Developmental Expression of Retinal Cone cGMP-Gated Channels: Evidence for Rapid Turnover and Trophic Regulation

Abstract

The cyclic GMP-gated cationic channels of vertebrate photoreceptors are essential for visual phototransduction. We have examined the developmental regulation of cGMP-gated channels in morphologically identified cones in the chick retina. Expression of cone-type cGMP-gated channel mRNA can be detected at embryonic day 6 (E6), but expression of functional channels, as accessed by patch-clamp recordings, cannot be detected until E8. Plasma membrane channels in embryonic cones have a high turnover rate because inhibition of protein synthesis or disruption of the Golgi apparatus causes an almost complete loss of functional cGMP-gated channels within 12 hr. Different subpopulations of cones begin to express functional channels at different developmental stages, but all cones express channels by E10. Expression of cGMP-gated channels in at least one cone subpopulation appears to require one or more soluble differentiation factors, which are presumably present in the normal microenvironment of the developing retina. Application of chick embryo extract (CEE), a rich source of trophic factors, causes marked stimulation of cGMP-gated channel expression in chick cones at E8, but not at E6. Inhibition of MAP kinase (Erk) signaling using PD98059, or inhibition of PI3 kinase signaling by LY294002, blocked the stimulatory effects of CEE on E8 cones. Several recombinant trophic factors were also tested, but none could mimic the stimulatory effects of CEE on channel expression. In summary, the developmental expression of cGMP-gated cationic channels in embryonic cones appears to be regulated by epigenetic factors. The ability of cones to respond to these epigenetic factors is also developmentally regulated. Key words: CNG channels; photoreceptor; cone; retina; development; chick embryoThe cGM P-gated cationic channels of photoreceptors are essential elements of vertebrate phototransduction cascades (for review, see Stryer, 1986;Molday and Molday, 1998). Considerable progress has been made toward understanding the molecular aspects of gating (Liu et al., 1996(Liu et al., , 1998Ruiz and Karpen, 1997;Matulef et al., 1999;Paoletti et al., 1999;Shammat and Gordon, 1999), permeation (Goulding et al., 1993; MacK innon, 1993, 1994;Dzeja et al., 1999;Seifert et al., 1999), and modulation (Gordon et al., 1992;Hsu and Molday, 1993;Molokanova et al., 1997Molokanova et al., , 1999a Molokanova et al., ,b, 2000Grunwald et al., 1998;Weitz et al., 1998) of these channels. In contrast, little is known about regulation of the developmental expression of these channels in photoreceptor plasma membranes. This is an important question, because reduced plasma membrane expression of these channels leads to photoreceptor degeneration in rodents (LeConte and Barnstable, 2000) and humans (Dry ja et al., 1995).In developing rat rods, the expression of cGM P-gated channel ␣-subunit transcripts can be detected by the time of birth (Ahmad et al., 1990). Immunochemically detectable rod-type cGM P-gated channel ␣-subunits are not initially detected until the se...

Nitric oxide regulates angiogenesis through a functional switch involving thrombospondin-1

“…3E), which stimulated guanylyl cyclase in endothelial cells (10). As reported, cGMP-mediated ERK phosphorylation was purported to provide a progrowth pathway (20,(35)(36)(37). In this study, NO mediated a cGMP-dependent down-regulation of TSP1 in association with enhanced proliferation.…”

Matrix metalloproteinase-9 and -2 enhance the ligand sensitivity of photoreceptor cyclic nucleotide-gated channels

“…5 ). Finally, the turnover of retinal CNG channels is thought to occur relatively rapidly, with a channel half-life likely less than 12 h. 68 Such rapid turnover rates could allow irreversible modifications—such as channel proteolysis—to participate in circadian regulation of ligand sensitivity. 69 Interestingly, we have observed MMP-dependent decreases in maximum current during extended time courses; thus, MMPs may contribute to channel turnover after prolonged MMP exposure.…”

Extrinsic regulation of T‐type Ca2+ channel expression in chick nodose ganglion neurons

“…Hearts from E7 or E20 chick embryos were excised, cleared of connective tissue, cut into small pieces to remove blood, and homogenized in icecold, serum-free phosphate buffered solution (PBS). To obtain whole chick extract, an E15 chick embryo was passed through a 10-mL syringe into a centrifuge tube containing 3 mL of serum-free medium prior to centrifugation (Ko et al, 2001). Tissue extracts were kept at 48C for 2 h and then centrifuged at 15,000 rpm for 75 min.…”