EXPRESSION OF THE HUMAN DP-71 (APO-DYSTROPHIN-1) GENE FROM A 760-KB DMD-YAC TRANSFERRED TO MOUSE CELLS

A 760-kb YAC was constructed by homologous recombination in yeast, con taining the genes located in the distal portion of the DMD gene. The Y AC was introduced in mouse LA-9 cells by PEG-mediated cell fusion. One transformant accommodated an intact DMD-YAC, i.e, a full copy of the DMD internal Dp 116, Dp 71 and Dp 40 genes (apo-dystrophin-2, -1 and - 3, respectively). We have studied the expression of the various gene p roducts derived from the introduced DMD-YAC. RT-PCR revealed expressio n of human Dp 71 but not of Dp 116 or Dp 40. Remarkably, differences w ere observed in processing of the 3' region of the endogenous mouse an d the human transcripts, due to different splicing of exons 71 (absent in human and present in mouse transcript) and 78 (present in human an d absent in mouse transcript). The splicing pattern of the human trans cript is the same as that of the major Dp 71 (apo-dystrophin-l) produc t in human blood. The observed splicing differences may be caused by e ither species-specific exon use and/or by cis-acting factors, e.g. the upstream transcript composition, because we have no evidence for endo genous Dp 71 expression.