Abstract
Abstract: :
Purpose: It has been hypothesized that members of the activin family of growth factors play important regulatory roles in chick embryo retinal development, based on their patterns of retinal expression in ovo, and on the effects of activin on retinal cells in culture (Belecky-Adams et al, Dev. Biol. 210:107-123, 1999). The purpose of the present study is to test this hypothesis through functional experiments in ovo. Methods: Loss-of-function experiments were carried out by RCAS retrovirus-mediated retinal overexpression of follistatin, a secreted protein that sequesters activin and prevents it from binding to its receptors. An RCAS retrovirus encoding green fluorescent protein (GFP) was used as control. Chick embryo eyes were injected intravitreally on embryonic day (ED) 3, allowed to develop for 5-12 additional days, and analyzed by light microscopy and immunocytochemistry (ICC) with a variety of antibodies. Results: ICC for viral antigens showed extensive retroviral infection with both follistatin and control RCAS on ED 8. At this stage, follistatin-treated retinas appeared less developed than GFP controls, particularly in the inner retina. The latter showed a marked decrease in the inner plexiform layer, corroborated by ICC with antibodies against synaptophysin and synaptic vesicle antigens. A population of calbindin (+) amacrine cell, present in the controls, was absent from follistatin-treated retinas, in which the ganglion cell layer also appeared somewhat reduced. Conclusion: These findings are consistent with previously observed effects of activin in vitro, and support the hypothesis that activin plays a significant role in the regulation of neuronal development in ovo. Ongoing studies are extending these studies to other developmental stages, and are investigating whether inhibitory effects of activin on photoreceptor differentiation, previously observed in culture, also take place in ovo.
Keywords: 564 retinal development • 423 growth factors/growth factor receptors • 419 gene transfer/gene therapy