Cerebellar gene expression profiles of mouse models for Rett syndrome reveal novel MeCP2 targets.
BACKGROUND
MeCP2, methyl-CpG-binding protein 2, binds to methylated cytosines at CpG dinucleotides, as well as to unmethylated DNA, and affects chromatin condensation. MECP2 mutations in females lead to Rett syndrome, a neurological disorder characterized by developmental stagnation and regression, loss of purposeful hand movements and speech, stereotypic hand movements, deceleration of brain growth, autonomic dysfunction and seizures. Most mutations occur de novo during spermatogenesis. Located at Xq28, MECP2 is subject to X inactivation, and affected females are mosaic. Rare hemizygous males suffer from a severe congenital encephalopathy.


METHODS
To identify the pathways mis-regulated by MeCP2 deficiency, microarray-based global gene expression studies were carried out in cerebellum of Mecp2 mutant mice. We compared transcript levels in mutant/wildtype male sibs of two different MeCP2-deficient mouse models at 2, 4 and 8 weeks of age. Increased transcript levels were evaluated by real-time quantitative RT-PCR. Chromatin immunoprecipitation assays were used to document in vivo MeCP2 binding to promoter regions of candidate target genes.


RESULTS
Of several hundred genes with altered expression levels in the mutants, twice as many were increased than decreased, and only 27 were differentially expressed at more than one time point. The number of misregulated genes was 30% lower in mice with the exon 3 deletion (Mecp2tm1.1Jae) than in mice with the larger deletion (Mecp2tm1.1Bird). Between the mutants, few genes overlapped at each time point. Real-time quantitative RT-PCR assays validated increased transcript levels for four genes: Irak1, interleukin-1 receptor-associated kinase 1; Fxyd1, phospholemman, associated with Na, K-ATPase;Reln, encoding an extracellular signaling molecule essential for neuronal lamination and synaptic plasticity; and Gtl2/Meg3, an imprinted maternally expressed non-translated RNA that serves as a host gene for C/D box snoRNAs and microRNAs. Chromatin immunoprecipitation assays documented in vivo MeCP2 binding to promoter regions of Fxyd1, Reln, and Gtl2.


CONCLUSIONS
Transcriptional profiling of cerebellum failed to detect significant global changes in Mecp2-mutant mice. Increased transcript levels of Irak1, Fxyd1, Reln, and Gtl2 may contribute to the neuronal dysfunction in MeCP2-deficient mice and individuals with Rett syndrome. Our data provide testable hypotheses for future studies of the regulatory or signaling pathways that these genes act on.
Jordan
ChaRandle
C
Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5323, USA. csjordan@stanford.edu
Li
Hong Hua
HH
Kwan
Helen C
HC
Francke
Uta
U
D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics; D002531:Cerebellum / Q000378:metabolism*; D004195:Disease Models, Animal; D016326:Extracellular Matrix Proteins / Q000235:genetics; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D051783:Methyl-CpG-Binding Protein 2 / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics; D011506:Proteins / Q000235:genetics; D062085:RNA, Long Noncoding; D000091042:Reelin Protein; D015518:Rett Syndrome / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000235:genetics
D015816:Cell Adhesion Molecules, Neuronal; D016326:Extracellular Matrix Proteins; C422882:MEG3 non-coding RNA, mouse; C497393:Mecp2 protein, mouse; D008565:Membrane Proteins; D051783:Methyl-CpG-Binding Protein 2; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D011506:Proteins; D062085:RNA, Long Noncoding; D000091042:Reelin Protein; C069141:phospholemman; D053592:Interleukin-1 Receptor-Associated Kinases; C507769:Irak1 protein, mouse; C000717127:RELN protein, human; C000717128:Reln protein, mouse; D012697:Serine Endopeptidases