|Barbara-Anne Battelle Lab|
Barbara-Anne Battelle, Ph.D.
Retinas and photoreceptors change their function during day and night. In order for the full range of day to night fluctuations in visual function to occur, two things are required: rhythmic changes in environmental light and signals from internal circadian clocks. We seek to understand the biochemical mechanisms by which light and clock input, separately and together, regulate retinal and photoreceptor functions. Through these studies we are gaining a more complete understanding of the requirements for normal vision.
The horseshoe crab Limulus polyphemus, offers a number of advantages for these studies. The influence of the circadian clock on the structure and function of Limulus photoreceptors is robust and well characterized. In addition, the unique circadian organization of the Limulus visual system permits easy experimental manipulation of the circadian input to the eyes. Specifically, the circadian clock that drives changes in visual function is located in the brain, and circadian signals reach the eyes via well-characterized efferent neuronal projections through the optic nerves. The efferent projection to the lateral eye can be conveniently cut to produce an eye lacking circadian efferent input while the circadian input to the other eye (Figure 1), and the circadian biology of the animal as a whole, is normal.
What are the functional consequences for photoreceptors of the nighttime clock-stimulated phosphorylation of a major photoreceptor protein? Much evidence from this lab and others indicates that circadian changes in Limulus photoreceptors are brought about by the release of the biogenic amine octopamine from the terminals clock-driven efferent neurons that project to the eyes, a subsequent rise in cAMP in photoreceptors and activation of cAMP-dependent protein kinase (PKA). Thus some clock-driven changes in photoreceptor function must involve the phosphorylation of specific proteins. (Figure 2)
A particularly interesting clock-regulated phosphoprotein we identified is Limulus myosin XXI, the Limulus homologue of the Drosophila ninaC gene products which are required for normal photoreceptor function in Drosophila.
Class XXI myosins are unconventional myosins in that have a kinase domain at their N-terminus, and as with most unconventional myosins, the functions of class XXI myosins are not known. Similar kinase-myosins are expressed in vertebrate photoreceptors and hair cells.
Major goals of our current research are to understand the functions of Limulus myosin XXI, how these functions are modified by phosphorylation, and how Limulus Myosin XXI phosphorylation influences photoreceptor function.
Does the clock influence dark-adaptive changes in photoreceptor biochemistry? In both vertebrates and invertebrates long-term light and dark-adaptation involves the translocation of proteins into and out of the photosensitive compartment of photoreceptors. The rhabdomeral level of one visual pigment opsin 1 is low during the day and high during the night. The rhabdomeral level of Gq, a protein activated by photoactivated rhodopsin, is also low during the day and is high during the night, while the rhabdomeral level of arrestin, a protein that stops phototransduction, is high during the day and low during the night. Light is a major driving force for these observed changes in proteins levels at the rhabdom. Ongoing studies are testing the hypothesis that at least some of these changes are regulated by signals from circadian clocks.
What are the functional consequences of the differential regulation of opsin co-expression in Limulus photoreceptors? Until relatively recently it had been thought that an individual photoreceptor expresses only one type of visual pigment or opsin. However, recent studies have revealed a growing number of examples of photoreceptors in both vertebrates and invertebrates that express more than one opsin. The functional relevance of opsin co-expression is still largely unknown.
We recently found that Limulus photoreceptors express at least two different types of opsins, Opsin 1-2 and opsin 5. The relative levels of these opsins in the photosensitive membrane of photoreceptors change with a diurnal rhythm (See the figure above) and that their expression in the photosensitive membrane is regulated differently by light and by the animal's circadian clock. A comparison of the amino acid sequences of these opsins indicates they may have different spectral sensitivities. Ongoing studies are examining the function of the newly identified opsin and the functional consequences in photoreceptors for the differential regulation of their expression.
Transcriptome analysis of Limulus photoreceptors. In collaborative studies with the Moroz laboratory at the Whitney Laboratory and the Oakley laboratory at UC Santa Barbara, we are examining the transcriptomes of Limulus ventral photoreceptors and lateral eye retinas. These studies are opening avenues of research that will provide new insights into photoreceptor function and evolution. Such analysis resulted in the identification Limulus 5.
Selected Publications (since 2005)
Dalal JS, Battelle B-A (2010) Circadian regulation of Limulus visual functions: A role for octopamine and cAMP. Current Zoology 56(5):518-536.
Katti C, Kempler K, Porter ML, Legg A, Gonzalez R, Garcia-Rivera E, Dugger D, Battelle B-A (2010) Opsin co-expression in Limulus photoreceptors: Differential regulation by light and a circadian clock. J Exp Biol 213(15):2589-2601.
Battelle B-A (2010) Limulus eyes and their circadian regulation. In: Encyclopedia of the Eye, Vol. 2. (Dratt DA ed) pp581-590. Oxford: Academic Press.
Katti C, Dalal JS, Dose AC, Burnside B, Battelle BA (2009) Cloning and distribution of Myosin 3B in the mouse retina: differential distribution in cone outer segments. Exp Eye Res 89:224-237.
Battelle B-A (2008) Circadian rhythms in visual function in Limulus. In: Comparative Aspects of Circadian Rhythm. (Fanjul-Moles ML, Roblero RA eds) 37/661. Kerala, India: Transworld Research Network.
Battelle, B-A, Brown NL (2008) Isolation and expression of Pax6 and atonal homologues in the American Horseshoe Crab, Limulus polyphemus. Dev Dyn 237:2209-2219.
Cardasis HL, Stevens SM, McClung S, Kempler KE, Powell DH, Eyler JR, Battelle B-A (2007) The actin-binding interface of a myosin III is phosphorylated in vivo in response to signals from a circadian clock. Biochemistry 46:13907-13919.
Kempler KE, Toth JE, Yamashita R, Mapel G, Robinson K, Cardasis HL, Stevens SM, Sellers JR, Battelle B-A (2007) Loop 2 of Limulus myosin III is phosphorylated by protein kinase A and autophosphorylation. Biochemistry 46:4280-4293.
Battelle B-A (2006) The eyes of Limulus polyphemus (Xiphosura, Chelicerata) and their afferent and efferent projections. Arthropod Struct Dev 35:261-274.
Harzsch S, Vilpoux K, Blackburn DC, Platchetzki D, Brown NL, Melzer R, Kempler KE, Battelle B-A (2006) Development of the eyes and central visual pathways of the horseshoe crab Limulus polyphemus Linneaus, 1758 (Chelicerata, Xiphosura). Dev Dyn 225:2641-2655.