CHICKEN HOMEOBOX GENE PROX-1 RELATED TO DROSOPHILA-PROSPERO IS EXPRESSED IN THE DEVELOPING LENS AND RETINA

Prox 1 is the vertebrate homolog of Drosophila prospero, a gene known to be expressed in the lens-secreting cone cells of fly ommatidia. Chi cken Prox 1 cDNAs were isolated from 14 day embryonic chicken lenses, and a complete open reading frame encoding an 83 kDa protein was eluci dated. The homeodomains of chicken and mouse Prox 1 are identical at t he amino acid level and are 65-67% similar to the homeodomains of Dros ophila and C. elegans prospero. The homology between these proteins ex tends beyond the homeodomain. There is 56% identity between chicken Pr ox 1 and Drosophila prospero in the C-terminal region downstream of th e homeodomain, whereas there is little similarity upstream of the home odomain. Prox 1 is expressed most actively in the developing lens and midgut; and at lower levels in the developing brain, heart, muscle, an d retina. cDNA sequencing has established that there are alternatively spliced forms of the single Prox 1 gene, which probably account for t he two abundant RNAs of about 2 and 8 kb and two less abundant RNAs cl ose to 3.5 kb in length in the lens. In the lens fibers, only the shor test mRNA was present, whereas, in the epithelial cells, both short an d long mRNAs were detected. By using in situ hybridization, expression of the Prox 1 gene was first detected at stage 14 in the early lens p lacode and slightly preceded the expression of delta 1-crystallin, the first crystallin gene expressed in the developing chicken lens. At la ter stages of development, Prox 1 mRNA was observed throughout the len s, but it appeared more abundant around the bow region of the equator than in the anterior epithelium or the fibers. In the retina, expressi on of the Prox 1 gene was detected mainly in the inner nuclear layer d uring later stages of histogenesis. The conserved pattern of Prox 1/pr ospero gene expression in vertebrates and Drosophila suggests that Pro x 1, like Pax-6, may be essential for eye development in different sys tematic groups. (C) 1996 Wiley-Liss, Inc.