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A novel function for fragile X mental retardation protein in translational activation.

Bechara EG, Didiot MC, Melko M, Davidovic L, Bensaid M, Martin P, Castets M, Pognonec P, Khandjian EW, Moine H, Bardoni B - PLoS Biol. (2009)

Bottom Line: To date, two RNA motifs have been found to mediate FMRP/RNA interaction, the G-quartet and the "kissing complex," which both induce translational repression in the presence of FMRP.The absence of FMRP results in decreased expression of Sod1.Because it has been observed that brain metabolism of FMR1 mice is more sensitive to oxidative stress, we propose that the deregulation of Sod1 expression may be at the basis of several traits of the physiopathology of the Fragile X syndrome, such as anxiety, sleep troubles, and autism.

View Article: PubMed Central - PubMed

Affiliation: Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France.

ABSTRACT
Fragile X syndrome, the most frequent form of inherited mental retardation, is due to the absence of Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein involved in several steps of RNA metabolism. To date, two RNA motifs have been found to mediate FMRP/RNA interaction, the G-quartet and the "kissing complex," which both induce translational repression in the presence of FMRP. We show here a new role for FMRP as a positive modulator of translation. FMRP specifically binds Superoxide Dismutase 1 (Sod1) mRNA with high affinity through a novel RNA motif, SoSLIP (Sod1 mRNA Stem Loops Interacting with FMRP), which is folded as three independent stem-loop structures. FMRP induces a structural modification of the SoSLIP motif upon its interaction with it. SoSLIP also behaves as a translational activator whose action is potentiated by the interaction with FMRP. The absence of FMRP results in decreased expression of Sod1. Because it has been observed that brain metabolism of FMR1 mice is more sensitive to oxidative stress, we propose that the deregulation of Sod1 expression may be at the basis of several traits of the physiopathology of the Fragile X syndrome, such as anxiety, sleep troubles, and autism.

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Decreased Levels of Sod1 Protein in Fmr1 Null Cells, Brain, and EmbryosWestern blot analysis of one FMR1+ STEK clone (where FMR1 was reintroduced) and one STEK FMR1  clone. The results shown on the left are representative of the different clonal cell lines. On the right, corresponding densitometric analyses show a significant decrease of Sod1 expression, after comparing five wild-type rescued clones and five FMR1 knockout clones. Three independent experiments were quantified. Results presented as the mean ± SEM (Student's t-test, *p < 0.05) are the average of Sod1 levels normalized for β-tubulin expression The same analysis described in (A) was applied for mouse total brain (B), mouse hippocampus (C), mouse cerebellum (B) and mouse 10dpc embryo extracts (E). Densitometric analysis showing a significant decrease in Sod1 expression. Three independent experiments were quantified using eight wild-type and eight Fmr1  mice. Results presented as the mean ± SEM (Student's t-test, **p < 0.01) are the average of Sod1 levels normalized for β-tubulin expression.
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pbio-1000016-g006: Decreased Levels of Sod1 Protein in Fmr1 Null Cells, Brain, and EmbryosWestern blot analysis of one FMR1+ STEK clone (where FMR1 was reintroduced) and one STEK FMR1 clone. The results shown on the left are representative of the different clonal cell lines. On the right, corresponding densitometric analyses show a significant decrease of Sod1 expression, after comparing five wild-type rescued clones and five FMR1 knockout clones. Three independent experiments were quantified. Results presented as the mean ± SEM (Student's t-test, *p < 0.05) are the average of Sod1 levels normalized for β-tubulin expression The same analysis described in (A) was applied for mouse total brain (B), mouse hippocampus (C), mouse cerebellum (B) and mouse 10dpc embryo extracts (E). Densitometric analysis showing a significant decrease in Sod1 expression. Three independent experiments were quantified using eight wild-type and eight Fmr1 mice. Results presented as the mean ± SEM (Student's t-test, **p < 0.01) are the average of Sod1 levels normalized for β-tubulin expression.

Mentions: To assess whether the reduction of the association of Sod1 mRNA with polyribosomes impairs the expression of the Sod1 protein in the absence of FMRP, we analyzed total protein extracts obtained from STEK cells expressing or not expressing a FMR1 transgene [5], and we observed that Sod1 protein expression is reduced by approximately 40% in Fmr1 cells, as compared to that of cells expressing FMRP and after normalization of its expression to that of β-tubulin (Figure 6A). Similarly, we observed a significant decrease in Sod1 level in total protein extracts from whole brain (Figure 6B), hippocampus (Figure 6C), and cerebellum (Figure 6D) of 12-day-old Fmr1 mice, as compared to those of wild-type littermates. Sod1 levels were also reduced in Fmr1 mice embryos at 10 days post coitum (10dpc) (Figure 6E). We therefore concluded that Sod1 levels are directly correlated with the reduced association of its mRNA on medium- and heavy-sedimenting polyribosomes in Fmr1 mice, suggesting that FMRP promotes the association of Sod1 mRNA to actively translating polyribosomes.


A novel function for fragile X mental retardation protein in translational activation.

Bechara EG, Didiot MC, Melko M, Davidovic L, Bensaid M, Martin P, Castets M, Pognonec P, Khandjian EW, Moine H, Bardoni B - PLoS Biol. (2009)

Decreased Levels of Sod1 Protein in Fmr1 Null Cells, Brain, and EmbryosWestern blot analysis of one FMR1+ STEK clone (where FMR1 was reintroduced) and one STEK FMR1  clone. The results shown on the left are representative of the different clonal cell lines. On the right, corresponding densitometric analyses show a significant decrease of Sod1 expression, after comparing five wild-type rescued clones and five FMR1 knockout clones. Three independent experiments were quantified. Results presented as the mean ± SEM (Student's t-test, *p < 0.05) are the average of Sod1 levels normalized for β-tubulin expression The same analysis described in (A) was applied for mouse total brain (B), mouse hippocampus (C), mouse cerebellum (B) and mouse 10dpc embryo extracts (E). Densitometric analysis showing a significant decrease in Sod1 expression. Three independent experiments were quantified using eight wild-type and eight Fmr1  mice. Results presented as the mean ± SEM (Student's t-test, **p < 0.01) are the average of Sod1 levels normalized for β-tubulin expression.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2628407&req=5

pbio-1000016-g006: Decreased Levels of Sod1 Protein in Fmr1 Null Cells, Brain, and EmbryosWestern blot analysis of one FMR1+ STEK clone (where FMR1 was reintroduced) and one STEK FMR1 clone. The results shown on the left are representative of the different clonal cell lines. On the right, corresponding densitometric analyses show a significant decrease of Sod1 expression, after comparing five wild-type rescued clones and five FMR1 knockout clones. Three independent experiments were quantified. Results presented as the mean ± SEM (Student's t-test, *p < 0.05) are the average of Sod1 levels normalized for β-tubulin expression The same analysis described in (A) was applied for mouse total brain (B), mouse hippocampus (C), mouse cerebellum (B) and mouse 10dpc embryo extracts (E). Densitometric analysis showing a significant decrease in Sod1 expression. Three independent experiments were quantified using eight wild-type and eight Fmr1 mice. Results presented as the mean ± SEM (Student's t-test, **p < 0.01) are the average of Sod1 levels normalized for β-tubulin expression.
Mentions: To assess whether the reduction of the association of Sod1 mRNA with polyribosomes impairs the expression of the Sod1 protein in the absence of FMRP, we analyzed total protein extracts obtained from STEK cells expressing or not expressing a FMR1 transgene [5], and we observed that Sod1 protein expression is reduced by approximately 40% in Fmr1 cells, as compared to that of cells expressing FMRP and after normalization of its expression to that of β-tubulin (Figure 6A). Similarly, we observed a significant decrease in Sod1 level in total protein extracts from whole brain (Figure 6B), hippocampus (Figure 6C), and cerebellum (Figure 6D) of 12-day-old Fmr1 mice, as compared to those of wild-type littermates. Sod1 levels were also reduced in Fmr1 mice embryos at 10 days post coitum (10dpc) (Figure 6E). We therefore concluded that Sod1 levels are directly correlated with the reduced association of its mRNA on medium- and heavy-sedimenting polyribosomes in Fmr1 mice, suggesting that FMRP promotes the association of Sod1 mRNA to actively translating polyribosomes.

Bottom Line: To date, two RNA motifs have been found to mediate FMRP/RNA interaction, the G-quartet and the "kissing complex," which both induce translational repression in the presence of FMRP.The absence of FMRP results in decreased expression of Sod1.Because it has been observed that brain metabolism of FMR1 mice is more sensitive to oxidative stress, we propose that the deregulation of Sod1 expression may be at the basis of several traits of the physiopathology of the Fragile X syndrome, such as anxiety, sleep troubles, and autism.

View Article: PubMed Central - PubMed

Affiliation: Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France.

ABSTRACT
Fragile X syndrome, the most frequent form of inherited mental retardation, is due to the absence of Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein involved in several steps of RNA metabolism. To date, two RNA motifs have been found to mediate FMRP/RNA interaction, the G-quartet and the "kissing complex," which both induce translational repression in the presence of FMRP. We show here a new role for FMRP as a positive modulator of translation. FMRP specifically binds Superoxide Dismutase 1 (Sod1) mRNA with high affinity through a novel RNA motif, SoSLIP (Sod1 mRNA Stem Loops Interacting with FMRP), which is folded as three independent stem-loop structures. FMRP induces a structural modification of the SoSLIP motif upon its interaction with it. SoSLIP also behaves as a translational activator whose action is potentiated by the interaction with FMRP. The absence of FMRP results in decreased expression of Sod1. Because it has been observed that brain metabolism of FMR1 mice is more sensitive to oxidative stress, we propose that the deregulation of Sod1 expression may be at the basis of several traits of the physiopathology of the Fragile X syndrome, such as anxiety, sleep troubles, and autism.

Show MeSH
Related in: MedlinePlus