THE HUMAN BETA-GLOBIN LOCUS INTRODUCED BY YAC TRANSFER EXHIBITS A SPECIFIC AND REPRODUCIBLE PATTERN OF DEVELOPMENTAL REGULATION IN TRANSGENIC MICE

The human beta globin locus spans an 80-kb chromosomal region encompas sing both the five expressed globin genes and the cis-acting elements that direct their stage-specific expression during ontogeny. Sequences proximal to the genes and in the locus control region, 60 kb upstream of the adult beta globin gene, are required for developmental regulat ion. Transgenic studies have shown that altering the structural organi zation of the locus disrupts the normal pattern of globin gene regulat ion Procedures for introducing yeast artificial chromosomes (YACs) con taining large genetic loci now make it possible to define the sequence s required for stage-restricted gene expression in constructs that pre serve the integrity of the beta globin locus. We demonstrate that inde pendent YAC transgenic lines exhibit remarkably similar patterns of gl obin gene expression during development. The switch from gamma to beta globin predominant expression occurs between day 11.5 and 12.5 of ges tation, with no more than twofold differences in human beta globin mRN A levels between lines. Human beta globin mRNA levels were twofold to fourfold lower than that of mouse beta(maj), revealing potentially sig nificant differences in the regulatory sequences of the two loci. Thes e findings provide an important basis for studying regulatory elements within the beta globin locus. (C) 1997 by The American Society of Hem atology.