TworibeyeGenes in Teleosts: The Role of Ribeye in Ribbon Formation and Bipolar Cell Development

Abstract

Ribeye is the only known protein specific to synaptic ribbon, but its function is unclear. We show that the teleost fish, Fugu and zebrafish, have two ribeye genes, ribeye a and ribeye b. Whole-mount in situ hybridization revealed that ribeye a is expressed in tissues containing synaptic ribbons, including the pineal gland, inner ear, and retina. Ribeye b is absent in the pineal gland. In the retina, ribeye a is expressed in both photoreceptors and bipolar cells, whereas ribeye b is detected only in photoreceptors. To study the function of Ribeye a in retina, we depleted it by morpholino antisense oligos. Fish deficient in Ribeye a lack an optokinetic response and have shorter synaptic ribbons in photoreceptors and fewer synaptic ribbons in bipolar cells. Their bipolar cells still target Syntaxin-3 proteins to the inner plexiform layer and have abundant vsx1 mRNA. However, they lack large synaptic terminals and show increased apoptosis. Rod bipolar cells are fewer in number and/or deficient in PKC␣. Recovery of Ribeye a levels rescues the optokinetic response, increases the number of PKC␣-positive bipolar cells, and stops apoptosis. We conclude that Ribeye a is important for late steps in bipolar cell development.

Multiple RIBEYE–RIBEYE Interactions Create a Dynamic Scaffold for the Formation of Synaptic Ribbons

“…The structural analysis of these proteins, e.g., of CtBP1, revealed the presence of two globular subdomains, namely an NAD(H)-binding subdomain (NBD) and the substrate-binding subdomain (SBD) (for a review, see Chinnadurai, 2002;Kumar et al, 2002;Nardini et al, 2003). Previous data indicated that RIBEYE is the major component of synaptic ribbons (Schmitz et al, 2000;Zenisek et al, 2004;Wan et al, 2005). In the present study, we analyzed functional properties of RIBEYE and demonstrate that RIBEYE is capable to interact with itself.…”

“…The cotransfection experiments demonstrated that RIBEYE proteins interact with each other and coaggregate into the same protein clusters. Given the fact that RIBEYE is the major component of synaptic ribbons (Schmitz et al, 2000;Zenisek et al, 2004;Wan et al, 2005), the multiple protein interactions of RIBEYE provide a molecular mechanism how the scaffold of the synaptic ribbon can be created. RIBEYE-RIBEYE interactions could directly link the individual RIBEYE units to each other.…”

“…The colocalization of RIBEYE with its physiological interaction partner bassoon in R28 cells emphasizes the physiological relevance of the RIBEYE-containing protein aggregates and suggest that the RIBEYE-containing aggregates fulfill partial ribbon-like functions. Because RIBEYE is not the only component of synaptic ribbons (Schmitz et al, 2000;Wan et al, 2005), it cannot be expected that RIBEYE alone makes fully mature ribbons, e.g., with a dense and regular association of synaptic vesicles. Very likely, additional ribbon components are necessary to provide full-ribbon function and structure.…”

“…RIBEYE is present in synaptic ribbons of all vertebrate ribbon synapses (Schmitz et al, 2000(Schmitz et al, , 2006Zenisek et al, 2004;Khimich et al, 2005;tom Dieck et al, 2005;Wan et al, 2005) (for review, see tom Dieck and Brandstätter, 2006).…”

Enhanced Functional Integration of Human Photoreceptor Precursors into Human and Rodent Retina in anEx VivoRetinal Explant Model System

“…38 The assembly of photoreceptor ribbon synapses involves the formation and trafficking of sphere-like protein aggregates of the ribbon matrix proteins BASSOON, RIBEYE, Piccolo, and RIM1. 38 In animal models lacking RIBEYE, the ribbon synapse fails to develop properly and the optokinetic response driven from photoreceptor connectivity to second-order neurons is lost, 39 highlighting the critical role of ribbon synapse formation in visual function. We used BASSOON and RIBEYE as markers in further assessing functional integration of PPCs into neurosensory retina.…”