Eurythermal fish acclimatization and nucleolar function: A review

The most dramatic adaptive responses of the carp fish to the seasonal environmental changes (mostly temperature and photoperiod) is the segregation of the nucleolar components during winter, concomitantly with a remarkable decay of rRNA synthesis and processing of their precursors. In contrast, summer-adapted fish depicts a nucleolar structure indicating an active state of ribosome biogenesis. The mRNA expression of ribosomal protein L41 and CK2β, as well as the CK2β protein is higher in summer. On the contrary, nucleolin mRNA expression is strongly induced in the cold- adapted carp, as it is the cognate nuclear protein content. The physiological up-regulation of nucleolin in the cold-acclimatized carp where rRNA transcription and processing are depressed is consistent with the rearrangement of the nucleolar components. Our observations indicate that rRNA transcription and nucleolar organelle dynamics are not constitutive. Both processes are strongly regulated by the environmental temperature of the habitat.