BASIC FIBROBLAST GROWTH-FACTOR IN RETINAL DEVELOPMENT - DIFFERENTIAL LEVELS OF BFGF EXPRESSION AND CONTENT IN NORMAL AND RETINAL DEGENERATION (RD) MUTANT MICE

The spatial and temporal patterns of expression and content of bFGF du ring postnatal development of the retina were established in C57BL/6J mice. Western blot analysis, using an anti-rodent bFGF antibody, shows multiple molecular weights of 18, 20.5, and 22 kDa of bFGF protein is olated from the adult retina. A bioassay indicates that this putative basic fibroblast growth factor (bFGF) stimulates proliferation of BALB /c 3T3 fibroblasts in a dose-dependent manner identical to an authenti c bFGF standard. Immunocytochemistry reveals that bFGF immunoreactivit y is located primarily in the immature photoreceptors during postnatal development and is associated with the photoreceptor outer segment/in terphotoreceptor matrix complex in the adult retina. bFGF mRNA express ion pattern and levels were evaluated using mouse bFGF riboprobes with in situ hybridization and quantitative ribonuclease protection assay. bFGF mRNA expression is not detectable in the retina until Postnatal Day 10 (P10), although high levels of bFGF mRNA signals were consisten tly observed in astrocytes in the optic disc at all postnatal ages exa mined. From P10 to the adult stage, bFGF mRNA was localized mainly to the photoreceptor inner segments, and the bFGF mRNA levels were approx imately the same at P10 and in the adult retina. The patterns of retin al bFGF expression and content during normal development established a bove were compared to these parameters in the retina of rd (C57BL/6J r d/rd), a spontaneous mouse mutant in which photoreceptors degenerate s hortly after birth. More bFGF immunoreactivity was detected in the out er retina during photoreceptor degeneration than was present in normal photoreceptors at equivalent ages. Densitometry measurements indicate that the level of immunoreactivity is 56% to 1.8-fold higher in rd th an in the normal retina between P6 and P10, respectively. This is at l east partially due to elevated bFGF mRNA expression in rd retinas duri ng photoreceptor degeneration. In situ hybridization showed more inten se bFGF mRNA hybridization signals in rd photoreceptors from P10 to P1 5, and RNase protection assay demonstrated much higher hybridization s ignals in rd retinas from P6 to P10 than in the normal retinas at thes e stages. More bFGF mRNA hybridization signals were also present in so me cells in the inner nuclear layer following photoreceptor cell death in the rd retina but were only weakly evident in the inner nuclear la yer in the normal adult retina. These results provide the first eviden ce that a naturally occurring neuronal degeneration is accompanied by elevated expression of bFGF in degenerating neurons prior to cell deat h. Our observations suggest that up-regulation in the expression of th is growth factor may reflect an endogenous protective mechanism which can be activated when neurons are subjected to metabolic stress. (C) 1 995 Academic Press, Inc.