Summary The ability to maintain quiescence is critical for the long-term maintenance of a functional stem cell pool. To date, the epigenetic and transcriptional characteristics of quiescent stem cells and how they change with age remain largely unknown. In this study, we explore the chromatin features of adult skeletal muscle stem cells, or satellite cells (SCs), which reside predominantly in a quiescent state in fully developed limb muscles of both young and aged mice. Using a ChIP-seq approach to obtain global epigenetic profiles of quiescent SCs (QSCs), we show that QSCs possess a permissive chromatin state in which few genes are epigenetically repressed by Polycomb group (PcG)-mediated histone 3 lysine 27 trimethylation (H3K27me3), and a large number of genes encoding regulators that specify nonmyogenic lineages are demarcated by bivalent domains at their transcription start sites (TSSs). By comparing epigenetic profiles of QSCs from young and old mice, we also provide direct evidence that, with age, epigenetic changes accumulate and may lead to a functional decline in quiescent stem cells. These findings highlight the importance of chromatin mapping in understanding unique features of stem cell identity and stem cell aging.

Abstract. It is common to use domain specific terminology -attributes -to describe the visual appearance of objects. In order to scale the use of these describable visual attributes to a large number of categories, especially those not well studied by psychologists or linguists, it will be necessary to find alternative techniques for identifying attribute vocabularies and for learning to recognize attributes without hand labeled training data. We demonstrate that it is possible to accomplish both these tasks automatically by mining text and image data sampled from the Internet. The proposed approach also characterizes attributes according to their visual representation: global or local, and type: color, texture, or shape. This work focuses on discovering attributes and their visual appearance, and is as agnostic as possible about the textual description.

Internet-based "online robots" now provide public access to remote locations such as museums and laboratories. The Tele-Actor is a collaborative online teleoperation system for distance learning that allows many students to simultaneously share control of a single mobile resource. Our goal is to preserve the educational advantages of field trips without the drawbacks of group travel.We propose the "Spatial Dynamic Voting" (SDV) interface for Multiple Operator Single Robot (MOSR) teleoperation. The SDV collects, displays, and analyzes a sequence of spatial votes from multiple online operators at their Internet browsers. The votes drive the motion of a single mobile robot or human "Tele-Actor". This paper describes Version 3.0 of the system architecture, SDV interface, algorithms for automated goal selection, and metrics for collaboration and leadership. We report results from a July 2001 field test with 56 remote users. See: www.tele-actor.net.

Inhibitory interneurons constitute ~20% of auditory cortical cells and are essential for shaping sensory processing. Connectivity patterns of interneurons in relation to functional organization principles are not well understood. We contrasted the connection patterns of parvalbumin-immunoreactive cells in two functionally distinct cortical regions, the tonotopic, narrowly frequency-tuned module (cNB) of cat central primary auditory cortex (AI), and the non-tonotopic, broadly tuned second auditory field (AII). Interneuronal connectivity patterns and laminar distribution were identified by combining a retrograde tracer (WAHG) with labeling of the Ca2+ binding protein, parvalbumin (Pv), a marker for the GABAergic interneurons usually described physiologically as fast-spiking neurons. In AI, PV+ cells constituted 13% of the retrograde labeled cells in the immediate vicinity of the injection site, compared to 10% in AII. The retrograde labeling of Pv+ cells along isofrequency countours was confined to cNB. The spatial spread of labeled excitatory neurons in AI was more than twice that found for Pv+ cells. By contrast, in AII, the spread of Pv+ cells was nearly equal to that of excitatory neurons. The retrograde labeling of Pv+ cells was anisotropic in AI and isotropic in AII. This demonstration of inhibitory networks in auditory cortex reveals that the connections of cat GABAergic AI and AII cells follow different anatomical plans and, thus, contribute differently to the shaping of neural response properties. The finding that local connectivity of parvalbumin-immunoreactive neurons in AI is closely aligned with spectral integration properties demonstrates the critical role of inhibition in creating distinct processing modules in AI.