Comprehensive Genetic Characterization of Mitochondrial Ca2+ Uniporter Components Reveals Their Different Physiological Requirements In Vivo

Abstract

Summary Mitochondrial Ca 2+ uptake is an important mediator of metabolism and cell death. Identification of components of the highly conserved mitochondrial Ca 2+ uniporter has opened it up to genetic analysis in model organisms. Here, we report a comprehensive genetic characterization of all known uniporter components conserved in Drosophila . While loss of pore-forming MCU or EMRE abolishes fast mitochondrial Ca 2+ uptake, this results in only mild phenotypes when young, despite shortened lifespans. In contrast, loss of the MICU1 gatekeeper is developmentally lethal, consistent with unregulated Ca 2+ uptake. Mutants for the neuronally restricted regulator MICU3 are viable with mild neurological impairment. Genetic interaction analyses reveal that MICU1 and MICU3 are not functionally interchangeable. More surprisingly, loss of MCU or EMRE does not suppress MICU1 mutant lethality, suggesting that this results from uniporter-independent functions. Our data reveal the interplay among components of the mitochondrial Ca 2+ uniporter and shed light on their physiological requirements in vivo .

Disarrangement of Endoplasmic reticulum-mitochondria communication impairs Ca2+homeostasis in FRDA

“…Furthermore, we have also observed that one of the consequences of reactivating MAMs in our cell culture model was the increase of mitochondrial Ca 2+ uptake. Therefore, we decided to genetically manipulate Ca 2+ transport into the mitochondria by altering the expression of the mitochondrial Ca 2+ uniporter (MCU), since misexpression of MCU or of other components of the MCU complex has been shown to change the mitochondrial Ca 2+ content (Choi et al, 2017;Drago & Davis, 2016;K.-S. Lee et al, 2018;Tufi et al, 2019). We observed that MCU mRNA levels were not altered in frataxin deficient flies ( Figure S3A).…”

“…Regarding MCU downregulation, unexpectedly a strong silencing using a RNAi line triggered preadult lethality when co-expressed with the fhRNAi-1 line, whereas such lethality was not observed in the control cross. To bypass this problem, we decided to use a mutant allele of MCU (MCU1, described in (Tufi et al, 2019)) in a heterozygous configuration. 50% reduction of MCU expression in glia cells did not induce on their own any effect in the three parameters analyzed (negative geotaxis, brain integrity and lipid accumulation, (Figure S3C-I), and it is not able to suppress too the locomotor deficit of FRDA flies ( Figure 5A) and the brain vacuolization ( Figure 5B-E).…”

“…However, reduction of MCU expression did not influence the presence of such lipid deposits ( Figure 5H). Next, we decided to increase MCU expression by means of two independent UAS lines (Tufi et al, 2019). Both lines trigger a 10-fold increase of MCU expression ( Figure S3B).…”

MICU1 regulates mitochondrial cristae structure and function independent of the mitochondrial calcium uniporter channel

“…Loss-of-function mutations in MICU1 induce proximal myopathy, learning difficulties, movement disorder, fatigue, and lethargy in humans (Lewis-Smith et al, 2016; Logan et al, 2014) and deletion of Micu1 in mouse models causes perinatal lethality (Antony et al, 2016; Liu et al, 2016). Recently, genetic mutants were generated to characterize mtCU regulation in Drosophila (Tufi et al, 2019). Intriguingly, Tufi et al reported that a MICU1 loss-of-function mutation resulted in Drosophila lethality, which could not be rescued by a concurrent MCU loss-of-function mutation that completely ablated mitochondrial Ca 2+ ( m Ca 2+ ) uptake and subsequent mitochondrial permeability transition pore opening (Tufi et al, 2019).…”

“…Recently, genetic mutants were generated to characterize mtCU regulation in Drosophila (Tufi et al, 2019). Intriguingly, Tufi et al reported that a MICU1 loss-of-function mutation resulted in Drosophila lethality, which could not be rescued by a concurrent MCU loss-of-function mutation that completely ablated mitochondrial Ca 2+ ( m Ca 2+ ) uptake and subsequent mitochondrial permeability transition pore opening (Tufi et al, 2019). This observation suggests that the lethal phenotype of MICU1-null flies was not solely a result of aberrant mtCU-dependent Ca 2+ uptake.…”