This review examines how birds use the annual cycle in photoperiod to ensure that seasonal events—breeding, molt, and song production—happen at the appropriate time of year. Differences in breeding strategies between birds and mammals reflect basic differences in biology. Avian breeding seasons tend to be of shorter duration and more asymmetric with respect to changes in photoperiod. Breeding seasons can occur at the same time each year (predictable) or at different times (opportunistic), depending on the food resource. In all cases, there is evidence for involvement of photoperiodic control, nonphotoperiodic control, and endogenous circannual rhythmicity. In predictable breeders (most nontropical species), photoperiod is the predominant proximate factor. Increasing photoperiods of spring stimulate secretion of gonadotropin-releasing hormone (GnRH) and consequent gonadal maturation. However, breeding ends before the return of short photoperiods. This is the consequence of a second effect of long photoperi...

Photoperiodic Control of Seasonality in Birds

G protein-coupled receptor kinases: more than just kinases and not only for GPCRs.

Opsins are the universal photoreceptor molecules of all visual systems in the animal kingdom. They can change their conformation from a resting state to a signalling state upon light absorption, which activates the G protein, thereby resulting in a signalling cascade that produces physiological responses. This process of capturing a photon and transforming it into a physiological response is known as phototransduction. Recent cloning techniques have revealed the rich and diverse nature of these molecules, found in organisms ranging from jellyfish to humans, functioning in visual and non-visual phototransduction systems and photoisomerases. Here we describe the diversity of these proteins and their role in phototransduction. Then we explore the molecular properties of opsins, by analysing site-directed mutants, strategically designed by phylogenetic comparison. This site-directed mutant approach led us to identify many key features in the evolution of the photoreceptor molecules. In particular, we will discuss the evolution of the counterion, the reduction of agonist binding to the receptor, and the molecular properties that characterize rod opsins apart from cone opsins. We will show how the advances in molecular biology and biophysics have given us insights into how evolution works at the molecular level.

http://www.alliot.fr/BIO/PDF/rstb20090051.pdf

Evolution of opsins and phototransduction.

https://openresearch-repository.anu.edu.au/bitstream/1885/84715/2/01_Lamb_Evolution_of_2013.pdf

Evolution of phototransduction, vertebrate photoreceptors and retina.

Phototransduction is the process by which light triggers an electrical signal in a photoreceptor cell. Image-forming vision in vertebrates is mediated by two types of photoreceptors: the rods and the cones. In this review, we provide a summary of the success in which the mouse has served as a vertebrate model for studying rod phototransduction, with respect to both the activation and termination steps. Cones are still not as well-understood as rods partly because it is difficult to work with mouse cones due to their scarcity and fragility. The situation may change, however.

/pdf/phototransduction-in-mouse-rods-and-cones-22ec8tw8un.pdf

Phototransduction in mouse rods and cones

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2898%2900138-0

Identification of rhodopsin in the pigeon deep brain.

Retinal cone cells exhibit distinctive photoresponse with a more restrained sensitivity to light and a more rapid shutoff kinetics than those of rods. To understand the molecular basis for these characteristics of cone responses, we focused on the opsin deactivation process initiated by G protein-coupled receptor kinase (GRK) 1 and GRK7 in the zebrafish, an animal model suitable for studies on retinal physiology and biochemistry. Screening of the ocular cDNAs identified two homologs for each of GRK1 (1A and 1B) and GRK7 (7–1 and 7–2), and they were classified into three GRK subfamilies, 1 A, 1B and 7 by phylogenetic analysis. In situ hybridization and immunohistochemical studies localized both GRK1B and GRK7-1 in the cone outer segments and GRK1A in the rod outer segments. The opsin/GRKs molar ratio was estimated to be 569 in the rod and 153 in the cone. The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. The reinforced activity of the cone kinase should provide a strengthened shutoff mechanism of the light-signaling in the cone and contribute to the characteristics of the cone responses by reducing signal amplification efficiency.

GRK1 and GRK7: unique cellular distribution and widely different activities of opsin phosphorylation in the zebrafish rods and cones.

Photoreceptive areas responsible for the regulation of photoperiodicity have been localized in the brain of some avian species. We found that immunoreactivities to rhodopsin and the α-subunit of rod-type transducin (Gt1α) were colocalized in cerebrospinal fluid (CSF) contacting neurons in the pigeon lateral septum, a possible site for photoreception. Furthermore, RT-PCR analyses showed specific gene expression of both cGMP-phosphodiesterase β-subunit and cone-type cGMP-gated cation channel α-subunit in this region. These results suggest that several components in rod/cone photoreceptors compositely contribute to the deep encephalic phototransduction cascade. J. Comp. Neurol. 428:138–144, 2000. © 2000 Wiley-Liss, Inc.

Phototransduction molecules in the pigeon deep brain

Non-technical summary  When rod and cone photoreceptors in the eye respond to light, they need to recover, and the first step in recovery involves a protein called G-protein receptor kinase (GRK). Rods, which underlie night vision, employ a variant called GRK1, whereas cones, which mediate day vision, typically employ a variant called GRK7. We have engineered rod cells in the zebrafish retina that additionally express the cone variant, GRK7. By recording electrically from these modified rods, we have found that they are less sensitive to light than normal rods, in that regard mimicking cones. We have also found evidence to suggest that the size of the cell's response to a single photon (the smallest particle of light) is normal when recovery is mediated by GRK1, but is small (and hence somewhat cone-like) when mediated by GRK7. These results help us understand the differences between rod and cone photoreceptors.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.2010.204156

Yasutaka Wada

Papers

Identification of rhodopsin in the pigeon deep brain.

GRK1 and GRK7: unique cellular distribution and widely different activities of opsin phosphorylation in the zebrafish rods and cones.

Phototransduction molecules in the pigeon deep brain

Ectopic expression of cone-specific G-protein-coupled receptor kinase GRK7 in zebrafish rods leads to lower photosensitivity and altered responses