ACIDIC FIBROBLAST GROWTH-FACTOR IS EXPRESSED ABUNDANTLY BY PHOTORECEPTORS WITHIN THE DEVELOPING AND MATURE RAT RETINA

In order to further understand the role(s) of fibroblast growth factor s (FGFs) in the development, differentiation and function of the centr al nervous system, we analysed the expression of the mRNA, and the pre sence and tissue distribution of the transLated product, of one member of the FGF family, acidic FGF (aFGF), within the mammalian retina. Fi rstly, the relative abundance of aFGF mRNA was assayed in embryonic (b etween 14 and 17 days of gestation), postnatal (between 1 and 17 days after birth) and adult rat retina by quantitative reverse transcriptio n-coupled polymerase chain reaction amplification using specific aFGF oligonucleotides. The level of expression remained uniformly low throu ghout the embryonic period and until postnatal day 7. Therefore the qu antity of aFGF mRNA increased rapidly, reaching 80% of adult levels by eye opening (postnatal day 13). Adult levels were three-fold higher t han at early developmental times. In situ hybridization of adult rat r etina using specific antisense aFGF riboprobes revealed labelling in a ll cellular layers. Antisera raised against recombinant human aFGF rev ealed very little labelling of 4-day postnatal retina, but by postnata l days 8 and 17 immunoreactive aFGF was localized mainly within the ph otoreceptor cell bodies. Western blots of retinal extracts derived fro m 17-day embryonic, 4-day postnatal and adult retina probed with the s ame antibody revealed a single immunoreactive band of the expected mol ecular weight (18 kDa) in all extracts. Thus aFGF is mostly transcribe d and translated within the retina subsequent to the major steps of ce ll birth, migration and differentiation, and seems to be abundantly ex pressed by maturing photoreceptor cells.