Society for Experimental Biology Annual Main Meeting6th – 10th July 2008, Marseille, France

C2 — CIRCADIAN CLOCKS

C2.1Inner retinal and extraretinal photoreceptor up-dates: Isolationand characterisation of VA opsin in Xenopus and the chicken

R. Foster (University of Oxford); S. Pires (University of Oxford); M.Turton (University of Oxford); S. Peirson (University of Oxford); L. Zheng(University of Oxford); J. Garcia-Fernández (University of Oviedo); M.Hankins (University of Oxford); S. Halford (University of Oxford)

Vertebrate Ancient (VA) opsin was first isolated from Atlantic salmonocular cDNA in 1997. Salmon VA-opsin shares 37–41% amino acid identitywith the classical retinal opsins and 42% identity with chicken P-opsin.Furthermore, Salmon VA-opsin forms a functional photopigment whenexpressed in vitro and reconstituted with 11-cis-retinal. Significantly, VA-opsin is expressed in a subset of horizontal and ganglion cells in the retinaand electrophysiological recordings have explored the photoreceptorcapacity of these retinal neurones. Subsequent in situhybridisation studiesdemonstrated that Salmon VA-opsin is also expressed in the pineal organand habenular region of the brain, both structures either known to be orimplicated inphotoreception. Similar findingshavebeen reported inmanyfish species including the common carp and zebrafish. Despite theisolation of a VA-opsin homologue from themarine lamprey, all attemptsto isolate VA-opsin from other vertebrate classes failed. This failure led tothe suggestion that the VA-opsinswere ancestral to the tetrapod P-opsinsand that direct homologues of VA-opsinswould not be found in terrestrialvertebrates. This assumptionwas incorrect. The presentationwill describethe isolation, characterisation, functional expression and distribution ofVA-opsins from bothXenopus and the chicken. In the chicken at least, thisdiscovery provides some insight as to how “deep brain photoreceptors”might regulate photoperiodic and circadian responses to light.

doi:10.1016/j.cbpa.2008.04.374

C2.2Neurobiology of food-entrainable circadian rhythms in mammals

R. Mistlberger (Simon Fraser University)

Circadian rhythms in mammals are regulated by a light-entrainable circadian pacemaker located in the hypothalamicsuprachiasmatic nucleus (SCN). In nocturnal rodents, SCN outputsuppresses activity and promotes sleep during the day, andpromotes activity, wake and feeding at night. If food is restrictedto one daytime meal, circadian oscillators outside of the SCN areengaged that generate a daily rhythm of food anticipatory activity,overriding SCN-mediated behavioral suppression. The properties offood-entrainable circadian rhythms have been well-characterized,but neurobiological analysis has been slow until recently. Progresshas been catalysed by the discovery that circadian clock genes at thecore of the SCN pacemaker also exhibit circadian rhythms ofexpression in numerous other brain regions and peripheral organs,and that in most cases the phase of these rhythms is set bymealtime. Knockout of the Per2 gene in mice confirms a role forthese clock genes in food-entrainable behavioral rhythms. The site ofoscillators critical for food-entrainable behavioral rhythms remainsan open question. Lesion experiments have ruled out numerousareas as necessary, but controversy has emerged over the role offood-entrainable oscillators in the hypothalamic dorsomedialnucleus (DMH). One lab has reported severe attenuation or loss offood-anticipatory rhythms after neurotoxic ablation of DMH cellbodies (Gooley et al., 2006), while two labs (Landry et al., 2006,2007; Moriya et al., 2007) report normal food-entrainable rhythmsafter radiofrequency ablation of this region. Discrepancies may beattributable to lesion and behavior methods, and can be accom-modated by assigning the DMH a role inhibiting SCN-dependentbehavioral suppression.

doi:10.1016/j.cbpa.2008.04.375

C2.3A genome-wide RNAi screen for novel components of themammalian circadian clock

A. Kramer, B. Maier, S. Wendt (Charité Universitätsmedizin Berlin)

Comparative Biochemistry and Physiology, Part A 150 (2008) S148–S154

Contents lists available at ScienceDirect

Comparative Biochemistry and Physiology, Part A

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