Wilhelm bernhard workshop on the cell nucleus

modifications OF Transcription and splicing in ageing

Malatesta M.¹, Bertoni-Freddari C.², Fattoretti P.², Baldelli B.¹, Battistelli S.¹, and Biggiogera M.<sup>3

1</sup>Istituto di Istologia e Analisi di Laboratorio, University of Urbino “Carlo Bo”; ²Neurobiology of Aging Laboratory, INRCA Research Department, Ancona; ³Dipartimento di Biologia Animale, Laboratorio di Biologia Cellulare, University of Pavia, Italy
Ageing involves changes in transcription and splicing pathways. In a previous study we described an unusual accumulation of perichromatin fibrils (PFs) – the in situ form of pre-mRNA transcription and early splicing – in hepatocyte nuclei of old rats in comparison to adult animals. In this study we investigated, by means of immunoelectron microscopy, the nature of such PFs, analysing the presence of transcription and splicing factors and the incorporation of bromouridine (BrU) in adult (9 months) and old (28 months) rats. Our observations revealed that no difference in anti-snRNP and anti-fibrillarin labelling occurs between adult and old rats, whereas old animals showed lower signals for anti-polymerase II and anti-SC-35 probes. Anti-BrU immunolabelling, located on PFs and on the nucleolar dense fibrillar component, demonstrated a lower incorporation in the nucleoplasm in old rats, whereas no difference was found in the nucleolus. On the basis of our previous and present data, we can hypothesise altered mRNA pathways in hepatocyte nuclei of old rats. In fact, the lower BrU incorporation in the nucleoplasm together with the lower amounts of polymerase II in old rats indicate a decrease in pre-mRNA transcription rate. Moreover, the low amounts of nucleoplasmic splicing factors as well as the accumulation of perichromatin granules - storage and/or transport sites of spliced mRNA – previously observed in old rats suggest also a slow down of PF processing and/or transport in ageing. Such phenomenon would explain the persistence in the nucleoplasm of pre-mRNA and/or mRNA as PFs in old animals. As for the nucleolus, our data indicate no modification in pre-rRNA transcription and early splicing in old rats. During ageing a general reduction in protein and RNA synthesis occurs in liver. It is possible that these changes would be related to the alterations in both transcription and processing of pre-mRNA.