Murine stem cell virus long terminal repeat (MSCV LTR) promoter
Retroviral LTR promoter engineered from a PCC4-cell-passaged myeloproliferative sarcoma virus (PCMV) enhancer combined with a dl-587rev-derived leader sequence, giving murine stem cell virus (MSCV) LTR activity in undifferentiated embryonic and hematopoietic cells that the parental PCMV/Moloney LTR lacks. A standard promoter for retroviral and lentiviral transgene delivery to stem and progenitor cells.
Origin: Engineered from PCMV murine retroviral LTR (dl-587rev leader replacement)
Characteristics
Hybrid retroviral LTR in which the PCMV 5' untranslated leader (positions +34 to +564) is replaced by the equivalent region from the dl-587rev retrovirus. This substitution raised G418-resistant colony formation in ES cell lines CCE and D3 by roughly 1,000-fold over parental PCMV, from an ES/NIH-3T3 neoR ratio of 2.5-7.5x10^-4 to 0.1-0.7, while leaving expression in fibroblasts largely unchanged; the PCMV enhancer itself remains functional in both cell types.
Applications: Used to drive transgene and selectable-marker expression from retroviral and lentiviral vectors in murine embryonic stem cells, embryonal carcinoma cells, and hematopoietic stem/progenitor cells, including bone marrow transplantation studies where expression persists in engrafted T and B lymphocyte and myeloid progeny.
Limitations: Retains the murine leukemia virus enhancer architecture and is therefore subject to the same class of position-dependent variegation and partial silencing seen in unmodified Moloney LTRs, though substantially less than the parental PCMV/Moloney LTR in pluripotent cells. Its viral enhancer raises genotoxicity/insertional-mutagenesis concerns relative to weaker cellular promoters, a consideration for therapeutic vector design.