This allele impairs mitochondrial function in neurons, causing a rapid loss of motor function and pre-wean death in homozygotes but providing a model for spinocerebellar ataxia type 28 in heterozygotes.
Dr. Ben Taylor, The Jackson Laboratory
This strain is congenic for Afg3l2Emv66, an ecotropic MuLV proviral insertion into intron 14 of a mitochondrial metalloprotease. This insertion results in a fusion transcript that is predicted to truncate AFG3L2 at amino acid 592 and add 24 novel amino acids, but Western blot analysis of mitochondrial extracts revealed no AFG3L2 protein in homozygotes, yet normal levels of paraplegin. Both homozygotes and heterozygotes have decreased assembly of mitochondrial complex I and III in mitochondrial extracts from brain, even though it was shown that homozygotes have normal levels of the protein components. ATP production was assessed in brain mitochondria and found decreased compared with that of controls. Swollen mitochondria with damaged cristae were found in neuronal cell bodies of both the central and peripheral nervous system of homozygotes but were not found as extensively in other tissues. In cerebellar mitochondria from heterozygotes at 12 months of age it was shown that in addition to impaired respiration there is an increased production of mitochondrial reactive oxygen species.
Homozygotes on this FVB congenic background are small by 1 week of age, progressively lose motor function in all limbs by 12-14 days, and rapidly degrade to complete paralysis and death with few homozygotes surviving beyond 16 day of age. There is a reduction in myelinated fiber density resulting from defective axonal development, not from axonal degeneration. The diameter of the spinal cord is reduced in homozygotes at 14 days of age and there are fewer large caliber axons and a corresponding increase in smaller caliber axons in the spinal cord and sciatic nerve. The paucity of myelin stems not from demyelination but rather from delayed or failed myelin development, with myelination appearing on par with controls at 1 day of age but diminished relative to controls at 7 and 14 days of age. The number of Purkinje cells, and neurons in spinal cord anterior horn and sensory dorsal root ganglia remains reasonably normal even at 14 days of age in homozygotes. Neuronal cell bodies show extensive vacuolization at 14 days of age with swollen mitochondria evident by electron microscopy. Such cytoplasmic vacuolization was found in sciatic nerve at 1 day of age and neurofilament architecture is also abnormal in sciatic nerve. (Maltecca et al., 2008)
Heterozygotes provide a model for spinocerebellar ataxia type 28 (SCA28). They initially appear normal and fertile, but an abnormal gait and diminished rotarod performance develop by approximately 4 month of age and become progressively worse. Abnormal limb clasping when suspended by the tail also develops later in life, consistent with neurological disease, but tremor, rigidity, or kyphosis were not observed in an assessment to up to 18 months of age. At 4 months of age Purkinje cells have altered cell morphology and dark cytoplasm with abnormal mitochondrial morphology. Granule cells also show abnormal mitochondrial morphology. By 6 months of age the molecular layer is thinner than normal with some Purkinje cell loss, and the remaining Purkinje cells are smaller than normal and dendritic stalks abnormal with poorly arborized dendritic branches. Apoptotic granule cell loss is also found by 6 months, but Purkinje cell death was found to not involve apoptosis. By 12 months there is significant loss of both Purkinje cells and granule cells with reactive gliosis prominent in the granule layer. However, unlike homozygotes, heterozygotes do not develop significant neuronal defects in the spinal cord. (Maltecca et al., 2009)
The Emv66 ecotropic MuLV proviral insertion was backcrossed from the linkage testing stock MEV/2Ty onto FVB/NJ in the laboratory of Dr. Ben Taylor at The Jackson Laboratory. Heterozygous males and +/? (either heterozygous or wildtype) females at generation N12 were intercrossed to generate embryos for cryopreservation. Because of the phenotype, homozygotes cannot be used as breeders to maintain this strain and heterozygotes have a short breeding lifespan.
|Allele Name||endogenous ecotropic MuLV 66|
|Allele Type||Not Applicable (Null/Knockout)|
|Gene Symbol and Name||Afg3l2, AFG3-like AAA ATPase 2|
|Strain of Origin||MEV/2Ty-Afg3l2Emv66|
|Molecular Note||An ecotropic murine leukemia proviral reinsertion occurred within intron 14 of the gene. RT-PCR analysis on several tissues showed that no transcript containing sequences derived from exon 13-15 is expressed from this allele. An aberrant transcript contaning sequences upstream of the insertion site is detectable. Western blot analysis on tissue mitochondrial preparations shows that the protein product is not detectable in homozygous mice.|
Because of the phenotype, homozygotes cannot be used as breeders to maintain this strain and heterozygotes have a short breeding lifespan.
When using the FVB.MEV2-Afg3l2Emv66/TyJ mouse strain in a publication, please cite the originating article(s) and include JAX stock #003494 in your Materials and Methods section.