Melanopsin, Pinopsin and Encephalic Photoreception in Birds Simon Bishop Alice Cowie Emily Purcell Jeannette Shipman Gemma...
Outline <ul><li>Photoreception in vertebrates </li></ul><ul><li>Importance of the pineal gland and melatonin </li></ul><ul...
Photoreception in Vertebrates <ul><li>Most vertebrates (birds included) have both  retinal   and  extra retinal  photorece...
Birds and Mammals Compared
Mammals and Birds compared <ul><li>Mammals: </li></ul><ul><ul><li>Eyes  are the only photoreceptors .  </li></ul></ul><ul>...
The Pineal Gland <ul><li>Particularly important in avian photoreception. </li></ul><ul><li>Small endocrine gland in the br...
Melatonin <ul><li>Indoleamine hormone.  </li></ul><ul><li>Rhythmically synthesised and released by cells in the pineal gla...
Phototransduction and Entrainment <ul><li>Experimental evidence suggests  two distinct transduction pathways  mediate the ...
What Evidence is there for 2 Phototransduction Pathways? <ul><li>Experiment 1: </li></ul><ul><ul><li>Deprive cultured pine...
Pinopsin <ul><li>mRNA rhythmically expressed. </li></ul><ul><li>Daily rhythm of expression regulated by  light  and an  in...
Melanopsin <ul><li>Rhythmically expressed (like pinopsin). </li></ul><ul><li>In constant darkness, daily amplitudes of mel...
Daily Cycles in Pinopsin and Melanopsin Levels <ul><li>Pinopsin and melanopsin levels low in early morning (ZT 0 – 6). </l...
Circadian Variations of Melanopsin and Pinopsin mRNA levels in Chick Pineal Glands under LD 12:12 In vivo In vitro Holthue...
Pinopsin – what is it? <ul><li>An opsin-like photopigment .  </li></ul><ul><li>Related to, but distinct from, other visual...
Melanopsin – what is it? <ul><li>Opsin-like photopigment, also called Opn4, first isolated from photosensitive  skin  and ...
How do they work? <ul><li>Melanopsin </li></ul><ul><ul><li>Knockout mice have attenuated phase shifting light response </l...
In Summary… <ul><li>Birds have multiple photoreceptors </li></ul><ul><li>Some involved in vision, others in temporal physi...
References <ul><li>Natesan A. et al (2002). Rhythm and Soul in the Avian Pineal.  Cell Tissue Res  309  35 – 45. </li></ul...
<ul><li>Bailey M.J. and Cassone V.M. (2005) Melanopsin Expression in the Chick Retina and Pineal Gland  Molecular Brain Re...
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  • melanopsin 332

    1. 1. Melanopsin, Pinopsin and Encephalic Photoreception in Birds Simon Bishop Alice Cowie Emily Purcell Jeannette Shipman Gemma Sykes
    2. 2. Outline <ul><li>Photoreception in vertebrates </li></ul><ul><li>Importance of the pineal gland and melatonin </li></ul><ul><li>Melanopsin and pinopsin – what are they? </li></ul><ul><li>How melanopsin and pinopsin entrain melatonin production by the pineal gland to light </li></ul>
    3. 3. Photoreception in Vertebrates <ul><li>Most vertebrates (birds included) have both retinal and extra retinal photoreceptors </li></ul><ul><li>These include: </li></ul><ul><ul><li>Lateral eyes </li></ul></ul><ul><ul><li>Deep brain photoreceptors </li></ul></ul><ul><ul><li>Intracranial pineal organ </li></ul></ul><ul><ul><li>Intracranial parapineal organ (fish only) </li></ul></ul><ul><ul><li>Extra-retinal “third eye” (reptiles and amphibians only) </li></ul></ul>
    4. 4. Birds and Mammals Compared
    5. 5. Mammals and Birds compared <ul><li>Mammals: </li></ul><ul><ul><li>Eyes are the only photoreceptors . </li></ul></ul><ul><ul><li>Signals sent from eyes along the retinohypothalamic tract to the SCN, which acts as a MASTER CLOCK. </li></ul></ul><ul><ul><li>SCN sends inhibitory or stimulatory information to the pineal gland to rhythmically control its production of melatonin. </li></ul></ul><ul><li>Birds: </li></ul><ul><ul><li>Much more complex! </li></ul></ul><ul><ul><li>Eyes , hypothalamus and pineal gland all act as photoreceptors AND circadian oscillators. </li></ul></ul><ul><ul><li>Melatonin production by the pineal gland can be directly entrained to the environmental light/dark cycle. </li></ul></ul>
    6. 6. The Pineal Gland <ul><li>Particularly important in avian photoreception. </li></ul><ul><li>Small endocrine gland in the brain, developmentally derived from diencephalic tissue. </li></ul><ul><li>Primary function to rhythmically synthesize and release melatonin . </li></ul>
    7. 7. Melatonin <ul><li>Indoleamine hormone. </li></ul><ul><li>Rhythmically synthesised and released by cells in the pineal gland. </li></ul><ul><li>Production of melatonin by the pineal gland is stimulated by darkness and inhibited by light. </li></ul><ul><li>Secretion of melatonin peaks in the middle of the night </li></ul><ul><li>Output must be entrained to the light dark cycle. </li></ul><ul><li>Entrainment achieved by photopigments. </li></ul>
    8. 8. Phototransduction and Entrainment <ul><li>Experimental evidence suggests two distinct transduction pathways mediate the effects of light on pineal gland melatonin output: </li></ul><ul><ul><li>One causes the acute suppression of melatonin output </li></ul></ul><ul><ul><li>One mediates phase shift entrainment of the pineal clock </li></ul></ul><ul><li>Each pathway is possibly controlled by a different photopigment. </li></ul>
    9. 9. What Evidence is there for 2 Phototransduction Pathways? <ul><li>Experiment 1: </li></ul><ul><ul><li>Deprive cultured pineal cells of Vitamin A </li></ul></ul><ul><ul><li>Acute effect of light on melatonin production is reduced </li></ul></ul><ul><ul><li>Phase shifts are unaffected </li></ul></ul><ul><li>Experiment 2: </li></ul><ul><ul><li>Apply pertussis toxin to cultured chick pineal cells (interferes with G proteins which are often coupled with photoreceptors) </li></ul></ul><ul><ul><li>Blocks acute , but not phase-shifting effects of light on melatonin production </li></ul></ul>
    10. 10. Pinopsin <ul><li>mRNA rhythmically expressed. </li></ul><ul><li>Daily rhythm of expression regulated by light and an intrapineal circadian oscillator . </li></ul><ul><li>Gene expression initially thought to be purely light-controlled. </li></ul><ul><li>However when chickens/isolated pineal glands were kept in constant darkness rhythmic pinopsin expression continued (albeit at a reduced level). </li></ul><ul><li>Therefore now know that circadian oscillators must also play a role in its control. </li></ul>
    11. 11. Melanopsin <ul><li>Rhythmically expressed (like pinopsin). </li></ul><ul><li>In constant darkness, daily amplitudes of melanopsin gene expression are not reduced, in some cases seem even to increase. </li></ul><ul><li>Therefore seems that regulation of melanopsin production is primarily controlled by the pineal circadian oscillator (unlike pinopsin). </li></ul>
    12. 12. Daily Cycles in Pinopsin and Melanopsin Levels <ul><li>Pinopsin and melanopsin levels low in early morning (ZT 0 – 6). </li></ul><ul><li>Increase in middle of day (ZT 6) by approx. 5-fold. </li></ul><ul><li>Reach a peak between ZT 10 – 12. </li></ul><ul><li>mRNA levels decrease after lights-off. </li></ul><ul><li>Return to low nocturnal levels within 4 – 6 hours. </li></ul>
    13. 13. Circadian Variations of Melanopsin and Pinopsin mRNA levels in Chick Pineal Glands under LD 12:12 In vivo In vitro Holthues H. et al (2004).
    14. 14. Pinopsin – what is it? <ul><li>An opsin-like photopigment . </li></ul><ul><li>Related to, but distinct from, other visual opsins. </li></ul><ul><li>First isolated from the pineal gland of the chicken ( Gallus domesticus ). </li></ul><ul><li>Expressed exclusively in the pineal gland (key difference with melanopsin). </li></ul><ul><li>Precise role still unclear. </li></ul><ul><li>Involved in ‘acute suppression’ pathway??? </li></ul>
    15. 15. Melanopsin – what is it? <ul><li>Opsin-like photopigment, also called Opn4, first isolated from photosensitive skin and retinal cells in the African Claw frog ( Xenopus laevis ). </li></ul><ul><li>In birds, found in: </li></ul><ul><ul><li>Specialised photosensitive ganglion cells in the retina </li></ul></ul><ul><ul><li>Iris muscles </li></ul></ul><ul><ul><li>Deep brain regions </li></ul></ul><ul><ul><li>Pineal gland </li></ul></ul><ul><ul><li>Skin cells </li></ul></ul><ul><li>Involved in ‘phase-shift entrainment’ pathway??? </li></ul>
    16. 16. How do they work? <ul><li>Melanopsin </li></ul><ul><ul><li>Knockout mice have attenuated phase shifting light response </li></ul></ul><ul><ul><li>Transfection makes non-photosensitive cells respond to light </li></ul></ul><ul><ul><li>Linked to Gq-type G-proteins and neuron depolarisation </li></ul></ul><ul><ul><li>But… G-proteins are indiscriminate and use varies between species </li></ul></ul><ul><li>Pinopsin </li></ul><ul><ul><li>PTX blocks Gi- and Gt-type G-proteins, blocking the acute effect of light on pinealocytes in vitro. </li></ul></ul><ul><ul><li>Transducin (Gt1 α ) is coupled with pinopsin in vivo. </li></ul></ul><ul><ul><li>Pinopsin activated Gt1 in vitro when illuminated </li></ul></ul><ul><ul><li>Therefore pinopsin-Gt1 pathway contributes to the acute pathway </li></ul></ul><ul><ul><li>But… Gq/11 α also localises with pinopsin, speculated to be involved with phase-shifting </li></ul></ul>
    17. 17. In Summary… <ul><li>Birds have multiple photoreceptors </li></ul><ul><li>Some involved in vision, others in temporal physiology </li></ul><ul><li>Pinopsin and melanopsin – two photopigments with a role in controlling daily melatonin output by the pineal gland </li></ul><ul><li>Exact functions still unknown but: </li></ul><ul><ul><li>Pinopsin – involved in ‘acute effect’…? </li></ul></ul><ul><ul><li>Melanopsin – involved in ‘phase-shift entrainment’ effect…? </li></ul></ul>
    18. 18. References <ul><li>Natesan A. et al (2002). Rhythm and Soul in the Avian Pineal. Cell Tissue Res 309 35 – 45. </li></ul><ul><li>Holthues H. et al (2004). Circadian gene expression patterns of melanopsin and pinopsin in the chick pineal gland. Biochem and Biophys Res Comm 326 160 – 165. </li></ul><ul><li>Oishi T. et al (2001). Multiphotoreceptor and multioscillator system in avian circadian organization Micros Res and Tech 53 43 – 47. </li></ul><ul><li>Peirson S. and Foster R.G. (2006). Melanopsin: Another Way of Signalling Light. Neuron 49 331-339 </li></ul><ul><li>Okano T. and Fukada Y. (2001). Photoreception and Circadian Clock System of the Chicken Pineal Gland. Micros Res and Tech 53 72-80 </li></ul><ul><li>Wada Y. et al (2000). Phototransduction Molecules in the Pigeon Deep Brain. J. Comp. Neuro . 428 138-144 </li></ul><ul><li>Kumar Nayak S. et al (2007). Role of a Novel Photopigment, Melanopsin, in Behavioural Adaptation to Light. Cell. Mol. Life. Sci 64 144-154 </li></ul>
    19. 19. <ul><li>Bailey M.J. and Cassone V.M. (2005) Melanopsin Expression in the Chick Retina and Pineal Gland Molecular Brain Research 134 345-398 </li></ul><ul><li>Foster R.G. and Soni B.G. (1998) Extraretinal Photoreceptors and Their Regulation of Temporal Physiology. Reviews of Reproduction 3 145-150 </li></ul><ul><li>Takanaka Y. et al (1998) Light-Dependent Expression of Pinopsin Gene in Chicken Pineal Gland. J. Neurochem . 70 908-913 </li></ul><ul><li>Fu Z. et al. (1998) Vitamin A Deficiency Reduces the Responsiveness of Pineal Gland to Light in Japanese Quail ( Coturnix japonica ) Comp. Biochem. Physiol . 119 593-598 </li></ul>
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