Rho Signaling Mediates Cytoskeletal Re-arrangements in Octopus Photoreceptors*

Abstract

Light sensitive rhabdoms in the octopus retina increase in cross-sectional area in the dark and shrink in the light. Growth in the dark is due to the formation of microvilli in an avillar region of the photoreceptor cell membrane and lengthening of rhabdomere microvilli already present. Diminution in the light is the result of the disassembly and shortening of the same microvilli. Each microvillus contains an actin filament core that must be assembled or disassembled in the dark or light, respectively. To understand the regulation of the construction and breakdown of rhabdomere microvilli in the light and dark, we used centrifugation to separate the rhabdom membranes followed by Western blotting and Rho pull-down assays to investigate the role of Rho GTPases in this process. Western blotting showed a difference in the distribution of Rho in rhabdom membrane and supernatant fractions. In the light, Rho was mostly present in the supernatant but in the dark it was found in the fraction enriched with rhabdom membranes. Complementing these results, pull-down assays showed that Rho is activated in the dark but in the light, Rho is mostly inactive. We believe that in the dark, activated Rho binds to the rhabdom membrane and initiates signaling pathways, leading to growth of rhabdomere microvilli. In the light, Rho is present in the soluble fraction, is inactivated, and is likely bound to a Rho GDI. Receptors involved in the activation of Rho in the dark are undetermined and may involve rhodopsin or another membrane protein.

Structural and functional protein network analyses predict novel signaling functions for rhodopsin

“…We were able to confirm that small GTPases Rac and the GTP-bound form of RhoA bind rhodopsin, as has been previously described (Wieland et al, 1990a, b;Balasubramanian and Slepak, 2003;Gray et al, 2008;Figure 4, link A). For this, we performed co-segregation/co-sedimentation experiments to reveal proteins within large complexes, as described previously to analyze the light-harvesting complex of photosystem II in plants ( Swiatek-de Lange et al, 2008;Supplemen-tary Figures S5 and S6A).…”

Environmental cues and symbiont microbe‐associated molecular patterns function in concert to drive the daily remodelling of the crypt‐cell brush border of the Euprymna scolopes light organ

“…Although the eye is photoreceptive and the light organ is photogenic, they have similar accessory tissues to modify light (Crookes et al ., ; Montgomery and McFall‐Ngai, ), as well as similar biochemistry and developmental induction (Peyer et al ., ; Tong et al ., ). Relevant here is that the shedding of microvilli in response to light is common in the rhabdomeric photoreceptors that are characteristic of certain invertebrate eyes, including those of cephalopods (Battelle, ; Gray et al ., ; Stark et al ., ). The renewal of portions of photoreceptors is common in both invertebrate and vertebrate eyes as a response to the photo‐oxidative reactions that can ultimately lead to retinal degeneration (Jinks et al ., ; Strauss, ).…”

Genetic mechanisms involved in the evolution of the cephalopod camera eye revealed by transcriptomic and developmental studies

“…We also identified genes involved in signal transduction cascades, homologs of rab5 protein (02945_Oc_5_065), ras-related protein rab-2 (DB916866), member ras oncogene family (ika1224-No19_E06_001, DB913730 and DB919285), ran gtpase-activating protein (DB912649), and dishevelled associated activator of morphogenesis 1 like (03249_Oc_5_081), which are possibly related to camera eye specification. Indeed, the Ras superfamily of small GTPases regulate many cellular regulatory and developmental pathways, including diurnal regulation of the octopus photoreceptors [ 35 ]. As previously reported [ 14 ], retinal arrestin (08322_Oc_5_073), retinal dehydrogenase (DB913426), neuron-specific enolase (5primeCluster0558), and gelsolin (07345_Oc_5_049, 08462_Oc_5_015) are commonly expressed and are thought to be involved in camera eye formation.…”