Arf6 and the 5'phosphatase of synaptojanin 1 regulate autophagy in cone photoreceptors.

Abnormalities in the ability of cells to properly degrade proteins have been identified in many neurodegenerative diseases. Recent work has implicated synaptojanin 1 (SynJ1) in Alzheimer's disease and Parkinson's disease, although the role of this polyphosphoinositide phosphatase in protein degradation has not been thoroughly described. Here, we dissected in vivo the role of SynJ1 in endolysosomal trafficking in zebrafish cone photoreceptors using a SynJ1-deficient zebrafish mutant, nrc(a14) . We found that loss of SynJ1 leads to specific accumulation of late endosomes and autophagosomes early in photoreceptor development. An analysis of autophagic flux revealed that autophagosomes accumulate because of a defect in maturation. In addition we found an increase in vesicles that are highly enriched for PI(3)P, but negative for an early endosome marker in nrc(a14) cones. A mutational analysis of SynJ1 enzymatic domains found that activity of the 5'phosphatase, but not the Sac1 domain, is required to rescue both aberrant late endosomes and autophagosomes. Finally, modulating activity of the PI(4,5)P2 regulator, Arf6, rescued the disrupted trafficking pathways in nrc(a14) cones. Our study describes a specific role for SynJ1 in autophagosomal and endosomal trafficking and provides evidence that PI(4,5)P2 participates in autophagy in a neuronal cell type.

Arf6 and the 5'phosphatase of Synaptojanin 1 regulate autophagy in cone photoreceptors.

Abnormalities in the ability of cells to properly degrade proteins have been identified in many neurodegenerative diseases. Recent work has implicated Synaptojanin 1 (SynJ1) in Alzheimer's disease and Parkinson's disease, although the role of this polyphosphoinositide phosphatase in protein degradation has not been thoroughly described. Here we dissected in vivo the role of SynJ1 in endolysosomal trafficking in zebrafish cone photoreceptors using a SynJ1-deficient zebrafish mutant, nrca14 . We found that loss of SynJ1 leads to specific accumulation of late endosomes and autophagosomes early in photoreceptor development. An analysis of autophagic flux revealed that autophagosomes accumulate due to a defect in maturation. In addition we found an increase in vesicles that are highly enriched for PI(3)P, but negative for an early endosome marker in nrca14 cones. A mutational analysis of SynJ1 enzymatic domains found that activity of the 5' phosphatase, but not the Sac1 domain, is required to rescue both aberrant late endosomes and autophagosomes. Finally, modulating activity of the PI(4,5)P2 regulator, Arf6, rescued the disrupted trafficking pathways in nrca14 cones. Our study describes a specific role for SynJ1 in autophagosomal and endosomal trafficking and provides evidence that PI(4,5)P2 participates in autophagy in a neuronal cell type.

The molecular biology of vertebrate olfaction.

The importance of chemosensation for vertebrates is reflected in the vast and variable nature of their chemosensory tissues, neurons, and genes, which we explore in this review. Immense progress has been made in elucidating the molecular biology of olfaction since the discovery of the olfactory receptor genes by Buck and Axel, which eventually won the authors the Nobel Prize. In particular, research linking odor ligands to olfactory receptors (ORs) is truly revolutionizing our understanding of how a large but limited number of chemosensory receptors can allow us to perceive the massive diversity of odors in our habitat. This research is providing insight into the evolution of genomes and providing the raw data needed to explore links between genotype and phenotype, still a grand challenge in biology. Research into olfaction is still developing and will no doubt continue until we have a clear understanding of how all odors are detected and the evolutionary forces that have molded the chemosensory subgenome in vertebrates. This knowledge will not only be a huge step in elucidating olfactory function, advancing scientific knowledge and techniques, but there are also commercial applications for this research. This review focuses on the molecular basis of chemosensation, particularly olfaction, its evolution across vertebrates and the recent molecular advances linking odors to their cognate receptors.

Synaptojanin 1 is required for endolysosomal trafficking of synaptic proteins in cone photoreceptor inner segments.

Highly polarized cells such as photoreceptors require precise and efficient strategies for establishing and maintaining the proper subcellular distribution of proteins. The signals and molecular machinery that regulate trafficking and sorting of synaptic proteins within cone inner segments is mostly unknown. In this study, we show that the polyphosphoinositide phosphatase Synaptojanin 1 (SynJ1) is critical for this process. We used transgenic markers for trafficking pathways, electron microscopy, and immunocytochemistry to characterize trafficking defects in cones of the zebrafish mutant, nrc(a14) , which is deficient in phosphoinositide phosphatase, SynJ1. The outer segments and connecting cilia of nrc(a14) cone photoreceptors are normal, but RibeyeB and VAMP2/synaptobrevin, which normally localize to the synapse, accumulate in the nrc(a14) inner segment. The structure of the Endoplasmic Reticulum in nrc(a14) mutant cones is normal. Golgi develop normally, but later become disordered. Large vesicular structures accumulate within nrc(a14) cone photoreceptor inner segments, particularly after prolonged incubation in darkness. Cone inner segments of nrc (a14) mutants also have enlarged acidic vesicles, abnormal late endosomes, and a disruption in autophagy. This last pathway also appears exacerbated by darkness. Taken altogether, these findings show that SynJ1 is required in cones for normal endolysosomal trafficking of synaptic proteins.

A cluster of olfactory receptor genes linked to frugivory in bats.

Diversity of the mammalian olfactory receptor (OR) repertoire has been globally reshaped by niche specialization. However, little is known about the variability of the OR repertoire at a shallower evolutionary timeframe. The vast bat radiation exhibits an extraordinary variety of trophic and sensory specializations. Unlike other mammals, bats possess a unique and diverse OR gene repertoire. We elucidated whether the evolution of the OR gene repertoire can be linked to ecological niche specializations, such as sensory modalities and diet. The OR gene repertoires of 27 bat species spanning the chiropteran radiation were amplified and sequenced. For each species, intact and nonfunctional genes were assessed, and the OR gene abundances in each gene family were analyzed and compared. We identified a unique OR pattern linked to the frugivorous diet of New World fruit-eating bats and a similar convergent pattern in the Old World fruit-eating bats. Our results show a strong association between niche specialization and OR repertoire diversity even at a shallow evolutionary timeframe.

Ecological adaptation determines functional mammalian olfactory subgenomes.

The ability to smell is governed by the largest gene family in mammalian genomes, the olfactory receptor (OR) genes. Although these genes are well annotated in the finished human and mouse genomes, we still do not understand which receptors bind specific odorants or how they fully function. Previous comparative studies have been taxonomically limited and mostly focused on the percentage of OR pseudogenes within species. No study has investigated the adaptive changes of functional OR gene families across phylogenetically and ecologically diverse mammals. To determine the extent to which OR gene repertoires have been influenced by habitat, sensory specialization, and other ecological traits, to better understand the functional importance of specific OR gene families and thus the odorants they bind, we compared the functional OR gene repertoires from 50 mammalian genomes. We amplified more than 2000 OR genes in aquatic, semi-aquatic, and flying mammals and coupled these data with 48,000 OR genes from mostly terrestrial mammals, extracted from genomic projects. Phylogenomic, Bayesian assignment, and principle component analyses partitioned species by ecotype (aquatic, semi-aquatic, terrestrial, flying) rather than phylogenetic relatedness, and identified OR families important for each habitat. Functional OR gene repertoires were reduced independently in the multiple origins of aquatic mammals and were significantly divergent in bats. We reject recent neutralist views of olfactory subgenome evolution and correlate specific OR gene families with physiological requirements, a preliminary step toward unraveling the relationship between specific odors and respective OR gene families.