Rr96^tm2Litt

The core region of a Cd4 cis-regulatory element that silences expression of the endogenous locus during T cell development (S4) was deleted from intron 1 via homologous recombination of a targeting construct lacking nucleotides 167 through 257. A single loxP site was left upstream of the deleted region, however analysis of a control allele indicated that the loxP site did not affect normal expression. Flow cytometric analysis of peripheral blood lymphocytes obtained from mutant mice showed no silencing of Cd4 expression. (J:80576)