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AMINO ACID TRANSPORT-RELATED PROTEINS APPARENTLY EXPRESSED IN PREIMPLANTATION MOUSE BLASTOCYSTS LIKELY ALSO ARE EXPRESSED IN EARLY HUMAN EMBRYOS.
Van Winkle, Lon1, Adjaye, James2, Campione, Allan1, 1 2
ABSTRACT- Nonessential amino acid transport benefits mouse embryo development until about the 8-cell stage, whereas essential amino acid transport improves preimplantation development subsequent to this stage (reviewed by Van Winkle, 2001, Biol. Reprod. 64, 1-12). Human embryos also are more viable when they develop in the presence of amino acids, but the mechanisms by which they transport amino acids are only now emerging. Specific primers and the polymerase chain reaction (or nested PCR) were used to amplify sequences in human embryo cDNA libraries (unfertilized oocytes, 2-, 4-, 8-cell and blastocyst stage embryos. Adjaye et al. 1999, GENE 237, 373-383) encoding amino acid transport-related proteins that are likely expressed in mouse embryos. Sequences encoding the transport-related proteins, system A amino acid transporter 1 (ATA1), system bo,+ amino acid transporter (bo,+AT), system y+L amino acid transporter 2 (y+LAT2), and 4F2hc (CD98), each were present in both human and mouse blastocyst libraries. Expression of these sequences likely underlies dramatic regulatory changes in the systems' transport activities near the time of implantation. System A expression is known to be developmentally regulated and localized to the inner cell masses of mouse blastocysts (op cit). In contrast, bo,+AT, y+LAT2, and their accessory protein, CD98, likely are expressed in the trophectoderm to increase uptake especially of leucine, tryptophan and arginine. Such uptake provides substrates for polyamine, nitric oxide and protein synthesis, and it likely helps to regulate the rate of protein synthesis via the target of rapamycin pathway. Concomitant T-cell tryptophan deprivation owing to tryptophan uptake and metabolism by blastocysts at sites of implantation may also help to prevent their immunologic rejection (op cit).
KEY WORDS: amino acid transport, preimplantation development, human/mouse embryo cDNA libraries, ovum implantation
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