PROPERTIES OF THE MOUSE ALPHA-GLOBIN HS-26 - RELATIONSHIP TO HS-40, THE MAJOR ENHANCER OF HUMAN ALPHA-GLOBIN GENE-EXPRESSION

HS-26, the mouse homologue of HS-40, is the major regulatory element o f the mouse alpha-globin gene locus. Like HS-40, HS-26 is located with in an intron of a house-keeping gene; comparison of the nucleotide seq uences of HS-26 and HS-40 reveals conservation of the sequences and po sitions of several DNA binding motifs in the 5' regions of both elemen ts (3 GATA, 2 NFE-2, and 1 CACCC sites) and the absence in HS-26 of th ree CACCC sites and one GATA site that are present in the 3' region of HS-40, suggesting that the two elements might not be identical. We re port here that when HS-26 is linked to a 1.5 kb PstI human alpha-globi n gene fragment, it has a weak enhancer activity in induced MEL cells and in transgenic embryos, and it does not have any detectable activit y in adult transgenic mice. This suggests that HS-26 does not have Loc us Control Region (LCR) activity but can act as an enhancer during the embryonic life when integrated at a permissive locus. To further test the importance of HS-26 at its natural locus, we have generated embry onic stem cells and chimeric animals in which 350 bp containing HS-26 have been replaced by a neomycin resistance gene by homologous recombi nation. The sizes of the chimeras' red cells were then estimated by me asuring forward scattering on a FacsScan apparatus in hypotonic condit ions. This revealed that a fraction of the chimeric animals' red cells were smaller than normal mouse red cells and were very similar to cel ls from mice heterozygous for alpha-thalassemia. Density gradient anal ysis also suggested the presence of thalassemic cells. These results i ndicated that despite its lack of LCR activity, HS-26 is important for the regulation of the mouse alpha-globin gene locus. (C) 1997 Wiley-L iss, Inc.