Fibroblast growth factor-2 (FGF2) has neurotrophic effects in vitro and in vivo. It has been demonstrated to decrease photoreceptor cell death in rats exposed to constant light and in rats with an inherited defect in retinal pigmented epithelium (RPE) phagocytosis, but the effects of intravitreous injections of FGF2 in mice are equivocal. In this study, we used transgenic mice with increased expression of FGF2 in photoreceptors (rhodopsin promoter/FGF2 transgenics) to investigate the effects of sustained increased expression of FGF2 in mice with various types of photoreceptor degeneration, including rd mice that are homozygous for mutated phosphodiesterase beta subunit, Q344ter mice that undergo photoreceptor degeneration because of expression of mutated rhodopsin, and mice exposed to 75% oxygen for 1 or 2 weeks. At P21, the outer nuclear layer was markedly reduced in rd mice or Q344ter mice regardless of whether they inherited the rhodopsin promoter/FGF2 transgene. However, after 2 weeks of exposure to 75% oxygen, outer nuclear layer thickness was significantly reduced in littermate control mice compared to FGF2 transgenic mice (P = 0.0001). These data indicate that increased expression of FGF2 in photoreceptors protects them from hyperoxia-induced damage, but does not decrease cell death related to expression of mutated proteins involved in the phototransduction pathway. This suggests that FGF2 protects photoreceptors from oxidative damage, which may play a role in complex genetic diseases such as age-related macular degeneration.

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A number of related enzymes like glutathione S-transferases (GSTs) and fatty acid ethyl ester synthases (FAEESs) have been implicated in detoxification and drug resistance. The anionic class of GSTs, π, and closely related FAEES-III exhibit tissue-specific and developmentally regulated expression, and the former has been shown to be overex-pressed or amplified in a variety of tumors. The GSTPl gene has previously been cloned and cytogenetically localized to human 11q13 by in situ hybridization. Using a series of previously described radiation-reduced somatic cell hybrids, we have sublocahzed GSTP1 to 11q13. We isolated a genomic clone containing the entire GSTPl gene and sequenced it. Analysis of the 5’ region revealed 23 (TAAAA) tandem repeats interrupted by a single TA and TAA insertion. This repeat number differs among individuals. Eleven alleles in a mostly Caucasian sample were observed. This repeat has a polymorphism information content of 0.74. Linkage analysis of the Venezuelan reference pedigree places GSTP1 5 cM distal to PYGM and 4 cM proximal to FGF3 thereby providing a genetic marker half-way between these two loci. The sublocalization and genetic characterization of GSTPl facilitates linkage analysis of several disease genes mapped to this chromosome band as well as the correlation of genetic and physical markers in the region.

In order for the retina to function properly, photoreceptor cell outer segments must be in contact with the adjacent retinal pigmented epithelium (RPE). A mouse model homozygous for the vitiligo mutation of the microphthalmia (Mitf) gene manifests disruption of the outer segment/RPE interdigitation and demonstrates progressive loss of the photoreceptor cells. The mouse nevertheless has near normal levels of rhodopsin for many weeks and it is not known whether there is an in vivo loss of adhesion or whether the disruption is visible following tissue processing for histology. To assess this, a mechanical separation experiment was performed in which neural retinas were peeled free from the RPE and examined for the amount of pigment adherent to them. The peeling experiment indicated that control neural retinas retained significant amounts of adherent pigment at all ages examined. Neural retinas of mutant mice at age 2 weeks demonstrated adherent pigment, but older animals retained minimal pigment. Scanning electron microscopy indicated that the RPE cells of control mice were markedly damaged upon peeling and displayed different planes of cleavage, whereas those of mutants showed minimal cellular damage upon peeling, suggestive of decreased adhesion. A recombination experiment revealed that the mutant RPE/eyecup could reappose mutant and control retinas under in vitro conditions, suggesting that RPE fluid transport abilities were intact. The data provide the first direct experimental evidence that the Mitfvit mutant mouse has a naturally occurring retinal detachment and hence support its value as a model for studies of retina/RPE adhesion.