In order to selectively inactivate genes in a tissue-specific manner many laboratories have developed Cre transgenic mouse strains in which the Cre recombinase is expressed under the control of a tissue-specific promoter.
The CD4-Cre Microinjected Mouse uses the mouse Cd4 promoter/enhancer/silencer, which first allows expression of CD4 as thymocytes enter the double positive stage.
The silencer region extinguishes transgene expression at the double negative stage as well as in CD4-CD8+ mature thymocytes.
This transgenic mouse shows a high degree of expression of the transgene in the thymus and the recombinase has been shown to bring about the selective deletion of genes flanked by loxP targeting sequences in most thymocytes at the double positive stage.
The mice were again made homozygous for the transgene by intracrossing followed by selection using test crosses to outbred mice.
This model has replaced model 4214 - it has been further backcrossed to C57BL/6 for 9 generations.
Origin: The Cd4-Cre Transgenic mouse was originally developed in the laboratory of Dr. Chris Wilson at the University of Washington. The Cd4-Cre construct was created by replacing the the lck proximal promoter of a construct used to make a Lck-Cre Transgenic mouse (Taconic line 4197) with the mouse Cd4 promoter/enhancer/silencer, which was provided by Dr. Dan Littman and Dr. Nigel Killeen. The original Lck-Cre mouse, which was generated in the laboratories of Wilson and Perlmutter, was designed by engineering a nuclear localization signal and optimum eukaryotic translation start site at the 5' end of Cre and inserting this downstream of the Lck proximal promoter. The Cd4-Cre mouse was created by pronuclear injection of the Cd4-Cre construct into B6D2F2 fertilized eggs. The founder line was first crossed three times to the C57BL/6J strain, and then bred to produce homozygotes. Later they were crossed to mice of a mixed B6;129Sv/J background. The resultant STOCK-Tg(Cd4-Cre) mice were screened for H-2 expression and offspring homozygous for H-2b were selected for breeding. Homozygous mice maintained on this mixed background were then transferred to the NIAID repository at Taconic for embryo rederivation by crossing with C57BL/6NTac mice. The ET derived mice were crossed one additional generation to C57BL/6NAi mice. PCR analysis was used to confirm that the derived pups carried the Cd4-Cre transgene. These pups were then backcrossed to C57BL/6NTac from N4 to N9. The line was then intracrossed to homozygosity.
Lee PP, Fitzpatrick DR, Beard C, Jessup HK, Lehar S, Makar KW, Perez- Melgosa M, Sweetser MT, Schlissel MS, Nguyen S, Cherry SR, Tsai JH, Tucker SM, Weaver WM, Kelso A, Jaenisch J and Wilson CB. A critical role for Dnmt1 and DNA methylation in T cell development, function and survival. Immunity Nov. 2001,15(5) 763-74