Overexpression of ubiquitin carboxyl terminal hydrolase impairs multiple pathways during eye development in Drosophila melanogaster

Therapeutic Potential of Polyscias fruticosa (L.) Harms Leaf Extract for Parkinson's Disease Treatment by Drosophila melanogaster Model

Parkinson's disease (PD) is characterized by progressive locomotive defects and loss of dopaminergic neurons. Polyscias fruticosa leaves are used by Vietnamese as herbal medicines to support the treatment of some diseases related to neurodegeneration such as Parkinson's and Alzheimer's diseases. However, recent scientific data have not provided sufficient evidence for the use of P. fruticosa leaves to treat PD or decelerate PD progression. In the present study, the capacity of P. fruticosa leaf extract for PD treatment on the dietary supplementation was investigated using dUCH-knockdown Drosophila model. The results indicated that P. fruticosa leaf extract decelerated dopaminergic neuron degeneration induced by dUCH knockdown in not only the larval stage but also the adult stage, which might result in the amelioration in locomotor ability of dUCH-knockdown larvae and flies. Furthermore, antioxidant activities and some key phytochemicals such as saponins, polyphenols, and flavonoids that might contribute to the effects of the P. fruticosa leaf extract were identified.

E3 ubiquitin ligase-mediated regulation of vertebrate ocular development; new insights into the function of SIAH enzymes

Developmental regulation of the vertebrate visual system has been a focus of investigation for generations as understanding this critical time period has direct implications on our understanding of congenital blinding disease. The majority of studies to date have focused on transcriptional regulation mediated by morphogen gradients and signaling pathways. However, recent studies of post translational regulation during ocular development have shed light on the role of the ubiquitin proteasome system (UPS). This rather ubiquitous yet highly diverse system is well known for regulating protein function and localization as well as stability via targeting for degradation by the 26S proteasome. Work from many model organisms has recently identified UPS activity during various milestones of ocular development including retinal morphogenesis, retinal ganglion cell function as well as photoreceptor homeostasis. In particular work from flies and zebrafish has highlighted the role of the E3 ligase enzyme family, Seven in Absentia Homologue (Siah) during these events. In this review, we summarize the current understanding of UPS activity during Drosophila and vertebrate ocular development, with a major focus on recent findings correlating Siah E3 ligase activity with two major developmental stages of vertebrate ocular development, retinal morphogenesis and photoreceptor specification and survival.

By the Tips of Your Cilia: Ciliogenesis in the Retina and the Ubiquitin-Proteasome System

Primary cilia are microtubule-based sensory organelles that are involved in the organization of numerous key signals during development and in differentiated tissue homeostasis. In fact, the formation and resorption of cilia highly depends on the cell cycle phase in replicative cells, and the ubiquitin proteasome pathway (UPS) proteins, such as E3 ligases and deubiquitinating enzymes, promote microtubule assembly and disassembly by regulating the degradation/availability of ciliary regulatory proteins. Also, many differentiated tissues display cilia, and mutations in genes encoding ciliary proteins are associated with several human pathologies, named ciliopathies, which are multi-organ rare diseases. The retina is one of the organs most affected by ciliary gene mutations because photoreceptors are ciliated cells. Photoreception and phototransduction occur in the outer segment, a highly specialized neurosensory cilium. In this review, we focus on the function of UPS proteins in ciliogenesis and cilia length control in replicative cells and compare it with the scanty data on the identified UPS genes that cause syndromic and non-syndromic inherited retinal disorders. Clearly, further work using animal models and gene-edited mutants of ciliary genes in cells and organoids will widen the landscape of UPS involvement in ciliogenesis and cilia homeostasis.

Evaluating the Potential of Portulaca oleracea L. for Parkinson's Disease Treatment Using a Drosophila Model with dUCH-Knockdown

Parkinson's disease (PD), which is characterized by the decreased motor function and the loss of dopaminergic neurons, is a common neurodegenerative disorder in elders. There have been numerous in vitro and in vivo models developed to study mechanisms of PD and screen potential drug. Recently, dUCH-knockdown Drosophila model has been established and showed potential for screening antioxidants for PD treatment. The dUCH-knockdown Drosophila model of PD mimics most of main PD pathologies such as dopaminergic neurons degeneration, locomotor dysfunction, and shortage of dopamine in the brain. Common purslane (Portulaca oleracea L.) is a nutritious vegetable containing a variety of antioxidants, levodopa, and dopamine, a neurotransmitter closely related to PD. Purslane has been reported to exert neuroprotective effects against several neurotoxins including rotenone and 6-OHDA in PD models. However, the recent data have not provided sufficient evidence for using purslane to treat PD or decelerate disease progression. Therefore, in this study, we utilized dUCH-knockdown fly to evaluate the capacity of purslane extracts for PD treatment. The results showed that purslane extracts improved locomotor ability in the larval stage and decelerated disease progression in the adult stage. Additionally, purslane extracts also reduced dopaminergic neuron degeneration. Taken together, our data strongly demonstrated that purslane extracts effectively rescued PD-like phenotypes in the fly model. This result contributed a foundation for further study on the application of purslane in PD treatment.

Drosophila Ubiquitin C-Terminal Hydrolase Knockdown Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide. Many factors have been shown to contribute to its pathogenesis including genetic and environmental factors. Ubiquitin C-terminal hydrolase L1 (UCHL1) is also known to be involved in the pathogenesis of PD. We herein modeled the study of UCHL1 in Drosophila melanogaster and investigated its functions in PD. The specific knockdown of the Drosophila ortholog of UCHL1 (dUCH) in dopaminergic neurons (DA neurons) led to the underdevelopment and/or degeneration of these neurons, specifically in DL1 DA neuron cluster in the larval brain lobe and PPM2, PPM3, PPL2ab, and VUM DA neuron clusters in the adult brain. These defects were followed by a shortage of dopamine in the brain, which subsequently resulted in locomotor dysfunction. The degeneration of DA neurons in dUCH knockdown adult brain, which occurred progressively and severely during the course of aging, mimics the epidemiology of PD. DA neuron and locomotor defects were rescued when dUCH knockdown flies were treated with vitamin C, a well-known antioxidant. These results suggest that dUCH knockdown fly is a promising model for studying the pathogenesis and epidemiology of PD as well as the screening of potential antioxidants for PD therapeutics.

Tumor suppressor gene OSCP1/NOR1 regulates apoptosis, proliferation, differentiation, and ROS generation during eye development of Drosophila melanogaster

OSCP1/NOR1 (organic solute carrier partner 1/oxidored nitrodomain-containing protein 1) is a known tumor suppressor protein. OSCP1 has been reported to mediate transport of various organic solutes into cells; however, its role during development has not yet been addressed. Here we report the results of studies on dOSCP1 (the Drosophila ortholog of hOSCP1) to elucidate the role of OSCP1/NOR1 during development. Knockdown of dOSCP1 in the eye imaginal discs induced a rough-eye phenotype in adult flies. This phenotype resulted from induction of caspase-dependent apoptosis followed by a compensatory cell proliferation and generation of reactive oxygen species in eye imaginal discs. The induction of apoptosis appears to be associated with down-regulation of the anti-apoptotic Buffy gene and up-regulation of the pro-apoptotic Debcl gene. These effects of knockdown of dOSCP1 lead to mitochondrial fragmentation, degradation, and a shortfall in ATP production. We also found that knockdown of dOSCP1 causes a defect in cone cell and pigment cell differentiation in pupal retinae. Moreover, mutations in epidermal growth factor receptor pathway-related genes, such as Spitz and Drk, enhanced the rough-eye phenotype induced by dOSCP1 knockdown. These results suggest that dOSCP1 positively regulates the epidermal growth factor receptor signaling pathway. Overall, our findings indicate that dOSCP1 plays multiple roles during eye development in Drosophila.

Flies with Parkinson's disease

Parkinson's disease is an incurable neurodegenerative disease. Most cases of the disease are of sporadic origin, but about 10% of the cases are familial. The genes thus far identified in Parkinson's disease are well conserved. Drosophila is ideally suited to study the molecular neuronal cell biology of these genes and the pathogenic mutations in Parkinson's disease. Flies reproduce quickly, and their elaborate genetic tools in combination with their small size allow researchers to analyze identified cells and neurons in large numbers of animals. Furthermore, fruit flies recapitulate many of the cellular and molecular defects also seen in patients, and these defects often result in clear locomotor and behavioral phenotypes, facilitating genetic modifier screens. Hence, Drosophila has played a prominent role in Parkinson's disease research and has provided invaluable insight into the molecular mechanisms of this disease.

Parkin-mediated K63-polyubiquitination targets ubiquitin C-terminal hydrolase L1 for degradation by the autophagy-lysosome system

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is a key neuronal deubiquitinating enzyme which is mutated in Parkinson disease (PD) and in childhood-onset neurodegenerative disorder with optic atrophy. Furthermore, reduced UCH-L1 protein levels are associated with a number of neurodegenerative diseases, whereas up-regulation of UCH-L1 protein expression is found in multiple types of cancer. However, very little is known about how UCH-L1 protein level is regulated in cells. Here, we report that UCH-L1 is a novel interactor and substrate of PD-linked E3 ubiquitin-protein ligase parkin. We find that parkin mediates K63-linked polyubiquitination of UCH-L1 in cooperation with the Ubc13/Uev1a E2 ubiquitin-conjugating enzyme complex and promotes UCH-L1 degradation by the autophagy-lysosome pathway. Targeted disruption of parkin gene expression in mice causes a significant decrease in UCH-L1 ubiquitination with a concomitant increase in UCH-L1 protein level in brain, supporting an in vivo role of parkin in regulating UCH-L1 ubiquitination and degradation. Our findings reveal a direct link between parkin-mediated ubiquitin signaling and UCH-L1 regulation, and they have important implications for understanding the roles of these two proteins in health and disease.

Proteasome, but not autophagy, disruption results in severe eye and wing dysmorphia: a subunit- and regulator-dependent process in Drosophila

Proteasome-dependent and autophagy-mediated degradation of eukaryotic cellular proteins represent the two major proteostatic mechanisms that are critically implicated in a number of signaling pathways and cellular processes. Deregulation of functions engaged in protein elimination frequently leads to development of morbid states and diseases. In this context, and through the utilization of GAL4/UAS genetic tool, we herein examined the in vivo contribution of proteasome and autophagy systems in Drosophila eye and wing morphogenesis. By exploiting the ability of GAL4-ninaE. GMR and P{GawB}Bx^MS1096 genetic drivers to be strongly and preferentially expressed in the eye and wing discs, respectively, we proved that proteasomal integrity and ubiquitination proficiency essentially control fly’s eye and wing development. Indeed, subunit- and regulator-specific patterns of severe organ dysmorphia were obtained after the RNAi-induced downregulation of critical proteasome components (Rpn1, Rpn2, α5, β5 and β6) or distinct protein-ubiquitin conjugators (UbcD6, but not UbcD1 and UbcD4). Proteasome deficient eyes presented with either rough phenotypes or strongly dysmorphic shapes, while transgenic mutant wings were severely folded and carried blistered structures together with loss of vein differentiation. Moreover, transgenic fly eyes overexpressing the UBP2-yeast deubiquitinase enzyme were characterized by an eyeless-like phenotype. Therefore, the proteasome/ubiquitin proteolytic activities are undoubtedly required for the normal course of eye and wing development. In contrast, the RNAi-mediated downregulation of critical Atg (1, 4, 7, 9 and 18) autophagic proteins revealed their non-essential, or redundant, functional roles in Drosophila eye and wing formation under physiological growth conditions, since their reduced expression levels could only marginally disturb wing’s, but not eye’s, morphogenetic organization and architecture. However, Atg9 proved indispensable for the maintenance of structural integrity of adult wings in aged flies. In toto, our findings clearly demonstrate the gene-specific fundamental contribution of proteasome, but not autophagy, in invertebrate eye and wing organ development.