Multiple functions of fibroblast growth factor-8 (FGF-8) in chick eye development

Fibroblast growth factor-8 (FGF-8) is an important signaling molecule in th e generation and patterning of the midbrain, tooth, and limb. In this study we show that it is also involved in eye development. In the chick, Fgf-8 t ranscripts first appear in the distal optic vesicle when it contacts the he ad ectoderm. Subsequently Fgf-8 expression increases and becomes localized to the central area of the presumptive neural retina (NR) only. Application of FGF-8 has two main effects on the eye. First, it converts presumptive r etinal pigment epithelium (RPE) into NR. This is apparent by the failure to express Bmp-7 and Mitf (a marker gene for the RPE) in the outer layer of t he optic cup, coupled with the induction of NR genes, such as Rx, Sgx-1 and Fgf-8 itself. The induced retina displays the typical multilayered cytoarc hitecture and expresses late neuronal differentiation markers such as synap totagmin and islet-1. The second effect of FGF-8 exposure is the induction of both lens formation and lens fiber differentiation. This is apparent by the expression of a lens specific marker, L-Maf, and by morphological chang es of lens cells. These results suggest that FGF-8 plays a role in the init iation and differentiation of neural retina and lens. (C) 2000 Elsevier Sci ence Ireland Ltd. All rights reserved.