SUN-471 Corresponding Primary Transcript and mRNA Levels for Pomc and Prss56 Suggest Oscillating Transcriptions in Adult Rat Tanycytes

We recently reported mRNA and protein expression patterns in adult rat hypothalamic tanycytes that suggest oscillatory gene expression, demonstrating highly variable pro-opiomelanocortin (Pomc) mRNA and protein expression in these cells with 40% of rats expressing high, 40% low, and another 20% intermediate levels (Wittmann et al., J Comp Neurol, 2017). In addition, we demonstrated that mRNA expression for Prss56 , a trypsin-like serine protease, is comparably variable but inversely proportional to that of Pomc in tanycytes (Wittmann and Lechan, J Comp Neurol, 2018), proposing that the most likely explanation for this variability is that the two genes are expressed in an out-of-phase, oscillatory manner. Since the amount of mRNA depends on both the rate of transcription and mRNA degradation, we investigated whether increased transcription drives the accumulation of Pomc and Prss56 mRNAs. Fluorescent in situ hybridization was used to detect Pomc and Prss56 primary transcripts (hnRNA) using probes against intronic sequences. As expected, intronic hybridization signal was localized in nuclei rather than the cytoplasm; while Prss56 primary transcript was represented by only 1 or 2 intensely fluorescent nuclear dots, the hybridization signal for Pomc primary transcript ranged from a single dot to filling the entire nucleus. A high correlation was found between the expression levels of primary transcripts and the respective mRNAs. In general, high Pomc or Prss56 mRNA levels were accompanied by high Pomc or Prss56 hnRNA levels in tanycytes, whereas low hnRNA levels corresponded to low mRNA levels. These data indicate that variable Pomc and Prss56 mRNA levels highly correlate with the transcriptional activity of these genes, raising the possibility of oscillatory expression and/or activity of certain transcription factors in adult rat tanycytes. We hypothesize that this phenomenon may be related to the stem/progenitor cell function of tanycytes (Prevot et al., Endocr Rev, 2018) and reminiscent of the oscillatory expression of transcription factors in neural progenitor cells during development (Kageyama et al., Neurosci Res, 2018).