Extraembryonic expression of the human MHC class I gene HLA-G in transgenic mice. Evidence for a positive regulatory region located 1 kilobase 5' to the start site of transcription.
Trophoblast, the only fetal tissue in direct contact with maternal cells, fails to express the polymorphic HLA class I molecules HLA-A and -B, but does express the nonpolymorphic class I molecule HLA-G. It is thought that HLA-G may provide some of the functions of a class I molecule without stimulating maternal immune rejection of the fetal semiallograft. As a first step in identifying the cis-acting DNA regulatory elements involved in the control of class I expression by extraembryonic tissue, several types of transgenic mice were produced. Two HLA-G genomic fragments were used, 5.7 and 6.0 kb in length. These included the entire HLA-G coding region, 1 kb of 3' flanking sequence, and 1.2 or 1.4 kb of 5' flanking sequence, respectively. A hybrid transgene, HLA-A2/G, was produced by replacing the 5' flanking sequence, first exon, and early first intron of HLA-G with the corresponding elements of HLA-A. Comparison of transgene mRNA expression patterns seen in HLA-A2/G and HLA-G transgenic mice suggests that 5' flanking sequences are largely responsible for the differing patterns of expression typical of the classical class I and HLA-G genes. Studies comparing the extraembryonic HLA-G expression levels of founder embryos transgenic for either the 5.7- or 6.0-kb HLA-G transgene showed that the 6.0-kb transgene directed HLA-G expression far more efficiently than did the 5.7-kb HLA-G transgene, producing extraembryonic HLA-G mRNA levels similar to those seen in human extraembryonic tissues. The results of these studies suggest that the 250-bp fragment present at the extreme 5' end of the 6.0-kb HLA-G transgene and absent from the 5.7-kb HLA-G transgene contains an important positive regulatory element. This 250-bp fragment lies further upstream than any of the previously documented class I regulatory regions and may function as a locus control region.
Schmidt
C M
CM
Institute of Human Genetics, University of Minnesota, Minneapolis 55455.
Ehlenfeldt
R G
RG
Athanasiou
M C
MC
Duvick
L A
LA
Heinrichs
H
H
David
C S
CS
Orr
H T
HT
D000818:Animals; D001483:Base Sequence; D004622:Embryo, Mammalian / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D005805:Genes, MHC Class I; D005809:Genes, Regulator; D006680:HLA Antigens / Q000235:genetics*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis; D014158:Transcription, Genetic
D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D012333:RNA, Messenger