Ontogeny of aromatase messenger ribonucleic acid in mouse brain: fluorometrical quantitation by polymerase chain reaction.

A sensitive method was developed for the determination of trace amounts of aromatase mRNA in various tissues. Aromatase mRNA was quantitated by subjecting it to reverse transcription in the presence of an internal standard RNA and then amplifying the resulting cDNA by polymerase chain reaction with a fluorescent primer. The tissue distribution of aromatase mRNA in mice was examined by this polymerase chain reaction method. Results showed that aromatase mRNA is expressed in the brain, testis, and ovary, but scarcely at all in other tissues, including the placenta. In mouse brain, aromatase is mainly located in the forebrain, especially the diencephalon. In adult male and female diencephala, aromatase mRNA levels were 0.022 +/- 0.004 and 0.014 +/- 0.003 attomoles/micrograms total RNA, respectively. Aromatase in the diencephalon is known to participate in brain differentiation and sexual behavior, so changes in its mRNA levels in the brain during development were examined. Aromatase mRNA was first detected in the 12-day-old fetus and was found to increase rapidly during the fetal and neonatal periods. Its mRNA levels in male and female brains reached maxima of 0.068 +/- 0.008 and 0.059 +/- 0.006 attomoles/micrograms total RNA, respectively, 3-4 days after birth and then gradually decreased to adult levels. These observations are consistent with previous data indicating that the marginal period of neonatal imprinting of sexual differences is within a week after birth and suggest that brain aromatase may be important in sexual differentiation and behavior.