MECP2

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Methyl CpG binding protein 2 (Rett syndrome)

PDB rendering based on 1qk9.
Available structures
PDB Ortholog search: PDBe, RCSB
Identifiers
Symbols MECP2 ; AUTSX3; MRX16; MRX79; MRXS13; MRXSL; PPMX; RS; RTS; RTT
External IDs OMIM300005 MGI99918 HomoloGene3657 GeneCards: MECP2 Gene
RNA expression pattern
PBB GE MECP2 202616 s at tn.png
PBB GE MECP2 202617 s at tn.png
PBB GE MECP2 202618 s at tn.png
More reference expression data
Orthologs
Species Human Mouse
Entrez 4204 17257
Ensembl ENSG00000169057 ENSMUSG00000031393
UniProt P51608 Q9Z2D6
RefSeq (mRNA) NM_001110792 NM_001081979
RefSeq (protein) NP_001104262 NP_001075448
Location (UCSC) Chr HG1497_PATCH:
153.23 – 153.34 Mb
Chr X:
74.03 – 74.14 Mb
PubMed search [1] [2]

MECP2 (methyl CpG binding protein 2 (Rett syndrome)) is a gene[1] that encodes the protein MECP2.[2] MECP2 appears to be essential for the normal function of nerve cells. The protein seems to be particularly important for mature nerve cells, where it is present in high levels. The MECP2 protein is likely to be involved in turning off ("repressing" or "silencing") several other genes. This prevents the genes from making proteins when they are not needed. Recent work has shown that MECP2 can also activate other genes.[3] The MECP2 gene is located on the long (q) arm of the X chromosome in band 28 ("Xq28"), from base pair 152,808,110 to base pair 152,878,611.

DNA methylation is a major modification of eukaryotic genomes and plays an essential role in mammalian development. Human proteins MECP2 (this protein), MBD1, MBD2, MBD3, and MBD4 comprise a family of nuclear proteins related by the presence in each of a methyl-CpG binding domain (MBD). Each of these proteins, with the exception of MBD3, is capable of binding specifically to methylated DNA. MECP2, MBD1 and MBD2 can also repress transcription from methylated gene promoters. In contrast to other MBD family members, MECP2 is X-linked and subject to X inactivation. MECP2 is dispensable in stem cells. MECP2 gene mutations are the cause of most cases of Rett syndrome, a progressive neurologic developmental disorder and one of the most common causes of mental retardation in females.[4]

Function[edit]

MECP2 protein is found in all cells in the body, including the brain, acting as a transcriptional repressor and activator, depending on the context. However, the idea that MECP2 functions as an activator is relatively new and remains controversial.[5] In the brain, it is found in high concentrations in neurons and is associated with maturation of the central nervous system (CNS) and in forming synaptic contacts.[6]

Mechanism of action[edit]

The MeCP2 protein binds to forms of DNA that have been methylated. The MeCP2 protein then interacts with other proteins to form a complex that turns off the gene. Methylation is a chemical alteration made to a "cytosine" (C) when it occurs in a particular DNA sequence, "CpG". Many genes have CpG islands, which frequently occur near the beginning of the gene. MECP2 does not bind to these islands in most cases, as they are not methylated. The expression of a few genes may be regulated through methylation of their CpG island, and MECP2 may play a role in a subset of these. Researchers have not yet determined which genes are targeted by the MeCP2 protein, but such genes are probably important for the normal function of the central nervous system. However, the first large-scale mapping of MECP2 binding sites in neurons found that only 6% of the binding sites are in CpG islands, and that 63% of MECP2-bound promoters are actively expressed and only 6% are highly methylated, indicating that MECP2's main function is something other than silencing methylated promoters.[7]

Once bound, MeCP2 will condense the chromatin structure, form a complex with histone deacetylases (HDAC), or block transcription factors directly. More recent studies have demonstrated that MeCP2 may also function as a transcriptional activator, through recruiting the transcription factor CREB1. This was an unexpected finding which suggests that MeCP2 is a key transcriptional regulator with potentially dual roles in gene expression. In fact, the majority of genes that are regulated by MeCP2 appear to be activated rather than repressed.[8] However, it remains controversial whether MeCP2 regulates these genes directly or whether these changes are secondary in nature.[5] Further studies have shown MeCP2 may be able to bind directly to un-methylated DNA in some instances.[9] MeCP2 has been implicated in regulation of imprinted genes and loci that include UBE3A and DLX5.[10]

Structure[edit]

MECP2 is part of a family of methyl-CpG-binding domain proteins (MBD), but possesses its own unique differences which help set it apart from the group. It has two functional domains:

  • a methyl-cytosine-binding domain (MBD) composed of 85 amino acids; and
  • a transcriptional repression domain (TRD) composed of 104 amino acids

The MBD domain forms a wedge and attaches to the methylated CpG sites on the DNA strands. The TRD region then reacts with SIN3A to recruit histone deacetylases (HDAC).[11] There are also unusual, repetitive sequences found at the carboxyl terminus. This region is closely related to the fork head family, at the amino acid level.[12]

Role in disease[edit]

Certain mutations in the MECP2 gene cause Rett syndrome. Several types of mutations have been identified in Rett syndrome patients. These mutations include changes in single DNA base pairs (SNP), insertions or deletions of DNA in the MECP2 gene, and changes that affect how the gene information is processed into a protein (RNA splicing). Mutations in the gene alter the structure of the MeCP2 protein or lead to reduced amounts of the protein. As a result, the protein is unable to bind to DNA or turn other genes on or off. Genes that are normally repressed by MeCP2 remain active when their products are not needed. Other genes that are normally activated by MeCP2 remain inactive leading to a lack of gene product. This defect probably disrupts the normal functioning of nerve cells, leading to the signs and symptoms of Rett syndrome.

This disease is mainly found in girls with a prevalence of around 1 in every 10,000. Patients are born with very hard to find signs of a disorder, but after about six months to a year and half, speech and motor function capabilities start to decrease. This is followed by seizures, growth retardation and cognitive and motor impairment.[13] The MECP2 locus is X-linked and the disease-causing alleles are dominant. Due to its prevalence in females, it has been linked to male lethality, or to a predominant transmission with the paternal X chromosome; nevertheless, in rare cases some males can also be affected by Rett Syndrome.[14] Males with gene duplications of MECP-2 at the Xq28 locus are also at risk for recurrent infections & meningitis in infancy.

Mutations in the MECP2 gene have also been identified in people with several other disorders affecting the central nervous system. For example, MECP2 mutations are associated with some cases of moderate to severe X-linked mental retardation. Mutations in the gene have also been found in males with severe brain dysfunction (neonatal encephalopathy) who live only into early childhood. In addition, several people with features of both Rett syndrome and Angelman syndrome (a condition characterized by mental retardation, problems with movement, and inappropriate laughter and excitability) have mutations in the MECP2 gene. Lastly, MECP2 mutations or changes in the gene's activity have been reported in some cases of autism (a developmental disorder that affects communication and social interaction).

More recent studies reported genetic polymorphisms in the MeCP2 genes in patients with systemic lupus erythematosus (SLE).[15] SLE is a systemic autoimmune disease that can affect multiple organs. MeCP2 polymorphisms have been reported so far in European-derived and Asian lupus patients.

The genetic loss of MECP2 has been identified as changing the properties of cells in the locus ceruleus the exclusive source of noradrenergic innervation to the cerebral cortex and hippocampus.[16]

Researchers have concluded that "Because these neurons are a pivotal source of norepinephrine throughout the brainstem and forebrain and are involved in the regulation of diverse functions disrupted in Rett syndrome, such as respiration and cognition, we hypothesize that the locus ceruleus is a critical site at which loss of MECP2 results in CNS dysfunction."[16]

Interactions[edit]

MECP2 has been shown to interact with SKI protein[17] and Nuclear receptor co-repressor 1.[17] In neuronal cells the MECP2 mRNA is thought to interact with miR-132, which silences the expression of the protein. This forms part of a homeostatic mechanism that could regulate MECP2 levels in the brain.[18]

MeCP2 and Hormones[edit]

MeCP2 in the developing rat brain regulates important social development in a sexually dimorphic manner. MeCP2 levels are different between males and females in the developing rat brain 24 hours after birth within the amygdala and hypothalamus, but this difference is no longer observed 10 days after birth. Specifically, males express less MeCP2 than females,[19] and this aligns with the steroid-sensitive time period of the neonatal rat brain. Reductions in MeCP2 with Small interfering RNA (siRNA) during the first few days of life reduce male levels of juvenile social play behavior to female typical levels, but do not affect female juvenile play behavior.[20]

MeCP2 is important in organizing hormone-related behaviors and sex differences in the developing rat amygdala. MeCP2 appears to regulate arginine vasopressin (AVP) and androgen receptor (AR) production in male rats but not in females. Vasopressin is known to regulate many social behaviors including pair bonding[21] and social recognition.[22] While male rats typically have higher levels of vasopressin in the amygdala,[23] MeCP2 reduction during the first 3 days of life causes a lasting reduction of vasopressin to female typical levels in this brain region that lasted through adulthood. Male rats with reduced MeCP2 levels also show a significant reduction of AR at two weeks following infusion, but this effect is gone by adulthood.[24]

Early life stress[edit]

MeCP2 monitors the response to early life stress. Early life stress is correlated with hyper-phosphorylation of the MeCP2 protein in the paraventricular nucleus of the hypothalamus.[25] This thus causes a reduced occupancy of MeCP2 at the AVP gene’s promotor region, and therefore elevated levels of AVP. Vasopressin is a primary hormone involved in the Hypothalmic-Pituitary-Adrenal Axis, the connectivity in the brain that regulates processing of and reaction to stress. Decreased functioning of the MeCP2 protein thus upregulates the neuronal stress response.

References[edit]

  1. ^ Amir RE, Van den Veyver IB, Wan M, Tran CQ, Francke U, Zoghbi HY (October 1999). "Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2". Nat. Genet. 23 (2): 185–8. doi:10.1038/13810. PMID 10508514. 
  2. ^ Lewis JD, Meehan RR, Henzel WJ, Maurer-Fogy I, Jeppesen P, Klein F, Bird A (June 1992). "Purification, sequence, and cellular localization of a novel chromosomal protein that binds to methylated DNA". Cell 69 (6): 905–14. doi:10.1016/0092-8674(92)90610-O. PMID 1606614. 
  3. ^ Chahrour M, et al. (2008). "MECP2, a key contributor to neurological disease, activates and represses transcription". Science 320 (5880): 1224–9. doi:10.1126/science.1153252. PMC 2443785. PMID 18511691. 
  4. ^ "Entrez Gene: MECP2 methyl CpG binding protein 2 (Rett syndrome)". 
  5. ^ a b Cohen S, Zhou Z, Greenberg ME (May 2008). "Medicine. Activating a repressor.". Science 320 (5880): 1172–3. doi:10.1126/science.1159146. PMC 2857976. PMID 18511680. 
  6. ^ Luikenhuis S, Giacometti E, Beard CF, Jaenisch R (April 2004). "Expression of MeCP2 in postmitotic neurons rescues Rett syndrome in mice". Proc. Natl. Acad. Sci. U.S.A. 101 (16): 6033–8. doi:10.1073/pnas.0401626101. PMC 395918. PMID 15069197. 
  7. ^ Yasui DH, Peddada S, Bieda MC, Vallero RO, Hogart A, Nagarajan RP, Thatcher KN, Farnham PJ, Lasalle JM (December 2007). "Integrated epigenomic analyses of neuronal MeCP2 reveal a role for long-range interaction with active genes". Proc. Natl. Acad. Sci. U.S.A. 104 (49): 19416–21. doi:10.1073/pnas.0707442104. PMC 2148304. PMID 18042715. 
  8. ^ Chahrour M, Jung SY, Shaw C, Zhou X, Wong ST, Qin J, Zoghbi HY (May 2008). "MeCP2, a key contributor to neurological disease, activates and represses transcription". Science 320 (5880): 1224–9. doi:10.1126/science.1153252. PMC 2443785. PMID 18511691. 
  9. ^ Georgel PT, Horowitz-Scherer RA, Adkins N, Woodcock CL, Wade PA, Hansen JC (August 2003). "Chromatin compaction by human MeCP2. Assembly of novel secondary chromatin structures in the absence of DNA methylation". J. Biol. Chem. 278 (34): 32181–8. doi:10.1074/jbc.M305308200. PMID 12788925. 
  10. ^ LaSalle JM (2007). "The odyssey of MeCP2 and parental imprinting". Epigenetics 2 (1): 5–10. doi:10.4161/epi.2.1.3697. PMC 1866173. PMID 17486180. 
  11. ^ Wakefield RI, Smith BO, Nan X, Free A, Soteriou A, Uhrin D, Bird AP, Barlow PN (September 1999). "The solution structure of the domain from MeCP2 that binds to methylated DNA". J. Mol. Biol. 291 (5): 1055–65. doi:10.1006/jmbi.1999.3023. PMID 10518942. 
  12. ^ Paul A. Wade
  13. ^ Caballero IM, Hendrich B (April 2005). "MeCP2 in neurons: closing in on the causes of Rett syndrome". Hum. Mol. Genet. 14 Spec No 1: R19–26. doi:10.1093/hmg/ddi102. PMID 15809268. 
  14. ^ Samaco RC, Nagarajan RP, Braunschweig D, LaSalle JM (March 2004). "Multiple pathways regulate MeCP2 expression in normal brain development and exhibit defects in autism-spectrum disorders". Hum. Mol. Genet. 13 (6): 629–39. doi:10.1093/hmg/ddh063. PMID 14734626. 
  15. ^ Sawalha AH, Webb R, Han S, Kelly JA, Kaufman KM, Kimberly RP, Alarc?n-Riquelme ME, James JA, Vyse TJ, Gilkeson GS, Choi CB, Scofield RH, Bae SC, Nath SK, Harley JB (2008). "Common variants within MECP2 confer risk of systemic lupus erythematosus". In Jin, Dong-Yan. PLoS ONE 3 (3): e1727. doi:10.1371/journal.pone.0001727. PMC 2253825. PMID 18320046. 
  16. ^ a b Taneja P, Ogier M, Brooks-Harris G, Schmid DA, Katz DM, Nelson SB (2009). "Pathophysiology of Locus Ceruleus Neurons in a Mouse Model of Rett Syndrome". Journal of Neuroscience 29 (39): 12187–12195. doi:10.1523/JNEUROSCI.3156-09.2009. PMC 2846656. PMID 19793977. 
  17. ^ a b Kokura K, Kaul SC, Wadhwa R, Nomura T, Khan MM, Shinagawa T, Yasukawa T, Colmenares C, Ishii S (September 2001). "The Ski protein family is required for MeCP2-mediated transcriptional repression". J. Biol. Chem. 276 (36): 34115–21. doi:10.1074/jbc.M105747200. PMID 11441023. 
  18. ^ Klein ME, Lioy DT, Ma L, Impey S, Mandel G, Goodman RH (December 2007). "Homeostatic regulation of MeCP2 expression by a CREB-induced microRNA". Nat. Neurosci. 10 (12): 1513–4. doi:10.1038/nn2010. PMID 17994015. 
  19. ^ Kurian JR, Forbes-Lorman RM, Auger AP (September 2007). "Sex difference in mecp2 expression during a critical period of rat brain development". Epigenetics 2 (3): 173–8. doi:10.4161/epi.2.3.4841. PMID 17965589. 
  20. ^ Kurian JR, Bychowski ME, Forbes-Lorman RM, Auger CJ, Auger AP (July 2008). "Mecp2 organizes juvenile social behavior in a sex-specific manner". J. Neurosci. 28 (28): 7137–42. doi:10.1523/JNEUROSCI.1345-08.2008. PMC 2569867. PMID 18614683. 
  21. ^ Winslow JT, Hastings N, Carter CS, Harbaugh CR, Insel TR (October 1993). "A role for central vasopressin in pair bonding in monogamous prairie voles". Nature 365 (6446): 545–8. doi:10.1038/365545a0. PMID 8413608. 
  22. ^ Bielsky IF, Hu SB, Szegda KL, Westphal H, Young LJ (March 2004). "Profound impairment in social recognition and reduction in anxiety-like behavior in vasopressin V1a receptor knockout mice". Neuropsychopharmacology 29 (3): 483–93. doi:10.1038/sj.npp.1300360. PMID 14647484. 
  23. ^ De Vries GJ, Panzica GC (2006). "Sexual differentiation of central vasopressin and vasotocin systems in vertebrates: different mechanisms, similar endpoints". Neuroscience 138 (3): 947–55. doi:10.1016/j.neuroscience.2005.07.050. PMC 1457099. PMID 16310321. 
  24. ^ Forbes-Lorman RM, Rautio JJ, Kurian JR, Auger AP, Auger CJ (March 2012). "Neonatal MeCP2 is important for the organization of sex differences in vasopressin expression". Epigenetics 7 (3): 230–8. doi:10.4161/epi.7.3.19265. PMC 3335947. PMID 22430799. 
  25. ^ Murgatroyd C, Patchev AV, Wu Y, Micale V, Bockmühl Y, Fischer D, Holsboer F, Wotjak CT, Almeida OF, Spengler D (December 2009). "Dynamic DNA methylation programs persistent adverse effects of early-life stress". Nat. Neurosci. 12 (12): 1559–66. doi:10.1038/nn.2436. PMID 19898468. 

Further reading[edit]

External links[edit]