Temporal and spatial expression of HLA-G messenger RNA in extraembryonic tissues of transgenic mice.

HLA-G, a nonclassical class I molecule, is expressed by trophoblasts, the only fetal cells in direct contact with maternal tissue. Results of previous experiments suggested that a 244-bp region located over 1 kb 5' from exon 1 is critical for extraembryonic expression of HLA-G in transgenic mice. We report here the production of HLA-G transgenic lines with a 6.0-kb HLA-G transgene that includes the 244-bp region. These lines exhibit copy number-dependent and developmentally appropriate transgene expression. One HLA-G transgenic line, G.3.2, exhibits extraembryonic HLA-G mRNA expression levels similar to those seen in human extraembryonic tissues. Studies of the cell-type-specific localization of HLA-G mRNA in placentas from the G.3.2 HLA-G transgenic mouse line show predominant localization of the HLA-G message in the spongiotrophoblast layer. This layer is in a similar anatomic location to the HLA-G-expressing human cytotrophoblast shell. The G.3.2 HLA-G transgenic mouse line should serve as an appropriate model for the study of HLA-G function at the maternal-fetal interface.