Regulation of Ped gene expression by TAP protein

The Fed (Preimplantation embryo development) gene regulates fast or slow cl eavage of preimplantation mouse embryos and their subsequent survival. The protein product of the Fed gene is the major histocompatibility complex (MH C) class Ib protein Qa-2. MHC class I expression on the cell surface requir es the assembly within the endoplasmic reticulum (ER) of an alpha heavy cha in, a beta(2) microglobulin light chain, and a small peptide. Small peptide s are primarily produced in the cytosol by the ubiquitin-proteasome pathway and then are transported into the ER by the transporter associated with an tigen processing (TAP) protein. However, some peptides can bind to MHC clas s I heavy chains in a TAP-independent manner. In this study, we assessed wh ether TAP protein regulates Qa-2 expression on the cell surface of preimpla ntation mouse embryos thereby influencing the FED phenotype of the embryos. We chose Tap 1 knockout mice and their control mice (B6.129) as our experi mental system. We analyzed Qa-2 mRNA expression by RT-PCR, total Qa-2 prote in expression by Western blotting, and cell surface Qa-2 protein expression by Immuno-PCR in preimplantation embryos of both Tap 1 knockout mice and c ontrol mice. Then we determined the FED phenotype of both Tap 1 knockout mo use embryos and control mouse embryos. The results showed that Qa-2 express ion on the cell surface of preimplantation embryos is dependent on TAP prot ein, and that Qa-2 expression on the cell surface is required for expressio n of the fast FED phenotype. (C) 2000 Elsevier Science Ireland Ltd. All rig hts reserved.