Search

Two lines of transgenic mice carrying a normal 40-kb KpnI β-globin cluster transgene lacking the locus control region (LCR) were analyzed for the expression of human γ- and β-globin genes during mouse development. After RIMase protection assays, the ratios of human Gγ-, Aγ-, or β-mRNAs relative to endogenous mouse ζ, + αmRNAs were obtained for each stage of development. The two γ transgenes were expressed in day-11.5 blood (embryonic stage) and day-13.5 blood (early fetal stage), but their expression was markedly decreased by day 16.5 of fetal life. Expression of the β transgene was essentially absent at day 13.5, appeared at a low level by day 16.5, and was maximal by day 18.5, reaching a level similar to that observed in adult mice. Therefore, developmentally regulated expression of the human γ- and β-globin transgenes was obtained in the absence of the LCR. The relative expression of human γ- and β-globin genes was also examined in mice carrying 40-kb KpnI β-cluster transgenes with two different base substitutions associated with nondeletion forms of hereditary persistence of fetal hemoglobin (HPFH), -202 C→G Gγ HPFH and -117 G→A Aγ HPFH. The ratio of Gγ- to β-globin transcripts was markedly increased in red blood cells of adult mice from three different lines carrying the transgene with the -202 Gγ HPFH mutation. This result confirms our previous preliminary results (Tanaka et al: Ann NY Acad Sci, 612:167,1990) indicating that the -202 Gγ HPFH phenotype was reproduced in transgenic mice. The relatively low levels of Gγ-mRNA expression in adult mice carrying the non-HPFH transgene excludes a major influence of the 3' β-globin enhancer, present upstream of the Gγ gene because of the tandem repeat insertion, as a factor in the persistent Gγ gene expression observed in blood of adult mice carrying the -202 Gγ HPFH transgene. This conclusion is also supported by the fact that, in mice carrying the -117 Aγ HPFH transgene, Gγ-globin mRNA was detected in blood of adult animals only at low levels similar to that observed in the non-HPFH lines. However, the Aγ-HPFH phenotype was not reproduced in the transgenic lines carrying the -117Aγ HPFH mice.