MOLECULAR-CLONING AND HORMONAL-REGULATION OF A MURINE EPIDIDYMAL RETINOIC ACID-BINDING PROTEIN MESSENGER-RIBONUCLEIC-ACID

A complementary DNA encoding the mouse epididymal secretory protein ME P 10 (mouse epididymal protein 10) was cloned and is now renamed murin e epididymal retinoic acid binding protein (mE-RABP). The analysis of the predicted primary amino acid sequence showed that mE-RABP has a 75 % identity with rat ESP I (epididymal secretory protein I), another ep ididymal retinoic acid-binding protein. The homology strongly suggests that mE-RABP is the mouse orthologue of rat ESP I. A computer analysi s of the predicted three-dimensional structure confirmed that mE-RABP can accommodate retinoic acid as Ligand. In the rat, ESP I messenger R NA (mRNA) is expressed in the efferent ducts and in the entire caput e pididymidis. However, in the mouse, the expression of a 950-bp mE-RABP mRNA was detected only in principal cells of the mid/distal caput epi didymidis, suggesting that the regulation of region-specific expressio n is different in rat and mouse. Northern blot analyses showed that mE -RABP gene expression is no longer detected 10 days after castration b ut progressively rebounds between days 15 and 60. However, mE-RABP pro tein could not be detected by Western blot 30 days after castration. A ndrogen replacement, begun 5 days after castration and continued for 4 days restored significant expression of mF-RABP mRNA. Efferent duct l igation for 10 days did not affect gene expression. Taken together, th ese results indicate that mE-RABP mRNA expression is regulated by andr ogens but not by testicular factors. The overall similarity in the pri mary amino acid sequence of mE-RABP with ESP I and other members of th e lipocalin superfamily suggests that they are evolutionarily related.