The developmental expression of the somatostatin (SRIF) gene was investigated in rat brain and stomach, two SRIF-rich tissues. The accumulation of raRNA encoding SRIF was determined in these organs during fetal and early (1-4 weeks) postnatal development using a sensitive radiodensitometric cDNA hybridization assay and a cloned preprosomatostatin cDNA. A single band of mRNA which hybridized specifically to the rat SRIF cDNA was detected in both tissues examined throughout ontogenesis, suggesting that the same SRIF gene is expressed in these tissues in the developing as well as in the adult rat. Whereas SRIF mRNA was undetectable in fetal stomach arid rose gradually only after birth, brain SRIF mRNA was already detectable by day 7 of embryonic life and reached concentrations corresponding to those in the adult brain by embryonic day 20. These marked differences may reflect basic differences in the developmental regulation of SRIF gene expression in neural vs. nonneural tissues or may be related to the onset of functional activity in the organs studied.
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