Mask exhibits trxG-like behavior and associates with H3K27ac marked chromatin.

The Trithorax group (trxG) proteins counteract the repressive effect of Polycomb group (PcG) complexes and maintain transcriptional memory of active states of key developmental genes. Although chromatin structure and modifications appear to play a fundamental role in this process, it is not clear how trxG prevents PcG-silencing and heritably maintains an active gene expression state. Here, we report a hitherto unknown role of Drosophila Multiple ankyrin repeats single KH domain (Mask), which emerged as one of the candidate trxG genes in our reverse genetic screen. The genome-wide binding profile of Mask correlates with known trxG binding sites across the Drosophila genome. In particular, the association of Mask at chromatin overlaps with CBP and H3K27ac, which are known hallmarks of actively transcribed genes by trxG. Importantly, Mask predominantly associates with actively transcribed genes in Drosophila. Depletion of Mask not only results in the downregulation of trxG targets but also correlates with diminished levels of H3K27ac. The fact that Mask positively regulates H3K27ac levels in flies was also found to be conserved in human cells. Strong suppression of Pc mutant phenotype by mutation in mask provides physiological relevance that Mask contributes to the anti-silencing effect of trxG, maintaining expression of key developmental genes. Since Mask is a downstream effector of multiple cell signaling pathways, we propose that Mask may connect cell signaling with chromatin mediated epigenetic cell memory governed by trxG.

Genome-wide RNAi screen in Drosophila reveals Enok as a novel trithorax group regulator.

BACKGROUND: Polycomb group (PcG) and trithorax group (trxG) proteins contribute to the specialization of cell types by maintaining differential gene expression patterns. Initially discovered as positive regulators of HOX genes in forward genetic screens, trxG counteracts PcG-mediated repression of cell type-specific genes. Despite decades of extensive analysis, molecular understanding of trxG action and regulation are still punctuated by many unknowns. This study aimed at discovering novel factors that elicit an anti-silencing effect to facilitate trxG-mediated gene activation. RESULTS: We have developed a cell-based reporter system and performed a genome-wide RNAi screen to discover novel factors involved in trxG-mediated gene regulation in Drosophila. We identified more than 200 genes affecting the reporter in a manner similar to trxG genes. From the list of top candidates, we have characterized Enoki mushroom (Enok), a known histone acetyltransferase, as an important regulator of trxG in Drosophila. Mutants of enok strongly suppressed extra sex comb phenotype of Pc mutants and enhanced homeotic transformations associated with trx mutations. Enok colocalizes with both TRX and PC at chromatin. Moreover, depletion of Enok specifically resulted in an increased enrichment of PC and consequently silencing of trxG targets. This downregulation of trxG targets was also accompanied by a decreased occupancy of RNA-Pol-II in the gene body, correlating with an increased stalling at the transcription start sites of these genes. We propose that Enok facilitates trxG-mediated maintenance of gene activation by specifically counteracting PcG-mediated repression. CONCLUSION: Our ex vivo approach led to identification of new trxG candidate genes that warrant further investigation. Presence of chromatin modifiers as well as known members of trxG and their interactors in the genome-wide RNAi screen validated our reverse genetics approach. Genetic and molecular characterization of Enok revealed a hitherto unknown interplay between Enok and PcG/trxG system. We conclude that histone acetylation by Enok positively impacts the maintenance of trxG-regulated gene activation by inhibiting PRC1-mediated transcriptional repression.

Robot Learning of Assistive Manipulation Tasks by Demonstration via Head Gesture-based Interface.

Assistive robotic manipulators have the potential to support the lives of people suffering from severe motor impairments. They can support individuals with disabilities to independently perform daily living activities, such as drinking, eating, manipulation tasks, and opening doors. An attractive solution is to enable motor impaired users to teach a robot by providing demonstrations of daily living tasks. The user controls the robot 'manually' with an intuitive human-robot interface to provide demonstration, which is followed by the robot learning of the performed task. However, the control of robotic manipulators by motor impaired individuals is a challenging topic. In this paper, a novel head gesture-based interface for hands-free robot control and a framework for robot learning from demonstration are presented. The head gesture-based interface consists of a camera mounted on the user's hat, which records the changes in the viewed scene due to the head motion. The head gesture recognition is performed using the optical flow for feature extraction and support vector machine for gesture classification. The recognized head gestures are further mapped into robot control commands to perform object manipulation task. The robot learns the demonstrated task by generating the sequence of actions and Gaussian Mixture Model method is used to segment the demonstrated path of the robot's end-effector. During the robotic reproduction of the task, the modified Gaussian Mixture Model and Gaussian Mixture Regression are used to adapt to environmental changes. The proposed framework was evaluated in a real-world assistive robotic scenario in a small study involving 13 participants; 12 able-bodied and one tetraplegic. The presented results demonstrate a potential of the proposed framework to enable severe motor impaired individuals to demonstrate daily living tasks to robotic manipulators.