Generation of retinal cells in the wallaby, Setonix brachyurus (quokka)

Harman, A.M.; Beazley, Lyn

doi:10.1016/0306-4522(89)90246-7

Cited by 78 publications

(73 citation statements)

References 37 publications

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“…The order of cell genesis in Xenopus retina apparent at the clonal level is very similar to that of other vertebrates [wallaby (Harman and Beazley, 1989); monkey (La Vail et al, 1991); rat (Rapaport et al, 2004)]. The only difference is that RPr are generated in close step with CPr in Xenopus, whereas in the wallaby, rat and non-foveal region of monkey retina, they are generated late, after Am.…”

Section: Research Articlesupporting

confidence: 52%

“…Were this model to operate one would expect consistent ordinal relationships between some cell types, but not between others. For example, if the phases of retinal cell birth reported in a number of vertebrates (Harman and Beazley, 1989;La Vail et al, 1991;Rapaport et al, 2004) represent competency periods for subsets of cell types, we would have expected to see variable ordinal relations within, but invariant relations between, phases. We always observe rigid ordinal relationships and this accords only with the stepwise model for shifting competence states of RPCs, a cell type at a time.…”

Section: Research Articlementioning

confidence: 99%

“…The dominant hypothesis accounting for these data was that RPCs produced uncommitted offspring that were acted upon by signals in the environment and instructed in what to mature as. Gradual change in environmental signals during development was invoked to account for the temporal periods of genesis for each retinal cell type (Harman and Beazley, 1989;La Vail et al, 1991;Prada et al, 1991;Rapaport et al, 2004). Specifically, RGCs are always the first cell type to be born, followed by a group including Ho, Am and CPr, and culminating with a group including RPr, BP and MG.…”

Section: Introductionmentioning

confidence: 99%

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Defining retinal progenitor cell competence inXenopus laevisby clonal analysis

Wong

Rapaport

2009

Development

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Extrinsic cues and intrinsic competence act in concert for cell fate determination in the developing vertebrate retina. However, what controls competence and how precise is the control are largely unknown. We studied the regulation of competence by examining the order in which individual retinal progenitor cells (RPCs) generate daughters. Experiments were performed in Xenopus laevis, whose full complement of retinal cells is formed in 2 days. We lineage-labeled RPCs at the optic vesicle stage. Subsequently we administered a cell cycle marker, 5-bromodeoxyuridine (BrdU) at early, middle or late periods of retinogenesis. Under these conditions, and in this animal, BrdU is not cleared by the time of analysis, allowing cumulative labeling. All retinal cell types were generated throughout nearly the entire retinogenesis period. When we examined the order that individual RPCs generated daughters, we discovered a regular and consistent sequence according to phenotype: RGC, Ho, CPr, RPr, Am, BP, MG. The precision of the order between the clones supports a model in which RPCs proceed through stepwise changes in competence to make each cell type, and do so unidirectionally. Because every cell type can be generated simultaneously within the same retinal environment, the change in RPC competence is likely to be autonomous.

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Section: Research Articlesupporting

confidence: 52%

Section: Research Articlementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Defining retinal progenitor cell competence inXenopus laevisby clonal analysis

Wong

Rapaport

2009

Development

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“…Distinguishing ganglion cells from other neurons in the retinal ganglion cell layer is, to some extent, problematic without using a retrograde tracer such as horseradish peroxidase [Harman and Beazley, 1989]. This was not possible with the animals available to us and so, in the present study, we have identified ganglion cells in Nissl stained retinae using standard morphological criteria.…”

Section: Cell Identificationmentioning

confidence: 94%

The Retinal Ganglion Cell Layer and Visual Acuity of the Camel

Harman¹,

Dann²,

Ahmat³

et al. 2001

Brain Behav Evol

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We examined the retinal ganglion cell layer of the dromedary camel, Camelus dromedarius. We have estimated that there are 8 million neurons in the ganglion cell layer of this large retina (mean area of 2,300 mm^–2). However, only approximately 1 million are considered to be ganglion cells. The ganglion cells are arranged as two areas of high cell density, one in the temporal and one in the nasal retina. Densities of ganglion cells between these two high density regions is much lower, often less than 100 per mm^–2. In between these two high density regions, on the nasal side of the optic nerve head, is a unique and dense vertical streak of mostly non-ganglion cells; the function of this specialization is unknown. On the basis of ganglion cell density we estimate that the peak acuity in the dromedary camel is about 10 and 9.5 cycles per degree in the temporal and nasal high density regions respectively and falls to 2–3 cycles per degree in the central retina. Behavioral acuity was estimated for one bactrian camel and was found to be approximately 10 cyc deg^–1. The camel has a retina with a mean thickness of 104 µm, less than the 143 µm thickness that has previously been thought to be necessary for a retinal vasculature. Nevertheless, there is an extensive vitreal vasculature that does not appear to spare any retinal region.

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“…During this phase, the retinae also undergo marked lateral expansion, particularly in the periphery, through the differential addition of second-phase cells to peripheral rather than central retina. 6 The retina is therefore potentially directly vulnerable to corticosteroid therapy, which has known antimitotic effects on DNA, RNA and protein synthesis in the nervous system. 7 , 8 Finally, although there is general agreement that low birthweight preterm infants are at risk for impaired motor development, recent evidence suggests they are also specifically vulnerable to impaired visual development.…”

mentioning

confidence: 99%