A new member of the hormonally regulated rodent submaxillary gland glycoprotein gene family: cDNA cloning and tissue specific expression.

Polymerase chain reaction was used to amplify and identify two related rat submaxillary gland glycoprotein (rSMGGP and rSMGGP1) cDNAs. They were 489 bp and 594 bp long respectively. The shorter cDNA (rSMGGP) was identical to the previously published rat spot-I protein. The longer cDNA (rSMGGP1) had an additional (117 bp) unique nucleotide sequence in the 3' coding region, and the overall homology between the two cDNAs was 78%. rSMGGP also had a 68% homology to the mouse submaxillary gland glycoprotein (mSMGGP) cDNA. The predicted translated product of rSMGGP1 was 130 amino acids long, 39 amino acids longer than the rSMGGP. The region of greatest diversity between the putative peptides of the two rat cDNAs and the mouse cDNA was in the carboxy terminus. Northern blot analysis, using both rat cDNAs as probes, showed hybridization to an mRNA transcript (650 bases) in the submaxillary and lacrimal gland of the normal adult male and female rat. A larger transcript (approximately 700 bases) was induced under conditions of altered hormonal profiles: hypophysectomy, pregnancy/lactation, and castration. Dihydrotestosterone administration inhibited expression of the two transcripts in both the lacrimal and submaxillary glands of male and female rats. The labelled 117 bp DNA fragment unique to the rSMGGP1 cDNA hybridized only to the 700 base transcript in the rat lacrimal and submaxillary gland suggesting that differential exon usage produces the two variant mRNAs. The regulation of the SMGGP gene expression may provide yet another useful model for studying the mechanism of down-regulation of genes by androgen and the identification of tissue specific factors in the lacrimal and submaxillary gland.