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Genetic Interactions between the Members of the SMN-Gemins Complex in Drosophila.

Borg RM, Bordonne R, Vassallo N, Cauchi RJ - PLoS ONE (2015)

Bottom Line: Despite multiple genetic studies, the Gemin proteins have not been identified as prominent modifiers of SMN-associated mutant phenotypes.We show a modifier effect by all three members of the minimalistic fly SMN-Gemins complex within the muscle compartment of the motor unit.The toxicity associated with increased Gemin2 levels is conserved in the yeast S. pombe in which we find that the cytoplasmic retention of Sm proteins, likely reflecting a block in the snRNP assembly pathway, is a contributing factor.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biochemistry, Faculty of Medicine and Surgery, University of Malta, Msida, Malta GC; Institut de Génétique Moléculaire de Montpellier, CNRS-UMR5535, Université Montpellier 1 and 2, Montpellier, France.

ABSTRACT
The SMN-Gemins complex is composed of Gemins 2-8, Unrip and the survival motor neuron (SMN) protein. Limiting levels of SMN result in the neuromuscular disorder, spinal muscular atrophy (SMA), which is presently untreatable. The most-documented function of the SMN-Gemins complex concerns the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). Despite multiple genetic studies, the Gemin proteins have not been identified as prominent modifiers of SMN-associated mutant phenotypes. In the present report, we make use of the Drosophila model organism to investigate whether viability and motor phenotypes associated with a hypomorphic Gemin3 mutant are enhanced by changes in the levels of SMN, Gemin2 and Gemin5 brought about by various genetic manipulations. We show a modifier effect by all three members of the minimalistic fly SMN-Gemins complex within the muscle compartment of the motor unit. Interestingly, muscle-specific overexpression of Gemin2 was by itself sufficient to depress normal motor function and its enhanced upregulation in all tissues leads to a decline in fly viability. The toxicity associated with increased Gemin2 levels is conserved in the yeast S. pombe in which we find that the cytoplasmic retention of Sm proteins, likely reflecting a block in the snRNP assembly pathway, is a contributing factor. We propose that a disruption in the normal stoichiometry of the SMN-Gemins complex depresses its function with consequences that are detrimental to the motor system.

No MeSH data available.


Related in: MedlinePlus

Gemin2 overexpressors display puparial and wing postural defects.Compared to wild-type flies, which have a dorsal wing posture (A), flies with a pan-muscular overexpression of full-length Gemin2 (Mef2-GAL4>Gem2FL) present with either droopy (B) or held-up (C) wings. (D) Top, Puparia of flies with a strong mesodermal overexpression of Gemin2 (how-GAL4>Gem2FL) and the GAL4 driver control (how-GAL4/+). Bottom, Chart showing that Gemin2 overexpressors (how-GAL4>Gem2FL) have a significantly larger puparial axial ratio when compared to controls (how-GAL4/+). The mean is marked by a horizontal line running through the data points and error bars are ± S.E.M. (****p<0.0001; how-GAL4/+, n = 14; how-GAL4>Gem2FL, n = 20).
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pone.0130974.g007: Gemin2 overexpressors display puparial and wing postural defects.Compared to wild-type flies, which have a dorsal wing posture (A), flies with a pan-muscular overexpression of full-length Gemin2 (Mef2-GAL4>Gem2FL) present with either droopy (B) or held-up (C) wings. (D) Top, Puparia of flies with a strong mesodermal overexpression of Gemin2 (how-GAL4>Gem2FL) and the GAL4 driver control (how-GAL4/+). Bottom, Chart showing that Gemin2 overexpressors (how-GAL4>Gem2FL) have a significantly larger puparial axial ratio when compared to controls (how-GAL4/+). The mean is marked by a horizontal line running through the data points and error bars are ± S.E.M. (****p<0.0001; how-GAL4/+, n = 14; how-GAL4>Gem2FL, n = 20).

Mentions: In view of our findings on the genetic relationship between Gemin3 and Gemin5 as well as that between Gemin3 and Smn, we next probed for an in vivo association between Gemin3 and Gemin2, which is the only SMN-Gemins complex member with the most phylogenetically conserved sequence and domain structure [3]. Surprisingly, when overexpressed in muscle starting from early development (Mef2-GAL4>Gem2FL), full-length Gemin2 is by itself detrimental, hence leading to motor defects early on during adulthood (Fig 6A). Furthermore, adult flies with this genetic manipulation exhibit different wing posture phenotypes, including droopy and held-up wings (Fig 7A–7C) when compared to controls in which wings typically run dorsal and parallel to the body. Survival of adult flies does not decline with age (data not shown). When Gemin2 expression is driven by a strong mesodermal driver (how-GAL4), flies failed to contract adequately during pupariation, consequently giving rise to significant differences in the puparial axial ratios when compared to the control genotype (Fig 7D), a phenotype we described previously following disruption of SMN or Gemin3 [25, 37].


Genetic Interactions between the Members of the SMN-Gemins Complex in Drosophila.

Borg RM, Bordonne R, Vassallo N, Cauchi RJ - PLoS ONE (2015)

Gemin2 overexpressors display puparial and wing postural defects.Compared to wild-type flies, which have a dorsal wing posture (A), flies with a pan-muscular overexpression of full-length Gemin2 (Mef2-GAL4>Gem2FL) present with either droopy (B) or held-up (C) wings. (D) Top, Puparia of flies with a strong mesodermal overexpression of Gemin2 (how-GAL4>Gem2FL) and the GAL4 driver control (how-GAL4/+). Bottom, Chart showing that Gemin2 overexpressors (how-GAL4>Gem2FL) have a significantly larger puparial axial ratio when compared to controls (how-GAL4/+). The mean is marked by a horizontal line running through the data points and error bars are ± S.E.M. (****p<0.0001; how-GAL4/+, n = 14; how-GAL4>Gem2FL, n = 20).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4476591&req=5

pone.0130974.g007: Gemin2 overexpressors display puparial and wing postural defects.Compared to wild-type flies, which have a dorsal wing posture (A), flies with a pan-muscular overexpression of full-length Gemin2 (Mef2-GAL4>Gem2FL) present with either droopy (B) or held-up (C) wings. (D) Top, Puparia of flies with a strong mesodermal overexpression of Gemin2 (how-GAL4>Gem2FL) and the GAL4 driver control (how-GAL4/+). Bottom, Chart showing that Gemin2 overexpressors (how-GAL4>Gem2FL) have a significantly larger puparial axial ratio when compared to controls (how-GAL4/+). The mean is marked by a horizontal line running through the data points and error bars are ± S.E.M. (****p<0.0001; how-GAL4/+, n = 14; how-GAL4>Gem2FL, n = 20).
Mentions: In view of our findings on the genetic relationship between Gemin3 and Gemin5 as well as that between Gemin3 and Smn, we next probed for an in vivo association between Gemin3 and Gemin2, which is the only SMN-Gemins complex member with the most phylogenetically conserved sequence and domain structure [3]. Surprisingly, when overexpressed in muscle starting from early development (Mef2-GAL4>Gem2FL), full-length Gemin2 is by itself detrimental, hence leading to motor defects early on during adulthood (Fig 6A). Furthermore, adult flies with this genetic manipulation exhibit different wing posture phenotypes, including droopy and held-up wings (Fig 7A–7C) when compared to controls in which wings typically run dorsal and parallel to the body. Survival of adult flies does not decline with age (data not shown). When Gemin2 expression is driven by a strong mesodermal driver (how-GAL4), flies failed to contract adequately during pupariation, consequently giving rise to significant differences in the puparial axial ratios when compared to the control genotype (Fig 7D), a phenotype we described previously following disruption of SMN or Gemin3 [25, 37].

Bottom Line: Despite multiple genetic studies, the Gemin proteins have not been identified as prominent modifiers of SMN-associated mutant phenotypes.We show a modifier effect by all three members of the minimalistic fly SMN-Gemins complex within the muscle compartment of the motor unit.The toxicity associated with increased Gemin2 levels is conserved in the yeast S. pombe in which we find that the cytoplasmic retention of Sm proteins, likely reflecting a block in the snRNP assembly pathway, is a contributing factor.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biochemistry, Faculty of Medicine and Surgery, University of Malta, Msida, Malta GC; Institut de Génétique Moléculaire de Montpellier, CNRS-UMR5535, Université Montpellier 1 and 2, Montpellier, France.

ABSTRACT
The SMN-Gemins complex is composed of Gemins 2-8, Unrip and the survival motor neuron (SMN) protein. Limiting levels of SMN result in the neuromuscular disorder, spinal muscular atrophy (SMA), which is presently untreatable. The most-documented function of the SMN-Gemins complex concerns the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). Despite multiple genetic studies, the Gemin proteins have not been identified as prominent modifiers of SMN-associated mutant phenotypes. In the present report, we make use of the Drosophila model organism to investigate whether viability and motor phenotypes associated with a hypomorphic Gemin3 mutant are enhanced by changes in the levels of SMN, Gemin2 and Gemin5 brought about by various genetic manipulations. We show a modifier effect by all three members of the minimalistic fly SMN-Gemins complex within the muscle compartment of the motor unit. Interestingly, muscle-specific overexpression of Gemin2 was by itself sufficient to depress normal motor function and its enhanced upregulation in all tissues leads to a decline in fly viability. The toxicity associated with increased Gemin2 levels is conserved in the yeast S. pombe in which we find that the cytoplasmic retention of Sm proteins, likely reflecting a block in the snRNP assembly pathway, is a contributing factor. We propose that a disruption in the normal stoichiometry of the SMN-Gemins complex depresses its function with consequences that are detrimental to the motor system.

No MeSH data available.


Related in: MedlinePlus