The myelin proteolipid protein (PLP) gene (Plp1) encodes the most abundant protein present in CNS myelin. Its expression in oligodendrocytes is tightly regulated. Mutations in the human gene have been shown to be associated with the X-linked dysmyelinating disorder Pelizaeus-Merzbacher disease (PMD) and some types of spastic paraplegia (SPG2). Dysmyelination can arise from either elevated levels of Plp1 gene expression or the lack, thereof. Hence accurate expression of the gene in is critical. With transgenic mice that harbor Plp1- lacZ fusion genes we have shown that Plp1 intron 1 DNA is essential for regulating the dramatic increase in Plp1 gene transcription in oligodendrocytes during the active myelination period of CNS development. The intron accounts for roughly one-half of the Plp1 gene, encompassing over 8 kb of DNA. We have identified a regulatory element within Plp1 intron 1 DNA and named it ASE for antisilencer/enhancer. We believe the ASE participates in the formation of a multi-protein nucleoprotein complex which acts as a potent transcriptional activator called an enhanceosome. Enhanceosomes are a new class of transcriptional regulators that are characterized by a higher-order nucleoprotein complex which functions as a unit. The precise three- dimensional structure permits synergy between factors and is obligatory to elicit gene activation. The intron also contains another enhancer, designated as wmN1, which has been roughly localized to a 1.2 kb segment of DNA. We hypothesize that the dramatic increase in Plp1 gene activity in oligodendrocytes during development is governed by the ASE and wmN1 enhancers and their associated (cognate) DNA-binding factors. Elucidation of the mechanisms controlling Plp1 gene expression will be an important step in the design of therapies aimed at enhancing remyelination since at the time of myelination, 10% of the total mRNA in oligodendrocytes is generated from the Plp1 gene. Developmental differences in factors present early in childhood versus those in adults may explain the rather poor levels of remyelination observed in MS patients. Cognate factors which bind the ASE and wmN1 enhancers may provide new therapeutic targets to enhance remyelination in these patients. As well, critical mutations in the ASE or wmN1 enhancer, or a mutation in a gene which encodes a cognate factor obligatory for enhancer function, would lead to under-expression of the Plp1 gene and consequently may result in a dysmyelinating disorder. In this study, deletion-transfection analysis with Plp1-lacZ constructs will be used to minimally map the wmN1 enhancer within the 1.2 kb segment of Plp1 intron 1 DNA. Transgenic mice will also be generated to test whether the ASE and wmN1 enhancer work independently, or in combination with one another, to significantly increase the levels of Plp1 gene expression during development.
The proposed work has direct relevance to patient suffering from demyelination conditions such as multiple sclerosis (MS), as well as patients whom have dysmyelinating disorders linked to the PLP1 gene, such as Pelizaeus-Merzbacher disease (PMD) and some types of spastic paraplegia (SPG2). Elucidation of the mechanisms controlling PLP1 gene expression will be an important step in the design of therapies aimed at enhancing remyelination since at the time of myelination, 10% of the total mRNA in oligodendrocytes is generated from the PLP1 gene. Developmental differences in factors present early in childhood, versus those in adults, may explain the rather poor levels of remyelination observed in MS patients. As well, critical mutations in either the ASE or wmN1 enhancer, or mutations in a gene which encodes a cognate factor obligatory for enhancer function, would lead to under-expression of the PLP1 gene and consequently may result in a dysmyelinating disorder. REFERENCES CITED 1. Baumann N. and Pham-Dinh D. (2001) Biology of oligodendrocyte and myelin in the mammalian central nervous system. Physiol. Rev. 81:871-927. 2. Campagnoni A.T. (1995) Molecular biology of myelination. In: Kettenmann H. and Ransom B.R. (Eds.), Neuroglia. Oxford University Press, New York, pp. 555-570. 3. Eng L.F., Chao R.C., Gerstl B., Pratt D. and Tavastsjerna M.G. (1968) The maturation of human white matter myelin: fractionation of the myelin membrane proteins. Biochemistry 7:4455-4465. 4. Norton W.T. and Poduslo S.E. (1973) Myelination in rat brain: changes in myelin composition during brain maturation. J. Neurochem. 21:759-773. 5. Gardinier M.V. and Macklin W.B. (1988) Myelin proteolipid protein gene expression in jimpy and jimpymsd mice. J. Neurochem. 51:360-369. 6. LeVine S.M., Wong D. and Macklin W.B. (1990) Developmental expression of proteolipid protein and DM-20 mRNAs and proteins in the rat brain. Dev. Neurosci. 12:235-250. 7. Cremers F.P.M., Pfeiffer R.A., van de Pol T.J.R., Hofker M.H., Kruse T.A., Wieringa B. and Ropers H.H. (1987) An interstitial duplication of the X-chromosome in a male allows physical fine mapping of probes from the Xq13-q22 region. Hum. Genet. 77:23-27. 8. Raskind W.H., Williams C.A., Hudson L.D. and Bird T.D. (1991) Complete deletion of the proteolipid protein gene (PLP) in a family with X-linked Pelizaeus-Merzbacher disease. Am. J. Hum. Genet. 49:1355-1360. 9. Hodes M.E., Pratt V.M. and Dlouhy S.R. (1993) Genetics of Pelizaeus-Merzbacher disease. Dev. Neurosci. 15:383-394. 10. Mastronardi F.G., Ackerley C.A., Arsenault L., Roots B.I. and Moscarello M.A. (1993) Demyelination in a transgenic mouse: a model for multiple sclerosis. J. Neurosci. Res. 36:315-324. 11. Ellis D. and Malcolm S. (1994) Proteolipid protein gene dosage effect in Pelizaeus-Merzbacher disease. Nat. Genet. 6:333-334. 12. Readhead C., Schneider A., Griffiths I. and Nave K.-A. (1994) Premature arrest of myelin formation in transgenic mice with increased proteolipid protein gene dosage. Neuron 12:583-595. 13. Kagawa T., Ikenaka K., Inoue Y., Kuriyama S., Tsujii T., Nakao J., Nakajima, K., Aruga J., Okano H. and Mikoshiba K. (1994) Glial cell degeneration and hypomyelination caused by overexpression of myelin proteolipid protein gene. Neuron 13:427-442. 14. Carango P., Funanage V.L., Quiros R.E., Debruyn C.S. and Marks H.G. (1995) Overexpression of DM20 messenger RNA in two brothers with Pelizaeus-Merzbacher disease. Ann. Neurol. 38:610-617. 15. Harding B., Ellis D. and Malcolm S. (1995) A case of Pelizaeus-Merzbacher disease showing increased dosage of the proteolipid protein gene. Neuropath. Appl. Neurobiol. 21:85-96. 16. Hodes M.E. and Dlouhy S.R. (1996) The proteolipid protein gene: double, double,...and trouble. Am. J. Hum. Genet. 59:12-15. 3 Program Director/Principal Investigator (Last, First, Middle): Wight, Patricia, A. 17. Inoue K., Osaka H., Sugiyama N., Kawanishi C., Onishi H., Nezu A., Kimura K., Yamada Y. and Kosaka K. (1996) Am. J. Hum. Genet. 59:32-39. 18. Garbern J.Y., Yool D.A., Moore G.J., Wilds I.B., Faulk M.W., Klugmann M., Nave K.-A. Sistermans E.A., van der Knaap M.S., Bird T.D., Shy M.E., Kamholz J.A. and Griffiths I.R. (2002) Patients lacking the major CNS myelin protein, proteolipid protein 1, develop length-dependent axonal degeneration in the absence of demyelination and inflammation. Brain 125:551-561. 19. Shy M.E., Hobson G., Jain M., Boespflug-Tanguy O., Garbern J., Sperle K., Li W., Gow A., Rodriguez D., Bertini E., Mancias P., Krajewski K., Lewis R., Kamholz J. (2003) Schwann cell expression of PLP1 but not DM20 is necessary to prevent neuropathy. Ann. Neurol. 53:354-365. 20. Wolf N.I., Sistermans E.A., Cundall M., Hobson G.M., Davis-Williams A.P., Palmer R., StubbsP., Davies S., Endziniene M., Wu Y., Chong W.K., Malcolm S., Surtees R., Garbern J.Y. and Woodward K.J. (2005) Three or more copies of the proteolipid protein gene PLP1 cause severe Pelizaeus-Merzbacher disease. Brain 128:743-751. 21. Karim S.A., Barrie J.A., McCulloch M.C., Montague P., Edgar J.M., Kirkham D., Anderson T.J., Nave K.A., Griffiths I.R., and McLaughlin M. (2007) PLP overexpression perturbs myelin protein composition and myelination in a mouse model of Pelizaeus-Merzbacher disease. Glia 55:341-351. 22. Hudson L.D. (2003) Pelizaeus-Merzbacher disease and spastic paraplegia type 2: two faces of myelin loss from mutations in the same gene. J. Child Neurol. 18:616-624. 23. Inoue K. (2005) PLP1-related inherited dysmyelinating disorders: Pelizaeus-Merzbacher disease and spastic paraplegia type 2. Neurogenetics 6:1-16. 24. Garbern J.Y. (2005) Pelizaeus-Merzbacher disease: pathogenic mechanisms and insights into the roles of proteolipid protein 1 in the nervous system. J. Neurol. Sci. 228:201-203. 25. Garbern J.Y. (2007) Pelizaeus-Merzbacher disease: Genetic and cellular pathogenesis. Cell. Mol. Life Sci. 64:50-65. 26. Li S., Moore C.L., Dobretsova A. and Wight P.A. (2002) Myelin proteolipid protein (Plp) intron 1 DNA is required to temporally regulate Plp gene expression in the brain. J. Neurochem. 83:193-201. 27. Wight P.A. and Dobretsova A. (1997) The first intron of the myelin proteolipid protein gene confers cell type-specific expression by a transcriptional repression mechanism in non-expressing cell types. Gene 201:111-117. 28. Dobretsova A. and Wight P.A. (1999) Antisilencing: myelin proteolipid protein gene expression in oligodendrocytes is regulated via derepression. J. Neurochem. 72:2227-2237. 29. Dobretsova A., Kokorina N.A. and Wight P.A. (2000) Functional characterization of a cis-acting DNA antisilencer region that modulated myelin proteolipid protein gene expression. J. Neurochem. 75:1368- 1376. 30. Tuason M.C., Rastikerdar A., Kuhlmann T., Goujet-Zalc C., Zalc B., Dib S., Friedman H., and Peterson A. (2008) Separate proteolipid protein/DM20 enhancers serve different lineages and stages of development. J. Neurosci. 28:6895-6903. 31. Thanos D. and Maniatis T. (1995) Virus induction of human IFN-? gene expression requires the assembly of an enhanceosome. Cell 83:1091-1100. 4
Showing the most recent 10 out of 16 publications
