Fig. 1. Localization of TGF-ß ligands and receptor in the developing chick retina. (A) An E6 chick eye showing the distribution of apoptotic nuclei (green stars). The main areas of cell death (ellipses) are localized in the vicinity of the optic nerve. The box outlines the region shown at higher magnification in B-F. (B-F) Expression of TGF-ß isoforms and receptor (TßRII) in the E6 chick retina (B-D, indirect fluorescence; E,F, DAB stain). (B) TßRII immunoreactivity is distributed evenly over the entire retinal surface. TGF-ß2 (C,E) and TGF-ß3 (D,F) immunoreactivity was observed mainly in the central retina in the region around the optic nerve head, where apoptosis is most prominent during the early period of PCD. In addition, TGF-ß3 is localized in the pigment epithelium (asterisk in D), in structures that span the neuroepithelium, resembling Müller glia cells or radial Müller fibers (arrowheads in D,F) and in the presumptive ganglion cell layer (arrows in D,F). le, lens; nr, neural retina; on, optic nerve; pe, pigment epithelium; vb, vitreous body; ov, optic ventricle. Scale bar: 50 µm.