%0 Journal Article
%T Axon-bearing and axon-less horizontal cell subtypes are generated consecutively during chick retinal development from progenitors that are sensitive to follistatin
%A Per-Henrik D Edqvist
%A Madelen Lek
%A Henrik Boije
%A Sarah M Lindb£¿ck
%A Finn Hallb£¿£¿k
%J BMC Developmental Biology
%D 2008
%I BioMed Central
%R 10.1186/1471-213x-8-46
%X In this work we have molecularly characterized three HC subtypes based on Lim1, Isl1, GABA and TrkA, a classification that is consistent with three chick HC subtypes previously defined by morphology. The axon-bearing and axon-less HC subpopulations molecularly defined by Lim1 and Isl1, are born consecutively on embryonic day (E) 3¨C4 and E4¨C5, respectively, and exhibit temporally distinguishable periods of migration. Their relative numbers are not adjusted by apoptosis. A sharp decrease of high endogenous levels of the activin-inhibitor follistatin at E3 coincides with the appearance of the Lim1 positive cells. Extending the follistatin exposure of the HC retinal progenitor cells by injection of follistatin at E3 increased the number of both Lim1- and Isl1 positive HCs when analysed at E9.The results imply that the axon-bearing and axon-less HC subgroups are defined early and are generated consecutively from a retinal progenitor cell population that is sensitive to the inhibitory action of follistatin. The results are consistent with a model wherein added follistatin causes HC-generating progenitors to proliferate beyond the normal period of HC generation, thus producing extra HCs of both types that migrate to the HC layer.During the development of the vertebrate retina, five types of neurons are born in a preserved sequential but overlapping order [1-3]. These are retinal ganglion cells, horizontal cells (HCs), amacrine cells, bipolar cells and photoreceptors. In the mature retina, these cell types are positioned within distinct laminas and can be further divided into subtypes based on morphology, neurochemical properties or function. At the end of the 19th century, Ram¨®n y Cajal recognized this complex lamination and morphological richness of the retina as well as identified retinal subtypes based on morphology. Today, neuronal subtypes are defined and distinguished by molecular and functional criteria rather than by morphology. Approximately 50¨C70 neuronal subtype
%U http://www.biomedcentral.com/1471-213X/8/46