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Motor and Sensory Deficits in the teetering Mice Result from Mutation of the ESCRT Component HGS.

Watson JA, Bhattacharyya BJ, Vaden JH, Wilson JA, Icyuz M, Howard AD, Phillips E, DeSilva TM, Siegal GP, Bean AJ, King GD, Phillips SE, Miller RJ, Wilson SM - PLoS Genet. (2015)

Bottom Line: These structural changes were accompanied by a reduction in spontaneous and evoked release of acetylcholine, indicating a deficit in neurotransmitter release at the NMJ.These deficits in synaptic transmission were associated with elevated levels of ubiquitinated proteins in the synaptosome fraction.Our results indicate that HGS has multiple roles in the nervous system and demonstrate a previously unanticipated requirement for ESCRTs in the maintenance of synaptic transmission.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, University of Alabama at Birmingham, Evelyn F. McKnight Brain Institute, Civitan International Research Center, Birmingham, Alabama, United States of America.

ABSTRACT
Neurons are particularly vulnerable to perturbations in endo-lysosomal transport, as several neurological disorders are caused by a primary deficit in this pathway. In this report, we used positional cloning to show that the spontaneously occurring neurological mutation teetering (tn) is a single nucleotide substitution in hepatocyte growth factor-regulated tyrosine kinase substrate (Hgs/Hrs), a component of the endosomal sorting complex required for transport (ESCRT). The tn mice exhibit hypokenesis, muscle weakness, reduced muscle size and early perinatal lethality by 5-weeks of age. Although HGS has been suggested to be essential for the sorting of ubiquitinated membrane proteins to the lysosome, there were no alterations in receptor tyrosine kinase levels in the central nervous system, and only a modest decrease in tropomyosin receptor kinase B (TrkB) in the sciatic nerves of the tn mice. Instead, loss of HGS resulted in structural alterations at the neuromuscular junction (NMJ), including swellings and ultra-terminal sprouting at motor axon terminals and an increase in the number of endosomes and multivesicular bodies. These structural changes were accompanied by a reduction in spontaneous and evoked release of acetylcholine, indicating a deficit in neurotransmitter release at the NMJ. These deficits in synaptic transmission were associated with elevated levels of ubiquitinated proteins in the synaptosome fraction. In addition to the deficits in neuronal function, mutation of Hgs resulted in both hypermyelinated and dysmyelinated axons in the tn mice, which supports a growing body of evidence that ESCRTs are required for proper myelination of peripheral nerves. Our results indicate that HGS has multiple roles in the nervous system and demonstrate a previously unanticipated requirement for ESCRTs in the maintenance of synaptic transmission.

No MeSH data available.


Related in: MedlinePlus

Effect of reduced HGS expression on ubiquitin conjugates in the nervous system of Hgstn/tn mice.(A) Representative immunoblot of ubiquitin conjugates from the nervous system of 4-week-old Hgs+/+ (wt) and Hgstn/tn (tn) mice. (B) Quantitation of immunoblots. n = 3 per genotype. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE. **p<0.001.
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pgen.1005290.g011: Effect of reduced HGS expression on ubiquitin conjugates in the nervous system of Hgstn/tn mice.(A) Representative immunoblot of ubiquitin conjugates from the nervous system of 4-week-old Hgs+/+ (wt) and Hgstn/tn (tn) mice. (B) Quantitation of immunoblots. n = 3 per genotype. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE. **p<0.001.

Mentions: HGS is involved in the sorting of ubiquitinated proteins, and our studies indicate that loss of HGS has a profound effect on synaptic transmission at the NMJ. To investigate whether HGS is required for the sorting of ubiquitinated proteins at the synapse, we examined the level of ubiquitinated proteins in both the total and synaptosomal fractions prepared from cerebral cortices of wild type and Hgstn/tn mice. While the level of ubiquitin conjugates in the spinal cord, sciatic nerve and cortex were similar between the Hgstn/tn mice and controls, we observed a 2-fold increase in the level of ubiquitinated proteins isolated from the cortical synaptosomes of the Hgstn/tn mice (Fig 11A and 11B). This compartment-specific effect of HGS reduction on the levels of ubiquitin conjugates suggests that HGS is involved in the sorting of ubiquitinated proteins at the synapse and that proper endosomal sorting at the NMJ is required to maintain synaptic transmission.


Motor and Sensory Deficits in the teetering Mice Result from Mutation of the ESCRT Component HGS.

Watson JA, Bhattacharyya BJ, Vaden JH, Wilson JA, Icyuz M, Howard AD, Phillips E, DeSilva TM, Siegal GP, Bean AJ, King GD, Phillips SE, Miller RJ, Wilson SM - PLoS Genet. (2015)

Effect of reduced HGS expression on ubiquitin conjugates in the nervous system of Hgstn/tn mice.(A) Representative immunoblot of ubiquitin conjugates from the nervous system of 4-week-old Hgs+/+ (wt) and Hgstn/tn (tn) mice. (B) Quantitation of immunoblots. n = 3 per genotype. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE. **p<0.001.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482608&req=5

pgen.1005290.g011: Effect of reduced HGS expression on ubiquitin conjugates in the nervous system of Hgstn/tn mice.(A) Representative immunoblot of ubiquitin conjugates from the nervous system of 4-week-old Hgs+/+ (wt) and Hgstn/tn (tn) mice. (B) Quantitation of immunoblots. n = 3 per genotype. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE. **p<0.001.
Mentions: HGS is involved in the sorting of ubiquitinated proteins, and our studies indicate that loss of HGS has a profound effect on synaptic transmission at the NMJ. To investigate whether HGS is required for the sorting of ubiquitinated proteins at the synapse, we examined the level of ubiquitinated proteins in both the total and synaptosomal fractions prepared from cerebral cortices of wild type and Hgstn/tn mice. While the level of ubiquitin conjugates in the spinal cord, sciatic nerve and cortex were similar between the Hgstn/tn mice and controls, we observed a 2-fold increase in the level of ubiquitinated proteins isolated from the cortical synaptosomes of the Hgstn/tn mice (Fig 11A and 11B). This compartment-specific effect of HGS reduction on the levels of ubiquitin conjugates suggests that HGS is involved in the sorting of ubiquitinated proteins at the synapse and that proper endosomal sorting at the NMJ is required to maintain synaptic transmission.

Bottom Line: These structural changes were accompanied by a reduction in spontaneous and evoked release of acetylcholine, indicating a deficit in neurotransmitter release at the NMJ.These deficits in synaptic transmission were associated with elevated levels of ubiquitinated proteins in the synaptosome fraction.Our results indicate that HGS has multiple roles in the nervous system and demonstrate a previously unanticipated requirement for ESCRTs in the maintenance of synaptic transmission.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, University of Alabama at Birmingham, Evelyn F. McKnight Brain Institute, Civitan International Research Center, Birmingham, Alabama, United States of America.

ABSTRACT
Neurons are particularly vulnerable to perturbations in endo-lysosomal transport, as several neurological disorders are caused by a primary deficit in this pathway. In this report, we used positional cloning to show that the spontaneously occurring neurological mutation teetering (tn) is a single nucleotide substitution in hepatocyte growth factor-regulated tyrosine kinase substrate (Hgs/Hrs), a component of the endosomal sorting complex required for transport (ESCRT). The tn mice exhibit hypokenesis, muscle weakness, reduced muscle size and early perinatal lethality by 5-weeks of age. Although HGS has been suggested to be essential for the sorting of ubiquitinated membrane proteins to the lysosome, there were no alterations in receptor tyrosine kinase levels in the central nervous system, and only a modest decrease in tropomyosin receptor kinase B (TrkB) in the sciatic nerves of the tn mice. Instead, loss of HGS resulted in structural alterations at the neuromuscular junction (NMJ), including swellings and ultra-terminal sprouting at motor axon terminals and an increase in the number of endosomes and multivesicular bodies. These structural changes were accompanied by a reduction in spontaneous and evoked release of acetylcholine, indicating a deficit in neurotransmitter release at the NMJ. These deficits in synaptic transmission were associated with elevated levels of ubiquitinated proteins in the synaptosome fraction. In addition to the deficits in neuronal function, mutation of Hgs resulted in both hypermyelinated and dysmyelinated axons in the tn mice, which supports a growing body of evidence that ESCRTs are required for proper myelination of peripheral nerves. Our results indicate that HGS has multiple roles in the nervous system and demonstrate a previously unanticipated requirement for ESCRTs in the maintenance of synaptic transmission.

No MeSH data available.


Related in: MedlinePlus