Nrl and Sp Nuclear Proteins Mediate Transcription of Rod-specific cGMP-phosphodiesterase β-Subunit Gene

Abstract

cGMP-phosphodiesterase (PDE) is the key effector in rod photoreceptor signal transduction. Mutations in the gene encoding its catalytic ␤-subunit (␤-PDE) cause retinal degenerations leading to blindness. We report that the short ؊93 to ؉53 sequence in the upstream region of this gene is sufficient for ␤-PDE transcription in both Y79 human retinoblastoma cells and Xenopus embryo heads maintained ex vivo. This sequence also functions as a minimal rod-specific promoter in transgenic Xenopus tadpoles. The Nrl transcription factor binds in vitro to the ␤Ap1/NRE regulatory element located within this region and transactivates it when overexpressed in nonretinal 293 embryonic kidney cells. We also found a G/Crich activator element, ␤/GC, important for promoter activity in Y79 retinoblastoma cells and Xenopus embryos. Both the ubiquitous Sp1 and the central nervous system-specific Sp4 transcription factors are expressed in retina and interact with this element in vitro. Electrophoretic mobilities of ␤/GC-Y79 nuclear protein complexes are altered by antibodies against Sp1 and Sp4. Thus, our results implicate Nrl, Sp1, and Sp4 in transcriptional regulation of the rod-specific minimal ␤-PDE promoter. We also conclude that Xenopus laevis is an efficient system for analyzing the human ␤-PDE promoter and may be used to study other human retinal genes ex vivo and in vivo.The vertebrate retina is a highly specialized sensory extension of the central nervous system responsible for light perception and conversion into a neural stimulus, phototransduction as well as the initial visual signal integration and processing. Phototransduction occurs both in rod and cone photoreceptors. During rod phototransduction, rhodopsin-activated transducin activates cGMP-phosphodiesterase (PDE), 1 which leads to the hydrolysis of cGMP and closure of the cGMP-gated transmembrane cationic channels causing hyperpolarization of the plasma membrane and photoreceptor signaling (1).The rod photoreceptor-specific cGMP-PDE is a membraneassociated heterotetrameric enzyme composed of two catalytic ␣-and ␤-subunits and two inhibitory ␥-subunits (2). Each of these subunits is essential for normal cGMP-PDE activity required for phototransduction and the maintenance of retinal health. Mutations in the ␤-subunit of cGMP-PDE (␤-PDE) are currently the most common known cause of autosomal recessive retinitis pigmentosa (3). In addition, mutations in the ␤-PDE gene result in congenital stationary night blindness (4) and retinal degeneration in animal models (5-8). Recently, genetic defects in transcription mechanisms that control the expression of several retina-specific genes have been linked to different types of retinal disorders (9 -12). Thus, it became important to elucidate the molecular events that regulate transcription of the ␤-PDE gene, because abnormalities in these control mechanisms may be detrimental for photoreceptor function and structural integrity.The objective of this investigation was to determine the cis-acting elements and the trans-acting nucle...

FIZ1 is expressed during photoreceptor maturation, and synergizes with NRL and CRX at rod-specific promoters in vitro

“…(Treisman, et al, 1988) Transcription factors that regulate the Rho gene also regulate other rod-specific genes that share a similar expression pattern. , Lerner, et al, 2001 Rho expression varies during development, dramatically increasing during maturation of rod outer-segments. (Bowes, et al, 1988) In mature retina, Rho expression continues to be regulated to follow the circadian patterns of rod outer-segment formation.…”

“…NRL binds to NRE elements in several rod-specific genes: Rho, Pde6b, Pde6a and Gnat-1. (Ahmad, 1995, DesJardin and Hauswirth, 1996, Lerner, et al, 2001, Morabito, et al, 1991, Nie, et al, 1996 NRL can bind directly with CRX to synergistically co-activate the Rho promoter. (Mitton, et al, 2000) FIZ1 represents a model to study an interface between these crucial transcription factors and the more ubiquitous regulatory machinery of the cell.…”

Regulation of photoreceptor gene expression by Crx-associated transcription factor network

“…Functional interactions with numerous other proteins have been reported. These include photoreceptor-specific transcription factors [Nrl and Nr2e3, discussed below; Qrx ] and general transcription factors [Sp family members (Lerner et al, 2001); and nuclear receptor Ror isoforms ]. Crx also interacts with chromatin remodeling factors [ataxin-7 (La Spada et al, 2001), HMG I/Y (Chau et al, 2000), Baf ], the transcription coactivators Cbp and p300 (Yanagi et al, 2000), and the STAGA coactivator/chromatin remodeling complex (Palhan et al, 2005).…”

Preventing polyglutamine-induced activation of c-Jun delays neuronal dysfunction in a mouse model of SCA7 retinopathy

“…Indeed, in the absence of one or the other, expressions of Rho and Gnat1 are negligible. Notably, Nrl is required for Pdeb expression, while Crx is not (Furukawa et al, 1999;Lerner et al, 2001;Mears et al, 2001). Since in JunAA-R7E mice Crx expression is as impaired as in CT-R7E mice, we hypothesized that Nrl primarily promotes Pdeb expression in our context.…”