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) wa s identical to the previously published rat spot-1 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 cDNA s was 78%. rSMGGP also had a 68% homology to the mouse submaxillary gl and glycoprotein (mSMGGP) cDNA. The predicted translated product of rS MGGP1 was 130 amino acids long, 39 amino acids longer than the rSMGGP. The region of greatest diversify between the putative peptides of the two rat cDNAs and the mouse cDNA was in the carboxy terminus. Norther n blot analysis, using both rat cDNAs as probes, showed hybridization to an mRNA transcript (650 bases) in the submaxillary and lacrimal gla nd of the normal adult male and female rat. A larger transcript (simil ar to 700 bases) was induced under conditions of altered hormonal prof iles: hypophysectomy, pregnancy/lactation, and castration. Dihydrotest osterone administration inhibited expression of the two transcripts in both the lacrimal and submaxillary glands of male and female rats. Th e labelled 117 bp DNA fragment unique to the rSMGGP1 cDNA hybridized o nly to the 700 base transcript in the rat lacrimal and submaxillary gl and suggesting that differential exon usage produces the two variant m RNAs. The regulation of the SMGGP gene expression may provide yet anot her useful model for studying the mechanism of down-regulation of gene s by androgen and the identification of tissue specific factors in the lacrimal and submaxillary gland.