Analysis of mRNA Levels for the MHC Class I-Like Molecules CD1 and FcRn in Preimplantation Mouse Embryos

PROBLEM: Major histocompatibility complex (MHC) antigens expressed on preimplantation embryos are important for the control of development, reproduction, and allo‐recognition of the embryo by the mother. Four types of MHC class I and MHC class I‐like antigens have recently been defined: class Ia, class Ib, class Ic, and class Id, based on their similar three‐dimensional protein structures. Class Ia and class Ib antigens are encoded in the MHC, whereas class Ic and class Id antigens are encoded by genes on other chromosomes. Both class Ia and class Ib MHC antigens are expressed on preimplantation mouse embryos. The function of the class Ia antigens on embryos is unknown, but the function of one class Ib antigen, Qa‐2, the product of the Ped gene, has been found to control the rate of early cleavage division and subsequent embryo survival. The expression of class Ic and class Id antigens on preimplantation embryos has not yet been evaluated. In the present study, we report the analysis of mRNA expression of two class Id genes, CD1 and FcRn, in preimplantation mouse embryos. METHOD OF STUDY: A reverse transcription‐polymerase chain reaction (RT‐PCR) assay was performed to analyze mRNA levels for CD1 and FcRn in 1‐cell, 2‐cell, 8‐cell, and blastocyst stage embryos from C57BL/6 mice. RESULTS: No expression of CD1 mRNA was found in any of the preimplantation embryos tested. As a by‐product of this study, we found a mistake in the published sequence of the mouse CD1 gene: nucleotide 746 in the cDNA is a G not a C. This base change is in a site recognized by the restriction enzyme PstI, thereby eliminating a PstI cleavage site. Expression of mRNA for FcRn was found in all preimplantation stages tested. Higher levels of mRNA for FcRn were detectable in 2‐cell and 8‐cell embryos compared to 1‐cell and blastocyst stage embryos. CONCLUSION: This study shows that mRNA for FcRn but not for CD1 is found in preimplantation mouse embryos.