Basics Flashcards
Biochemical process of methylation?
Addition of methyl group (CH5) to the C5 position of cytosine to firm 5-methylcytosine
2 main ways to modify his tones
Acetylation/deacytylayion
Methylation/demethylation
Examples of epigenetic diseases
Di George - DGCR8 -RNA binding protein
Rubinstein Taybi - CREBBP (histone acetylation)
ATRX - hypomethylation of repeat elements
Rett - MECP2 - 5MeC binding protein
FRAX - methylation promoter
FSHD
COFFIN - Lowry - RSK2 (histone phosphorylation)
SOTOS -NSD1 - histone methyltransferase
BWS/RS - abnormal methylation 11p
PWS/AS Ann methylation 15q11-13
How does methylation causes cancer?
Hypomethylation leads to increased genomic instability
Loss of imprinting e.g. IGF2 - lung, liver, CFC
Switching off TSG e.g. MLH1
Hypermethylation can lead to instability at micro satellites
Change in histone modification patterns - HAT genes altered leading to loss of H3 acetylation on TSGS
Imprinted genes - how many?
40-60 e.g. UBE3A, SNRPN, GNAS
Imprinting disorders
Beckwith- wiedemann Russell silver Prader willi Angelman Maternal UPD14 Paternal UPD14 transient neonatal diabetes mellitus familial nonchromaffin paraganglioma PHP1b, Albright hereditary osteodystrophy
Mechanisms leading to imprinting disorder
UPD
Deletion e.g. Pws/AS
Duplication e.g. IC1 region of 11p
Mutation on active allele
Epimutation - loss or gain mutation without change to DNA sequence
How big is the mitochodrial genome and how many genes?
16.6kb circular dsDNA molecule With 37 genes (13 polypeptides of OXPHOS system, 2 ribosomal RNAs and 22 tRNAS)
Features of mitochondrial DNA
No introns
Very few non-coding based
Termination coding are created post transcriptionally
Higher mutation frequency than nDNA (10x) - possibly due to close proximity to inner mt membrane - increased damage through leakage of reactive oxygen species
Transmitted through maternal line
Each cell can contain thousands of copies of genome (depends energy demand)
What sorts of disorders do mt DNA cause?
Primary mt disease
Neurodegenerstion
Cancer
Also contributes to decline in tissue integrity with age
Dysfunction of mt respiratory chain (if cell can’t produce enough ATP via OXPHOS may shunt lyric are to lactate causing systemic lactic acidosis)
What tissues might be affected by mitochondrial disease?
Some multi organ typically Tissue with high metabolic rate E.g. Nervous system, skeletal, cardiac B cells of islets of langherhans Inner hair cells of cochlea Renal tubules
Some single organ e.g. eye in LHON
3 mitochondrial deletion syndromes
Pearson - pancytopoenia, anaemia, lactic acidosis, pancreatic failure, infancy
Kearns-sayre - progressive myopathy, deafness, opthalmoplegia, cardiomyopathy, adult
Chronic progressive external Opthalmoplegia -opthalmoplegia, ptosis, impaired eye movement
All several genes, all heteroplasmic, usually sporadic
7 point mutation mitochondrial genome conditions
MELAS MERFF LHON LEIGH AID NARP MIDD
MELAS - symptoms and gene
Mitochondrial Encepalopathy, lactic acidosis and strike-like symptoms
Mt TL1 gene
MERRF?
Myoclonic epilepsy and red ragged fibres
Myopathy, cerebral ataxia
NARP?
Neurogenic weakness, ataxia, retinitis pigmentosa. ATP6
MIDD
Maternally inherited diabetes and deafness. Mt TL1 - sane mutation as MELAS
Leigh/Leigh like mito syndrome?
Encephalopathy, lactic acidosis
LHON?
Lever hereditary optic neuropathy
Sub acute bilateral vision failure and optic atrophy
Mitochondrial mutation for aminoglycide induced deafness
M.1555A>G
Mechanisms of mitochondria disease
Mutations in mt DNA
Mutations in nDNA affecting mtDNA maintenance and expression
Mutation nDNA NOT affecting mt maintenance/expression
Features of ASO?
Antisense oligonucleotide
Small single stranded DNA/RNA molecule
Affect translation by binding mRNA and blocking or altering translational mechanism
Can block production of aberrant protein, correct aberrations by exon skipping or correction splicing mutations
Chemicals modified to prevent nuclear degradation
Enter cell via endocytosis so need to survive endosome until broken down and released cytoplasm
Challenges of using ASO in drug treatment?
Delivery to target tissue
Achieve sustained effect
Require re administration
Difficult to achieve complete inhibition as large quantities of mRNA and lower levels ASO within the cell
How many protein coding genes in exome?
23,000
