THE HLA-G GENE IS EXPRESSED AT A LOW MESSENGER-RNA LEVEL IN DIFFERENTHUMAN-CELLS AND TISSUES

Recently, HLA-G transgenic mice were shown to exhibit transgene transc ription in several extraembryonic tissues. To determine whether HLA-G mRNAs are also expressed in other human tissues, we have undertaken No rthern blot and RT-PCR assays using HLA-G locus-specific probe and pri mers. These studies demonstrate that the HLA-G gene is transcribed in a variety of cells and adult tissues obtained from different individua ls (peripheral blood leukocytes, placenta, skin, spleen, thymus, prost ate, testicle, ovary, small intestine, colon, heart, brain, lung, live r, and kidney), as well as in fetal tissues (heart, lung, liver, and k idney). The HLA-G mRNA level observed in most tissues is orders of mag nitude lower than the level of classic class I genes in the same tissu es. RT-PCR studies have demonstrated that alternative splicing of the HLA-G primary transcript is different from tissue to tissue and could be regulated in a tissue-specific fashion. Sequencing of keratinocyte transcripts has confirmed previous observations: (a) three different a lternative splicing transcripts are produced (a full-length transcript , an mRNA lacking exon 3, and a transcript devoid of exon S and 4) and (b) HLA-G polymorphism is limited in the coding regions. In view of t his wide HLA-G tissue distribution, a new hypothesis dealing with poss ible HLA-G function is proposed.