SEASONAL ACCLIMATIZATION OF THE CARP INVOLVES DIFFERENTIAL EXPRESSIONOF 5.8S RIBOSOMAL-RNA IN PITUITARY-CELLS

In the carp, nucleolar reorganization is one of the most remarkable fe atures of the cellular adjustment thai: occurs upon seasonal acclimati zation. To assess if the level of cellular expression of a specific rR NA is maintained between both seasonal adaptive states, we isolated a carp 5.8S rRNA gene. Sequence analyses showed its high conservation du ring evolution. The level of expression of 5.8S rRNA was determined by in situ hybridization assays in pituitary sections from summer-and wi nter acclimatized carp. The quantification of the positive hybridizati on signals demonstrated a statistically significant difference between the acclimatization states. Transcription of 5.8S rRNA was considerab ly higher in summer-than in winter-acclimatized carp. These results in dicate that the level of rRNA expression in eurythermal fish is not co mparable between seasons and suggest that rRNA genes may be not consti tutive. Thus, rRNA transcription should be used with caution as a refe rence to quantitate transcripts chat are modulated as part of the accl imatization process in eurythermal fish. (C) 1997 Elsevier Science Inc .