Immunocytochemical localization of gamma-glutamyltranspeptidase during fetal development of mouse kidney.

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Abstract
In the fully developed kidney, gamma-glutamyltranspeptidase is localized predominantly to the apical plasma membrane of the proximal tubules. The appearance of this activity during murine fetal nephrogenesis was quantitated using a sensitive fluorometric assay, and development of membrane polarity was assessed by immunocytochemistry. Specific activity of the transpeptidase in 13-day fetal kidney was approximately 1 mU/mg protein. Between 13-21 days of gestation, total transpeptidase activity increased 7500-fold, whereas specific activity increased 50-fold. At 13 days of gestation, gamma-glutamyltranspeptidase immunoreactivity is localized to the apical surfaces of developing renal vesicles and the proximal segment of the S-shaped tubules. The organized cell structures have tight tubular junctions but lack a well-defined brush-border membrane. By 15 days of gestation, immunostaining of the apical surface of developing proximal segments is more prominent, and slight reactivity of the basolateral membrane is evident. By 17 days of gestation, the kidney is organized into discrete zones. The large increase in gamma-glutamyltranspeptidase activity correlates with the appearance of increased immunostaining of the developing brush-border membranes of the proximal tubules contained in the inner cortex. A very similar although somewhat delayed pattern of appearance of transpeptidase activity and immunostaining was observed in metanephric organ culture. Induction of proximal tubular cyst formation had no effect on the increase in transpeptidase activity that occurred during organotypic nephrogenesis.