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Abstract
Objectives: The age-related changes in distribution of α-gustducin–immunoreactive structures in the larynx of Sprague-Dawley rats were studied. Methods: For this purpose, tissues obtained from 12 male rats ranging in age from 5 to 21 weeks were compared with respect to the distribution and morphology of laryngeal taste buds immunoreactive for α-gustducin, the α-subunit of a taste cell–specific G protein. Results: Three different morphological types of α-gustducin–immunoreactive structures were seen: typical gemmal forms, clusters composed of 2 or 3 cells, and isolated immunoreactive cells not associated with taste buds. α-Gustducin–immunoreactive structures were most abundant in the epiglottis in all age groups. α-Gustducin–immunoreactive cells in rats seem to be located along the lateral food channels, in which they may come in contact with food. The total number of these α-gustducin–immunoreactive structures did not show any age-related changes, but the percentage of solitary immunoreactive cells in 5-week-old rats was significantly larger than the percentages in 8-, 14-, and 21-week-old animals. Conclusions: Solitary α-gustducin–immunoreactive cells, which are abundant in 5-week-old rats but are found in fewer numbers along the base of the epiglottis in mature rats, may be nociceptic in function, whereas the chemosensory clusters or buds that contain α-gustducin–positive cells and are distributed along the lateral food channels on the pharyngeal side of the larynx may have a role in gustatory reception.
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Affiliation(s)
- Takeshi Nishio
- Department of Otolaryngology-Head and Neck Surgery, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kyoto 602-8566, Japan
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Yasumatsu K, Kusuhara Y, Shigemura N, Ninomiya Y. Recovery of two independent sweet taste systems during regeneration of the mouse chorda tympani nerve after nerve crush. Eur J Neurosci 2007; 26:1521-9. [PMID: 17714496 DOI: 10.1111/j.1460-9568.2007.05761.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In rodents, section of the taste nerve results in degeneration of the taste buds. Following regeneration of the cut taste nerve, however, the taste buds reappear. This phenomenon can be used to study the functional reformation of the peripheral neural system responsible for sweet taste. In this study we examined the recovery of sweet responses by the chorda tympani (CT) nerve after nerve crush as well as inhibition of these responses by gurmarin (Gur), a sweet response inhibitor. After about 2 weeks of CT nerve regeneration, no significant response to any taste stimuli could be observed. At 3 weeks, responses to sweet stimuli reappeared but were not significantly inhibited by Gur. At 4 weeks, Gur inhibition of sweet responses reached statistically significant levels. Thus, the Gur-sensitive (GS) component of the sweet response reappeared about 1 week later than the Gur-insensitive (GI) component. Moreover, single CT fibers responsive to sucrose could be classified into distinct GS and GI groups at 4 weeks. After 5 weeks or more, responses to sweet compounds before and after treatment with Gur became indistinguishable from responses in the intact group. During regeneration, the GS and GI components of the sucrose response could be distinguished based on their concentration-dependent responses to sucrose. These results suggest that mice have two different sweet-reception systems, distinguishable by their sensitivity to Gur (the GS and GI systems). These two sweet-reception systems may be reconstituted independently during regeneration of the mouse CT nerve.
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Affiliation(s)
- Keiko Yasumatsu
- Section of Oral Neuroscience, Graduate School of Dental Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
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Rosenzweig DH, Nair KS, Wei J, Wang Q, Garwin G, Saari JC, Chen CK, Smrcka AV, Swaroop A, Lem J, Hurley JB, Slepak VZ. Subunit dissociation and diffusion determine the subcellular localization of rod and cone transducins. J Neurosci 2007; 27:5484-94. [PMID: 17507570 PMCID: PMC2655354 DOI: 10.1523/jneurosci.1421-07.2007] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Activation of rod photoreceptors by light induces a massive redistribution of the heterotrimeric G-protein transducin. In darkness, transducin is sequestered within the membrane-enriched outer segments of the rod cell. In light, it disperses throughout the entire neuron. We show here that redistribution of rod transducin by light requires activation, but it does not require ATP. This observation rules out participation of molecular motors in the redistribution process. In contrast to the light-stimulated redistribution of rod transducin in rods, cone transducin in cones does not redistribute during activation. Remarkably, when cone transducin is expressed in rods, it does undergo light-stimulated redistribution. We show here that the difference in subcellular localization of activated rod and cone G-proteins correlates with their affinity for membranes. Activated rod transducin releases from membranes, whereas activated cone transducin remains bound to membranes. A synthetic peptide that dissociates G-protein complexes independently of activation facilitates dispersion of both rod and cone transducins within the cells. This peptide also facilitates detachment of both G-proteins from the membranes. Together, these results show that it is the dissociation state of transducin that determines its localization in photoreceptors. When rod transducin is stimulated, its subunits dissociate, leave outer segment membranes, and equilibrate throughout the cell. Cone transducin subunits do not dissociate during activation and remain sequestered within the outer segment. These findings indicate that the subunits of some heterotrimeric G-proteins remain associated during activation in their native environments.
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Affiliation(s)
- Derek H. Rosenzweig
- Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami Miller School of Medicine, Miami, Florida 33136
| | - K. Saidas Nair
- Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami Miller School of Medicine, Miami, Florida 33136
| | | | - Qiang Wang
- Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami Miller School of Medicine, Miami, Florida 33136
| | - Greg Garwin
- Ophthalmology, University of Washington, Seattle, Washington 98195
| | - John C. Saari
- Ophthalmology, University of Washington, Seattle, Washington 98195
| | - Ching-Kang Chen
- Department of Biochemistry, Virginia Commonwealth University, Richmond, Virginia 23284
| | - Alan V. Smrcka
- Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14603
| | - Anand Swaroop
- Departments of Ophthalmology and Visual Sciences, and Human Genetics, University of Michigan, Ann Arbor, Michigan 48109, and
| | - Janis Lem
- Molecular Cardiology Research Institute, Tufts–New England Medical Center, Boston, Massachusetts 02111
| | | | - Vladlen Z. Slepak
- Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami Miller School of Medicine, Miami, Florida 33136
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Lobanova ES, Finkelstein S, Song H, Tsang SH, Chen CK, Sokolov M, Skiba NP, Arshavsky VY. Transducin translocation in rods is triggered by saturation of the GTPase-activating complex. J Neurosci 2007; 27:1151-60. [PMID: 17267570 PMCID: PMC6673185 DOI: 10.1523/jneurosci.5010-06.2007] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Light causes massive translocation of G-protein transducin from the light-sensitive outer segment compartment of the rod photoreceptor cell. Remarkably, significant translocation is observed only when the light intensity exceeds a critical threshold level. We addressed the nature of this threshold using a series of mutant mice and found that the threshold can be shifted to either a lower or higher light intensity, dependent on whether the ability of the GTPase-activating complex to inactivate GTP-bound transducin is decreased or increased. We also demonstrated that the threshold is not dependent on cellular signaling downstream from transducin. Finally, we showed that the extent of transducin alpha subunit translocation is affected by the hydrophobicity of its acyl modification. This implies that interactions with membranes impose a limitation on transducin translocation. Our data suggest that transducin translocation is triggered when the cell exhausts its capacity to activate transducin GTPase, and a portion of transducin remains active for a sufficient time to dissociate from membranes and to escape from the outer segment. Overall, the threshold marks the switch of the rod from the highly light-sensitive mode of operation required under limited lighting conditions to the less-sensitive energy-saving mode beneficial in bright light, when vision is dominated by cones.
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Affiliation(s)
- Ekaterina S. Lobanova
- Albert Eye Research Institute, Duke University Medical Center, Durham, North Carolina 27710
| | - Stella Finkelstein
- Albert Eye Research Institute, Duke University Medical Center, Durham, North Carolina 27710
| | - Hongman Song
- Department of Biochemistry, West Virginia University School of Medicine, Morgantown, West Virginia 26506
| | - Stephen H. Tsang
- Brown Glaucoma Laboratory, Edward Harkness Eye Institute, Columbia University, New York, New York 10032
| | - Ching-Kang Chen
- Department of Biochemistry, Virginia Commonwealth University, Richmond, Virginia 23298, and
| | - Maxim Sokolov
- Sensory Neuroscience Research Center and West Virginia University Eye Institute, Morgantown, West Virginia 26506
| | - Nikolai P. Skiba
- Albert Eye Research Institute, Duke University Medical Center, Durham, North Carolina 27710
| | - Vadim Y. Arshavsky
- Albert Eye Research Institute, Duke University Medical Center, Durham, North Carolina 27710
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6
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Abstract
Taste cells have a limited life span and are replaced from a basal cell population, although the specific factors involved in this process are not well known. Short- and long-term cultures of other sensory cells have facilitated efforts to understand the signals involved in proliferation, differentiation, and senescence, yet few studies have reported successful primary culture protocols for taste cells. Furthermore, no studies have demonstrated both proliferation and differentiation in vitro. In this study, we have developed an in vitro culture system to maintain and utilize rat primary taste cells for more than 2 months without losing key molecular and biochemical features. Gustducin, phospholipase C-beta2 (PLC-beta2), T1R3, and T2R5 mRNA were detected in the cultured cells by reverse transcriptase-polymerase chain reaction. Western blot analysis demonstrated gustducin and PLC-beta2 expression in the same samples, which was confirmed by immunocytochemistry. Labeling with bromo-2-deoxyuridine (BrdU) demonstrated proliferation, and a subset of BrdU-labeled cells were also immunoreactive for either gustducin or PLC-beta2, indicating differentiation of newly generated cells in vitro. Cultured cells also exhibited increases in intracellular calcium in response to several taste stimuli. These results indicate that taste cells from adult rats can be generated and maintained under the described conditions for at least 2 months. This system will enable further studies of the processes involved in proliferation, differentiation, and function of mammalian taste receptor cells in an in vitro preparation.
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Affiliation(s)
- Hakan Ozdener
- Monell Chemical Senses Center, Philadelphia, PA 19104-3308, USA.
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7
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Abstract
Galanin, a 29-amino-acid neuropeptide, was initially isolated from porcine intestine. It has a wide spread distribution in the central nervous system and is also present in the primary sensory neuron. Galanin has been suggested to be involved in numerous neuronal and endocrine functions as a neurotransmitter and neuromodulator. We examined the expression of galanin and galanin receptors by using a reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and in situ hybridization. RT-PCR analysis showed that mRNA of galanin and GalR2 were detected in the taste bud-containing epithelium of the circumvallate papilla of rats. Immunohistochemical analyses detected galanin was detected in a subset of taste bud cells of the circumvallate papillae. Double-label studies showed that galanin colocalized with alpha-gustducin, NCAM, and PLCbeta2. Our results of double staining with galanin and taste cell markers indicate that galanin-expressing taste cells are type II and type III cells. Taken together with previous studies, these findings show that galanin may function as a taste bud neurotransmitter. Furthermore, GalR2 mRNA was expressed in some taste bud cells. This suggests that, galanin release may not only excite the peripheral afferent nerve fiber but also may act on neighboring taste receptor cells via the activation of GalR2.
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Affiliation(s)
- Yuji Seta
- Division of Oral Histology and Neurobiology, Department of Biosciences, Kyushu Dental College, Japan.
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Miura H, Kato H, Kusakabe Y, Ninomiya Y, Hino A. Temporal changes in NCAM immunoreactivity during taste cell differentiation and cell lineage relationships in taste buds. Chem Senses 2005; 30:367-75. [PMID: 15800217 DOI: 10.1093/chemse/bji031] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Neural cell adhesion molecule (NCAM) is a type III cell marker in the taste buds. In order to clarify the cell type of Mash1-expressing cells in taste buds, expression of NCAM was examined in Mash1-expressing taste cells of adult mice in comparison with gustducin- and T1r3-expressing cells, using a combination of NCAM immunohistochemistry and in situ hybridization. About 98% of Mash1-expressing cells were NCAM immunopositive (IP), suggesting that Mash1-expressing cells should be categorized as type III cells. Unexpectedly, small subsets of gustducin- and T1r3-expressing cells were also found to be NCAM-IP, contradicting previous immunohistochemical studies in rats, in which gustducin-IP cells were observed specifically in type II cells, which do not have NCAM immunoreactivity. Examinations of developing taste buds showed temporal changes in the ratio of NCAM-IP cells in gustducin- and T1r3-expressing cells; the ratio of NCAM-IP cells in these gene-expressing cells were approximately 90% at 0.5 days after birth and decreased markedly during development. In contrast, the majority of Mash1-expressing cells showed constant NCAM immunoreactivity throughout development. In addition, BrdU-labeling experiments showed that the differentiation of Mash1-expressing cells precedes those of gustducin- and T1r3-expressing cells in taste buds of adult mice. These results suggest that T1r3- and gustducin-expressing cells are NCAM-IP at the beginning of cell differentiation, and that NCAM immunoreactivity in gustducin- and T1r3-expressing cells might remain from the previous developmental stage expressing Mash1.
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Affiliation(s)
- Hirohito Miura
- National Food Research Institute, 2-1-12 Kannondai, Ibaraki 305-8642, Japan.
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Giessl A, Pulvermüller A, Trojan P, Park JH, Choe HW, Ernst OP, Hofmann KP, Wolfrum U. Differential expression and interaction with the visual G-protein transducin of centrin isoforms in mammalian photoreceptor cells. J Biol Chem 2004; 279:51472-81. [PMID: 15347651 DOI: 10.1074/jbc.m406770200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Photoisomerization of rhodopsin activates a heterotrimeric G-protein cascade leading to closure of cGMP-gated channels and hyperpolarization of photoreceptor cells. Massive translocation of the visual G-protein transducin, Gt, between subcellular compartments contributes to long term adaptation of photoreceptor cells. Ca(2+)-triggered assembly of a centrin-transducin complex in the connecting cilium of photoreceptor cells may regulate these transducin translocations. Here we demonstrate expression of all four known, closely related centrin isoforms in the mammalian retina. Interaction assays revealed binding potential of the four centrin isoforms to Gtbetagamma heterodimers. High affinity binding to Gtbetagamma and subcellular localization of the centrin isoforms Cen1 and Cen2 in the connecting cilium indicated that these isoforms contribute to the centrin-transducin complex and potentially participate in the regulation of transducin translocation through the photoreceptor cilium. Binding of Cen2 and Cen4 to Gbetagamma of non-visual G-proteins may additionally regulate G-proteins involved in centrosome and basal body functions.
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Affiliation(s)
- Andreas Giessl
- Institut für Zoologie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany
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10
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Kusakabe Y, Miura H, Hashimoto R, Sugiyama C, Ninomiya Y, Hino A. The neural differentiation gene Mash-1 has a distinct pattern of expression from the taste reception-related genes gustducin and T1R2 in the taste buds. Chem Senses 2002; 27:445-51. [PMID: 12052781 DOI: 10.1093/chemse/27.5.445] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Taste bud cells have a limited lifespan and are continuously replaced just like other epithelial cells. Although there is some evidence that taste buds may arise from the local epithelium, taste receptor cells have neuronal properties. This implies that there must be a critical stage at which the epithelial precursor cells for taste receptor cells start to exhibit neural properties during the differentiation of the taste receptor cells. The expression of the neural-specific transcription factors Mash-1 and Prox-1 in the nervous system is transient and precedes neuronal differentiation. Therefore, we examined the expression of Mash-1 and Prox-1 in the epithelium of circumvallate papillae of the tongue in order to clarify the localization of the precursor cells with neural properties and observed that both expressions are restricted to the taste buds. Two-colour in situ hybridization showed that the signals for Mash-1 did not overlap those for taste receptor cell-specific genes such as gustducin and T1R2. In the process of development and regeneration of the taste buds, the expression of Mash-1 preceded that of gustducin and T1R2. These observations suggest that Mash-1 could be a candidate for a marker of immature taste receptor cells, including the cells that express gustducin and/or T1R2 at a later stage.
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Affiliation(s)
- Yuko Kusakabe
- National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan.
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Ma J, Znoiko S, Othersen KL, Ryan JC, Das J, Isayama T, Kono M, Oprian DD, Corson DW, Cornwall MC, Cameron DA, Harosi FI, Makino CL, Crouch RK. A visual pigment expressed in both rod and cone photoreceptors. Neuron 2001; 32:451-61. [PMID: 11709156 DOI: 10.1016/s0896-6273(01)00482-2] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Rods and cones contain closely related but distinct G protein-coupled receptors, opsins, which have diverged to meet the differing requirements of night and day vision. Here, we provide evidence for an exception to that rule. Results from immunohistochemistry, spectrophotometry, and single-cell RT-PCR demonstrate that, in the tiger salamander, the green rods and blue-sensitive cones contain the same opsin. In contrast, the two cells express distinct G protein transducin alpha subunits: rod alpha transducin in green rods and cone alpha transducin in blue-sensitive cones. The different transducins do not appear to markedly affect photon sensitivity or response kinetics in the green rod and blue-sensitive cone. This suggests that neither the cell topology or the transducin is sufficient to differentiate the rod and the cone response.
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Affiliation(s)
- J Ma
- Department of Ophthalmology, Medical University of South Carolina, Charleston, SC 29425, USA.
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Rubenzik M, Varga E, Stropova D, Roeske WR, Yamamura HI. Expression of alpha-transducin in Chinese hamster ovary cells stably transfected with the human delta-opioid receptor attenuates chronic opioid agonist-induced adenylyl cyclase superactivation. Mol Pharmacol 2001; 60:1076-82. [PMID: 11641436 DOI: 10.1124/mol.60.5.1076] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To investigate the role of G-protein beta gamma subunits in delta-opioid signal transduction, we have transfected Chinese hamster ovary (CHO) cells stably expressing the human delta-opioid receptor (hDOR/CHO cells) with the G(alpha)-subunit of transducin-1 (hDOR/T1/CHO). Inhibition of forskolin-stimulated adenylyl cyclase and phospholipase C beta (PLC beta) activation was measured in each of these cell lines. Because PLC beta(3) activation in CHO cells has been shown to be mediated by free G(beta gamma) subunits derived from G(alpha i/o), the action of transducin was confirmed by measuring a significant attenuation of (+)-4-[(alpha R)-alpha-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80)-mediated maximal inositol-1,4,5-trisphosphate formation in transducin-expressing cells of 59 +/- 12% compared with control cells. The acute inhibition of cAMP formation was unchanged between control and transducin-expressing cells. We show that cells stably expressing the human delta-opioid receptor exhibited a pertussis toxin-sensitive cAMP overshoot in response to chronic application of SNC80. After 4 h of pretreatment and washout with 100 nM SNC80, maximal forskolin-stimulated cAMP formation in hDOR/CHO cells increased by 229 +/- 37% compared with buffer-treated cells. Expression of transducin in hDOR/CHO cells diminished this response: hDOR/T1/CHO cells showed no significant change in maximal forskolin-stimulated cAMP formation after pretreatment and washout. These data indicate that the expression of alpha-transducin scavenges free G(beta gamma) subunits and, furthermore, that free G(beta gamma) subunits play a role in opioid-mediated PLC beta activation and adenylyl cyclase superactivation, but not acute inhibition of forskolin-stimulated cAMP formation in hDOR/CHO cells.
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Affiliation(s)
- M Rubenzik
- Department of Pharmacology, College of Medicine, University of Arizona Health Sciences Center, Tucson, 85724, USA
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Johnson PT, Williams RR, Reese BE. Developmental patterns of protein expression in photoreceptors implicate distinct environmental versus cell-intrinsic mechanisms. Vis Neurosci 2001; 18:157-68. [PMID: 11347813 DOI: 10.1017/s0952523801181150] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The present study has examined the spatial and temporal expression patterns of various proteins associated with the structure and function of mature photoreceptor outer segments in the developing ferret's retina using immunocytochemistry and RT-PCR. One set of proteins, including rod opsin, arrestin, and recoverin, was detected progressively in photoreceptors as they became postmitotic, being expressed well before the differentiation of outer segments. A second set of proteins, including beta- and gamma-transducin, cGMP-phosphodiesterase, phosducin, rhodopsin kinase, rod cGMP-gated cation channel protein, and peripherin, displayed a contrasting temporal onset and pattern of spatial emergence. These latter proteins first became detectable either shortly before or coincident with outer segment formation, and were expressed simultaneously in both older and younger photoreceptor cells. A third set, the short wavelength-sensitive (SWS) and medium wavelength-sensitive (MWS) cone opsin proteins, was the last to be detected, but materialized in a spatio-temporal pattern reminiscent of the neurogenetic gradient of the cones. These different spatial and temporal patterns indicate that cellular maturation must play a primary role in regulating the onset of expression of some of these proteins, while extrinsic signals must act to coordinate the expression of other proteins across photoreceptors of different ages.
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Affiliation(s)
- P T Johnson
- Neuroscience Research Institute, and Department of Molecular, Cellular and Developmental Biology, University of California at Santa Barbara, 93106-5060, USA
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Bertazolli-Filho R, Ghosh S, Huang W, Wollmann G, Coca-Prados M. Molecular evidence that human ocular ciliary epithelium expresses components involved in phototransduction. Biochem Biophys Res Commun 2001; 284:317-25. [PMID: 11394879 DOI: 10.1006/bbrc.2001.4970] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Here we report the expression, in the human ocular ciliary epithelium and in a human nonpigmented (NPE) ciliary epithelial cell line, of genes usually restricted to cone and rod photoreceptor cells of the retina. By RT-PCR and DNA sequencing we identified the expression of rhodopsin and components linked to its deactivation, including rhodopsin kinase, recoverin, and visual arrestin. We also detected the expression of transducin (T-alpha), phosphodiesterase (PDE-alpha), and cGMP-gated channel alpha-subunits. Cultured NPE cells responded to treatment with phorbol ester by enhancing the expression of rhodopsin mRNA three- to fourfold. Indirect immunofluorescence of the intact ciliary epithelium with monoclonal antibodies (MAbs) against rhodopsin, rhodopsin kinase, and visual arrestin revealed labeling preferentially restricted to the NPE cells. Furthermore, Western blot analysis of whole lysates from the pars plicata region of the human ciliary epithelium with MAbs demonstrated immunochemical cross-reactivity with proteins of molecular mass similar to rhodopsin (36 kDa), rhodopsin kinase (64 to 66 kDa), and arrestin (48-52 kDa) from the human retina. These results provide the first molecular evidence that components of a non-visual phototransduction pathway are expressed in the human ocular NPE ciliary epithelium, which may be linked to circadian entrainment tasks.
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Affiliation(s)
- R Bertazolli-Filho
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, 330 Cedar Street, New Haven, Connecticut 06510, USA
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15
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Clapp TR, Stone LM, Margolskee RF, Kinnamon SC. Immunocytochemical evidence for co-expression of Type III IP3 receptor with signaling components of bitter taste transduction. BMC Neurosci 2001; 2:6. [PMID: 11346454 PMCID: PMC31433 DOI: 10.1186/1471-2202-2-6] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2001] [Accepted: 04/23/2001] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Taste receptor cells are responsible for transducing chemical stimuli into electrical signals that lead to the sense of taste. An important second messenger in taste transduction is IP3, which is involved in both bitter and sweet transduction pathways. Several components of the bitter transduction pathway have been identified, including the T2R/TRB taste receptors, phospholipase C beta2, and the G protein subunits alpha-gustducin, beta3, and gamma13. However, the identity of the IP3 receptor subtype in this pathway is not known. In the present study we used immunocytochemistry on rodent taste tissue to identify the IP3 receptors expressed in taste cells and to examine taste bud expression patterns for IP3R3. RESULTS Antibodies against Type I, II, and III IP3 receptors were tested on sections of rat and mouse circumvallate papillae. Robust cytoplasmic labeling for the Type III IP3 receptor (IP3R3) was found in a large subset of taste cells in both species. In contrast, little or no immunoreactivity was seen with antibodies against the Type I or Type II IP3 receptors. To investigate the potential role of IP3R3 in bitter taste transduction, we used double-label immunocytochemistry to determine whether IP3R3 is expressed in the same subset of cells expressing other bitter signaling components. IP3R3 immunoreactive taste cells were also immunoreactive for PLCbeta2 and gamma13. Alpha-gustducin immunoreactivity was present in a subset of IP3R3, PLCbeta2, and gamma13 positive cells. CONCLUSIONS IP3R3 is the dominant form of the IP3 receptor expressed in taste cells and our data suggest it plays an important role in bitter taste transduction.
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Affiliation(s)
- Tod R Clapp
- Department of Anatomy and Neurobiology, Colorado State University, Fort Collins, CO 80523 and the Rocky Mountain Taste and Smell Center, University of Colorado Health Sciences Center, Denver, CO 80262, USA
| | - Leslie M Stone
- Department of Anatomy and Neurobiology, Colorado State University, Fort Collins, CO 80523 and the Rocky Mountain Taste and Smell Center, University of Colorado Health Sciences Center, Denver, CO 80262, USA
| | - Robert F Margolskee
- Howard Hughes Medical Institute and Department of Physiology and Biophysics, Mount Sinai School of Medicine of New York University, Box 1677, 1425 Madison Avenue, New York, NY 10029, USA
| | - Sue C Kinnamon
- Department of Anatomy and Neurobiology, Colorado State University, Fort Collins, CO 80523 and the Rocky Mountain Taste and Smell Center, University of Colorado Health Sciences Center, Denver, CO 80262, USA
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16
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Barinaga M. Family of bitter taste receptors found. Science 2000; 287:2133-5. [PMID: 10744529 DOI: 10.1126/science.287.5461.2133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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17
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Abstract
The expression of alpha-gustducin, a G protein alpha subunit involved in bitter and sweet taste transduction, was investigated in chemosensory tissues of adult mice. By immunohistochemistry, alpha gustducin was absent in the olfactory neuroepithelium. Instead, alpha gustducin was expressed in a subset of bipolar cells in the proliferative zone of the vomeronasal neuroepithelium as well as in taste buds. Northern blot analysis confirmed the presence of alpha gustducin in isolated vomeronasal organs. Moreover, immunohisto- chemistry revealed the expression of alpha gustducin in scattered cells of the nasal respiratory epithelium. These results show for the first time that alpha gustducin is expressed in chemosensory tissue outside the alimentary tract, suggesting that common transduction mechanisms could be shared by apparently unrelated chemosensory tissues.
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Affiliation(s)
- C Zancanaro
- Dipartimento di Scienze Morfologico-Biomediche, Sezione di Anatomia e Istologia, Università di Verona, Italy.
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18
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Abstract
The aim was to demonstrate functional properties of transplanted histologically normal photoreceptors. Subretinal intact-sheet transplants of fetal E17-E20 rat retinas to light-damaged albino rat eyes were fixed in light or dark, 2 to 42 weeks after transplantation, and stained immunohistochemically for certain phototransduction proteins. In light adapted transplants, transducin was predominantly found in inner segments of parallel-organized photoreceptors. Transducin shifted to the outer segments with dark-adaptation. S-antigen distribution was opposite to transducin. Rhodopsin distribution did not change. The shift of signal transduction proteins correlated to the light conditions indicates that normal phototransduction processes were established in photoreceptors of transplanted retinal sheets.
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Affiliation(s)
- M J Seiler
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, KY 40202, USA.
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19
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Bevan N, Scott S, Shaw PE, Lee MG, Marshall FH, Rees S. Nociception activates Elk-1 and Sap1a following expression of the ORL1 receptor in Chinese hamster ovary cells. Neuroreport 1998; 9:2703-8. [PMID: 9760105 DOI: 10.1097/00001756-199808240-00003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Nociceptin stimulation of the ORL1 receptor expressed in Chinese hamster ovary (CHO) cells results in the activation of the extracellular signal regulated kinases ERK1 and ERK2. ERK1/ERK2 activation is inhibited by pertussis toxin, the MEK inhibitor PD 98059 and by transient expression of alpha-transducin, indicating that ORL1 up-regulation of these kinases occurs as a consequence of the release of the G-protein betagamma complex following the activation of pertussis-toxin sensitive Galphai-family G-proteins. Using specific reporter genes we demonstrate that the transcription factors Elk-1 and Sapla are activated in a pertussis toxin-sensitive manner as a consequence of ORL1 upregulation of ERK1/ERK2 to induce changes in gene expression. The activation of these transcription factors is also inhibited following treatment with PD 98059 and following coexpression of alpha-transducin.
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Affiliation(s)
- N Bevan
- Receptor Systems Unit, Glaxo Wellcome Research and Development, Hertfordshire, UK
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20
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Blackshaw S, Snyder SH. Developmental expression pattern of phototransduction components in mammalian pineal implies a light-sensing function. J Neurosci 1997; 17:8074-82. [PMID: 9334383 PMCID: PMC6573733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Whereas the pineal organs of lower vertebrates have been shown to be photosensitive, photic regulation of pineal function in adult mammals is thought be mediated entirely by retinal photoreceptors. Extraretinal regulation of pineal function has been reported in neonatal rodents, although both the site and molecular basis of extraretinal photoreception have remained obscure. In this study we examine the developmental expression pattern of all of the principal components of retinal phototransduction in rat pineal via cRNA in situ hybridization. All of the components needed to reconstitute a functional phototransduction pathway are expressed in the majority of neonatal pinealocytes, although the expression levels of many of these genes decline dramatically during development. These findings strongly support the theory that the neonatal rat pineal itself is photosensitive. In addition, we observe in neonatal pinealocytes the expression of both rod-specific and cone-specific phototransduction components, implying the existence of functionally different subtypes of pinealocytes that express varying combinations of phototransduction enzymes.
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Affiliation(s)
- S Blackshaw
- Johns Hopkins University School of Medicine, Department of Neuroscience, Baltimore, Maryland 21205, USA
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21
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Boughter JD, Pumplin DW, Yu C, Christy RC, Smith DV. Differential expression of alpha-gustducin in taste bud populations of the rat and hamster. J Neurosci 1997; 17:2852-8. [PMID: 9092606 PMCID: PMC6573105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The G-protein subunit alpha-gustducin, which is similar to rod transducin, has been implicated in the transduction of both sweet- and bitter-tasting substances. In rodents, there are differences in sensitivity to sweet and bitter stimuli in different populations of taste buds. Rat fungiform taste buds are more responsive to salts than to sweet stimuli, whereas those on the palate respond predominantly to sweet substances. In contrast, hamster fungiform taste buds are more sensitive to sweet-tasting stimuli. Taste buds in the vallate and foliate papillae of both species are sensitive to bitter compounds. These differences in sensitivity should be reflected in the numbers of gustducin-containing cells in different taste bud populations. We examined taste buds in the rat and hamster for immunoreactivity to an antibody against alpha-gustducin. Immunofluorescence of labeled taste cells was examined by confocal microscopy, and the cells were counted. Gustducin-positive cells were seen in all taste bud regions; they were spindle-shaped, with circular cross-sections and apical processes that extended to the taste pore. Cells with this characteristic shape in rat vallate taste buds are Type II (light) cells. In the rat, taste buds of the fungiform papillae had fewer gustducin-positive cells (3.1/taste bud) than those of other regions, including the posterior tongue and palate (>8.9/taste bud). Hamster fungiform taste buds contained twice as many gustducin-expressing cells (6.8/taste bud) as those of the rat. These data support the hypothesis that alpha-gustducin is involved in the transduction of both sweet- and bitter-tasting stimuli by mammalian taste receptor cells.
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Affiliation(s)
- J D Boughter
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, Maryland 21201-1509, USA
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22
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Morris TA, Fong WB, Ward MJ, Hu H, Fong SL. Localization of upstream silencer elements involved in the expression of cone transducin alpha-subunit (GNAT2). Invest Ophthalmol Vis Sci 1997; 38:196-206. [PMID: 9008644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
PURPOSE To localize cis-acting elements involved in the expression of the cone-specific G-protein, cone transducin alpha-subunit (GNAT2). METHODS In this study, the authors used a genomic clone, HGLG3, to sequence 3139 base pairs of the upstream region of the GNAT2 gene and to localize cis-acting elements involved in the expression of GNAT2. Upstream elements were localized functionally by transfection of chloramphenicol acetyltransferase gene constructs containing nested deletions of this upstream region into WERI-Rb1 cells. Cell specificity of the localized elements was determined by transfection of the HeLa cells. Trans-acting factor-binding sites to functional cis-acting elements were determined by DNasel footprinting. Cell specificity of protein interaction with footprinted regions was tested by electrophoretic mobility shifts with nuclear extracts from WERI-Rb1 and HeLa cells. RESULTS Transfection of WERI-Rb1 and HeLa cells revealed the presence of a strong, noncell-specific silencer region between -1130 and -23, a weak, cell-specific promoter between -151 and -10, and a stronger, noncell-specific element between +143 and +167. DNaseI footprinting showed three major footprints (S1, S2, and S3) between -807 and -176, indicating the binding sites for putative negative trans-acting factors. Individual footprinted sequences had similar electrophoretic mobility shifts when they were incubated with nuclear extracts from either WERI-Rb1 or HeLa cells, suggesting that these cells express the same negative factors. CONCLUSIONS The expression of the GNAT2 gene is controlled by a strong silencer region, a weak upstream cell-specific promoter, and a strong downstream element. The silencer region interacts with similar proteins from retina- and nonretina-derived cell lines.
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Affiliation(s)
- T A Morris
- Department of Ophthalmology, Indiana University, Indianapolis 46202, USA
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23
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Ohguro H, Kitamura K, Konari K, Sohma H, Fukada Y, Akino T. The differences in the expressions of visual pigments and transducin in photoreceptor cell differentiation. TOHOKU J EXP MED 1996; 178:233-40. [PMID: 8727705 DOI: 10.1620/tjem.178.233] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The distribution and accumulation of visual pigments, i.e., rod pigment, rhodopsin and red sensitive cone pigment, iodopsin, and transducin in the retina of chicken and chicken embryo were investigated immunohistochemically using their specific antibodies. The immunoreactivities of these proteins appeared at the early stage of photoreceptor differentiation (embryonal day 15) and increased in the photoreceptor cells appeared to reach maximum at the end of the embryonal period (embryonal day 20). On the other hand, although the immunoreactivity of beta gamma subunit of transducin (T beta gamma) was detected at embryonal day 15, the expression level of T beta gamma still remained in low level during the embryonal period. These observations suggest that both T beta gamma and visual pigments are expressed during the embryonic period in chicken photoreceptor cells, but their accumulations in the cells are different.
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Affiliation(s)
- H Ohguro
- Department of Ophthalmology, Sapporo Medical University, Japan
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24
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Kisselev O, Pronin A, Ermolaeva M, Gautam N. Receptor-G protein coupling is established by a potential conformational switch in the beta gamma complex. Proc Natl Acad Sci U S A 1995; 92:9102-6. [PMID: 7568081 PMCID: PMC40932 DOI: 10.1073/pnas.92.20.9102] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Receptor-G protein interaction is characterized by cycles of association and dissociation. We present evidence which indicates that during receptor-G protein interaction, the C-terminal tail of the G protein gamma subunit, which is masked in the beta gamma complex, is exposed and establishes high-affinity contact with the receptor. This potential conformational switch provides a mechanism to regulate receptor-G protein coupling. This switch may also be significant for the role of the beta gamma complex in regulation of effector function.
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Affiliation(s)
- O Kisselev
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA
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25
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Albor A, Notario V. The Gnb5 gene is a novel beta-transducin homolog transcribed from a divergent promoter located immediately upstream of the Syrian hamster p53 P1 promoter. Mamm Genome 1995; 6:236-41. [PMID: 7613025 DOI: 10.1007/bf00352407] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Regulatory regions controlling p53 gene transcription in Syrian hamster embryo cells were characterized by use of chloramphenicol acetyl-transferase (CAT) constructs encompassing various subfragments of its 5'-flanking sequences. This analysis identified a 961 bp PstI-SacI (PS) fragment upstream from the p53 P1 promoter, which exhibited promoter activity only in the reverse orientation relative to the p53 gene. Northern hybridizations of mRNA from hamster embryo cells with genomic probes containing the PS fragment detected a 2.1-kb transcript expressed at much lower levels than the p53 mRNA. Steady-state levels of the 2.1-kb mRNA were threefold higher in actively growing cells than in cells from confluent cultures. Library screenings with PS-containing probes resulted in the isolation from exponentially growing cells of a cDNA, the nucleotide sequence of which showed no significant homology to genes previously described. This novel gene, named Gnb5, for guanine nucleotide-binding protein, beta 5, codes for a protein of 538 amino acids with a highly acidic amino terminus containing a proline-rich domain, followed by a neutral domain with five repeat units of the beta-transducin (WD-40) motif. The homology with beta subunits of G proteins and with other WD-40 repeat-containing proteins was restricted to the repeats. The Gnb5 gene is well conserved in rodents and primates, as the hamster Gnb5 cDNA recognized, under high stringency conditions, the human and mouse counterparts in Southern and Northern hybridizations. Expression of Gnb5 in adult tissues was detected preferentially in testes, in both hamsters and humans.
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Affiliation(s)
- A Albor
- Department of Radiation Medicine, Georgetown University Medical Center, Washington, D.C. 20007, USA
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26
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Spring DJ, Neer EJ. A 14-amino acid region of the G protein gamma subunit is sufficient to confer selectivity of gamma binding to the beta subunit. J Biol Chem 1994; 269:22882-6. [PMID: 8077239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Heterotrimeric guanine nucleotide-binding proteins are important signaling molecules composed of an alpha, beta, and gamma subunit. The beta subunits must form dimers with gamma subunits to function. Several subtypes of beta and gamma have been identified, but not all combinations of beta and gamma subtypes can form dimers. For example, the gamma 2 subunit can form dimers with beta 1 and beta 2, but gamma 1 forms dimers only with beta 1, not with beta 2. Selective dimerization may play a role in the regulation of beta gamma dimer-mediated signal transduction. In order to identify the region of gamma responsible for selective dimer formation, a series of gamma 1/gamma 2 chimeras was constructed, transcribed, and translated in vitro. The ability of these gamma chimeras to form dimers with beta 1 and beta 2 was assayed by trypsin protection and chemical cross-linking. When amino acids 36-49 of gamma 1 were substituted for 33-46 of gamma 2, the chimera behaved like gamma 1 and dimerized only with beta 1; the reciprocal chimera, in which 14 residues from gamma 2 were substituted for the corresponding amino acids of gamma 1, behaved like gamma 2 and interacted with both beta 1 and beta 2. This 14-amino acid region was sufficient for gamma 1 to discriminate between the beta subunits. All gamma chimeras were functional because they were able to interact with beta 1, which is capable of forming dimers with both gamma 1 and gamma 2. All dimers of chimeric gamma subunits plus beta 1 were able to interact with purified alpha o subunit, indicating that beta gamma dimers containing chimeric gamma molecules were capable of interacting with an appropriate third molecule. This lays the foundation for using these gamma chimeras to study selective dimer interactions with various effectors and receptors.
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Affiliation(s)
- D J Spring
- Cardiovascular Division, Brigham and Women's Hospital, Boston, Massachusetts 02115
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27
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Kumar S, Matsuzaki T, Yoshida Y, Noda M. Molecular cloning and biological activity of a novel developmentally regulated gene encoding a protein with beta-transducin-like structure. J Biol Chem 1994; 269:11318-26. [PMID: 8157664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In the developing mammalian central nervous system, neural precursor cells show a tightly regulated inverse relationship between cell proliferation and differentiation. The molecular mechanisms which control the inter-relationship between these two events are poorly understood. To approach this problem, we previously identified several novel genes which are most prominently expressed in the early embryonic brain. Further cloning and sequencing of one such gene, Nedd1, revealed that it can encode a protein with a M(r) of 71,000, the amino-terminal half of which shares significant structural similarity with the beta-subunit of heterotrimeric GTP-binding proteins. Nedd1 mRNA is strongly expressed in early embryonic brain, but it can be detected at low levels in a number of adult tissues as well as cell lines and is up-regulated in an embryonal carcinoma cell line upon retinoic acid-induced differentiation. Ectopic expression of Nedd1 gene by means of eukaryotic vectors in various cell lines resulted in varying degrees of growth suppression. The strongest effects were evident in differentiation-competent neuroblastoma-derived cell lines. Our results suggest that the Nedd1 gene may play a role in the differentiation-coupled growth arrest in neuronal cells.
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Affiliation(s)
- S Kumar
- Cancer Institute, Japanese Foundation for Cancer Research, Tokyo
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28
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Fukada Y, Matsuda T, Kokame K, Takao T, Shimonishi Y, Akino T, Yoshizawa T. Effects of carboxyl methylation of photoreceptor G protein gamma-subunit in visual transduction. J Biol Chem 1994; 269:5163-70. [PMID: 8106497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
G protein gamma-subunits are isoprenylated and carboxyl-methylated at the C-terminal cysteine, which is indispensable for the function of photoreceptor G protein transducin (T alpha beta gamma). However, the physiological role of the methylation and its reversibility have been unclear. Here we isolated methylated and non-methylated forms of farnesylated T beta gamma, and demonstrated that the methylation remarkably facilitates not only the membrane association of T beta gamma but also the subunit interaction between T alpha and T beta gamma. Consequently, the functional coupling of transducin with light-activated receptor, metarhodopsin II, was stabilized by the methylation, resulting in acceleration of GTP gamma S (guanosine 5'-3-O-(thio) triphosphate) binding to T alpha. An examination of the reversibility of the methylation suggested that T gamma is kept fully methylated in rod outer segments. These observations indicate that the methylation of T gamma plays an important role in the most efficient photon-signal transduction process in rod cells.
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Affiliation(s)
- Y Fukada
- Department of Pure and Applied Sciences, College of Arts and Sciences, University of Tokyo, Japan
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29
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Timmers AM, Newton BR, Hauswirth WW. Synthesis and stability of retinal photoreceptor mRNAs are coordinately regulated during bovine fetal development. Exp Eye Res 1993; 56:257-65. [PMID: 8386100 DOI: 10.1006/exer.1993.1034] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Steady state photoreceptor specific mRNA levels in bovine retina were studied during fetal maturation for five gene transcripts, including rhodopsin, arrestin (S-antigen), rod alpha-subunit of transducin, interphotoreceptor retinoid-binding protein (IRBP) and rod alpha-subunit of cGMP phosphodiesterase in order to understand mechanisms of gene regulation during photoreceptor development. A 10-15-fold increase in each transcript level begins between 5.5 and 6 months of gestation for each gene, suggesting a single coordinate induction event at this time. Quantitative analysis of transcriptional rates for each gene by nuclear run-on also reveals a coordinate increase at approximately the same time, demonstrating that induction is achieved by transcriptional activation. Interestingly, however, gene specific transcription rates in the pre-induction retina do not appear to parallel mRNA steady state levels. During fetal development neither the transcript level of each gene relative to the others nor relative mRNA turnover rates change substantially after the induction event at 5.5-6.0 months. However, at earlier times all genes exhibit higher mRNA turnover, implying that differential mRNA stability may also play an important role in determining steady-state levels.
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Affiliation(s)
- A M Timmers
- Department of Ophthalmology, University of Florida College of Medicine, Gainesville 32610
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30
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Abstract
Protein prenylation with farnesyl or geranylgeranyl moieties is an important posttranslational modification that affects the activity of such diverse proteins as the nuclear lamins, the yeast mating factor mata, and the ras oncogene products. In this article, we show that whole retinal cultures incorporate radioactive mevalonic acid into proteins of 23-26 kDa and one of 8 kDa. The former proteins are probably the "small" guanine nucleotide-binding regulatory proteins (G proteins) and the 8-kDa protein is the gamma subunit of the well-studied retinal heterotrimeric G protein (transducin). After deprenylating purified transducin and its subunits with Raney nickel or methyl iodide/base, the adducted prenyl group can be identified as an all-trans-farnesyl moiety covalently linked to a cysteine residue. Thus far, prenylation reactions have been found to occur at cysteine in a carboxyl-terminal consensus CAAX sequence, where C is the cysteine, A is an aliphatic amino acid, and X is undefined. Both the alpha and gamma subunits of transducin have this consensus sequence, but only the gamma subunit is prenylated. Therefore, the CAAX motif is not necessary and sufficient to direct prenylation. Finally, since transducin is the best understood G protein, both structurally and mechanistically, the discovery that it is farnesylated should allow for a quantitative understanding of this post-translational modification.
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Affiliation(s)
- R K Lai
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
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31
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Abstract
A single photon can be detected by a rod photoreceptor cell. The absorption of light by rhodopsin triggers a cascade of reactions that amplifies the photon signal and results in ion channel closure with hyperpolarization of the rod photoreceptor cell. Light-induced conformational changes in rhodopsin facilitate the binding of a guanosine nucleotide-binding protein, transducin, which then undergoes a GTP-GDP exchange reaction and dissociation of the transducin complex. A subunit of transducin then activates a phosphodiesterase complex that hydrolyzes cyclic GMP. In darkness, cyclic GMP binds to cation channels of the photoreceptor plasma membrane, maintaining them in an open configuration. The light-induced reduction in cyclic GMP concentration dissociates the bound cyclic GMP, resulting in channel closure and hyperpolarization. Down-regulation of the cascade involves other proteins that block the interaction of transducin with rhodopsin and another protein that may interfere with transducin recycling. Cone photoreceptors possess a light-activated cascade that follows the rod format, but it is composed of proteins that are homologous to those of rod photoreceptors. Phototransduction in invertebrate photoreceptors uses rhodopsin to activate a cascade that uses phosphoinositides and calcium ion to regulate membrane polarization.
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Affiliation(s)
- R N Lolley
- Department of Anatomy and Cell Biology, University of California, Los Angeles 90024
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