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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

Sub-cellular Gemin5 expression pattern in rescued mutant flies.(A) Larval muscles of wild-type or mutant flies ubiquitously expressing a GFP-tagged Gemin5 fusion protein. Whereas Gemin5 overexpression induces supernumerary bodies that are largely nuclear, its expression in a mutant background reduces the number of foci, which are mostly restricted to the cytoplasm. (B) Tip of male accessary gland showing GFP expression in secondary cells is higher in flies overexpressing Gemin5 compared to rescued mutants. Secondary cells have a spherical appearance and multiple, large vacuoles (arrowhead).
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pone.0130974.g002: Sub-cellular Gemin5 expression pattern in rescued mutant flies.(A) Larval muscles of wild-type or mutant flies ubiquitously expressing a GFP-tagged Gemin5 fusion protein. Whereas Gemin5 overexpression induces supernumerary bodies that are largely nuclear, its expression in a mutant background reduces the number of foci, which are mostly restricted to the cytoplasm. (B) Tip of male accessary gland showing GFP expression in secondary cells is higher in flies overexpressing Gemin5 compared to rescued mutants. Secondary cells have a spherical appearance and multiple, large vacuoles (arrowhead).

Mentions: In Drosophila ovaries, Gemin5 is enriched with other SMN-Gemins complex members and snRNPs in discrete cytoplasmic structures known as U bodies [35, 44]. SMN-Gemins complexes also tend to congregate in conspicuous nuclear bodies, known as gems [36, 45]. Consequently, we have recently reported that overexpression of a fluorescent reporter-tagged gene in a wild-type background results in the localisation of Gemin5 to supernumerary foci of variable size that are predominantly nuclear within the muscular tissue [37]. In this regard, we asked whether this expression pattern is maintained in rescued Gemin5 mutants. We find that this is not the case; hence, we observe a decrease in the number of bodies that remain predominantly confined within the cytoplasm (Fig 2A). It is noteworthy that this expression pattern probably reflects that of the endogenous protein.


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

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

Sub-cellular Gemin5 expression pattern in rescued mutant flies.(A) Larval muscles of wild-type or mutant flies ubiquitously expressing a GFP-tagged Gemin5 fusion protein. Whereas Gemin5 overexpression induces supernumerary bodies that are largely nuclear, its expression in a mutant background reduces the number of foci, which are mostly restricted to the cytoplasm. (B) Tip of male accessary gland showing GFP expression in secondary cells is higher in flies overexpressing Gemin5 compared to rescued mutants. Secondary cells have a spherical appearance and multiple, large vacuoles (arrowhead).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130974.g002: Sub-cellular Gemin5 expression pattern in rescued mutant flies.(A) Larval muscles of wild-type or mutant flies ubiquitously expressing a GFP-tagged Gemin5 fusion protein. Whereas Gemin5 overexpression induces supernumerary bodies that are largely nuclear, its expression in a mutant background reduces the number of foci, which are mostly restricted to the cytoplasm. (B) Tip of male accessary gland showing GFP expression in secondary cells is higher in flies overexpressing Gemin5 compared to rescued mutants. Secondary cells have a spherical appearance and multiple, large vacuoles (arrowhead).
Mentions: In Drosophila ovaries, Gemin5 is enriched with other SMN-Gemins complex members and snRNPs in discrete cytoplasmic structures known as U bodies [35, 44]. SMN-Gemins complexes also tend to congregate in conspicuous nuclear bodies, known as gems [36, 45]. Consequently, we have recently reported that overexpression of a fluorescent reporter-tagged gene in a wild-type background results in the localisation of Gemin5 to supernumerary foci of variable size that are predominantly nuclear within the muscular tissue [37]. In this regard, we asked whether this expression pattern is maintained in rescued Gemin5 mutants. We find that this is not the case; hence, we observe a decrease in the number of bodies that remain predominantly confined within the cytoplasm (Fig 2A). It is noteworthy that this expression pattern probably reflects that of the endogenous protein.

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