Gene array and expression of mouse retina guanylate cyclase activating proteins 1 and 2

Baylor College of Medicine, Houston, Texas, United States
Investigative Ophthalmology & Visual Science (Impact Factor: 3.4). 06/1998; 39(6):867-75.
Source: PubMed


To identify gene arrangement, chromosomal localization, and expression pattern of mouse guanylate cyclase activating proteins GCAP1 and GCAP2, retina-specific Ca2+-binding proteins, and photoreceptor guanylate cyclase activators.
The GCAP1 and GCAP2 genes were cloned from genomic libraries and sequenced. The chromosomal localization of the GCAP array was determined using fluorescent in situ hybridization. The expression of GCAP1 and GCAP2 in mouse retinal tissue was determined by immunocytochemistry.
In this study, the mouse GCAP1 and GCAP2 gene array, its chromosomal localization, RNA transcripts, and immunolocalization of the gene products were fully characterized. The GCAP tail-to-tail array is located at the D band of chromosome 17. Each gene is transcribed into a single transcript of 0.8 kb (GCAP1) and 2 kb (GCAP2). Immunocytochemistry showed that both GCAP genes are expressed in retinal photoreceptor cells, but GCAP2 was nearly undetectable in cones. GCAP2 was also found in amacrine and ganglion cells of the inner retina. Light-adapted and dark-adapted retinas showed no significant difference in the distribution of the most intense GCAP2 staining within the outer segment and outer plexiform layers.
Identical GCAP gene structures and the existence of the tail-to-tail gene array in mouse and human suggest an ancient gene duplication-inversion event preceding mammalian diversification. Identification of both GCAPs in synaptic regions, and of GCAP2 in the inner retina suggest roles of these Ca-binding proteins in addition to regulation of phototransduction.

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    • "^*Total concentration of GCAPs 1 and 2 in mouse rods is likely between 3 and 9 μM. From Howes et al., 1998; Imanishi et al., 2002,2004; Baehr et al., 2007; Rätscho et al., 2009; Takemoto et al., 2009; Peshenko et al., 2011; Scholten and Koch, 2011. "
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    ABSTRACT: In vertebrate rods and cones, photon capture by rhodopsin leads to the destruction of cyclic GMP (cGMP) and the subsequent closure of cyclic nucleotide gated ion channels in the outer segment plasma membrane. Replenishment of cGMP and reopening of the channels limit the growth of the photon response and are requisite for its recovery. In different vertebrate retinas, there may be as many as four types of membrane guanylyl cyclases (GCs) for cGMP synthesis. Ten neuronal Ca(2+) sensor proteins could potentially modulate their activities. The mouse is proving to be an effective model for characterizing the roles of individual components because its relative simplicity can be reduced further by genetic engineering. There are two types of GC activating proteins (GCAPs) and two types of GCs in mouse rods, whereas cones express one type of GCAP and one type of GC. Mutant mouse rods and cones bereft of both GCAPs have large, long lasting photon responses. Thus, GCAPs normally mediate negative feedback tied to the light-induced decline in intracellular Ca(2+) that accelerates GC activity to curtail the growth and duration of the photon response. Rods from other mutant mice that express a single GCAP type reveal how the two GCAPs normally work together as a team. Because of its lower Ca(2+) affinity, GCAP1 is the first responder that senses the initial decrease in Ca(2+) following photon absorption and acts to limit response amplitude. GCAP2, with a higher Ca(2+) affinity, is recruited later during the course of the photon response as Ca(2+) levels continue to decline further. The main role of GCAP2 is to provide for a timely response recovery and it is particularly important after exposure to very bright light. The multiplicity of GC isozymes and GCAP homologs in the retinas of other vertebrates confers greater flexibility in shaping the photon responses in order to tune visual sensitivity, dynamic range and frequency response.
    Full-text · Article · Jun 2014 · Frontiers in Molecular Neuroscience
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    • "Prominent transcription and/ or expression are observed for all GCAPs in the outer vertebrate retina , in particular in the outer and inner segments of photoreceptor cells. In addition, GCAP specific staining was also observed in cone somata, cell bodies, axons, axon terminals and synaptic pedicles [7] [8] [28] [29], but their functional role in these cell compartments is not understood, in contrast to their well-known function as Ca 2+ -sensitive regulators of GC activity. GCAPs interact with their main targets, membrane bound sensory GCs, and thereby activate GCs, when they are Ca 2+ -free and inhibit GCs, when they are Ca 2+ loaded . "
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    ABSTRACT: Zebrafish express in the retina a large variety of three different membrane-bound guanylate cyclases and six different guanylate cyclase-activating proteins (zGCAPs) belonging to the family of neuronal calcium sensor proteins. Although these proteins are predominantly localized in rod and cone photoreceptor cells of the retina, they differ in their spatial-temporal expression profiles. Further, each zGCAP has a different affinity for Ca(2+) and displays different Ca(2+)-sensitivities of guanylate cyclase activation. Thus, zGCAPs operate as cytoplasmic Ca(2+)-sensors that sense incremental changes of cytoplasmic Ca(2+)-concentration in rod and cone cells and control the activity of their target guanylate cyclases in a Ca(2+)-relay mode fashion.
    Preview · Article · May 2013 · FEBS letters
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    • "GCAP2 is also capable of regulating cGMP production by retGC1 in a Ca2+-dependent manner [17]. Since GCAP2 is predominantly expressed in rods [4], [42], [43], the loss of Ca2+-sensitivity due to the E155G mutation in GCAP1 may be compensated for by GCAP2 to a greater extent in rods than in cones, and may thereby account for the increased loss of cones compared with rods in both the animal model and human disease. In contrast, as shown by the GCAP1 and GCAP2 double knock-out, the loss of all GCAP function does not result in retinal degeneration [17]. "
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    ABSTRACT: Cone dystrophy 3 (COD3) is a severe dominantly inherited retinal degeneration caused by missense mutations in GUCA1A, the gene encoding Guanylate Cyclase Activating Protein 1 (GCAP1). The role of GCAP1 in controlling cyclic nucleotide levels in photoreceptors has largely been elucidated using knock-out mice, but the disease pathology in these mice cannot be extrapolated directly to COD3 as this involves altered, rather than loss of, GCAP1 function. Therefore, in order to evaluate the pathology of this dominant disorder, we have introduced a point mutation into the murine Guca1a gene that causes an E155G amino acid substitution; this is one of the disease-causing mutations found in COD3 patients. Disease progression in this novel mouse model of cone dystrophy was determined by a variety of techniques including electroretinography (ERG), retinal histology, immunohistochemistry and measurement of cGMP levels. It was established that although retinal development was normal up to 3 months of age, there was a subsequent progressive decline in retinal function, with a far greater alteration in cone than rod responses, associated with a corresponding loss of photoreceptors. In addition, we have demonstrated that accumulation of cyclic GMP precedes the observed retinal degeneration and is likely to contribute to the disease mechanism. Importantly, this knock-in mutant mouse has many features in common with the human disease, thereby making it an excellent model to further probe disease pathogenesis and investigate therapeutic interventions.
    Full-text · Article · Mar 2011 · PLoS ONE
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