Initiating the transcriptional activation of neuronal genes, DNA topoisomerase IIβ (topo IIβ) has a crucial role in neural differentiation and brain development. Inhibition of topo IIβ activity causes shorter axons and deteriorated neuronal connections common in neurodegenerative diseases. We previously reported that topo IIβ silencing could give rise to neurodegeneration through dysregulation of Rho GTPases and may contribute to pathogenesis of neurodegenerative diseases. Although there are several studies available proposing a link between Parkinson\'s Disease (PD) and Rho GTPases, there have been no reports analyzing the topo IIβ-dependent association of PD and Rho GTPases. Here, for the first time, we identified that topo IIβ has a regulatory role on Rho GTPases contributing to PD-like pathology. We analyzed the association between topo IIβ and PD by comparing topo IIβ expression levels of Retinoic Acid (RA) and Brain-derived neutrophic factor (BDNF) induced and MPP+-intoxicated SH-SY5Y cells used as an in vitro PD model. While both mRNA and protein levels of topo IIβ increase in neural differentiated cells, a significant decrease is detected in the PD model. Additionally, silencing of topo IIβ by specific siRNAs caused phenotypic alterations like deteriorated neural connections and transcriptional regulations such as upregulation of RhoA and downregulation of Cdc42, Rac1, and tyrosine hydroxylase gene expressions. Our results suggest that topo IIβ downregulation may cause neurodegeneration through dysregulation of Rho-GTPases leading to PD-like pathology.

DNA topoisomerase IIβ (topo IIβ) is known to regulate neural differentiation by inducing the neuronal genes responsible for critical neural differentiation events such as neurite outgrowth and axon guidance. However, the pathways of axon growth controlled by topo IIβ have not been clarified yet. Microarray results of our previous study have shown that topo IIβ silencing in neural differentiated primary human mesenchymal stem cells (hMSCs) significantly alters the expression pattern of genes involved in neural polarity, axonal growth, and guidance, including Rho-GTPases. This study aims to further analyze the regulatory role of topo IIβ on the process of axon growth via regulation of Rho-GTPases.
For this purpose, topo IIβ was silenced in neurally differentiated hMSCs. Cells lost their morphology because of topo IIβ deficiency, becoming enlarged and flattened. Additionally, a reduction in both neural differentiation efficiency and neurite length, upregulation in RhoA and Rock2, downregulation in Cdc42 gene expression were detected. On the other hand, cells were transfected with topo IIβ gene to elucidate the possible neuroprotective effect of topo IIβ overexpression on neural-induced hMSCs. Topo IIβ overexpression prompted all the cells to exhibit neural cell morphology as characterized by longer neurites. RhoA and Rock2 expressions were downregulated, whereas Cdc42 expression was upregulated. Nurr1 expression level correlated with topo IIβ in both topo IIβ-overexpressed and -silenced cells. Furthermore, differential translocation of Rho-GTPases was detected by immunostaining in response to topo IIβ.
Our results suggest that topo IIβ deficiency could give rise to neurodegeneration through dysregulation of Rho-GTPases. However, further in-vivo research is needed to demonstrate if re-regulation of Rho GTPases by topo IIβ overexpression could be a neuroprotective treatment in the case of neurodegenerative diseases.

DNA topoisomerase IIβ (topo IIβ) plays a crucial role in neural differentiation and axonogenesis. Inhibition of topo IIβ activity in vitro and in vivo results in shorter axons and increased DNA damage. These molecular events also involve in Alzheimer\'s disease (AD); however, the role of topo IIβ in the pathogenesis of AD remains to be elucidated.
We aimed to investigate the role of topo IIβ association with Nuclear receptor related 1 protein (Nurr1) in the onset of AD.
In vitro AD model was established by the incubation of fibrillar amyloid-β 1-42 (Aβ1-42) for 48 hours with cultured cerebellar granule neurons (CGNs) isolated from post-natal eight-day rats. The regulatory role of topo IIβ on the transcription of Nurr1 was analyzed in topo IIβ silenced CGNs, and also topo IIβ silenced and overexpressed in a neurally-differentiated human mesenchymal (hMSC) cell line.
Aβ1-42 fibrils led to the upregulation of Presenilin1 and Cofilin1 genes as measured at mRNA levels and hyperphosphorylation of tau protein, all are distinctive characteristics of AD pathology. A significant decrease in topo IIβ expression at mRNA and protein levels and Nurr1 at mRNA level was also observed. In both cell types, Nurr1 expression was dramatically down-regulated due to topo IIβ deficiency, and was increased in topo IIβ overexpressing hMSCs.
Our findings suggest that topo IIβ could be a down-stream target of signaling pathways contributing to AD-like pathology. However, further studies must be carried out in vivo to elucidate the precise association topo IIβ with AD.

DNA topoisomerases pass DNA strands through each other, a function essential for all DNA metabolic processes that create supercoils or entanglements of DNA. Topoisomerases play an ambivalent role in nuclear genome maintenance: Deficiency compromises gene transcription, replication and chromosome segregation, while the inherent DNA-cleavage activity of the enzymes endangers DNA integrity. Indeed, many DNA-damaging agents act through enhancing topoisomerase DNA cleavage. Mitochondrial DNA (mtDNA) clearly requires topoisomerase activity for transcription and replication, because it is a closed, double-stranded DNA molecule. Three topoisomerases have so far been found in mammalian mitochondria (I, IIβ, IIIα), but their precise role in mtDNA metabolism, mitochondrial maintenance and respiratory function remains mostly unclear. It is a reasonable surmise that these enzymes exhibit similar ambiguity with respect to genome maintenance and gene transcription as their nuclear counterparts. Here, we review what is known about the physiological roles of mitochondrial topoisomerases and draft three scenarios of how these enzymes possibly contribute to ageing-related mtDNA attrition and respiratory chain dysfunction. These scenarios are: mtDNA attrition by exogenously stimulated topoisomerase DNA cleavage, unbalancing of mitochondrial and nuclear transcription by direct effects on mitochondrial transcription, and contributions to enhanced mtDNA entanglement and recombination.

The Eighth International Biennial Conference on RNA polymerases I and III (the \'Odd Pols\') was held June 7-11, 2012 at The Airlie Center in Warrenton Virginia, USA. It was sponsored by the Universite Laval and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, and organized by Rich Maraia and Tom Moss. The meeting honored the memory of Pierre Thuriaux (Jan 1, 1950-March 18, 2012) and David Schneider reminisced on the important accomplishments his mentor Masayasu Nomura (1927-2011). The goal of the conference was to bring together the world\'s experts on RNA polymerase I and RNA polymerase III to highlight and share their latest results and varied experimental approaches. The meeting drew attendees from twelve countries and most contributed through oral and poster presentations. The talks were organized into several sessions subdivided into 10 distinct topics. The keynote speaker, Ian Willis, opened the meeting with his presentation entitled \"New Regulators of Signaling to Odd Pols\" and the closing presentation was given by Patrick Cramer with his presentation \"Conservation of the RNA polymerase I, II and III transcription initiation machineries\". Here we present some of the highlights from the meeting using summaries provided by the participants.

hMSCs (human mesenchymal stem cells) express two isoforms of DNA topo II (topoisomerase II). Although both isoforms have the same catalytic activity, they are specialized for different functions in the cell: while topo IIα is essential for chromosome segregation in mitotic cells, topo IIβ is involved in more specific cellular functions. A number of inhibitors are available that inhibit the catalytic activity of both topo II isoforms. However, in order to investigate the isoform-specific inhibition of these two enzymes, it is necessary to use other techniques such as siRNA (small interfering RNA) interference to selectively silence either one of the isoforms individually. Depending on the lipid charge densities and protein varieties of the cell membrane, previous studies have demonstrated that transfection efficiencies of siRNAs to hMSCs are very low. In the study reported here, we demonstrate the use of Lipofectamine RNAiMAX as an efficient transfection reagent to introduce siRNAs into human mesenchymal stem cells with significantly great efficiency to silence topo IIβ selectively. A high level of transfection efficiency (80%) was achieved by using unlabelled topo IIβ-specific siRNA oligos. Specifically, it was confirmed repeatedly that green labelled siRNAs interfere with the transfection of siRNAs. The reagent induced minimal cytotoxicity (3.5-4.5%), and cell viability of the transfected hMSCs decreased 20-30% compared with untreated cells, depending on the concentration of the reagent.