Limits...
A transgene carrying an A2G missense mutation in the SMN gene modulates phenotypic severity in mice with severe (type I) spinal muscular atrophy.

Monani UR, Pastore MT, Gavrilina TO, Jablonka S, Le TT, Andreassi C, DiCocco JM, Lorson C, Androphy EJ, Sendtner M, Podell M, Burghes AH - J. Cell Biol. (2003)

Bottom Line: We suggest that only in the presence of low levels of full-length SMN is the A2G transgene able to form partially functional higher order SMN complexes essential for its functions.Animals homozygous for the mutant transgene are less severely affected than heterozygotes.This demonstrates the importance of SMN levels in SMA even if the protein is expressed from a mutant allele.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Ohio State University, Columbus, OH 43210, USA. monani.2@osu.edu

ABSTRACT
5q spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans and the leading genetic cause of infantile death. Patients lack a functional survival of motor neurons (SMN1) gene, but carry one or more copies of the highly homologous SMN2 gene. A homozygous knockout of the single murine Smn gene is embryonic lethal. Here we report that in the absence of the SMN2 gene, a mutant SMN A2G transgene is unable to rescue the embryonic lethality. In its presence, the A2G transgene delays the onset of motor neuron loss, resulting in mice with mild SMA. We suggest that only in the presence of low levels of full-length SMN is the A2G transgene able to form partially functional higher order SMN complexes essential for its functions. Mild SMA mice exhibit motor neuron degeneration, muscle atrophy, and abnormal EMGs. Animals homozygous for the mutant transgene are less severely affected than heterozygotes. This demonstrates the importance of SMN levels in SMA even if the protein is expressed from a mutant allele. Our mild SMA mice will be useful in (a) determining the effect of missense mutations in vivo and in motor neurons and (b) testing potential therapies in SMA.

Show MeSH

Related in: MedlinePlus

Immunocytochemical staining of spinal cord, and hematoxylin and eosin staining of muscle. Staining of SMN in spinal cord sections of (A) 1-mo-old SMN A2G;SMN2;Smn−/− type III SMA mouse and (B) an age-matched Smn+/−control. Type III SMA mice express SMN in the motor neurons (arrows). However, nuclear gems in these animals are less intense and not as numerous as those seen in normal littermates. (600× magnification). Gastrocnemius from the same animals was sectioned and stained with hematoxylin and eosin. Numerous angulated and atrophied fibers (arrows) are evident in (C) type III SMA muscle as compared with (D) normal muscle (200× magnification).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172739&req=5

fig4: Immunocytochemical staining of spinal cord, and hematoxylin and eosin staining of muscle. Staining of SMN in spinal cord sections of (A) 1-mo-old SMN A2G;SMN2;Smn−/− type III SMA mouse and (B) an age-matched Smn+/−control. Type III SMA mice express SMN in the motor neurons (arrows). However, nuclear gems in these animals are less intense and not as numerous as those seen in normal littermates. (600× magnification). Gastrocnemius from the same animals was sectioned and stained with hematoxylin and eosin. Numerous angulated and atrophied fibers (arrows) are evident in (C) type III SMA muscle as compared with (D) normal muscle (200× magnification).

Mentions: One of the most striking features of spinal muscular atrophy is the loss of the anterior horn cells (α motor neurons) of the spinal cord and a greatly reduced amount of SMN in these cells. We have previously shown that there is little or no staining of SMN in the motor neurons of type I SMA mice (Monani et al., 2000). To ascertain whether type III SMA mice express SMN in their spinal motor neurons, spinal cord sections from the lumbar and thoracic regions of 1-mo-old type III SMA mice, with a single copy of SMN2 and heterozygous for the A2G transgene, and age-matched Smn+/− controls were immunocytochemically stained (Fig. 4, A and B). Based on the cytoplasmic staining and presence of gems in the spinal cord of diseased animals, it is clear that SMN is restored in motor neurons (Fig. 4 A). To quantitate the number of gems in the motor neurons of normal (n = 2) and type III SMA mice (n = 3), 10 different fields, under 600× magnification, from spinal cord sections of each mouse were selected and the gems counted. An average of 4.5 nuclear gems were counted per field (∼60 nuclei) in type III SMA mice versus 9.8 nuclear gems in the age-matched controls. Thus it is clear that although SMN is easily detected in the spinal motor neurons of type III SMA mice, it is only a partial restoration.


A transgene carrying an A2G missense mutation in the SMN gene modulates phenotypic severity in mice with severe (type I) spinal muscular atrophy.

Monani UR, Pastore MT, Gavrilina TO, Jablonka S, Le TT, Andreassi C, DiCocco JM, Lorson C, Androphy EJ, Sendtner M, Podell M, Burghes AH - J. Cell Biol. (2003)

Immunocytochemical staining of spinal cord, and hematoxylin and eosin staining of muscle. Staining of SMN in spinal cord sections of (A) 1-mo-old SMN A2G;SMN2;Smn−/− type III SMA mouse and (B) an age-matched Smn+/−control. Type III SMA mice express SMN in the motor neurons (arrows). However, nuclear gems in these animals are less intense and not as numerous as those seen in normal littermates. (600× magnification). Gastrocnemius from the same animals was sectioned and stained with hematoxylin and eosin. Numerous angulated and atrophied fibers (arrows) are evident in (C) type III SMA muscle as compared with (D) normal muscle (200× magnification).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172739&req=5

fig4: Immunocytochemical staining of spinal cord, and hematoxylin and eosin staining of muscle. Staining of SMN in spinal cord sections of (A) 1-mo-old SMN A2G;SMN2;Smn−/− type III SMA mouse and (B) an age-matched Smn+/−control. Type III SMA mice express SMN in the motor neurons (arrows). However, nuclear gems in these animals are less intense and not as numerous as those seen in normal littermates. (600× magnification). Gastrocnemius from the same animals was sectioned and stained with hematoxylin and eosin. Numerous angulated and atrophied fibers (arrows) are evident in (C) type III SMA muscle as compared with (D) normal muscle (200× magnification).
Mentions: One of the most striking features of spinal muscular atrophy is the loss of the anterior horn cells (α motor neurons) of the spinal cord and a greatly reduced amount of SMN in these cells. We have previously shown that there is little or no staining of SMN in the motor neurons of type I SMA mice (Monani et al., 2000). To ascertain whether type III SMA mice express SMN in their spinal motor neurons, spinal cord sections from the lumbar and thoracic regions of 1-mo-old type III SMA mice, with a single copy of SMN2 and heterozygous for the A2G transgene, and age-matched Smn+/− controls were immunocytochemically stained (Fig. 4, A and B). Based on the cytoplasmic staining and presence of gems in the spinal cord of diseased animals, it is clear that SMN is restored in motor neurons (Fig. 4 A). To quantitate the number of gems in the motor neurons of normal (n = 2) and type III SMA mice (n = 3), 10 different fields, under 600× magnification, from spinal cord sections of each mouse were selected and the gems counted. An average of 4.5 nuclear gems were counted per field (∼60 nuclei) in type III SMA mice versus 9.8 nuclear gems in the age-matched controls. Thus it is clear that although SMN is easily detected in the spinal motor neurons of type III SMA mice, it is only a partial restoration.

Bottom Line: We suggest that only in the presence of low levels of full-length SMN is the A2G transgene able to form partially functional higher order SMN complexes essential for its functions.Animals homozygous for the mutant transgene are less severely affected than heterozygotes.This demonstrates the importance of SMN levels in SMA even if the protein is expressed from a mutant allele.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Ohio State University, Columbus, OH 43210, USA. monani.2@osu.edu

ABSTRACT
5q spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans and the leading genetic cause of infantile death. Patients lack a functional survival of motor neurons (SMN1) gene, but carry one or more copies of the highly homologous SMN2 gene. A homozygous knockout of the single murine Smn gene is embryonic lethal. Here we report that in the absence of the SMN2 gene, a mutant SMN A2G transgene is unable to rescue the embryonic lethality. In its presence, the A2G transgene delays the onset of motor neuron loss, resulting in mice with mild SMA. We suggest that only in the presence of low levels of full-length SMN is the A2G transgene able to form partially functional higher order SMN complexes essential for its functions. Mild SMA mice exhibit motor neuron degeneration, muscle atrophy, and abnormal EMGs. Animals homozygous for the mutant transgene are less severely affected than heterozygotes. This demonstrates the importance of SMN levels in SMA even if the protein is expressed from a mutant allele. Our mild SMA mice will be useful in (a) determining the effect of missense mutations in vivo and in motor neurons and (b) testing potential therapies in SMA.

Show MeSH
Related in: MedlinePlus