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Silence of the Genes Genetics • The study of inheritance Gregor Mendel (1823-1884) Quic k Ti me™ and a T IFF (Unc om pres s ed) dec om pres s or are needed to s ee t his pic t ure. Mendelian Ratios Quick Time™a nd a TIFF ( Uncomp res sed) deco mpre ssor are n eede d to s ee this picture . Mutation Phenotype ATGCGATCGAGT Genotype ATGCGAGCGAGT Epigenetics • Heritable changes in gene expression that do not involve changes in DNA sequence. Epi-mutation Phenotype ATGCGATCGAGT Genotype ATGCGAACGAGT DNA Modifications Histone Modifications Proteins Nucleosome QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. DNA QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. histones DNA Methylation QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. CH3 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. histones Histone Methylation QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. CH3 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. histones Examples of Epigenetics X-Inactivation male XY female unequal expression XX inactivation XY equal expression X X Qu i ck Ti me ™a nd a TIFF (Unc om pres se d) de co mp re ss or are n ee de d to s ee th is pi ctu re . Barr Body Barr Body Quic kTime™ and a TIFF (Uncompres sed) dec ompres sor are needed to see this picture. Calico Cat black allele o Quick Time™a nd a TIFF ( Uncomp res sed) deco mpre ssor are n eede d to s ee this picture . X o XO black sector X X O orange allele oX X O orange sector Other Examples of Epigenetics Imprinting • Imprinted genes are expressed differently depending on whether they are inherited through the maternal or paternal parent. Horses and Donkeys QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. male female male female Quick Time™a nd a TIFF ( Uncomp res sed) deco mpre ssor are n eede d to s ee this picture . Gynogenotes • Embryos containing two female genomes – do not develop normally – fail due to underdeveloped extraembryonic placental tissue Androgenotes • Embryos containing two paternal genomes – result in abnormal (often overgrown) embryo – display overdeveloped extraembryonic placental tissue Maternal vs. Paternal Imprinting • Male genome wants to promote growth. • Female genome wants to inhibit growth. Resetting Methylation Patterns Primordial Germ Cells methylation male female developmental time Battle for Maintaining DNA Methylation Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Battle to Maintain Methylation methylation Fertilization developmental time Female Strategy Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Genes that promote growth Fertilization Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Male Strategy Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Genes that inhibit growth Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Antisense Fertilization Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Resetting Imprints is Important for Proper Development Dolly QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. • First mammal to be cloned from an adult cell. • Developed illness common in older sheep (arthritis) • Probably due to abnormal imprinting Gene Silencing Heterochromatin Densely staining condensed chromosomal regions; believed to be transcriptionally inert. Euchromatin A chromosomal region that stains normally; thought to contain the normally functioning genes. Heterochromatin B. McClintock Paul Fransz IV Heterochromatin • Centromeric regions • Telomeric regions Position Effect Variegation W+ heterochromatin W+ spreading W+ suppressed W+ enhanced Post-Transcriptional Gene Silencing Anti-Sense Sense Also Works? Guo and Kemphues, (1995) What is Causing Silencing? ? dsRNA Post Transcriptional ? Fire et al. (1998) RNAi ? Fire et al. (1998) RNAi dsRNA Dicer RISC AA A AA A RNAi dsRNA Dicer RISC AA A AA A RNA Silencing QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. cosuppression RNA Silencing Quick Time™a nd a TIFF ( Uncomp res sed) deco mpre ssor are n eede d to s ee this picture . quelling RNA Silencing Quic k Ti me™ and a T IFF (Unc om pres s ed) dec om pres s or are needed to s ee t his pic t ure. Post Transcriptional Gene Silencing (PTGS) RNA Silencing Quick Time™a nd a TIFF ( Uncomp res sed) dec ompr esso r ar e need ed to see this pictur e. QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. RNA Interference (RNAi) RNA Interference Quick Time™a nd a TIFF ( Uncomp res sed) deco mpre ssor are n eede d to s ee this picture . QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. Quick Time™a nd a TIFF ( Uncomp res sed) dec ompr esso r ar e need ed to see this pictur e. QuickTi me™ and a T IFF (Uncom pressed) decom pressor are needed to see t his pict ure. Quic k Ti me™ and a T IFF (Unc om pres s ed) dec om pres s or are needed to s ee t his pic t ure. DNA Methylation Mette et al. (2000) RNAi and Transcriptional Silencing Transcriptional Silencing Mette et al. (2000) Micro RNAs dicer Grishok et al. (2001) RNAi Genes in S. pombe? RNAi Genes in pombe? • Yes!! • Mutation of these genes results in loss of centromeric silencing. • Loss of RNAi reveals centromeric transcripts. • dsRNA from centromere targets transcriptional silencing. Cen Cen RNAi Small RNAs Cen RNAi Silencing Machinery Small RNAs Silencing Machinery Cen RNAi Small RNAs Cen RNAi • Is important for initiation and maintenance of heterochromatin at the centromere. • Could be involved in other silencing phenomena Where else may RNAi be functioning to silence genes? X Chromosome Inactivation (RNAi?) Xist Tsix Heard et al (2001) X Chromosome Inactivation (RNAi?) Silencing Machinery RNAi Xist Tsix Heard et al (2001) X Chromosome Inactivation (RNAi?) Silencing Machinery RNAi Xist Tsix Heard et al (2001) Imprinting (RNAi?) Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Silencing Machinery RNAi Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Antisense Small RNAs Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Q ui ck Ti m e ™ an d a T I FF ( U nc om p r es se d) de co m pr e ss or ar e n ee de d t o se e t hi s p i ct u re . Imprinting (RNAi?) Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Antisense Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Qu i ck Ti m e ™ an d a T IF F ( Un co m p re ss ed ) d ec om pr es so r a r e ne ed ed to se e t hi s p ic t ur e. Imprinting (RNAi?) Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Quick Time™a nd a TIFF ( Uncomp res sed) deco mpr esso r ar e need ed to see this pictur e. Silencing Machinery RNAi Heterochromatin Densely staining condensed chromosomal regions; are not necessarily transcriptionally inert. RNAi is important for its initiation and maintenance. Euchromatin Chromosomal regions that do not densely stain; thought to contain functioning genes that may be transcriptionally active.