Biomedical subjects

Lyn Beazley

Publications and source records attributed to Lyn Beazley.

5 recordsLinked to original sources

PubMed2006

Retinal ganglion cell axons regenerate in the presence of intact sensory fibres.

A novel allograft paradigm was used to test whether adult mammalian central axons regenerate within a peripheral nerve environment containing intact sensory axons. Retinal ganglion cell axon regeneration was compared following anastomosis of dorsal root ganglia grafts or conventional peripheral nerve grafts to the adult rat optic nerve. Dorsal root ganglia grafts comprised intact sensory and degenerate motor axons, whereas conventional grafts comprised both degenerating sensory and motor axons. Retinal ganglion cell axons were traced after 2 months. Dorsal root ganglia survived with their axons persisting throughout the graft. Comparable numbers of retinal ganglion cells regenerated axons into both dorsal root ganglia (1053+/-223) and conventional grafts (1323+/-881; P>0.05). The results indicate that an intact sensory environment supports central axon regeneration.

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PubMed2006

A multiphasic role for Pax7 in tectal development.

The optic tectum differentiates from the mesencephalic alar plate and matures into a characteristically laminated structure. Evidence presented here suggests a role for Pax7 in all stages of development of tectal architecture, from regionalisation to specification of neurons and tectal topography. Analysis of Pax7 expression profiles over a range of developmental stages (E2-E12) suggests a biphasic role for Pax7: initially Pax7 expressing cells in the proliferative neuroepithelial layer establish tectal polarity whereas later Pax7 is expressed in neurons of the retino-recipient precursor stratum griseum et fibrosum superficiale (sgfs) laminae where graded levels may establish tectal topography. Furthermore, co-localisation immunofluorescence confirmed that Pax7 is initially expressed in the majority of proliferative neuroepithelial cells and later in a subset of neurons of the sgfs laminae.

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PubMed2004

Expression profiles suggest a role for Pax7 in the establishment of tectal polarity and map refinement.

The role for Pax7 in establishing tectal polarity and map refinement was authenticated by gene expression studies in vivo and in vitro. Throughout development (stages E2-E12 were examined) a rostral(low)-caudal(high) and dorsal(high)-ventral(low) Pax7 expression gradient was detected immunohistochemically in the chick optic tectum, indicating a role for Pax7 in establishing tectal polarity. Chick retino-recipient tectal cells positive for Pax7 also co-expressed ephrin-A2, a molecule involved in the establishment and refinement of the retinotopic map. In vitro, PAX7 up-regulated ephrin-A2 when transfected into undifferentiated P19 cells; cells became negative for both Pax7 and ephrin-A2 protein following treatment with anti-sense oligonucleotides. These results suggest that in addition to being involved in the early establishment of tectal polarity, Pax7 plays a later role in retino-tectal map formation and refinement.

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PubMed2004

Characterisation of tectal ephrin-A2 expression during optic nerve regeneration in goldfish: implications for restoration of topography.

EphA receptors and their ligands the ephrin-As, expressed as retinal and tectal gradients, are required for the development of retino-tectal topography [Neuron 25 (2000) 563] and its restoration during goldfish optic nerve regeneration [Mol. Cell. Neurosci. 25 (2004) 56]. We have reported previously that, during regeneration, a transient EphA3/A5 gradient is formed by differential expression across the entire retinal ganglion cell (RGC) population [Neurosci. Abs. 33 (2003) 358.2; Exp. Neurol. 183 (2003) 593]. In retino-recipient tectal layers, ephrin-A2 is normally expressed by only a sub-population of cells, but during regeneration, there is a graded increase with more expressing cells caudally than rostrally [Exp. Neurol. 166 (2000) 196]. Here, we examine the characteristics of tectal ephrin-A2 expression during regeneration. We report that the level of ephrin-A2 expression is comparable for all ephrin-A2-positive cells in normal animals and during regeneration. Using double-labelling immunohistochemistry for ephrin-A2 and specific cell markers (NeuN for neurons, GA5 for astrocytes, NN-1 for microglia/endothelial cells and 6D2 for oligodendrocytes), we demonstrate that ephrin-A2-expressing cells, as in normal animals, are exclusively neuronal. Moreover, double labelling with BrdU showed that ephrin-A2 is expressed in resident cells and not those generated during optic nerve regeneration [Brain Res. 854 (2000) 178, 153 (1978) 345].

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PubMed2003

A dorso-ventral gradient of Pax6 in the developing retina suggests a role in topographic map formation.

Expression of the transcription factor Pax6 was assessed immunohistochemically in embryonic chick retina during retino-tectal map formation. A low dorsal to high ventral gradient was found that correlated with expression of the axonal guidance cue EphB2. Furthermore, transfection of Pax6 into undifferentiated P19 cells up-regulated EphB2. The results raise the possibility that Pax6 is upstream of EphB2 and that its graded expression defines the dorso-ventral axis of the retino-tectal projection.

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