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The Ontogeny of Steroid Sulfatase Expression in the Ovine Fetal Brain

Steroid sulfatase (STS), the enzyme that deconjugates sulfoconjugated estrogens, is expressed in various estrogen target tissues, including fetal brain. We have demonstrated the presence of STS in the ovine fetal brain. In other experiments, we have demonstrated that estrogen potently augments fetal stress responsiveness. In the present experiments, we measured the expression of STS mRNA in four brain regions as a function of fetal gestational age. mRNA expression levels were measured at five fetal ages (80, 100, 120, 130, and 145 days gestation: term = 147 days in sheep) and three postnatal ages (1 and 7 days and adult). Sheep were euthanized humanely and tissues (hypothalamus, hippocampus, cerebellum, and brainstem) were rapidly dissected and frozen in liquid nitrogen. mRNA was extracted using Trizol®. We found STS expression in all of the tissues included in this study. Furthermore, the expression of STS in the cerebellum and hypothalamus was increased as the fetus matured prior to parturition. The highest levels were found in late gestational fetuses relative to younger and older fetuses. The brainstem and hippocampus display very low levels throughout most of the ontogeny. We conclude that the ovine fetal brain expresses STS in hypothalamus, hippocampus, cerebral cortex, cerebellum, and brainstem, and that the expression is increased in hypothalamus and cerebellum. We suggest that these results are consistent with the conclusion that there is increased deconjugation and action of (and therefore sensitivity to) sulfoconjugated estrogen in fetal hypothalamus and cerebellum at the end of gestation.