Activin and activin receptors in the normal urinary bladder: immunohistochemistry, in situ hybridization, and RT-PCR.

To determine whether rat urinary bladder produces activin-A, a multifunctional growth factor in the transforming growth factor beta superfamily (TGF beta), we have conducted immunohistochemistry using specific antibodies for activin beta A-subunit which were raised against a synthetic cyclic fragment of the beta A-subunit of activin. The mature activin-A molecule was identified at transitional epithelial cells, smooth muscle, and endothelial cells. To determine if messenger RNAs for the beta A-subunits of activin-A and activin receptors are expressed in these cells, both in situ hybridization with specific probes and the reverse transcription-polymerase chain reaction (RT-PCR) technique with primers specific for the beta A-subunit of activin and activin receptors, respectively, were used. Messenger RNA expression of the beta A-subunit of activin-A and activin receptors were detected by RT-PCR and localized in the transitional epithelial, smooth muscle, and endothelial cells as determined by in situ hybridization. In addition, the identity of the cDNA product of RT-PCR was verified with DNA sequencing. The localization of mature activin-A protein and its corresponding message as well as that of activin receptors to urinary bladder cells suggest that activin-A may have an autocrine function in the urinary bladder, perhaps in the transitional epithelial, smooth muscle, and endothelial cells themselves.