MFF-2 (F55F8.6) is one of two C. elegans homologs of mitochondrial fission factor (Mff; Tango11 family), the other being MFF-1 (F11C1.2). It is a small (161 aa) tail-anchored protein with a single C-terminal transmembrane segment. It sits in the mitochondrial outer membrane with its N-terminal domain facing the cytosol. In vertebrates, Mff recruits the dynamin-related GTPase Drp1 to mitochondria and peroxisomes. In C. elegans, mff-1 and mff-2 act redundantly: single mutants have weak effects, while the double mutant has elongated, interconnected mitochondria and tubular peroxisomes, a fission defect similar to but milder than loss of drp-1. Unlike in mammalian cells, DRP-1 still forms foci and associates with mitochondria in the mff-1 mff-2 double mutant, and ionophore-induced fragmentation still occurs. So worm Mff proteins promote mitochondrial and peroxisomal fission but are not essential for DRP-1 recruitment.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000266 mitochondrial fission | IEA GO_REF:0000104 | ACCEPT | Summary: Mitochondrial fission, an IEA transferred by UniRule from the Mff family. Reason: Worm genetics support this term. The mff-1; mff-2 double mutant has a mitochondrial fission defect close to that of drp-1, and the single mutants have weak effects, which shows redundancy. Supporting Evidence: PMID:24196833 mff-1 and mff-2 single mutants have weak effects, and that the Mff double mutant has a mitochondrial fission defect similar to but not as strong as the drp-1 defect |
| GO:0005737 cytoplasm | IEA GO_REF:0000117 | ACCEPT | Summary: Cytoplasm, from an ARBA machine-learning IEA. Reason: In GO, cytoplasm includes the mitochondria, and the functional domain of MFF-2 faces the cytosol, so the term is not wrong. It is much less informative than the mitochondrial outer membrane location, which is also annotated. Supporting Evidence: PMID:21248201 We used antibodies against a C. elegans Mff homologue, encoded by the F55F8.6 gene, as a control for proteins exposed to the cytosol |
| GO:0005741 mitochondrial outer membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Mitochondrial outer membrane, from the UniProt subcellular location (UniRule). The F55F8.6 protein was used as a cytosol-exposed outer-membrane control in protease-protection experiments on isolated worm mitochondria. Reason: The location fits the C-terminal tail anchor and Mff family biology, and is supported by worm biochemistry. Supporting Evidence: PMID:21248201 We used antibodies against a C. elegans Mff homologue, encoded by the F55F8.6 gene, as a control for proteins exposed to the cytosol |
| GO:0005777 peroxisome | IEA GO_REF:0000120 | ACCEPT | Summary: Peroxisome, from the UniProt subcellular location (UniRule) based on Mff family members. Reason: Mff is dual-targeted to mitochondria and peroxisomes in mammals. In worms, the Mff double mutant has tubular peroxisomes, which fits a peroxisomal site of action. Direct localisation of MFF-2 to worm peroxisomes has not been reported. Supporting Evidence: PMID:24196833 Analogous results were obtained with a peroxisome marker, showing punctate peroxisomes in wild-type and Fis1 mutants and tubular peroxisomes in drp-1 mutant and Mff double mutants |
| GO:0090141 positive regulation of mitochondrial fission | IEA GO_REF:0000104 | ACCEPT | Summary: Positive regulation of mitochondrial fission, a UniRule IEA from the Mff family. Reason: MFF-2 promotes fission, redundantly with MFF-1. GO uses both direct fission and positive regulation of fission terms for Mff family adaptors, and the worm genetics support a fission-promoting role. Supporting Evidence: PMID:24196833 We conclude that C. elegans Mff homologues affect mitochondrial and peroxisome fission, whereas Fis1 homologues have no obvious effects. |
| GO:0090314 positive regulation of protein targeting to membrane | IEA GO_REF:0000104 | MARK AS OVER ANNOTATED | Summary: Positive regulation of protein targeting to membrane, a UniRule IEA reflecting mammalian Mff recruitment of Drp1 to the outer membrane. Reason: In C. elegans, DRP-1 foci and the amount of DRP-1 in mitochondrial fractions are unchanged in mff-1; mff-2 double mutants. The authors conclude that worm Mff is not essential for DRP-1 recruitment. Some contribution to DRP-1 targeting cannot be ruled out, but the family-level transfer overstates what is known for the worm protein. Supporting Evidence: PMID:24196833 We conclude that Mff affects fission, but Mff and Fis1 are not essential for fission or for Drp1 recruitment to mitochondria in C. elegans. |
| GO:0016559 peroxisome fission | IMP PMID:24196833 Mutations in Fis1 disrupt orderly disposal of defective mito... | NEW | Summary: Peroxisomes are tubular rather than punctate in the mff-1; mff-2 double mutant, as in drp-1 mutants. Reason: The Mff family adaptor is part of the fission machinery at the organelle surface, so it does part of the work rather than being a substrate. In the comparator check (same role, same process), human MFF and the DRP1 GTPase (DNM1L) are annotated to peroxisome fission, and this paper shows the worm phenotype. The double-mutant evidence covers MFF-2 together with MFF-1. Supporting Evidence: PMID:24196833 We conclude that C. elegans Mff homologues affect mitochondrial and peroxisome fission, whereas Fis1 homologues have no obvious effects. |
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Download this section (compressed HTML)Q: Does MFF-2 bind DRP-1 directly in C. elegans? If DRP-1 recruitment does not need Mff, what step of fission does MFF-2 promote (for example DRP-1 oligomerisation or activation at ER contact sites)?
Q: Do MFF-1 and MFF-2 differ in tissue expression or in how they divide between peroxisomes and mitochondria?
Q: PMID:21248201 calls F55F8.6 both mff-2 and "MFF-1 (F55F8.6)". Which antibody and locus were actually used for the outer-membrane control?
Experiment: Endogenous tagging of MFF-1 and MFF-2 with distinct fluorophores, co-imaged with peroxisome and mitochondrial markers and DRP-1, to test dual targeting and redundancy at single fission sites.
Experiment: In vitro binding of recombinant MFF-2 cytosolic domain to DRP-1, and DRP-1 GTPase/oligomerisation assays in its presence.
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