Additional levels of regulation

Transcription

1 Transcription Regulation And Gene Expression in Eukaryotes Cycle G2 (lecture 13709) P. Matthias, May 26th, 2010 Additional levels of regulation Gene organization/localization Allelic exclusion AIRE: a special (?) example of gene regulation DNA Methylation

2 Some cellular structures: interdependency of compartments?

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4 Gene gating: it s all about location Actin Myc TGFb

5 Chromosome territories and various nuclear bodies

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7 The nuclear periphery: lamins and others

8 Lamins

9 Lamins network

10 Lamins mutations

11 Lamin mutations disrupt heterochromatin organization HGPS: Hutchinson-Gilford progeria syndrome (Point mutation in LaminA gene)

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13 Choreography within the cell nucleus: Ig genes and allelic exclusion Stem cell prob cell preb cell

14 Choreography within the cell nucleus: Ig genes

15 Odorant receptor (OR) genes: > 1000 genes, only 1 expressed

16 Odorant receptor (OR) genes: > 1000 genes, only 1 expressed

17 Odorant receptor (OR) genes: > 1000 genes, only 1 expressed

18 An interesting example of gene regulation: AIRE

19 Immune Tolerance State of immune system unresponsiveness to an antigen. Failure to respond to an antigen Tolerance to self antigens: Essential feature of the immune system Loss of tolerance to self: Destruction of self tissues, autoimmunity Central Tolerance: Tolerance established in lymphocytes developing in central lymphoid organs Peripheral Tolerance: Tolerance acquired by mature lymphocytes in the peripheral tissues.

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21 An interesting example of gene regulation: AIRE APECED: Autoimmune Polyendocrinopathy-Candidiasis- Ectodermal Dystrophy APSI: Autoimmune Polyglandular Syndrome type I OMIM Nr Destructive autoimmune reactions against e.g. parathyroid or thyroid glands, adrenal cortex, gonads, β cells (pancreas), gastric parietal cells, Gene responsible for disease was cloned: AIRE/aire

22 The AIRE protein

23 Transcription activation by AIRE

24 How does AIRE work?

25 Promiscuous gene expression

26 Promiscuous gene expression

27 Promiscuous gene expression

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29 Clustering of AIRE-regulated genes

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32 Effects of DNA methylation: biological Methylation causes (correlates with): Promoters to be switched off by changing the interaction between DNA and transcription factors and/or chromatin structure X-chromosome inactivation Lack of expression from repetitive and parasite DNA sequences Imprinting Cancer

33 Effects of DNA methylation: biochemical The presence of the methyl group alters the appearance of the major groove of DNA and thus can affect the binding of transcription factors The positions of 5-methyl cytosine can be passed on during DNA replication (by maintenance methylases ) and thus act as a long-term molecular markers

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35 Significance of CpG dinucleotides In mammalian genomes the dinucleotide sequence CpG occurs at only 25% of the expected frequency >98% of C residues in CpG motifs are methylated Methylated C residues mutate to T (deamination) at a very high rate CpG deficiency thus corresponds precisely to expectations based on C -> T mutation rates!

36 Distribution of DNA methylation in the gene(ome) Weber & Schübeler, COCB 2007

37 DNA methyltransferases

38 Establishment of DNA methylation patterns

39 Methylation-free CpG islands

40 Establishment of DNA methylation patterns

41 Methylated DNA binding proteins

42 Mechanisms of repression

43 Dynamic regulation by methylation

44 Dynamic regulation by methylation

45 MeCP2 MeCP2 is an abundantly expressed DNA-binding protein, located in the nucleus and associated with 5-methylcytosine-rich heterochromatin Two known functional domains an 84 aa methyl-cpg-binding domain (MBD) a 104 aa transcriptional repression domain (TRD) The MBD binds to symmetrically methylated CpG dinucleotides, and the TRD recruits the co-repressor Sin3A

46 MeCP1 is a complex

47 Diseases caused by mutations in the methylation machinery

48 Diseases caused by mutations in the methylation machinery

49 Diseases caused by mutations in the methylation machinery

50 Diseases caused by mutations in the methylation machinery