RESUMEN
A shuttle plasmid pMCLacI/neo with two copies of LacI was integrated into mouse genome and a novel system which could detect in vivo mutation of both expression and silence genes was constructed, enabling the comparative analysis of their mutation spectra and mutant frequencies. 486 fertilized eggs from C57BL/6 mice with microinjected pMCLacI/neo plasmid were transferred into oviducts of 18 pseudo-pregnant mice, and 32 alive offsprings were screened and identified by using PCR and Southern blotting. Genomes of 5 mice had pMCLacI/neo plasmid integrated, as verified by Southern blot after the PCR screening. Only one of the two LacI in pMCLacI/neo was in expression state; and this established a model, that the status in vivo of both gene expression and silencing could be simulated. This kind of mice might be used as a novel bifunctional mutation detection system in vivo.