Search for a human homologue of the mouse Ped gene

The Fed gene influences the rate of cleavage division of preimplantation mo use embryos and subsequent embryonic survival. The mouse Fed gene product i s a major histocompatibility complex (MHC) class Ib protein called Qa-2. St udies from many human in-vitro fertilization (IVF) clinics suggest that the mouse Fed gene has a human homologue because embryos fertilized at the sam e time have different cleavage rates, and those embryos that cleave at a fa ster rate are more likely to result in a viable pregnancy. Candidates for t he human homologue of the mouse Fed gene include the MHC class Ib genes HLA -E, HLA-F, and HLA-G. The presence of mRNA for these three genes was tested in 108 spare day 3 human preimplantation embryos from 25 couples by using reverse transcription-polymerase chain reaction (RT-PCR). Of the 86 embryos tested for HLA-E mRNA, 72 were positive (84%), and of the 88 embryos teste d for HLA-G mRNA, 39 were positive (44%). None of the 17 embryos tested for HLA-F mRNA were positive (0%). Studies of expression of HLA-G protein were undertaken to ascertain whether HLA-G was attached to the cell membrane vi a a glycosylphosphatidylinositol (GPI) linkage similar to that found in Qa- 2 protein. Treatment of JEG-3 cells, an HLA-G expressing cell line, with ph ospholipase C did not result in removal of HLA-G showing that HLA-G, unlike Qa-2, is not GPI linked to the cell surface. The pros and cons of HLA-E, H LA-F, and HLA-G as candidates for the human Fed gene are discussed.