C57BL/6-Mecp2^{em4(MECP2*)Gfng}/LutzyJ

Stock number: 039182
Product name: Mecp2 huExon4*T158M
Research areas: Cell Biology Research, Developmental Biology Research, Mouse/Human Gene Homologs, Neurobiology Research

Description

B6-MeCP2-huExon4*T158M knock-in mice express a humanized exon 4 and the T158M (threonine to stop) amino acid substitution in the Mecp2 (methyl CpG binding protein 2) locus. The T158M mutation is associated with Rett Syndrome (RTT). These mice may be useful in studies of Rett syndrome and in testing human-sequence-identical gene editing-based therapies in vivo.

Of note, as controls, we recommend B6-MeCP2-huExon4 mice (Stock No. 037256) or Mecp2-huExon3/4 mice (Stock No. 040861), which each carry a humanized region but lack the RTT-associated mutations.

Detailed description

MECP2 is a nucleus protein named for its ability to selectively recognize methylated DNA. The Mecp2 gene is located on the X-chromosome and mutations in Mecp2 are the major cause of Rett Syndrome (RTT), an X-linked neurodevelopmental disorder. The majority of RTT mutations cluster in exon 4 and are C to T transitions, which typically arise due to hypermutability at mCpG dinucleotides within the MECP2 locus.

B6-MeCP2-huExon4*T158M knock-in mice were created using base editing to introduce the MECP2 T158M mutation (threonine-to-methionine) on the MeCP2 Exon4 humanized wild-type allele, Mecp2 huExon4, which was previously generated in the same lab and deposited at The Jackson Laboratory as Stock No. 037256. MeCP2-huExon4*T158M mice carry a humanized exon 4 along with the Rett-associated T158M missense mutation. Heterozygous females are viable but exhibit Rett-associated neurological defects and experience reduced fertility as the disease progresses. The donating investigator has not attempted to generate homozygous females. Hemizygous males are viable but not fertile. They typically exhibit severe neurological symptoms and die prematurely, usually before reaching sexual maturity. However, their sperm can be used successfully for in vitro fertilization (IVF).

Of note, The Jackson Laboratory offers a series of MeCP2-huExon4 mutant mouse lines:
Mecp2 huExon4*R270X as Stock No. 037255
Mecp2 huExon4*T158M as Stock No. 039182
Mecp2 huExon4*R306C as Stock No. 039183

As controls, we recommend B6-MeCP2-huExon4 mice (Stock No. 037256) or Mecp2-huExon3/4 mice (Stock No. 040861), which each carry a humanized region but lack the RTT-associated mutations.

Development

The Mecp2^em4Gfng (Mecp2 huExon4*T158M) allele was generated by Dr. Guoping Feng and Dr. Chenjie Shen at MIT using cytosine base editor (CBE) on a Mecp2 huExon4 mouse background (Stock No. 037256). The ACG to ATG mutation at position T158 of MeCP2 was introduced, resulting in a threonine-to-methionine (T158M) amino acid substitution through C-to-T deamination mediated by CBE. CBE mRNA and guide RNA were mixed and injected into the cytoplasm of fertilized homozygous humanized Mecp2 huExon4 zygotes. Embryos were then transferred to pseudopregnant females, and correctly targeted pups were bred to humanized Mecp2 huExon4 mice for germline transmission. The donating laboratory reported maintaining the colony by backcrossing Mecp2 huExon4*T158M to the C57BL/6J genetic background for at least 10 generations. The donating laboratory reported maintaining their colony on the C57BL/6J genetic background (Stock No. 000664). In 2024, sperm from hemizygous males were sent to The Jackson Laboratory where the strain was rederived via IVF using C57BL/6J inbred females. Subsequently, the strain was cryopreserved as hemizygous sperm.

Allele

Symbol: Mecp2^{em4(MECP2*)Gfng}
Name: endonuclease-mediated mutation 4, Guoping Feng
MGI accession ID: MGI:8172563
Generation method: Endonuclease-mediated
Attributes: Inserted expressed sequence; Humanized sequence
Synonyms: Mecp2 huExon4*T158M
Marker symbol: Mecp2
Marker name: methyl CpG binding protein 2
Marker synonyms: 1500041B07Rik; AUTSX3; D630021H01Rik; Mbd5; MECP2_e1; MRX16; MRX79; MRXS13; MRXSL; PPMX; RS; RTS; RTT; WBP10
Chromosome: X
Strain of origin: C57BL/6J
Molecular note: Using CRISPR technology, the ACG to ATG mutation at position T158 of MeCP2 was introduced in homozygous zygote with Mecp2^{em2(MECP2)Gfng} alleles, resulting in a threonine-to-methionine (T158M) amino acid substitution.