Role of epithelial-mesenchymal interactions in the differentiation and spatial organization of visceral smooth muscle.

Uterine mesenchyme from newborn (0-day) rats was grown in association with epithelia from the adult cornea, urinary bladder, oesophagus, mammary gland, 1-day skin, and 1-day uterus. Following 1 month of growth, the differentiation of uterine mesenchyme into actin-positive smooth muscle cells was assessed immunocytochemically with antibodies to smooth muscle actin. Whereas grafts of uterine mesenchyme produced only small amounts of myometrium, all types of epithelia induced extensive myometrial differentiation in the uterine mesenchyme, which indicates that this effect is non-specific. The role of cell-cell interactions in the morphological patterning of smooth muscle layers was assessed by analysing tissue recombinants composed of adult prostatic epithelium (PRE) plus mesenchyme of the urogenital sinus (UGM), or seminal vesicle (SVM), or adult bladder epithelium (BLE) plus UGM or SVM. Prostatic ducts developed in all of these tissue recombinants (UGM + BLE, SVM + BLE, UGM + PRE and SVM + PRE). When UGM was used (UGM + PRE and UGM + BLE recombinants), actin-positive smooth muscle cells became organized into thin sheaths resembling the prostatic pattern. Conversely, when SVM was grown in association with PRE or BLE, the induced prostatic ducts were surrounded by thick layers of smooth muscle cells exhibiting the seminal vesicle pattern of organization. Smooth muscle cells were unorganized in grafts of SVM or UGM alone. These observations suggest that in male urogenital glands the mesenchyme dictates the spatial organization of the smooth muscle layers.(ABSTRACT TRUNCATED AT 250 WORDS)