Analysis of control elements for position-independent expression of human alpha-lactalbumin YAC

A major problem in the production of transgenic animal bioreactors using mi croinjections is the low production rate of high-expressing transgenic anim als due to the position effect. We previously reported that transgenic rats carrying the 210 kb yeast artificial chromosome (YAC) including the human alpha-lactalbumin gene express the transgene in a position-independent mann er. The 210 hb YAC was thought to have all the elements necessary for posit ion-independent expression. In this paper, we constructed fragmented YAC cl ones and a cosmid clone, and produced transgenic rats to analyze these elem ents. Transgenic rats with both the 50 kb upstream and downstream regions o f the alpha-lactalbumin gene had position-independent expression. Transgeni c rats with the 20 kb upstream and downstream regions, however, had positio n-dependent expression, Therefore, all the elements necessary for position- independent expression are thought to be located in the 50 kb upstream to 5 0 hb downstream region of the alpha-lactalbumin gene. Furthermore, we repla ced the human alpha-lactalbumin promoter with the bovine alpha S1-casein pr omoter in the 210 kb YAC and produced transgenic rats. Position-dependent e xpression was observed. The elements required for position-independent expr ession of the bovine alpha S1-casein gene are different from those required for the human alpha-lactalbumin gene, despite the fact that the two genes have the same tissue and developmental specificity. (C) 1999 Wiley-Liss, In c.