Landsberger: Lecture XXIII

Question 1

What are the main mechanisms in which defects in DNA methylation can cause human disorders?

Answer 1

damages on DNA: cause tumors or genetic disorders

aberrant silencing of gene expression: causes genetic disorders (RTT, ICF) *aberrant means large number of genes are affected

aberrant expression of specific genes: cancer

diseases associated with imprinting Beckwith-Wiederman syndrome, Angelman syndrome (genes that are not usually expressed become expressed)

Question 2

What is Rett Syndrome (RTT)?

Answer 2

genetic and progressive neurological disorder, which is rare as it only occurs in 1/6,000 humans

mainly in girls1st cause of severe intellectual disability in girls

Question 3

What are some features associated with RTT/

Answer 3

severe ID
loss of expressive language
purposeful hand use
apraxia
breathing abnormalities
epilepsy
hypotonia
scoliosis
constipation
osteoporosis
bruxism
minor heart problems

Question 4

What is RTT linked to?

Answer 4

X chromosome since the pathology mainly affects females & it is sporadic

caused by McCP2

Question 5

What is MeCP2?

Answer 5

reader of DNA methylation that brings histone acetylases on DNA → transcriptional repressor that binds methylated DNA and silences gene expression reading methylated CpGs without sequence specificity

Question 6

What does MeCP2 do in neurons?

Answer 6

functions as a chromatin condensing factor

Question 7

What other gene has been linked to RTT?

Answer 7

CDKL5 (kinase ubiquitously expressed and the cause for an independent genetic disorder)

Question 8

WHat other disorders can a mutation in MeCP2 cause?

Answer 8

RTT in females

neurological disorder in males

neonatal encephalotomy

Klinefelter condition where 1/2 MeCP2 alleles located on the X chromosome is mutant

Question 9

What are loss of function mutations?

Answer 9

autism
Angelman like syndrome
X-linked mental retardation
learning disabilites
schitzophrenia

Question 10

What are gain of function mutations?

Answer 10

duplication of the wild type gene (usually in boys)

*now called MeCP2 duplication syndrome

Question 11

What 2 functions can mutations on MeCP2 cause?

Answer 11

gain or loss of function

Question 12

What happens when a boy has a MeCP2 duplication syndrome disorder?

Answer 12

they have 2 or 3 copies of the wild gene (more copies increases severity)

usually die due to food getting stuck in the lungs

Question 13

What is the clinical severity of RTT affected by?

Answer 13

X activation patterns (generally skewed)
MeCP2 mutations
presence of modifier genes

Question 14

What is a problem with the null mice that are being used to study RTT?

Answer 14

the studies are being performed in males, but we cannot propose a clinical trial without testing a females (which is difficult since females respond diversely to drugs due to hormones)

Question 15

What is MeCP2 required for?

Answer 15

everything in our brain, neurons and astrocytes

Question 16

What goes on in the brain of the mice depleted of MeCP2?

Answer 16

there is a reduced volumed believed to be caused by neurons that do not contain MeCP2, which are smaller in the soma, less arborized, and have less spine in synaptic contacts

*this leads to a brain with the number of cells that are the same as a normal one, but everything has higher densities and leads to a smaller brain

Question 17

What kind of disorder is RTT?

Answer 17

synaptogenesis disorder

there are less contacts so networks are not functioning properly

Question 18

Why did Adrian bird inject tamoxifen into mice that lacked MeCP2?

Answer 18

in order to remove the stop codon and reactivate the endogenous gene → disorder is reversed in mice

Question 19

How can we treat MeCP2 mutations in humans?

Answer 19

augmentative gene therapy or protein therapies, the conventional gene therapies

Question 20

What are some problems with treating MeCP2 with augmentative gene therapy or protein therapies?

Answer 20

it is hard to get good viruses with good diffusions in the brain and be able to control dosage levels

there is general toxicity of the high dosage of MeCP2 that the virus could induce

Question 21

What is MePC2 relevant for?

Answer 21

wildtype neurons and astrocytes

Question 22

What exactly is Rett syndrome?

Answer 22

a disorder in which the lack of an epigenetic reader causes gene expression to be affected

*probably caused by a subtle activation or deactivation of different genes

**dominant disorder

Question 23

What does ICF syndrome stand for?

Answer 23

immunodeficiency, centromere instability, and facial anomalies syndrome

Question 24

What is ICF syndrome?

Answer 24

genetic recessive disorder where the mutated gene is mainly DNMT3B (50% of patients)

Question 25

How can we diagnose patients with ICF syndrome?

Answer 25

have lots of infections due to terrible immunity

blood test is performed and shows aberrant chromosome shape

patients usually only survive to 10 years

Question 26

The bottom line is we are going to get ICF if the DNMT3B is not ____

Answer 26

properly targeted on the right region of the genome or if the protein is not functining in a proper way

Question 27

What are 2 contradictory features usually found in cancer?

Answer 27

hypomethylation and hypermethylation

Question 28

What does hypomethylation affect?

Answer 28

regions where methylation mostly occurs (ones relevent for genome defense: transposons, viruses, repetitive elements)

Question 29

What can hypomethylation do?

Answer 29

induce activation (dangerous for genome stability)

activate sequences (start to jump and produce viruses)

Question 30

What kind of genome do cancer cells need?

Answer 30

unstable genome

Question 31

What are the genes that are usually hypermethylated?

Answer 31

tumor supressor genes

Question 32

Why is the pattern of methylation in tumor suppressor genes important?

Answer 32

helps us discriminate different kinds of cancers

helps us see the progression and see how much the cancer is advancing