|Coordinate||77,948,299 bp (GRCm38)|
|Base Change||T ⇒ A (forward strand)|
|Gene Name||ectopic P-granules autophagy protein 5 homolog (C. elegans)|
|Chromosomal Location||77,938,467-78,035,027 bp (+)|
FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] This gene encodes a large coiled coil domain-containing protein that functions in autophagy during starvation conditions. Mutations in this gene cause Vici syndrome. [provided by RefSeq, Aug 2015]
PHENOTYPE: Mice homozygous for a knock-out allele exhibit dysfunctional autophagy that leads to aggregate inclusions in motor neurons, motor neuron degeneration, denervation, muscle degeneration and premature death. [provided by MGI curators]
|Amino Acid Change||Cysteine changed to Stop codon|
|Institutional Source||Beutler Lab|
|Gene Model||predicted gene model for protein(s): [ENSMUSP00000038681]|
AA Change: C70*
|Predicted Effect||probably null|
|Meta Mutation Damage Score||0.9755|
|Is this an essential gene?||Probably essential (E-score: 0.937)|
|Candidate Explorer Status||CE: excellent candidate; human score: 0.5; ML prob: 0.66|
Linkage Analysis Data
|Alleles Listed at MGI|
|Mode of Inheritance||Unknown|
|Local Stock||Live Mice|
|Last Updated||2019-09-04 9:38 PM by Anne Murray|
|Record Created||2018-01-10 8:14 AM by Jamie Russell|
The stitch phenotype was identified among G3 mice of the pedigree R5858, some of which showed circling as well as abnormal front limb movement (i.e., some of their front limbs are very jerky with more frequent movement and others appear to constantly vibrate).
|Nature of Mutation|
Whole exome HiSeq sequencing of the G1 grandsire identified 52 mutations. The neurological phenotype was linked by continuous variable mapping to a mutation in Epg5: a T to A transversion at base pair 77,948,299 (v38) on chromosome 18, or base pair 9,892 in the GenBank genomic region NC_000084. Linkage was found with an additive model of inheritance (2.737 x 10-5; Figure 2). Nine affected mice were either homozygous for the variant allele (N = 4), heterozygous (N = 4), or homozygous for the reference allele (N = 1); 42 unaffected mice were either heterozygous (N = 19) or homozygous for the reference allele (N = 23).
The mutation corresponds to residue 243 in the mRNA sequence NM_001195633 within exon 2 of 44 total exons.
The mutated nucleotide is indicated in red. The mutation results in substitution of cysteine 70 for a premature stop codon (C70*) in the EPG5 protein.
Epg5 encodes ectopic P granules protein 5 (EPG5). EPG5 has no defined functional domains, but the predicted structure of EPG5 includes a membrane remodeling domain, a karyopherin-like domain, and a coiled-coil region (Figure 3) (1). If present, the karyopherin-like domain putatively promotes interactions with molecules that are transported between the cytoplasm and nucleus.
The Stitch mutation results in substitution of cysteine 70 for a premature stop codon (C70*).
EPG5 is ubiquitously expressed, with highest expression in the brain, central nervous system, heart, skeletal muscle, immune cells, thymus, lungs, liver, kidneys, and ovary (1;2). Human EPG5 localizes in the cytoplasm and on late endosomes/lysosomes (3). Upon autophagy induction, EPG5 localizes with amphisomes/autolysosomes (3).
Autophagy is a method of degradation that is involved in cellular maintenance and development. In canonical autophagy, a portion of the cytoplasm is sequestered within double-membrane vesicles known as autophagosomes and delivered to the lysosome whereby the contents are degraded. Studies showed that EPG5 is a Rab7 effector that determines the fusion specificity of autophagosomes with late endosomes/lysosomes during autophagy (Figure 4) (3). EPG5 directly interacts with Rab7 and the late endosomal/lysosomal R-SNARE VAMP7/8, which recruits EPG5 to the late endosomes/lysosomes. EPG5 also binds to LC3 and to assembled STX17-SNAP29 Qabc SNARE complexes on autophagosomes. EPG5 stabilizes and facilitates the assembly of STX17-SNAP29-VAMP7/8 trans-SNARE complexes, and promotes STX17-SNAP29-VAMP7-mediated fusion of reconstituted proteoliposomes. Loss of EPG5 function in C. elegans, mice, and humans results in blockade of autophagosome maturation into degradative autolysosomes (4-6). Loss of EPG5 function also results in impaired endosomal trafficking (5). Reduced EPG5 expression resulted in slowed endocytic degradation and delayed endocytic recycling (5).
EPG5 is essential for the transport of the TLR9 (see the record CpG1) ligand CpG to the late endosomal/lysosomal compartment as well as for TLR9-associated signaling (1). CpG is internalized by immune cells and interacts with TLR9 proteins within endosomes. For information about TLR9-associated signaling, see the record for CpG1. TLR9-associated signaling promotes the expression of several genes, including those that encode IL-6, IL-1, tumor necrosis factor (TNF), IL-12p40, and type I interferon (IFN), cytokines required for the inflammatory response. Together with ligands on antigen-presenting cells (APCs) that bind to activating receptors on lymphocytes, these cytokines mediate adaptive immune activation.
Mutations in EPG5 are associated with Vici syndrome (OMIM: #242840) (7-11). Patients with Vici syndrome can exhibit psychomotor retardation, developmental delays, agenesis of the corpus callosum, hypopigmentation, cataracts, progressive cardiomyopathy, myopathy, progressive microcephaly, sensorineural deafness, skeletal muscle myopathy, failure to thrive, and variable immunodeficiency (e.g., loss of B cells) due to defects in autophagy (e.g., accumulation of autophagic cargo and the impaired fusion with lysosomes). Due to the progressive nature of Vici syndrome, it often leads to lethality with a mean survival of 24 months of age. Patients commonly die due to respiratory failure due to airway infections secondary to immunodeficiency as wel las due to the progressive cardiomyopathy and neurological phenotypes.
Epg5-deficient (Epg5-/-) mice exhibited progressive neurological defects (e.g., severe muscle atrophy and muscle denervation), limb grasping, impaired coordination, and hind limb paralysis at 10 months of age (4;5). The Epg5-/- mice died at 10 to 12 months. The mice also showed thin corpus callosum and muscle atrophy. The Epg5-/- mice showed postnatal growth retardation, reduced body weights (females show later phenotype compared to male mice), kyphosis, and rough coat. Epg5-/- mice also showed features of retinitis pigmentosa, including impaired retina function along with progressive loss of retina photoreceptor cells and increased numbers of apoptotic cells in the outer nuclear layer (12). Autophagic flux was also impaired in the Epg5-/- retina (12).
Epg5 deficiency impaired autophagic flux by blocking the maturation of autophagosomes into degradative autolysosomes, leading to accumulation of p62 aggregates and ubiquitin-positive inclusions in neurons and glial cells (4;5).
1) 94°C 2:00
The following sequence of 402 nucleotides is amplified (chromosome 18, + strand):
1 tcctcatgct gaaaccacta gctcttttat atctcctgcc ttgcttgtag gaaaagaaga
Primer binding sites are underlined and the sequencing primers are highlighted; the mutated nucleotide is shown in red.
1. Piano Mortari, E., Folgiero, V., Marcellini, V., Romania, P., Bellacchio, E., D'Alicandro, V., Bocci, C., Carrozzo, R., Martinelli, D., Petrini, S., Axiotis, E., Farroni, C., Locatelli, F., Schara, U., Pilz, D. T., Jungbluth, H., Dionisi-Vici, C., and Carsetti, R. (2018) The Vici Syndrome Protein EPG5 Regulates Intracellular Nucleic Acid Trafficking Linking Autophagy to Innate and Adaptive Immunity. Autophagy. 14, 22-37.
2. Nagase, T., Kikuno, R., Nakayama, M., Hirosawa, M., and Ohara, O. (2000) Prediction of the Coding Sequences of Unidentified Human Genes. XVIII. the Complete Sequences of 100 New cDNA Clones from Brain which Code for Large Proteins in Vitro. DNA Res. 7, 273-281.
3. Wang, Z., Miao, G., Xue, X., Guo, X., Yuan, C., Wang, Z., Zhang, G., Chen, Y., Feng, D., Hu, J., and Zhang, H. (2016) The Vici Syndrome Protein EPG5 is a Rab7 Effector that Determines the Fusion Specificity of Autophagosomes with Late Endosomes/Lysosomes. Mol Cell. 63, 781-795.
4. Zhao, Y. G., Zhao, H., Sun, H., and Zhang, H. (2013) Role of Epg5 in Selective Neurodegeneration and Vici Syndrome. Autophagy. 9, 1258-1262.
5. Zhao, H., Zhao, Y. G., Wang, X., Xu, L., Miao, L., Feng, D., Chen, Q., Kovacs, A. L., Fan, D., and Zhang, H. (2013) Mice Deficient in Epg5 Exhibit Selective Neuronal Vulnerability to Degeneration. J Cell Biol. 200, 731-741.
6. Tian, Y., Li, Z., Hu, W., Ren, H., Tian, E., Zhao, Y., Lu, Q., Huang, X., Yang, P., Li, X., Wang, X., Kovacs, A. L., Yu, L., and Zhang, H. (2010) C. Elegans Screen Identifies Autophagy Genes Specific to Multicellular Organisms. Cell. 141, 1042-1055.
7. Cullup, T., Kho, A. L., Dionisi-Vici, C., Brandmeier, B., Smith, F., Urry, Z., Simpson, M. A., Yau, S., Bertini, E., McClelland, V., Al-Owain, M., Koelker, S., Koerner, C., Hoffmann, G. F., Wijburg, F. A., ten Hoedt, A. E., Rogers, R. C., Manchester, D., Miyata, R., Hayashi, M., Said, E., Soler, D., Kroisel, P. M., Windpassinger, C., Filloux, F. M., Al-Kaabi, S., Hertecant, J., Del Campo, M., Buk, S., Bodi, I., Goebel, H. H., Sewry, C. A., Abbs, S., Mohammed, S., Josifova, D., Gautel, M., and Jungbluth, H. (2013) Recessive Mutations in EPG5 Cause Vici Syndrome, a Multisystem Disorder with Defective Autophagy. Nat Genet. 45, 83-87.
8. Ehmke, N., Parvaneh, N., Krawitz, P., Ashrafi, M. R., Karimi, P., Mehdizadeh, M., Kruger, U., Hecht, J., Mundlos, S., and Robinson, P. N. (2014) First Description of a Patient with Vici Syndrome due to a Mutation Affecting the Penultimate Exon of EPG5 and Review of the Literature. Am J Med Genet A. 164A, 3170-3175.
9. Maillard, C., Cavallin, M., Piquand, K., Philbert, M., Bault, J. P., Millischer, A. E., Moshous, D., Rio, M., Gitiaux, C., Boddaert, N., Masson, C., Thomas, S., and Bahi-Buisson, N. (2017) Prenatal and Postnatal Presentations of Corpus Callosum Agenesis with Polymicrogyria Caused by EGP5 Mutation. Am J Med Genet A. 173, 706-711.
10. Shimada, S., Hirasawa, K., Takeshita, A., Nakatsukasa, H., Yamamoto-Shimojima, K., Imaizumi, T., Nagata, S., and Yamamoto, T. (2018) Novel Compound Heterozygous EPG5 Mutations Consisted with a Missense Mutation and a Microduplication in the Exon 1 Region Identified in a Japanese Patient with Vici Syndrome. Am J Med Genet A. 176, 2803-2807.
11. Waldrop, M. A., Gumienny, F., Boue, D., de Los Reyes, E., Shell, R., Weiss, R. B., and Flanigan, K. M. (2018) Low-Level Expression of EPG5 Leads to an Attenuated Vici Syndrome Phenotype. Am J Med Genet A. 176, 1207-1211.
|Science Writers||Anne Murray|
|Illustrators||Diantha La Vine|
|Authors||Lauren Prince, Jamie Russell, and Bruce Beutler|