Expression and possible function of fibroblast growth factor 9 (FGF9) and its cognate receptors FGFR2 and FGFR3 in postnatal and adult retina

Abstract

Fibroblast growth factors (FGFs) are important regulators of retinal development and survival. We examined the expression and distribution of FGF9 and its preferred receptors FGFR2IIIc and FGFR3IIIc in this tissue. FGF9 transcripts in whole rat retina were detected by RT-PCR but were not present in purified cultured Muller glia. Transcripts appeared as 3.2-kb and 4.0-kb bands on Northern blots, and Western blotting of whole retina revealed FGF9-immunoreactive bands at 30 and 55 kDa. FGF9 mRNA demonstrated a biphasic expression profile, elevated at birth and adulthood, but relatively decreased during terminal retinal differentiation (4-14 days postnatal). Antibody labeling broadly reflected these findings: staining in vivo was observed mainly in the inner retina (and outer plexiform layer in adults) whereas FGF9 was not detectable in cultured Muller glia. In adults, FGF9 in situ hybridization also showed a detectable signal in inner retina. FGFR2IIIc and FGFR3IIIc were detected by RT-PCR, and Western blotting showed both FGFRs existed as multiple forms between approximately 100-200 kDa. FGFR2 and FGFR3 antibodies showed prominent labeling in the inner retina, especially in proliferating cultured Muller glia. Exogenous FGF9 elicited a dose-dependent increase in Muller glial proliferation in vitro. These data suggest a role for FGF9 in retinal differentiation and maturation, possibly representing a neuronally derived factor acting upon glial (and other) cells.

Sip1 regulates sequential fate decisions by feedback signaling from postmitotic neurons to progenitors

“…When it is ectopically expressed in retinal pigment epithelium, these cells lose their retinal pigment epithelium character, undergo a cell-fate switch and become neural retina 41 . Also, exogenous application of Fgf9 induces proliferation of Fgfr2/3-positive Müller glial cells in vitro 42 . In the neocortex, analysis of both Fgfr2 and Gfap conditional knockouts and Fgfr1/Fgfr2 and Gfap double mutants showed a decrease in the density of astrocytes in the dorsal neocortex 43 .…”

Localization patterns of fibroblast growth factor 1 and its receptors FGFR1 and FGFR2 in postnatal mouse retina

“…We have also observed faint FGF1 immunoreac- tivity in the photoreceptor inner and outer segments, consistent with previous reports of the presence of FGF1 in photoreceptors or in the ONL of various mammalian retinas (Bugra and Hicks 1997;Bugra et al 1993;Caruelle et al 1989;Jacquemin et al 1990Jacquemin et al , 1993Kitaoka et al 1994;Lovicu et al 1997;Noji et al 1990). FGF2, FGF5, and FGF9 have also been detected in photoreceptors, the ONL, or the interphotoreceptor matrix of mammalian retinas (Bugra and Hicks 1997;Cinaroglu et al 2005;Hageman et al 1991;Kitaoka et al 1994;Lovicu et al 1997;Ohsato et al 1997).…”

“…These observations are probably consistent with our finding of FGF1 immunoreactivity within IPL nerve fibers, which do not appear to belong to ganglion cell dendritic trees. Several studies suggest the presence of other members of the FGF family, mainly FGF2 but also FGF5, FGF9, and FGF21, in amacrine cells and in horizontal and/or bipolar cells (Cinaroglu et al 2005;Connolly et al 1992;Gao and Hollyfield 1992;Kitaoka et al 1994;Kurose et al 2004;Lovicu et al 1997;Miyashiro et al 1998;Ohsato et al 1997;Yamamoto et al 1996). We have also observed faint FGF1 immunoreac- tivity in the photoreceptor inner and outer segments, consistent with previous reports of the presence of FGF1 in photoreceptors or in the ONL of various mammalian retinas (Bugra and Hicks 1997;Bugra et al 1993;Caruelle et al 1989;Jacquemin et al 1990Jacquemin et al , 1993Kitaoka et al 1994;Lovicu et al 1997;Noji et al 1990).…”

SIK2 Is Involved in the Negative Modulation of Insulin-Dependent Müller Cell Survival and Implicated in Hyperglycemia-Induced Cell Death

“…29 Following blocking with 1% BSA, 5% skimmed milk powder in 150 mM NaCl, 20 mM Tris-HCl, pH 8.0, 0.1% Tween 20 for 1 hour at room temperature, the membranes were incubated with one of the primary antibodies. Polyclonal SIK2 antibody (rabbit; Novus Biologicals) was used at 1:2500 dilution, anti-GFP (rabbit; Abcam) at 1:1000, anti-pAkt, rabbit or pan-Akt, rabbit (Cell Signaling Technologies, Danvers, MA) at 1:2000 and 1:1000 dilutions, respectively; pERK, ERK2, IRS1, phosphotyrosine antibodies were obtained from Santa Cruz Biotechnology and used at 1:1000 dilution.…”

“…Primary cultures of purified Müller glia were prepared from PN10 rat retina as described previously. 29 Cells were allowed to grow to confluence in DMEM-10% fetal calf serum for RNA isolation.…”