Behavior of RNAs transcripts during nucleolus assembly and disassembly in Vicia faba root meristematic cells under normal conditions and after colchicine treatment

Konrad Winnicki

doi:10.1007/s11738-012-0936-8

Abstract

To study the behavior of newly synthesized RNA molecules during unperturbed mitosis and after induction of aneuploid nuclei, a novel method based on the incorporation of 5-ethynyl uridine was applied. This approach allows revealing transcription in cytological specimens by omitting immunocytochemical procedures. The obtained results indicate that RNAs synthesized in the preceding cell cycle behave similarly as nucleolar proteins and participate in post-mitotic nucleolar assembly not only during unperturbed nuclear divisions. Colocalization of nucleolar proteins and RNAs seems also to occur in aneuploid nuclei devoid of functional nucleolar organizer regions (NORs) or NOR per se. This paper also shows the presence of nucleoplasmic gene expression in aberrant aneuploid nuclei and micronuclei, despite occurrence of their genetic material disorganization. Moreover, experiments showing the effect of transcription and replication inhibition on the induction of aneuploid nuclei were also performed. Presented data shed new light on nucleologenesis and co-existence of nucleolar proteins with RNAs in prenucleolar bodies formed in aneuploid nuclei devoid of functional NORs.

Highlights

A great number of reviews about nucleolar architecture in animal and plant cell nuclei have been written so far, and a lot of experiments have proved close structural and functional relationships regarding three main elements discernible under an electron microscope, i.e., fibrillar centers (FCs), dense fibrillar component (DFC) and granular component (GC) (Hernandez-Verdun 2006a, b; McKeown and Shaw 2009; Olson and Dundr 2005; Raska et al 2006; Sirri et al 2008)
Since the most intense fluorescent signal has been localized to the nucleolus, the main fraction of transcripts can seemingly be attributed to rRNAs
It has been proposed that RNA polymerase I (Pol I) activity is necessary for the assembly of nucleolar material around nucleolar organizer regions (NORs) (Benavente et al 1987), more recent data suggest that recruitment of early-processing proteins in some cases may be independent of transcription activation (Sirri et al 2000, 2002)

Summary

Introduction

A great number of reviews about nucleolar architecture in animal and plant cell nuclei have been written so far, and a lot of experiments have proved close structural and functional relationships regarding three main elements discernible under an electron microscope, i.e., fibrillar centers (FCs), dense fibrillar component (DFC) and granular component (GC) (Hernandez-Verdun 2006a, b; McKeown and Shaw 2009; Olson and Dundr 2005; Raska et al 2006; Sirri et al 2008). It has been reported that during mitosis rDNA transcription machinery proteins are positioned close to the nucleolar organizer regions (NORs), whereas rRNA processing machinery proteins are located at the chromosomal peripheries (Hernandez-Verdun 2006b; Sirri et al 2008). Biochemical studies showed that in metaphase-arrested cells another nucleolar protein, nucleolin, remains associated with both fibrillarin and B23, and all these proteins form RNP complexes together with pre-rRNA. The integrity of such complexes is closely dependent on the presence of RNAs (Pinol-Roma 1999), indicating that proteins functioning within the nucleolar area can be held together during mitosis

Methods

Results

Conclusion