Differential Expression of Mouse β/Goat β^c, Mouse β/Goat β^F, and Mouse β/Goat ε^II Hybrid Globin Genes in Murine Erythroleukemia Cells

Abstract

We assembled three hybrid β-globin genes by fusing the mouse β-major promoter and initial transcribed region to one of three goat β-like globin gene bodies: β^c (preadult), β^F (fetal), or ε^II (embryonic). Thymidine kinase (tk)-deficient murine erythroleukemia (MEL) cells were cotransformed with one of these constructs and a separate plasmid bearing the tk gene. Half of the 24 cell lines containing either the mouse β/goat β^c or mouse β/goat β^F genes expressed the transferred genes at significant levels; in many cases the hybrid genes were, like the endogenous β-globin genes, inducible with dimethyl sulfoxide. We obtained 13 cell lines containing the mouse β/goat ε^II hybrid gene, 6 of which were cotransfected with a mouse β/human β fusion gene known to function in MEL cells. In contrast to the results with the other fusion genes, the mouse β/goat ε^II hybrid was very poorly expressed: in two separate experiments, 0 of 13 and 2 of 13 lines showed significant mouse β/goat ε^II RNA levels after induction. In all these lines the endogenous mouse β and cotransfected mouse β/human β genes were expressed. As an initial test of possible reasons for the inactivity of the mouse β/goat ε^II hybrid, we recloned this fusion gene into a tk-bearing plasmid, adjacent to the tk gene. Of 12 cell lines transformed with this plasmid, 11 produced mouse β/goat ε^II RNA; in 6 cases the expression was both strong and dimethyl sulfoxide inducible.