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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

Gene dosage effects of HGS expression on motor and sensory function in 3- to 4-week-old mice.(A) Reduced HGS expression results in clawed paws in Hgstn/tn mice. Behavioral assays of (B) open field, (C) rotarod, (D) elevated beam, (E) von Frey and (F) forelimb grip strength for Hgs+/+ (black), Hgstn/+, Hgstn/tn and HgsKO/+ mice. n = 6 mice per genotype for all assays except rotarod, where n = 4. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE and n>6 animals per genotype for all assays except rotarod, where n = 4. A two-way anova demonstrated a significant effect of genotype on rotarod and elevated beam performance. Data are shown as mean ± SE. *p<0.05, **p<0.01 and ***p<0.001.
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pgen.1005290.g004: Gene dosage effects of HGS expression on motor and sensory function in 3- to 4-week-old mice.(A) Reduced HGS expression results in clawed paws in Hgstn/tn mice. Behavioral assays of (B) open field, (C) rotarod, (D) elevated beam, (E) von Frey and (F) forelimb grip strength for Hgs+/+ (black), Hgstn/+, Hgstn/tn and HgsKO/+ mice. n = 6 mice per genotype for all assays except rotarod, where n = 4. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE and n>6 animals per genotype for all assays except rotarod, where n = 4. A two-way anova demonstrated a significant effect of genotype on rotarod and elevated beam performance. Data are shown as mean ± SE. *p<0.05, **p<0.01 and ***p<0.001.

Mentions: Several neurological diseases are caused by mutations that lie within genes involved in the endosomal sorting of membrane proteins [45–48]. To examine whether HGS deficiency resulted in motor and sensory deficits commonly seen in patients with inherited neuropathies, we performed a series of behavioral assays on our mutant Hgs mouse lines. By 3 weeks of age, the Hgstn/tn mice exhibited significant motor deficits as demonstrated by the presence of clawed paws, decreased locomotion in an open field assay, impaired rotarod performance and an increased time to transverse an elevated beam compared to controls (Fig 4A–4D). In addition, the Hgstn/tn mice also demonstrated increased tactile sensitivity that was consistent with a heightened pain response when examined using the von Frey assay (Fig 4E) and had reduced forelimb muscle strength as compared to age-matched controls (Fig 4F).


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)

Gene dosage effects of HGS expression on motor and sensory function in 3- to 4-week-old mice.(A) Reduced HGS expression results in clawed paws in Hgstn/tn mice. Behavioral assays of (B) open field, (C) rotarod, (D) elevated beam, (E) von Frey and (F) forelimb grip strength for Hgs+/+ (black), Hgstn/+, Hgstn/tn and HgsKO/+ mice. n = 6 mice per genotype for all assays except rotarod, where n = 4. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE and n>6 animals per genotype for all assays except rotarod, where n = 4. A two-way anova demonstrated a significant effect of genotype on rotarod and elevated beam performance. Data are shown as mean ± SE. *p<0.05, **p<0.01 and ***p<0.001.
© Copyright Policy
Related In: Results  -  Collection

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

pgen.1005290.g004: Gene dosage effects of HGS expression on motor and sensory function in 3- to 4-week-old mice.(A) Reduced HGS expression results in clawed paws in Hgstn/tn mice. Behavioral assays of (B) open field, (C) rotarod, (D) elevated beam, (E) von Frey and (F) forelimb grip strength for Hgs+/+ (black), Hgstn/+, Hgstn/tn and HgsKO/+ mice. n = 6 mice per genotype for all assays except rotarod, where n = 4. Symbols represent unpaired t-tests corrected for multiple comparisons using the Holm-Sidak method. Data are shown as mean ± SE and n>6 animals per genotype for all assays except rotarod, where n = 4. A two-way anova demonstrated a significant effect of genotype on rotarod and elevated beam performance. Data are shown as mean ± SE. *p<0.05, **p<0.01 and ***p<0.001.
Mentions: Several neurological diseases are caused by mutations that lie within genes involved in the endosomal sorting of membrane proteins [45–48]. To examine whether HGS deficiency resulted in motor and sensory deficits commonly seen in patients with inherited neuropathies, we performed a series of behavioral assays on our mutant Hgs mouse lines. By 3 weeks of age, the Hgstn/tn mice exhibited significant motor deficits as demonstrated by the presence of clawed paws, decreased locomotion in an open field assay, impaired rotarod performance and an increased time to transverse an elevated beam compared to controls (Fig 4A–4D). In addition, the Hgstn/tn mice also demonstrated increased tactile sensitivity that was consistent with a heightened pain response when examined using the von Frey assay (Fig 4E) and had reduced forelimb muscle strength as compared to age-matched controls (Fig 4F).

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