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The Retinol-Binding Protein of the Expanding Pig Blastocyst: Molecular Cloning and Expression in Trophectoderm and Embryonic Disc

Department of Animal Science, University of Missouri Columbia, Missouri 65211
Department of Animal Science, University of Tennessee Knoxville, Tennessee 37901

Address requests for reprints to: Dr. R. M. Roberts, Animal Sciences Department, University of Missouri, 158 Animal Science Department, Columbia, Missouri 65211.

Abstract

Retinot-binding protein (RBP) is a major secretory product of the porcine conceptus. Using an oligonucleotide probe corresponding to a highly conserved region of all known mammalian RBP, we have isolated an apparently full-length cDNA clone for porcine conceptus RBP from a cDNA library constructed from pig conceptuses collected between days 13–17 of pregnancy. The cDNA was 937 basepairs in length and coded for a protein whose inferred amino-terminal sequence was identical to that reported for both porcine conceptus RBP and porcine serum RBP. Its length was consistent with the size (1 kilobase) of the RBP message in porcine conceptuses. Porcine conceptus RBP and human serum RBP share 91% amino acid sequence identity. The inferred differences in sequence were evenly distributed throughout the length of the polypeptide. RBP mRNA was detectable within the trophoblast of day 11 porcine conceptuses by in situ hybridization with a 618-basepair ³⁵S-labeled probe corresponding to the 3' end of porcine RBP. Silver grain density was distributed relatively uniformly over the trophoblast and the inner cell mass. Western blot analysis of conceptus culture medium demonstrated that the conceptuses of cattle (on day 19) and sheep (on day 15) as well as pigs secrete RBP during early pregnancy. Secretion of large quantities of RBP by the trophoblast of preimplantation pig conceptuses suggests important roles for vitamin A and RBP near the time of conceptus elongation.

FOOTNOTES

This work was supported by USDA Grant 89–37240–4586. Funds for construction of the porcine conceptus cDNA library were provided through USDA Grant CRCR 88–01288, the Tennessee Agricultural Experiment Station, and the College of Veterinary Medicine, Center of Excellence. This is journal paper 11,391 from the University of Missouri Agriculture Experiment Station. The porcine RB cDNA sequence has been assigned the Genbank accession number M68860.

Received for publication July 26, 1991. Revision received July 18, 1991. Accepted for publication July 26, 1991.

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