Axon-bearing and axon-less horizontal cell subtypes are generated consecutively during chick retinal development from progenitors that are sensitive to follistatin

Background  

Horizontal cells are retinal interneurons that modulate the output from photoreceptors. A rich literature on the morphological classification and functional properties of HCs in different animals exists, however, the understanding of the events underlying their development is still limited. In most vertebrates including chicken, two main horizontal cell (HC) subtypes are identified based on the presence or absence of an axon.