics (MGI) Allele Detail entry (Sst^{tm2.1(cre)Zjh}). This same information would also be found searching the MGI Recombinase Activity database.

Development

The Sst-IRES-Cre knock-in allele (or SOM-IRES-Cre) was designed by Dr. Z. Josh Huang (Cold Spring Harbor Laboratory). A targeting vector was designed to insert an internal ribosome entry site (IRES), a Cre recombinase sequence, a polyA sequence, and an frt-flanked neo cassette into the 3' untranslated region (after the translational termination site) of the somatostatin locus (Sst or SOM) on chromosome 16. This construct was electroporated into (C57BL/6 x 129S4Sv/Jae)-derived V6.5 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts. Chimeric males were bred with Actin-FLPe females (on a C57BL/6 congenic background (N10); see Stock No. 005703) to achieve germline transmission and to remove the neo selection cassette. The resulting pups harboring the cre targeted mutation were selected. These Sst-IRES-Cre mice were subsequently bred to C57BL/6 inbred mice for two generations and/or together for several generations (and the FLPe transgene was removed). In 2010, Sst-IRES-Cre knock-in mice on a mixed genetic background (mostly C57BL/6;129S4 ; with agouti 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. 013044, which was thereafter maintained by breeding mutant mice together.

In 2014, Dr. Melissa R. Warden (Cornell University) purchased some Stock No. 013044 animals (total backcross generation N1 onto C57BL/6J). They further backcrossed them to C57BL/6J inbred mice for at least six additional generations. The resulting C57BL/6J-congenic strain, called Sst-IRES-Cre knock-in (C57BL/6J), were sent to The Jackson Laboratory Repository in 2016 as Stock No. 028864. Upon arrival, males were used to cryopreserve sperm. To establish the living mouse colony, an aliquot of the frozen sperm was used to fertilize oocytes from C57BL/6J inbred mice (Stock No. 000664).

Of note, Dr. Warden's lab reports that, at least once during backcrossing, a heterozygous female was bred to a C57BL/6J inbred male (thus the Y chromosome of the congenic strain is of C57BL/6J origin).

Allele

Symbol: Sst^{tm2.1(cre)Zjh}
Name: targeted mutation 2.1, Z Josh Huang
MGI accession ID: MGI:4838416
Generation method: Targeted
Attributes: Recombinase-expressing; Knockdown
Marker symbol: Sst
Marker name: somatostatin
Chromosome: 16
Strain of origin: (C57BL/6 x 129S4/SvJae)F1
Expressed genes: cre,cre recombinase,bacteriophage P1
Site of expression: Cre recombinase activity is observed in somatostatin positive neurons (including dendritic inhibitory interneurons such as Martinotti cells and Oriens-Lacunosum-Moleculare cells).
Molecular note: A targeting vector was designed to insert an internal ribosome entry site (IRES), a Cre recombinase sequence, a polyA sequence, and an frt-flanked neo cassette into the 3' untranslated region (after the translational termination site) of the somatostatin locus (Sst). This construct was electroporated into C57BL/6;129 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts. Chimeric males were bred with Actin-FLPe females (on a C57BL/6 congenic background) to achieve germline transmission and to remove the neo selection cassette. This mutation results in a dosage-dependent knock-down of endogenous Sst expression J:279254 .