Development of pro-TRH gene expression in primary cultures of fetal hypothalamic cells

Little is known about the temporal relationship and the sequential steps fo r peptide biosynthesis during the terminal differentiation of the peptide p henotype in central nervous system. Analysis of the TRH phenotype in primar y cultures of rat fetal day 17 hypothalamic cells has shown that TRH levels start increasing only after a week in culture, in contrast with in vivo da ta showing a steady increase during late fetal life. The purpose of this st udy was to compare the developmental patterns of TRH and pro-TRH mRNA level s in vitro to determine whether the initial low and steady levels of TRH ar e due to deficient transcription. Pro-TRH mRNA levels were detected by semi -quantitative RT-PCR through the development of primary cultures of serum-s upplemented hypothalamic fetal cells from 17 day old embryos. Pro-TRH mRNA levels per dish increased steadily since the beginning of the culture. In c ontrast, TRH levels per dish were low and stable during the first week incr easing afterwards, but remaining low compared to equivalent in vivo values. Pro-TRH mRNA levels per hypothalamus increased between fetal day 17 and po stnatal 14, suggesting that the in vitro pattern of pro-TRH mRNA developmen t mimics that occurring in vivo. These data show that pro-TRH gene expressi on does not limit TRH accumulation in vitro suggesting that the transcripti onal and post-transcriptional programs. leading to peptide accumulation are established independently. (C) 2001 Elsevier Science B.V. All rights reser ved.