Igk-J^tm1(CD4*)Mss

The Igk-J cluster has two promoter/transcription start sites upstream of the cluster that generate sterile (i.e. germline) transcripts. The proximal element is 100 bp upstream of Igk-J1 and the distal element is about 3.5 kb upstream of Igk-J1. The distal element was targeted by the following construct. An AvrII restriction site was placed 250 bp downstream of the distal transcription start site and all the ATG codons between the start site and AvrII site were mutated to alternate codons. A human CD4 cDNA lacking the 33 C-terminal amino acids (signaling domain) and possessing a Y43I mutation (to abolish interaction with MHC class II) along with a SV40 intron/polyA and a floxed neomycin resistance gene were cloned into the AvrII site. This construct was introduced into ES cells containing a Prm1-cre transgene and male chimeric mice were generated. Expression of the cre transgene in male germline cells removed the neo cassette. The Prm1-cre transgene was bred out of the resulting mice. Surface expression of the human CD4 was detected on almost all pre-B cells in the bone marrow of heterozygote mice and in about half of the splenic B cells. (J:143876)