Vitronectin in the cytoplasm of Leydig cells in the rat testis

Vitronectin is a multifunctional protein present in serum and in extracellular matrices, but its localization has not been fully elucidated. In the present study, immunoblotting with anti-rat vitronectin antibody showed that rat testes contained vitronectin in both Triton-soluble and -insoluble fractions. Immunofluorescence microscopy demonstrated that this immunoreactivity was localized mainly in the interstitial Leydig cells. Occasionally vitronectin was shown in some spermatocytes and around blood vessels. Immunoelectron microscopy with nanogold probes showed that vitronectin was present in the cytoplasm of Leydig cells but not in the nucleus or in the mitochondria and probably not on the luminal side of the endoplasmic reticulum. In situ hybridization with synthetic oligonucleotides, however, showed that vitronectin mRNA was not present in Leydig cells, although a faint reaction was shown in spermatogonia and/or in early spermatocytes. This observation was supported by the results of reverse transcriptase polymerase chain reaction, which showed that vitronectin mRNA was not present in the Leydig cell fraction, whereas a band corresponding to vitronectin gene product was detected in the seminiferous tubule fraction. These results indicate that Leydig cells contain vitronectin but do not synthesize it. The source of vitronectin in Leydig cells seemed to be either spermatogenic cells or blood.