Nuclear Receptor Rev-erb Alpha (Nr1d1) Functions in Concert with Nr2e3 to Regulate Transcriptional Networks in the Retina

The majority of diseases in the retina are caused by genetic mutations affecting the development and function of photoreceptor cells. The transcriptional networks directing these processes are regulated by genes such as nuclear hormone receptors. The nuclear hormone receptor gene Rev-erb alpha/Nr1d1 has been widely studied for its role in the circadian cycle and cell metabolism, however its role in the retina is unknown. In order to understand the role of Rev-erb alpha/Nr1d1 in the retina, we evaluated the effects of loss of Nr1d1 to the developing retina and its co-regulation with the photoreceptor-specific nuclear receptor gene Nr2e3 in the developing and mature retina. Knock-down of Nr1d1 expression in the developing retina results in pan-retinal spotting and reduced retinal function by electroretinogram. Our studies show that NR1D1 protein is co-expressed with NR2E3 in the outer neuroblastic layer of the developing mouse retina. In the adult retina, NR1D1 is expressed in the ganglion cell layer and is co-expressed with NR2E3 in the outer nuclear layer, within rods and cones. Several genes co-targeted by NR2E3 and NR1D1 were identified that include: Nr2c1, Recoverin, Rgr, Rarres2, Pde8a, and Nupr1. We examined the cyclic expression of Nr1d1 and Nr2e3 over a twenty-four hour period and observed that both nuclear receptors cycle in a similar manner. Taken together, these studies reveal a novel role for Nr1d1, in conjunction with its cofactor Nr2e3, in regulating transcriptional networks critical for photoreceptor development and function

Functional analysis of NR2E3 in retinal degenerations

The vertebrate retina is a model system of the development of the central nervous system. Because of its rapid development and the availability of many molecular tools the zebrafish is an established model of retinal development. Development and maintenance of the retina is driven by a complex regulatory network of transcription factors. For instance, the development of photoreceptors is initiated by cone-rod homeobox (Crx), and neural leucine zipper (Nrl), and the nuclear receptors Trβ2 and PNR/Nr2e3 further determine proper rod and cone development. Recessive mutations in NR2E3 cause Goldmann-Favre syndrome also called enhanced S-cone syndrome and a unique dominant mutation located in the DNA-binding domain p.G56R causes severe retinitis pigmentosa. In the present study, the first aim consisted of generating a transgenic zebrafish line expressing hemizygously the dominant NR2E3p.G56R mutant protein to study the mechanism underlying retinitis pigmentosa. The human mutant protein was expressed in the retina of transgenic zebrafish but a severe clinical phenotype could not be recapitulated. However, dysregulation of opsin gene expression was observed. A second transgenic zebrafish line expressing the fluorescent mCherry protein under the control of a potential nr2e3 promoter was generated. This promoter fragment was sufficient to drive retina-specific mCherry expression in larvae and adult and might become a valuable tool to drive transgene expression in a spatio-temporal manner in the retina. In addition, we studied the coregulation and protein interactions between NR2E3 and the nuclear receptor Rev-erb α (NR1D1) as well as with the photoreceptor-specific transcription factors CRX and NRL. Finally, we performed functional and structural analysis of the NR2E3 ligand-binding domain (LBD) and identified dimerization potential as a new molecular mechanism in Goldmann-Favre syndrome. Notably, we identified the first genotype-phenotype correlation for two mutations located in the NR2E3 LBD

A behavior-based circuit model of how outcome expectations organize learned behavior in larval Drosophila

Drosophila larvae combine a numerically simple brain, a correspondingly moderate behavioral complexity, and the availability of a rich toolbox for transgenic manipulation. This makes them attractive as a study case when trying to achieve a circuit-level understanding of behavior organization. From a series of behavioral experiments, we suggest a circuitry of chemosensory processing, odor–tastant memory trace formation, and the “decision” process to behaviorally express these memory traces—or not. The model incorporates statements about the neuronal organization of innate vs. conditioned chemosensory behavior, and the types of interaction between olfactory and gustatory pathways during the establishment as well as the behavioral expression of odor–tastant memory traces. It in particular suggests that innate olfactory behavior is responsive in nature, whereas conditioned olfactory behavior is captured better when seen as an action in pursuit of its outcome. It incorporates the available neuroanatomical and behavioral data and thus should be useful as scaffold for the ongoing investigations of the chemo-behavioral system in larval Drosophila