Biomedical subjects

Rachael A Pearson

Publications and source records attributed to Rachael A Pearson.

4 recordsLinked to original sources

PubMed2006

Absence of chx10 causes neural progenitors to persist in the adult retina.

PURPOSE: Mutation of the Chx10 homeobox gene in mice and humans causes congenital blindness and microphthalmia (small eyes). This study used Chx10-/- (ocular retardation) mice to investigate how lack of Chx10 affects progenitor/stem cell behavior in the retina and ciliary epithelium (CE). METHODS: The distribution of mitotic retinal progenitor cells (RPCs) during embryonic development was analyzed using phosphohistone 3 (H3)-labeling. DNA flow cytometry was used to measure DNA content. The distribution and phenotype of dividing cells in the postnatal retina and CE was analyzed by incorporation of the thymidine analogue BrdU and immunohistochemistry. RESULTS: The Chx10-/- embryonic retina maintained a constantly sized population of mitotic RPCs during development, causing the mitotic index to increase markedly over time compared with the wild type. Also, the proportion of cells in the G1 phase of the cell cycle was increased compared with the wild type. Of interest, division of RPC-like cells with neurogenic properties persisted in the adult Chx10-/- retina. Colabeling for BrdU and the neural progenitor marker nestin or the neuronal markers beta3-tubulin, syntaxin, and VC1.1 showed that new amacrine-like neurons developed in the adult central retina. By contrast, cells with these characteristics were not observed in the mature wild-type retina. In the mature CE, BrdU-positive cells were observed in both wild-type and Chx10-/- mice. However, neurogenesis from this cell population was not evident. CONCLUSIONS: Without Chx10, proliferative expansion of the embryonic RPC pool is markedly reduced. In the adult retina, lack of Chx10 results in a population of dividing neural progenitor cells that persist and produce new neurons in the central retina.

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PubMed2005

Gap junctions modulate interkinetic nuclear movement in retinal progenitor cells.

During early retinal development, progenitor cells must divide repeatedly to expand the progenitor pool. During G(1) and G(2) of the cell cycle, progenitor cell nuclei migrate back-and-forth across the proliferative zone in a process termed interkinetic nuclear movement. Because division can only occur at the ventricular surface, factors that affect the speed of nuclear movement could modulate the duration of the cell cycle. Gap-junctional coupling and gap junction-dependent Ca(2+) activity are common features of proliferating cells in the immature nervous system. Furthermore, both gap-junctional coupling and changes in [Ca(2+)](i) have been shown to be positively correlated with the migration of a number of immature cell types. Using time-lapse confocal microscopy, we describe the nature and rate of progenitor cell interkinetic nuclear movement. We show that nuclear movement is usually, but not always, associated with Ca(2+) transients and that buffering of these transients with BAPTA slows movement. Furthermore, we show for the first time that gap-junctional communication is an important requirement for the maintenance of normal nuclear movement in retinal progenitor cells. Conventional blockers of gap junctions and transfection of cells with dominant-negative constructs of connexin 43 (Cx43) and Cx43-specific antisense oligodeoxynucleotides (asODNs) all act to slow interkinetic nuclear movement. The gap junction mimetic peptide Gap26 also acts to slow movement, an effect that we show may be attributable to the blockade of gap junction hemichannels.

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PubMed2005

ATP released via gap junction hemichannels from the pigment epithelium regulates neural retinal progenitor proliferation.

The retinal pigment epithelium (RPE) plays an essential role in the normal development of the underlying neural retina, but the mechanisms by which this regulation occurs are largely unknown. Ca2+ transients, induced by the neurotransmitter ATP acting on purinergic receptors, both increase proliferation and stimulate DNA synthesis in neural retinal progenitor cells. Here, we show that the RPE regulates proliferation in the underlying neural retina by the release of a soluble factor and identify that factor as ATP. Further, we show that this ATP is released by efflux through gap junction connexin 43 hemichannels, the opening of which is evoked by spontaneous elevations of Ca2+ in trigger cells in the RPE. This release mechanism is localized within the RPE cells to the membranes facing the neural retina, a location ideally positioned to influence neural retinal development. ATP released from RPE hemichannels speeds both cell division and proliferation in the neural retina.

Adenosine Triphosphate↗

PubMed2004

Ca(2+) signalling and gap junction coupling within and between pigment epithelium and neural retina in the developing chick.

Development of the neural retina is controlled in part by the adjacent retinal pigment epithelium (RPE). To understand better the mechanisms involved, we investigated calcium signalling and gap junctional coupling within and between the RPE and the neural retina in embryonic day (E) 5 chick. We show that the RPE and the ventricular zone (VZ) of the neural retina display spontaneous Ca(2+) transients. In the RPE, these often spread as waves between neighbouring cells. In the VZ, the frequency of both Ca(2+) transients and waves was lower than in RPE, but increased two-fold in its presence. Ca(2+) signals occasionally crossed the boundary between the RPE and VZ in either direction. In both tissues, the frequency of propagating Ca(2+) waves, but not of individual cell transients, was reduced by gap junction blockers. Use of the gap junction permeant tracer Neurobiotin showed that neural retina cells are coupled into clusters that span the thickness of the retina, and that RPE cells are both coupled together and to clusters of cells in the neural retina. Immunolabelling for Cx43 showed this gap junction protein is present at the junction between the RPE and VZ and thus could potentially mediate the coupling of the two tissues. Immunolabelling for beta-tubulin and vimentin showed that clusters of coupled cells in the neural retina comprised mainly progenitor cells. We conclude that gap junctions between progenitor cells, and between these cells and the RPE, may orchestrate retinal proliferation/differentiation, via the propagation of Ca(2+) or other signalling molecules.

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