Mullerian inhibiting substance binding and uptake

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Abstract
Mullerian inhibiting substance (MIS) is a 140,000 Mr Sertoli cell derived glycoprotein with a critical regulatory role in the male fetus initiated presumably by ligand binding with receptor. To localize this binding species we performed time course incubations of cultured fetal rat lungs or control tissues with MIS, applied rabbit anti‐MIS IgG, and fluorescein conjugated antirabbit IgG, and examined specimens with laser confocal microscopy. Punctate surface fluorescence followed by cytosolic and nuclear localization in lung consistent with specific adsorptive endocytosis was seen. Confocal imaging also detected MIS binding to the Mullerian duct in the urogenital ridge. Crosslinking of 125I‐MIS with plasma membranes revealed a high molecular mass binder with signal displaceable by excess unlabeled ligand. These data support the hypothesis that a specific plasma membrane binding protein for MIS exists.