Wilhelm bernhard workshop on the cell nucleus

CARP FISH NUCLEOLAR DYNAMICS

Vera M. I., Krauskopf M., Alvarez M., Molina A., Quezada C., Navarro C. and Pinto R. Laboratorio de Biología Celular y Molecular, Universidad Andrés Bello and MIFAB, Santiago, Chile
One of the most dramatic adaptive responses of the carp to the seasonal environmental changes is the segregation of the nucleolar components during winter, concomitantly with a remarkable decay of rRNA synthesis and processing of their precursors. On the contrary, in summer-adapted fish, the nucleolar structure agrees with an active state of ribosome biogenesis. To understand the molecular mechanisms that trigger this phenomenon, we have being studying some genes and their expression concerning ribosome synthesis, ribosomal protein L41, protein kinase CK2 and nucleolin, among others. Nucleolin is a major substrate of CK2, implicated in different steps of ribosome synthesis. In summer, the mRNA expression of ribosomal protein L41 and CK2ß, as well as the CK2ß protein are higher than in winter-adapted carp. On the contrary, both, the content of nucleolin and its mRNA, showed higher expression levels in tissues from winter-adapted carp. Recently, it has been proposed that nucleolin could repress the rRNA transcription. To evaluate this hypothesis in our seasonal regulated model, we characterized the carp rRNA cistron, nucleolin gene and two different nucleolin cDNAs. In silico analysis of the rRNA intergenic spacer (IGS) revealed a number of sequence repeats most likely involved in transcriptional regulation. In addition, we perform a phylogenetic study of the 18S carp rRNA. Our results suggest at least three genes coding for nucleolin in carp, organized in 16 exons. Introns 7, 9 and 14 code for U82, U20 and U23 snoRNAs, respectively. Throughout in silico modeling we have established secondary structures for all these three snoRNAs and we assessed their seasonal expression. In conclusion, the rRNA transcription and nucleolar gene expression in a eurythermal fish are not constitutive, on the contrary, they are strongly regulated by environmental parameters.

Grants: FONDECYT 1000061, DI/UNAB 93-01 and 94-01