Perception of patterned vibratory stimulation: An evaluation of the tactile vision substitution system

Sensory substitution--The replacing of an impaired sensory channel by a properly functioning one--is possibly best manifested today in attempts to provide visual aids for the blind. The tactile vision substitution system (T.V.S.S.) is an example of one such visual aid. The system presents patterned tactile stimulation to the skin of the observer provided by the output of a closed-circuit television system. Research conducted with congenitally blind Ss in evaluation of the T.V.S.S. has provided useful information concerning the potentialities and limitations of the prototype systems, similarities and differences between tactile and visual perception, and the development of visual perception in the congenitally blind Investigation demonstrated that the congenitally blind Ss can learn to make valid judgements of three-dimensional displays with the T.V.S.S. Such judgements are made on the basis of properties contained in the proximal stimulation properties analogous to the monocular clues of depth presence in vision, such as linear-perspective, apparent elevation in the visual field, size change as a function of distance, occlusion, and texural gradients. Similarities have been noted between judgements made by sighted Ss using vision and by blind Ss using the T.V.S.S. on comparable tasks. A display consisting of two slightly displaced alternating lights is perceived in both situations as a single spot of light moving back-and-forth between two display boundaries. A rotating drum made up of alternate black and white stripes is, when stopped, perceived as briefly moving in the opposite direction. External localization of the source of stimulation also occurs with both sensory inputs. The major differences between the visual and tactile inputs that have been noted have occurred in form recognition tacks. Although blind Ss using the patterned tactile stimulation are able to identify both geometric forms and abstract patterns, accuracy is consistently lower than that of sighted Ss using vision, and the latencies for the blind Ss are significantly longer. It is hypothesized that the longer latencies for the blind Ss using the T.V.S.S. can be accounted for primarily by the need to hand-position the television camera during scanning. A major factor in the lower accuracy for the tactile group is the noted difficulty in detecting and identifying display features located within a mass of stimulation. This difficulty with internal display detail may be a function of sensory inhibition and/or masking. The research findings support a concept of sensory substitution as well as a theory of perception which stresses the modality of many qualities contained in visible displays. Further research is needed to determine the significance of sensor movement--either eye movements or camera manipulation--in the perceptual process

Advancing Stem Cell Biology toward Stem Cell Therapeutics

Here, the International Society for Stem Cell Research (ISSCR) Clinical Translation Committee introduces a series of articles outlining the current status, opportunities, and challenges surrounding the clinical translation of stem cell therapeutics for specific medical conditions

Tic-TACs: Refreshing Hair Growth

Although stem cells are subject to niche control, evidence is emerging that they also contribute to generating the niche through their offspring. Using the hair follicle as a model, Hsu at al. demonstrate that the transient-amplifying cells, downstream of stem cells and well-known cell producers, signal back to stem cells to maintain long-term regenerative capacity

Stem Cells and DNA Damage: Persist or Perish?

Stem cells repopulate tissues after injury while also renewing themselves, but this makes them vulnerable to genotoxic damage. Mohrin et al. (2010) and Milyavsky et al. (2010) now show that mouse and human hematopoietic stem cells make opposing decisions about whether to die or to persist in response to DNA damage

Prospects for Stem Cell-Based Therapy

Resident pools of somatic stem cells in many organs are responsible for tissue maintenance and repair. The goal of regenerative medicine is to exploit these cells either by transplanting them from an exogenous source or by activating endogenous stem cells pharmacologically. For diseases caused by mutations in a single gene, the therapeutic goal is tissue replacement using stem cells engineered to correct the genetic defect. However, a number of technical hurdles must be overcome before therapies based on pluripotent human stem cells can enter the clinic

Cleavage of dsRNAs hyper-edited by ADARs occurs at preferred editing sites

Long double-stranded RNAs (dsRNAs) may undergo covalent modification (hyper-editing) by adenosine deaminases that act on RNA (ADARs), whereby up to 50–60% of adenosine residues are converted to inosine. Previously, we have described a ribonuclease activity in various cell extracts that specifically targets dsRNAs hyper-edited by ADARs. Such a ribonuclease may play an important role in viral defense, or may alternatively be involved in down-regulation of other RNA duplexes. Cleavage of hyper-edited dsRNA occurs within sequences containing multiple IU pairs but not in duplexes that contain either isosteric GU pairs or Watson–Crick base pairs. Here, we describe experiments aimed at further characterizing cleavage of hyper-edited dsRNA. Using various inosine-containing dsRNAs we show that cleavage occurs preferentially at a site containing both IU and UI pairs, and that inclusion of even a single GU pair inhibits cleavage. We also show that cleavage occurs on both strands within a single dsRNA molecule and requires a 2′-OH group. Strikingly, we show that ADAR1, ADAR2 or dADAR all preferentially generate the preferred cleavage site when hyper-editing a long dsRNA

Proteins that contain a functional Z-DNA-binding domain localize to cytoplasmic stress granules

Long double-stranded RNA may undergo hyper-editing by adenosine deaminases that act on RNA (ADARs), where up to 50% of adenosine residues may be converted to inosine. However, although numerous RNAs may undergo hyper-editing, the role for inosine-containing hyper-edited double-stranded RNA in cells is poorly understood. Nevertheless, editing plays a critical role in mammalian cells, as highlighted by the analysis of ADAR-null mutants. In particular, the long form of ADAR1 (ADAR1(p150)) is essential for viability. Moreover, a number of studies have implicated ADAR1(p150) in various stress pathways. We have previously shown that ADAR1(p150) localized to cytoplasmic stress granules in HeLa cells following either oxidative or interferon-induced stress. Here, we show that the Z-DNA-binding domain (Zα(ADAR1)) exclusively found in ADAR1(p150) is required for its localization to stress granules. Moreover, we show that fusion of Zα(ADAR1) to either green fluorescent protein (GFP) or polypyrimidine binding protein 4 (PTB4) also results in their localization to stress granules. We additionally show that the Zα domain from other Z-DNA-binding proteins (ZBP1, E3L) is likewise sufficient for localization to stress granules. Finally, we show that Z-RNA or Z-DNA binding is important for stress granule localization. We have thus identified a novel role for Z-DNA-binding domains in mammalian cells