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 factors (FGFs) in the development, differentiation and function of the central nervous system, we analysed the expression of the mRNA, and the presence and tissue distribution of the translated product, of one member of the FGF family, acidic FGF (aFGF), within the mammalian retina. Firstly, the relative abundance of aFGF mRNA was assayed in embryonic (between 14 and 17 days of gestation), postnatal (between 1 and 17 days after birth) and adult rat retina by quantitative reverse transcription-coupled polymerase chain reaction amplification using specific aFGF oligonucleotides. The level of expression remained uniformly low throughout the embryonic period and until postnatal day 7. Therefore the quantity of aFGF mRNA increased rapidly, reaching 80% of adult levels by eye opening (postnatal day 13). Adult levels were three-fold higher than at early developmental times. In situ hybridization of adult rat retina using specific antisense aFGF riboprobes revealed labelling in all cellular layers. Antisera raised against recombinant human aFGF revealed very little labelling of 4-day postnatal retina, but by postnatal days 8 and 17 immunoreactive aFGF was localized mainly within the photoreceptor cell bodies. Western blots of retinal extracts derived from 17-day embryonic, 4-day postnatal and adult retina probed with the same antibody revealed a single immunoreactive band of the expected molecular weight (18 kDa) in all extracts. Thus aFGF is mostly transcribed and translated within the retina subsequent to the major steps of cell birth, migration and differentiation, and seems to be abundantly expressed by maturing photoreceptor cells.