Molecular characterization of a hamster oviduct-specific glycoprotein

There is growing evidence that the oviduct is not a passive conduit for gamete and embryo transport but serves a function for the gametes and/or embryos. The oviductal epithelium secretes one or more specific glycoproteins that associate with the egg after ovulation. Several published reports including our preliminary studies have suggested that the egg-associating glycoprotein(s) from the oviduct exists in several mammalian species including golden hamster. However, little or almost no biochemical characterization of the hamster oviduct-specific glycoprotein (HOGP) has been reported. To analyze the molecular structure of the HOGP in detail, we have attempted molecular cloning of cDNA corresponding to HOGP. A cDNA library constructed from the hamster oviduct in the phage vector lambda ZAPII was screened with digoxigenin-labeled, baboon oviduct-specific glycoprotein cDNA as the probe. A single positive clone was isolated, and the nucleotide sequence of the isolated cDNA was determined. Rapid amplification of cDNA end was carried out to obtain a proximal 5' cDNA end of the clone. The cDNA clone consisted of 2387 bp, and the coding region contained 2013 bp translating to 671 amino acids. The amino acid sequence deduced from the cDNA sequence confirmed the chemically determined NH2-terminal sequence of a HOGP and suggested that the derived amino acid sequence contained a signal peptide region (21 amino acids) and 650 amino acids (70,890 daltons) of the mature form of the HOGP region. The amino acid sequence of HOGP appeared to have eight potential N-glycosylation sites. Northern blot analysis revealed that a single message of approximately 2.5 kb was present in oviductal RNA but not in the RNA of several other hamster tissues. The HOGP showed high amino acid sequence homology with baboon, bovine, and human oviduct-specific glycoprotein. These results demonstrate that an oviduct-specific glycoprotein homologue gene exists in various mammalian species including rodent.