Neuroscience 2004 Abstract
| Presentation Number: | 750.5 |
|---|---|
| Abstract Title: | Does the circadian clock downregulate photoreceptor cell gene expression to prime the lateral eye of <I>Limulus</I> for transient rhabdom shedding? |
| Authors: |
Williams, K. E.*1
; Brenneman, R. J.1
; McCormick, S. M.1
; Jinks, R. N.1
1Dept. of Biol., Franklin & Marshall Col., Lancaster, PA |
| Primary Theme and Topics |
Sensory Systems - Vision -- Retina and photoreceptors |
| Secondary Theme and Topics | Sensory Systems<br />- Invertebrate Sensory Systems |
| Session: |
750. Retina: Adaptation and Circadian Rhythms Poster |
| Presentation Time: | Tuesday, October 26, 2004 1:00 PM-2:00 PM |
| Location: | San Diego Convention Center - Hall A-H, Board # R21 |
| Keywords: | RETINA, SECOND MESSENGER, PROTEIN KINASE A, PROTEIN SYNTHESIS |
Transient rhabdom shedding (TRS), the invertebrate analog of rod outer segment disc shedding, is primed by >3-5 h of overnight circadian efferent outflow and triggered by dawn in the horseshoe crab Limulus (J. Neurosci. 4:2792). Efferent input to the lateral eye is octopaminergic and activates adenylate cyclase through a G-protein coupled receptor leading to a rise in [cAMP]i and activation of cAMP-dependent protein kinase (PKA). The long-term activation of PKA required to prime the retina for TRS suggests that efferent input may regulate photoreceptor gene expression. We investigated whether protein synthesis is required for octopaminergic priming for TRS.
Microinjection (1.4 μl/min) of 40 μM octopamine (OA) into lateral eyes (n=7) for 6 h in darkness during subjective day (no efferent input) primed 47.5% of 70 photoreceptors examined for TRS. TRS was triggered by a 20-min pulse of broad-spectrum artificial lighting (2400 cd/m2). Co-injection of 1 mM cycloheximide (CHX; protein synthesis inhibitor) and 40 μM OA primed 83% of 70 photoreceptors (n=7 eyes) for TRS and increased the amount of rhabdom shed by 105% relative to OA alone. 10 mM CHX and 40 μM OA primed 97% of 70 photoreceptors (n=7 eyes) for TRS and increased the amount of rhabdom shed by 256% relative to OA alone. Electroretinograms measured before and after 1 mM CHX injection (n=4 eyes) are indistinguishable, suggesting that CHX is not cytotoxic at that concentration. Injection of 1 mM CHX alone primes eyes (n=2) for TRS upon post-injection light exposure, but does not trigger TRS in eyes (n=2) fixed in post-injection darkness.
Cycloheximide causes a dose-dependent increase in the probability that a photoreceptor will shed its rhabdom in response to a light trigger, suggesting that OA primes the retina for TRS by downregulating the expression of one or more photoreceptor proteins.
Microinjection (1.4 μl/min) of 40 μM octopamine (OA) into lateral eyes (n=7) for 6 h in darkness during subjective day (no efferent input) primed 47.5% of 70 photoreceptors examined for TRS. TRS was triggered by a 20-min pulse of broad-spectrum artificial lighting (2400 cd/m2). Co-injection of 1 mM cycloheximide (CHX; protein synthesis inhibitor) and 40 μM OA primed 83% of 70 photoreceptors (n=7 eyes) for TRS and increased the amount of rhabdom shed by 105% relative to OA alone. 10 mM CHX and 40 μM OA primed 97% of 70 photoreceptors (n=7 eyes) for TRS and increased the amount of rhabdom shed by 256% relative to OA alone. Electroretinograms measured before and after 1 mM CHX injection (n=4 eyes) are indistinguishable, suggesting that CHX is not cytotoxic at that concentration. Injection of 1 mM CHX alone primes eyes (n=2) for TRS upon post-injection light exposure, but does not trigger TRS in eyes (n=2) fixed in post-injection darkness.
Cycloheximide causes a dose-dependent increase in the probability that a photoreceptor will shed its rhabdom in response to a light trigger, suggesting that OA primes the retina for TRS by downregulating the expression of one or more photoreceptor proteins.
Supported by NIH EY13196, HHMI
Sample Citation:
[Authors]. [Abstract Title]. Program No. XXX.XX. 2004 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2004. Online.
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