Pericentromeric heterochromatin domains are maintained without accumulation of HP1

The heterochromatin protein 1 (HP1) family is thought to be an important structural component of heterochromatin. HP1 proteins bind via their chromodomain to nucleosomes methylated at lysine 9 of histone H3 (H3K9me). To investigate the role of HP1 in maintaining heterochromatin structure, we used a dominant negative approach by expressing truncated HP1alpha or HP1beta proteins lacking a functional chromodomain. Expression of these truncated HP1 proteins individually or in combination resulted in a strong reduction of the accumulation of HP1alpha, HP1beta, and HP1gamma in pericentromeric heterochromatin domains in mouse 3T3 fibroblasts. The expression levels of HP1 did not change. The apparent displacement of HP1alpha, HP1beta, and HP1gamma from pericentromeric heterochromatin did not result in visible changes in the structure of pericentromeric heterochromatin domains, as visualized by DAPI staining and immunofluorescent labeling of H3K9me. Our results show that the accumulation of HP1alpha, HP1beta, and HP1gamma at pericentromeric heterochromatin domains is not required to maintain DAPI-stained pericentromeric heterochromatin domains and the methylated state of histone H3 at lysine 9 in such heterochromatin domains.     

The European Renal Genome Project: An Integrated Approach Towards Understanding the Genetics of Kidney Development and Disease

Rapid progress in genome research creates a wealth of information on the functional annotation of mammalian genome sequences. However, as we accumulate large amounts of scientific information we are facing problems of how to integrate and relate the data produced by various genomic approaches. Here, we propose the novel concept of an organ atlas where diverse data from expression maps to histological findings to mutant phenotypes can be queried, compared and visualized in the context of a three-dimensional reconstruction of the organ. We will seek proof of concept for the organ atlas by elucidating genetic pathways involved in development and pathophysiology of the kidney. Such a kidney atlas may provide a paradigm for a new systems-biology approach in functional genome research aimed at understanding the genetic bases of organ development, physiology and disease.Key Words: EuReGene, kidney, genome, development, pathophysiology, genetics     

iTBS-Induced LTP-Like Plasticity Parallels Oscillatory Activity Changes in the Primary Sensory and Motor Areas of Macaque Monkeys

Recently, neuromodulation techniques based on the use of repetitive transcranial magnetic stimulation (rTMS) have been proposed as a non-invasive and efficient method to induce in vivo long-term potentiation (LTP)-like aftereffects. However, the exact impact of rTMS-induced perturbations on the dynamics of neuronal population activity is not well understood. Here, in two monkeys, we examine changes in the oscillatory activity of the sensorimotor cortex following an intermittent theta burst stimulation (iTBS) protocol. We first probed iTBS modulatory effects by testing the iTBS-induced facilitation of somatosensory evoked potentials (SEP). Then, we examined the frequency information of the electrocorticographic signal, obtained using a custom-made miniaturised multi-electrode array for electrocorticography, after real or sham iTBS. We observed that iTBS induced facilitation of SEPs and influenced spectral components of the signal, in both animals. The latter effect was more prominent on the θ band (4–8 Hz) and the high γ band (55–90 Hz), de-potentiated and potentiated respectively. We additionally found that the multi-electrode array uniformity of β (13–26 Hz) and high γ bands were also afflicted by iTBS. Our study suggests that enhanced cortical excitability promoted by iTBS parallels a dynamic reorganisation of the interested neural network. The effect in the γ band suggests a transient local modulation, possibly at the level of synaptic strength in interneurons. The effect in the θ band suggests the disruption of temporal coordination on larger spatial scales.     

Transient association of MCM complex proteins with the nuclear matrix during initiation of mammalian DNA replication

The minichromosome maintenance complex (MCM2-7) is the putative DNA helicase in eukaryotes, and essential for DNA replication. By applying serial extractions to mammalian cells synchronized by release from quiescence, we reveal dynamic changes to the sub-nuclear compartmentalization of MCM2 as cells pass through late G1 and early S phase, identifying a brief window when MCM2 becomes transiently attached to the nuclear-matrix. The data distinguish 3 states that correspond to loose association with chromatin prior to DNA replication, transient highly stable binding to the nuclear-matrix coincident with initiation, and a post-initiation phase when MCM2 remains tightly associated with chromatin but not the nuclear-matrix. The data suggests that functional MCM complex loading takes place at the nuclear-matrix.