GUINEA-PIG APOLIPOPROTEIN-D RNA DIVERSITY, AND DEVELOPMENTAL AND GESTATIONAL MODULATION OF MESSENGER-RNA LEVELS

We have isolated and characterized two molecular types of guinea pig ( GP) apolipoprotein D (apoD) cDNA. The sequences of cDNA clones GP APO D-20 and -38 are 100% homologous in their putative exons 2-5, as deter mined by analogy with human apoD gene, but they differ totally in thei r putative exon 1. RNase protection assays showed the presence of both apoD RNA types 20 and 38 in cauda epididymis. Northern blot analysis revealed four polyadenylated apoD bands at 3.2, 2.7, 1.7, and 1.0 kb. Types 20 and 38 specific probes hybridized with the major l-kb mRNA an d two of the three other minor RNA transcripts, respectively. Southern blot analysis revealed that the guinea pig genome probably contains o ne apoD gene. Our data also demonstrated that the cauda epididymis and fallopian tubes had an apoD mRNA concentration 100-fold higher than t he liver, suggesting that the apoD gene expression could be associated with the presence of steroids. The levels of the l-kb mRNA increased in the fallopian tubes and ovaries during gestation and were lower in fetal reproductive tissues and liver than in mature animals. No positi ve correlation was found between apoD and 3 beta-hydroxysteroid dehydr ogenase/Delta 5-Delta 4 isomerase (3 beta-HSD) mRNA levels in these ti ssues, thus suggesting that high amounts of apoD mRNA are not necessar ily associated with in situ progesterone synthesis. Taken together, ou r results indicate that both the guinea pig epididymis and fallopian t ubes are excellent models to study the local role of apoD in steroid t arget tissues.