CEP89 is required for mitochondrial metabolism and neuronal function in man and fly

Abstract

It is estimated that the human mitochondrial proteome consists of 1000-1500 distinct proteins. The majority of these support the various biochemical pathways that are active in these organelles. Individuals with an oxidative phosphorylation disorder of unknown cause provide a unique opportunity to identify novel genes implicated in mitochondrial biology. We identified a homozygous deletion of CEP89 in a patient with isolated complex IV deficiency, intellectual disability and multisystemic problems. CEP89 is a ubiquitously expressed and highly conserved gene of unknown function. Immunocytochemistry and cellular fractionation experiments showed that CEP89 is present both in the cytosol and in the mitochondrial intermembrane space. Furthermore, we ascertained in vitro that downregulation of CEP89 resulted in a severe decrease in complex IV in-gel activity and altered mobility, suggesting that the complex is aberrantly formed. Two-dimensional BN-SDS gel analysis revealed that CEP89 associates with a high-molecular weight complex. Together, these data confirm a role for CEP89 in mitochondrial metabolism. In addition, we modeled CEP89 loss of function in Drosophila. Ubiquitous knockdown of fly Cep89 decreased complex IV activity and resulted in complete lethality. Furthermore, Cep89 is required for mitochondrial integrity, membrane depolarization and synaptic transmission of photoreceptor neurons, and for (sub)synaptic organization of the larval neuromuscular junction. Finally, we tested neuronal Cep89 knockdown flies in the light-off jump reflex habituation assay, which revealed its role in learning. We conclude that CEP89 proteins play an important role in mitochondrial metabolism, especially complex IV activity, and are required for neuronal and cognitive function across evolution.

Open Sesame: How Transition Fibers and the Transition Zone Control Ciliary Composition

“…However, whether the mammalian orthologs are also present or function at TFs is unclear. An individual with a homozygous deletion covering a portion of CEP89 displayed impaired cognitive and neuronal function, but this may be caused by a mitochondrial and not a TF role of Cep89 (van Bon et al 2013). No ciliopathic mutations have yet been identified for FBF1, ODF2, and CBY1.…”

De novo loss-of-function mutations in WAC cause a recognizable intellectual disability syndrome and learning deficits in Drosophila

“…RNAi was induced using the UAS-Gal4 system and the panneuronal driver lines: elav-Gal4 w 1118 ; 2xGMR-wIR; elav-Gal4, UAS-Dicer-2 or nSyb-Gal4 w 1118 , UAS-Dicer-2; nSyb-Gal4.. 9,24 Flies were reared and tested at 25°C (elav-Gal4) and 28°C (nSyb-Gal4) and 70% humidity. The ubiquitous actin-Gal4 driver w 1118 ; P(w[+mC] = Act5c-Gal4)/CyO obtained from Bloomington Drosophila Stock Center, 25 was used to generate RNAi-mediated knockdown for quantitative PCR (qPCR).…”

“…31,32 Using the light-off jump reflex habituation, we have previously identified learning deficits in number of Drosophila ID models. 9,24,26 Two independent inducible RNAi lines targeting the Drosophila WAC orthologue CG8949 (vdrc48307 and vdrc107328) and their corresponding genetic background control lines (vdrc60000 and vdrc60100) were obtained (Vienna Drosophila RNAi Center 22 ) and fly stocks were kept under standard conditions. Expression of CG8949 was specifically downregulated in neurons using the UAS-Gal4 system.…”

Human Intellectual Disability Genes Form Conserved Functional Modules in Drosophila

“…Because our past work determined significant differences in knockdown levels induced by RNAi using this toolbox (20–60% of wt mRNA levels [39]–[42]) and because we consistently found morphological eye phenotypes with two independent RNAi constructs only for 54% of the investigated ID genes, it seems likely that a number of RNAi lines are not efficient enough to evoke phenotypes. To limit the impact of such false-negatives on our analyses, we included phenotypes caused by single RNAi lines.…”