Efficient male and female germline transmission of a human chromosomal vector in mice

A small accessory chromosome that was mitotically stable in human fibroblas ts was transferred into the hprt(-) hamster cell line CH and developed as a human chromosomal vector (HCV) by the introduction of a selectable marker and the 3' end of an HPRT minigene preceded by a loxP sequence. This HCV is stably maintained in the hamster cell line. It consists mainly of alphoid sequences of human chromosome 20 and a Fragment of human chromosome region lp22, containing the tissue Factor gene F3. The vector has an active centro mere, and telomere sequences are lacking. By transfecting a plasmid contain ing the 5' end of HPRT and a Cre-encoding plasmid into the HCV+ hamster cel l line, the HPRT minigene was reconstituted by Cre-mediated recombination a nd expressed by the cells. The HCV was then transferred to male mouse R1-ES cells and it did segregate properly. Chimeras were generated containing th e HCV as an independent chromosome in a proportion of the cells. Part of th e male and female offspring of the chimeras did contain the HCV. The HCV+ F l animals harbored the extra chromosome in >80% of the cells. The HCV was p resent as an independent chromosome with an active centromere and the human F3 gene was expressed from the HCV in a human-tissue-specific manner. Both male and female Fl mice did transmit the HCV to F2 offspring as an indepen dent chromosome with properties similar to the original vector. This modifi ed small accessory chromosome, thus, shows the properties of a useful chrom osomal vector: It segregates stably as an independent chromosome, sequences can be inserted in a controlled way and are expressed from the vector, and the HCV is transmitted through the male and female germline in mice.