Developmental expression patterns of bone morphogenetic proteins, receptors, and binding proteins in the chick retina

Bone morphogenetic proteins (BMPs), a large subfamily of the transforming growth factor-beta (TGF-beta) superfamily of growth factors, have been implicated in patterning of the central nervous system, but their role in the retina is much less well known. As an initial step in addressing this issue, we have investigated by in situ hybridization the expression patterns of BMP-2, -4, -5, -6, and -7, BMP receptor kinases (BRKs) -1, -2, and -3, and BMP binding proteins noggin and chordin, in the chick embryonic eye at embryonic day 3 (E3), and in isolated retinas at E6, E8, and E18. Strikingly, all mRNAs examined had spatially restricted patterns of expression in the early eye, with the receptors found primarily in the ventral portion of the retina and in the optic stalk, and the ligands and binding proteins localized to other regions of the retina and/or retinal pigment epithelium. Dorso-ventrally restricted patterns of expression persisted at E8, but were no longer apparent at E18, whereas layer-specific patterns of expression were detectable at both E8 and E18. This distribution of BMP family members, receptors, and binding proteins within the retina appears consistent with a possible role in patterning and/or differentiation of this tissue.