DEVELOPMENTAL EXPRESSION OF H-2K MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I TRANSGENES REQUIRES THE PRESENCE OF PROXIMAL INTRONS

The pattern of expression of the H-2K major histocompatibility complex (MHC) class I gene is complex. During embryonic development H-2K mRNA , detectable from midgestation, is poorly expressed, In the adult, H-2 K expression is nearly ubiquitous but transcriptional regulation occur s leading to different mRNA levels in the different organs of the mous e. In vitro studies have shown that most of the regulatory elements co ntrolling H-2K gene transcription are located in the 5' region of the gene. However, using fusion transgenes in which reporter genes were un der the control of 2 kb of H-2K 5' regulatory region, we have previous ly shown that this region was not sufficient to ensure correct develop mental transgene expression, By contrast, a native 9.25 kb H-2K transg ene was expressed appropriately both in the adult and in the embryo, I n order to localise more precisely the cis-acting regulatory sequences involved in H-2K developmental expression, we have now constructed ne w transgenic lines containing H-2K(b) transgenes that were deleted fro m specific parts of the H-2K(b) gene. We show that deletion of either the H-2K 3' flanking region or the 5 (out of 7) distal introns results in an expression of the transgenes which is similar to that of the en dogenous H-2K gene, both in the adult and during embryonic development . By contrast, deletion of all the introns or of the two proximal ones abrogates H-2K transgene expression. Our data reveal the complexity o f H-2K regulation and highlight the crucial role of proximal introns i n H-2K expression in the living organism. (C) 1995 Wiley-Liss, Inc.