Fragile X

Fragile-X syndrome includes mental and physical defects and is the most common form of inherited mental retardation (reviewed in: 1, 2-5). Defects have been observed in dendritic spines (6) and there are defects in the number and function of synapses (7). The disease is associated with loss-of-function mutations in the FMR1 gene, usually by trinucleotide repeat expansion (8-12). FMR1 encodes an RNA binding protein (FMRP) which is widely expressed and has been proposed to act in the regulation of mRNA trafficking from the nucleus to specific cytoplasmic compartments and/or to have a role in the regulation of translation (13-27). There are two similar genes in humans (FXR1 and FXR2) and their products may act somewhat redundantly with FMRP (28-30). Some other proteins have been found in a ribonucleoprotein (RNP) complex with FMRP, and there are likely to be more (22, 31-33). A mouse model has been developed (by gene disruption), but this has produced some contradictory results (34-43). A single FMR1 homolog has been found in Drosophila and ectopic expression of this protein in the fly causes developmental defects (44).

While progress has been made in identifying protein partners of FMRP and its mRNA targets this work has been difficult and there are likely to be many more genes that interact functionally with FMR1. We are working to discover and characterize novel genes that interact with FMR1 towards the long term objective of improved therapeutic intervention. We have developed an F1 genetic screen based on the modification of the Drosophila Fmr1 misexpression phenotype in the compound eye and pilot runs have validated our approach.

PES is a transgene that ectopically expresses fly FMR1 in the eye. Eye morphology of dominant modifiers of PES compared to the parent stock. Note that the regularity of the ommatidial array is restored in the suppressor (left) and more disrupted in the enhancer (right). This is distinct from eye size, which may be unaffected.

Papers Cited
1] Warren, S. T. and Nelson, D. L. (1994). Advances in molecular analysis of fragile X syndrome. Jama 271, 536-542.
2] Nelson, D. L. (1995). The fragile X syndromes. Semin Cell Biol 6, 5-11.
3] Oostra, B. A. and Willems, P. J. (1995). A fragile gene. Bioessays 17, 941-947.
4] Chakrabarti, L. and Davies, K. E. (1997). Fragile X syndrome. Curr Opin Neurol 10, 142-147.
5] Jin, P. and Warren, S. T. (2000). Understanding the molecular basis of fragile X syndrome. Hum Mol Genet 9, 901-908.
6] Hinton, V. J., Brown, W. T., Wisniewski, K. and Rudelli, R. D. (1991). Analysis of neocortex in three males with the fragile X syndrome. Am J Med Genet 41, 289-294.
7] Weiler, I. J. and Greenough, W. T. (1999). Synaptic synthesis of the Fragile X protein: possible involvement in synapse maturation and elimination. Am J Med Genet 83, 248-252.
8] Fu, Y. H., Kuhl, D. P., Pizzuti, A., Pieretti, M., Sutcliffe, J. S., Richards, S., Verkerk, A. J., Holden, J. J., Fenwick, R. G., Jr., Warren, S. T., Oostra, B. A., Nelson, D. L. and Caskey, C. T. (1991). Variation of the CGG repeat at the fragile X site results in genetic instability: resolution of the Sherman paradox. Cell 67, 1047-1058.
9] Kremer, E. J., Pritchard, M., Lynch, M., Yu, S., Holman, K., Baker, E., Warren, S. T., Schlessinger, D., Sutherland, G. R. and Richards, R. I. (1991). Mapping of DNA instability at the fragile X to a trinucleotide repeat sequence p(CCG)n. Science 252, 1711-1714.
10] Pieretti, M., Zhang, F. P., Fu, Y. H., Warren, S. T., Oostra, B. A., Caskey, C. T. and Nelson, D. L. (1991). Absence of expression of the FMR-1 gene in fragile X syndrome. Cell 66, 817-822.
11] Verkerk, A. J., Pieretti, M., Sutcliffe, J. S., Fu, Y. H., Kuhl, D. P., Pizzuti, A., Reiner, O., Richards, S., Victoria, M. F., Zhang, F. P., Eussen, B. E., Vanommen, G. J. B., Blonden, L. A. J., Riggins, G. J., JL, C., Kunst, C. B., Galjaard, H., Caskey, C. T., Nelson, D. L., Oostra, B. A. and Warren, S. T. (1991). Identification of a gene (FMR-1) containing a CGG repeat coincident with a breakpoint cluster region exhibiting length variation in fragile X syndrome. Cell 65, 905-914.
12] Yu, S., Pritchard, M., Kremer, E., Lynch, M., Nancarrow, J., Baker, E., Holman, K., Mulley, J. C., Warren, S. T., Schlessinger, D., Sutherland, G. R. and Richards, R. I. (1991). Fragile X genotype characterized by an unstable region of DNA. Science 252, 1179-1181.
13] Ashley, C. T. J., Wilkinson, K. D., Reines, D. and Warren, S. T. (1993). FMR1 protein: conserved RNP family domains and selective RNA binding. Science 262, 563-566.
14] Gibson, T. J., Rice, P. M., Thompson, J. D. and Heringa, J. (1993). KH domains within the FMR1 sequence suggest that fragile X syndrome stems from a defect in RNA metabolism. Trends Biochem Sci 18, 331-333.
15] Siomi, H., Siomi, M. C., Nussbaum, R. L. and Dreyfuss, G. (1993). The protein product of the fragile X gene, FMR1, has characteristics of an RNA-binding protein. Cell 74, 291-298.
16] Siomi, H., Choi, M., Siomi, M. C., Nussbaum, R. L. and Dreyfuss, G. (1994). Essential role for KH domains in RNA binding: impaired RNA binding by a mutation in the KH domain of FMR1 that causes fragile X syndrome. Cell 77, 33-39.
17] Feng, Y., Zhang, F., Lokey, L. K., Chastain, J. L., Lakkis, L., Eberhart, D. and Warren, S. T. (1995). Translational suppression by trinucleotide repeat expansion at FMR1. Science 268, 731-734.
18] Eberhart, D. E., Malter, H. E., Feng, Y. and Warren, S. T. (1996). The fragile X mental retardation protein is a ribonucleoprotein containing both nuclear localization and nuclear export signals. Hum Mol Genet 5, 1083-1091.
19] Fridell, R. A., Benson, R. E., Hua, J., Bogerd, H. P. and Cullen, B. R. (1996). A nuclear role for the Fragile X mental retardation protein. Embo J 15, 5408-5414.
20] Siomi, M. C., Zhang, Y., Siomi, H. and Dreyfuss, G. (1996). Specific sequences in the fragile X syndrome protein FMR1 and the FXR proteins mediate their binding to 60S ribosomal subunits and the interactions among them. Mol Cell Biol 16, 3825-3832.
21] Tamanini, F., Meijer, N., Verheij, C., Willems, P. J., Galjaard, H., Oostra, B. A. and Hoogeveen, A. T. (1996). FMRP is associated to the ribosomes via RNA. Hum Mol Genet 5, 809-813.
22] Willemsen, R., Bontekoe, C., Tamanini, F., Galjaard, H., Hoogeveen, A. and Oostra, B. (1996). Association of FMRP with ribosomal precursor particles in the nucleolus. Biochem Biophys Res Commun 225, 27-33.
23] Bardoni, B., Sittler, A., Shen, Y. and Mandel, J. L. (1997). Analysis of domains affecting intracellular localization of the FMRP protein. Neurobiol Dis 4, 329-336.
24] Corbin, F., Bouillon, M., Fortin, A., Morin, S., Rousseau, F. and Khandjian, E. W. (1997). The fragile X mental retardation protein is associated with poly(A)+ mRNA in actively translating polyribosomes. Hum Mol Genet 6, 1465-1472.
25] Feng, Y., Gutekunst, C. A., Eberhart, D. E., Yi, H., Warren, S. T. and Hersch, S. M. (1997). Fragile X mental retardation protein: nucleocytoplasmic shuttling and association with somatodendritic ribosomes. J Neurosci 17, 1539-1547.
26] Laggerbauer, B., Ostareck, D., Keidel, E. M., Ostareck-Lederer, A. and Fischer, U. (2001). Evidence that fragile X mental retardation protein is a negative regulator of translation. Hum Mol Genet 10, 329-338.
27] Li, Z., Zhang, Y., Ku, L., Wilkinson, K. D., Warren, S. T. and Feng, Y. (2001). The fragile X mental retardation protein inhibits translation via interacting with mRNA. Nucleic Acids Res 29, 2276-2283.
28] Siomi, M. C., Siomi, H., Sauer, W. H., Srinivasan, S., Nussbaum, R. L. and Dreyfuss, G. (1995). FXR1, an autosomal homolog of the fragile X mental retardation gene. Embo J 14, 2401-2408.
29] Gecz, J., Gedeon, A. K., Sutherland, G. R. and Mulley, J. C. (1996). Identification of the gene FMR2, associated with FRAXE mental retardation. Nat Genet 13, 105-108.
30] Gu, Y., Shen, Y., Gibbs, R. A. and Nelson, D. L. (1996). Identification of FMR2, a novel gene associated with the FRAXE CCG repeat and CpG island. Nat Genet 13, 109-113.
31] Bardoni, B., Schenck, A. and Mandel, J. L. (1999). A novel RNA-binding nuclear protein that interacts with the fragile X mental retardation (FMR1) protein. Hum Mol Genet 8, 2557-2566.
32] Ceman, S., Brown, V. and Warren, S. T. (1999). Isolation of an FMRP-associated messenger ribonucleoprotein particle and identification of nucleolin and the fragile X-related proteins as components of the complex. Mol Cell Biol 19, 7925-7932.
33] Ceman, S., Nelson, R. and Warren, S. T. (2000). Identification of mouse YB1/p50 as a component of the FMRP-associated mRNP particle. Biochem Biophys Res Commun 279, 904-908.
34] Consortium, D.-B. F. X. (1994). Fmr1 knockout mice: a model to study fragile X mental retardation. Cell 78, 23-33.
35] Godfraind, J. M., Reyniers, E., De Boulle, K., D'Hooge, R., De Deyn, P. P., Bakker, C. E., Oostra, B. A., Kooy, R. F. and Willems, P. J. (1996). Long-term potentiation in the hippocampus of fragile X knockout mice. Am J Med Genet 64, 246-251.
36] Kooy, R. F., D'Hooge, R., Reyniers, E., Bakker, C. E., Nagels, G., De Boulle, K., Storm, K., Clincke, G., De Deyn, P. P., Oostra, B. A. and Willems, P. J. (1996). Transgenic mouse model for the fragile X syndrome. Am J Med Genet 64, 241-245.
37] Comery, T. A., Harris, J. B., Willems, P. J., Oostra, B. A., Irwin, S. A., Weiler, I. J. and Greenough, W. T. (1997). Abnormal dendritic spines in fragile X knockout mice: maturation and pruning deficits. Proc Natl Acad Sci U S A 94, 5401-5404.
38] D'Hooge, R., Nagels, G., Franck, F., Bakker, C. E., Reyniers, E., Storm, K., Kooy, R. F., Oostra, B. A., Willems, P. J. and De Deyn, P. P. (1997). Mildly impaired water maze performance in male Fmr1 knockout mice. Neuroscience 76, 367-376.
39] Oostra, B. A. and Hoogeveen, A. T. (1997). Animal model for fragile X syndrome. Ann Med 29, 563-567.
40] Slegtenhorst-Eegdeman, K. E., de Rooij, D. G., Verhoef-Post, M., van de Kant, H. J., Bakker, C. E., Oostra, B. A., Grootegoed, J. A. and Themmen, A. P. (1998). Macroorchidism in FMR1 knockout mice is caused by increased Sertoli cell proliferation during testicular development. Endocrinology 139, 156-162.
41] Steward, O., Bakker, C. E., Willems, P. J. and Oostra, B. A. (1998). No evidence for disruption of normal patterns of mRNA localization in dendrites or dendritic transport of recently synthesized mRNA in FMR1 knockout mice, a model for human fragile-X mental retardation syndrome. Neuroreport 9, 477-481.
42] Fisch, G. S., Hao, H. K., Bakker, C. and Oostra, B. A. (1999). Learning and memory in the FMR1 knockout mouse. Am J Med Genet 84, 277-282.
43] Dobkin, C., Rabe, A., Dumas, R., El Idrissi, A., Haubenstock, H. and Brown, W. T. (2000). Fmr1 knockout mouse has a distinctive strain-specific learning impairment. Neuroscience 100, 423-429.
44] Wan, L., Dockendorff, T. C., Jongens, T. A. and Dreyfuss, G. (2000). Characterization of dFMR1, a Drosophila melanogaster homolog of the fragile X mental retardation protein. Mol Cell Biol 20, 8536-8547.

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