The sulfation of the adrenal steroid dehydroepiandrosterone (DHEA) is a critical step in the provision of substrates for estrogen biosynthesis by the placenta during pregnancy. This enzyme reaction is catalyzed by a cytosolic sulfotransferase (ST) found in many key body tissues, and we have examined the ontogeny and localization of expression of this important enzyme in three tissues: the liver, adrenal, and kidney. Hepatic DHEA ST expression increased with advancing gestational age before reaching near-adult levels in the early postnatal period, suggesting an increased requirement for this enzyme in the liver as development progresses, whereas in the adrenal and kidney there was no obvious ontogenic pattern. The enzyme was expressed at a 5-fold higher level in the adrenal than in the liver and some 40-fold higher than in the kidney. Comparison of enzyme activity measurements and quantitation of the expression of DHEA ST by immunodot blot analysis with an anti-DHEA ST antibody preparation demonstrated the fragility of the enzyme activity and suggested that immunoquantitation was a superior method for assessment of levels of expression of this enzyme in widely different tissue sources. Examination of the localization of DHEA ST in these tissues by immunohistochemistry showed that in liver, DHEA ST was expressed in embryonic hepatocytes and continued to be expressed in these cells into adulthood, when there was some concentration of immunostaining around central veins. In the fetus, the adrenal enzyme was expressed in the fetal zone, whereas in adult tissue, staining was localized principally to the zona reticularis. Renal DHEA ST was present in the proximal and distal tubules, loops of Henle, collecting ducts, and their progenitors, but was at no time expressed in the vascular glomerulus. In light of the broad substrate specificity of this enzyme toward other steroids, in particular bile acids and cholesterol, the information presented forms a strong basis for further studies into the role of DHEA ST in modulating the activity of a number of biologically active and potentially toxic steroids in the developing human.
The objective of our study was to determine the cellular localisation of glucose-6-phosphatase in developing human kidney using monospecific antiserum and a standard immunohistochemical method (peroxidase-antiperoxidase, PAP) on formalin fixed and paraffin embedded tissue. In embryonic and early fetal development of the metanephric kidney, glucose-6-phosphatase is located primarily in derivatives of the ureteric bud such as the pelvis, calyces and collecting ducts. In mid-fetal life as nephrons evolve and develop they become increasingly immunoreactive to glucose-6-phosphatase, such that in mature metanephric kidney the proximal tubules are highly reactive for glucose-6-phosphatase with other elements of the nephron also immunopositive albeit at lower reactivities. In addition the parietal layer of Bowman's capsule and some cells of the visceral layer are immunopositive. Only with the development of nephrons does the early predominance of glucose-6-phosphatase immunoreactivity to ureteric bud derivatives change: in mature kidney the reactivity in the collecting ducts is a small proportion of the total. In proximal tubular cells the distribution of glucose-6-phosphatase immunoreactivity is relatively uniform throughout development in contrast to collecting ducts where in fetal life this reactivity is displaced to the apices and basal areas by intracellular glycogen deposits. The mesonephric kidney has a similar pattern of glucose-6-phosphatase immunoreactivity to that of metanephric kidney. The availability of monospecific antiserum to glucose-6-phosphatase and immunohistochemical methods now allows an alternative approach to cellular localisation. Many of the difficulties in the fixation of tissue and assay of glucose-6-phosphatase activity inherent in conventional histochemical methods are avoided by such methods.
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