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A. J. Fischer, J. Stanke, K. Ghai; The Development of Bullwhip Cells in the Embryonic Chicken Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5691.
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© ARVO (1962-2015); The Authors (2016-present)
Bullwhip cells are large, unipolar, axon-forming neurons that regulate the proliferation of progenitors in the circumferential marginal zone (CMZ) of the postnatal chicken retina. There are only about 240 bullwhip cells in the entire retina and these cells are easily identified by their unique morphology and immunoreactivity for glucagon, glucagon-like peptide 1 and substance P. The purpose of this study was to investigate the development of the bullwhip cells in the embryonic chicken retina.
BrdU-birthdating and standard methods of immunocytochemistry were used to identify differentiating bullwhip cells. Retinal explants and dissociated cell cultures were used to assay for the factors that influence the survival of the bullwhip cells.
Glucagon peptide was first detected in bullwhip cells at about E10, whereas substance P was not detected in the bullwhip cells until E15. Morphological differentiation of the bullwhip cells begins at about E14 and is completed by E18. By using BrdU-birthdating, we found that the bullwhip cells are generated very early during retinal development, between E4 and E5. The bullwhip cells are greatly over-produced and nearly 80% of these cells undergo apoptotic cell death during late stages of embryonic development. The bullwhip cells fail to survive in dissociated cell cultures, whereas explants of the retina maintained the survival and differentiation of numerous bullwhip cells. The survival of the bullwhip cells was severely compromised by disruption of microtubules with brief exposure to colchicine, suggesting that retrograde transport of target-derived trophic signals support the survival of these cells. Although glucagon peptide is not present in the E8 retina, we detected mRNA for pro-glucagon, glucagon-receptor and GLP1-receptor at E8.
We conclude that cells fated to become bullwhip neurons are generated long before they begin to differentiate, and that their differentiation and survival depends on the environment provided by the intact retina and perhaps trophic support from target cells.
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