Molecular characterization of retinal stem cells and their niches in adult zebrafish

BACKGROUND: The persistence in adult teleost fish of retinal stem cells that exhibit all of the features of true 'adult stem cells' – self-renewal, multipotency, and the capacity to respond to injury by mitotic activation with the ability to regenerate differentiated tissues – has been known for several decades. However, the specialized cellular and molecular characteristics of these adult retinal stem cells and the microenvironmental niches that support their maintenance in the differentiated retina and regulate their activity during growth and regeneration have not yet been elucidated. RESULTS: Our data show that the zebrafish retina has two kinds of specialized niches that sustain retinal stem cells: 1) a neuroepithelial germinal zone at the interface between neural retina and ciliary epithelium, called the ciliary marginal zone (CMZ), a continuous annulus around the retinal circumference, and 2) the microenvironment around some Müller glia in the differentiated retina. In the uninjured retina, scattered Müller glia (more frequently those in peripheral retina) are associated with clusters of proliferating retinal progenitors that are restricted to the rod photoreceptor lineage, but following injury, the Müller-associated retinal progenitors can function as multipotent retinal stem cells to regenerate other types of retinal neurons. The CMZ has several features in common with the neurogenic niches in the adult mammalian brain, including access to the apical epithelial surface and a close association with blood vessels. Müller glia in the teleost retina have a complex response to local injury that includes some features of reactive gliosis (up-regulation of glial fibrillary acidic protein, GFAP, and re-entry into the cell cycle) together with dedifferentiation and re-acquisition of phenotypic and molecular characteristics of multipotent retinal progenitors in the CMZ (diffuse distribution of N-cadherin, activation of Notch-Delta signaling, and expression of rx1, vsx2/Chx10, and pax6a) along with characteristics associated with radial glia (expression of brain lipid binding protein, BLBP). We also describe a novel specific marker for Müller glia, apoE. CONCLUSION: The stem cell niches that support multi-lineage retinal progenitors in the intact, growing and regenerating teleost retina have properties characteristic of neuroepithelia and neurogenic radial glia. The regenerative capacity of the adult zebrafish retina with its ability to replace lost retinal neurons provides an opportunity to discover the molecular regulators that lead to functional repair of damaged neural tissue

The role of voltage-gated potassium channel auxiliary subunit Kvbeta2 in neuronal excitability, synaptic plasticity, and cognition in mice.

Voltage-gated potassium (Kv) channels are important regulators of normal neuronal function. In neurons, membrane excitability is regulated through Kv channels by maintaining or returning the cell to resting membrane potential and by modulating action potential threshold, duration, and frequency. Kv channels are composed of tetramers of pore-forming transmembrane subunits that associate with tetramers of cytoplasmic beta (beta) subunits. Alterations in Kv channels or their auxiliary beta subunits have been shown to affect neuronal processes such as long term potentiation (LTP) and neuronal excitability that are thought to be cellular correlates of learning and memory (L&M). Kvbeta2, the most abundant Kvbeta subunit in the brain, is a functional aldo-ketoreductase (AKR) and its catalytic activity has been linked to the regulation of K+ current. The role of Kvbeta2 in L&M, neuronal excitability, and LTP was examined using two strains of mice, one with a targeted deletion of the gene encoding Kvbeta2 (Kcnab2) and the other with a single amino acid mutation in Kvbeta2 that abolishes AKR catalytic activity (Y9OF point mutant). I demonstrated that Kvbeta2 null mice are impaired in spatial and emotional learning. Though these mice exhibited normal LTP in the hippocampus and the amygdala, they were shown to have increased neuronal excitability in the amygdala as measured by spike accommodation and post burstafterhyperpolarization. These results indicate that Kvbeta2 is an important regulator of neuronal excitability and that the loss of this function in vivo may contribute to the observed L&M impairment in Kvbeta2 null mice. For the Y90F point mutant mice, impairment in spatial learning and memory emerged only in aged mice in the absence of changes in LTP in the amygdala. These results indicate that the loss of AKR catalytic activity does not significantly contribute to the phenotype of Kvbeta2 null mice in spatial and emotional learning at a young age. However, once aged, Y90F point mutant mice exhibit similar learning deficits as young Kvbeta2 null mice, potentially indicating a role for an age-related increase in oxidative stress in the emergence of the Y90F point mutant phenotype.Ph.D.Biological SciencesNeurosciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127098/2/3354051.pd

Multi-input Volistor Logic XNOR Gates

A novel approach utilising the emerging memristor technology is introduced for realising a 2-input primitive XNOR gate. This gate enables in-memory computing and is used as a building block of multi-input XNOR gates. The XNOR gate is realised with eight memristors of two crossbar arrays. The average power consumption of an 8-input XNOR gate is calculated and compared with its counterpart realised with CMOS technology – the XNOR gate consumes less power. ESOP realisation can be directly implemented with XNOR gates. Our simulation results and comparisons show the benefit of the proposed XNOR gate in terms of delay, area, and power. Volistor logic XNOR gate. (a) Circuit diagram of two-input volistor logic XNOR gate. Input voltages are applied to memristors S1 and S2 through horizontal wires Win1 and Win2, and the output which is logical AND of states S1 and S2 is calculated by applying VREAD to vertical wire WXNOR. (b) Block diagram of two-input volistor logic gate. (c) A multi-input volistor logic XNOR gate can be implemented by connecting two XNOR gates though CMOS switches