PAX-6, PROX-1, AND CHX10 HOMEOBOX GENE-EXPRESSION CORRELATES WITH PHENOTYPIC FATE OF RETINAL PRECURSOR CELLS

Purpose. To study the expression patterns of the homeobox genes Pax-6, Prox 1, and Chx10 during chick retinal development in vivo and in vit ro. Methods. Sections of paraformaldehyde-fixed, paraffin-embedded eye s were obtained at a range of developmental stages. In situ hybridizat ion was carried out on tissue sections using digoxigenin-labelled sens e and antisense RNA probes that recognize chicken Pax-6 and Prox 1 (wh ose sequences were already available), and chicken Chx10 (which was cl oned and sequenced as part of this study). Selected developmental stag es were also studied by immunocytochemistry With antibodies against Pa x-6 and Prox 1, and by Northern blot analysis using (32)p-labelled pro bes. Results. Until embryonic day (ED) 5, in situ hybridization shows widespread, diffuse distribution of all three genes. Between ED 6 and ED 8, however, they acquire distinct, topographically specific pattern s of expression. The Prox 1 signal is predominantly expressed in the p rospective horizontal cell layer of the neuroepithelium, decreases vit really, and is absent from ganglion cells and the prospective photorec eptor layer. Pax-6 is strongly expressed only in the prospective gangl ion-cell and amacrine-cell regions at the same stages, and is not dete cted in prospective photoreceptors. Chx10 expression becomes concentra ted in the future bipolar-cell region of the inner nuclear layer. Simi lar patterns are maintained by ED 15 through ED 18, after cell differe ntiation has taken place, Pax-6 and Prox 1 immunoreactive materials sh owed nuclear localization and a pattern of laminar distribution equiva lent to that seen by in situ hybridization. Conclusions. These results suggest that the differentiated fate of retinal precursor cells may b e influenced by Pax-6, Prox 1, or Chx10; this hypothesis is now being tested using dissociated chick embryo retinal cell cultures. Invest Op hthalmol Vis Sci. 1997;38:1293-1303.