alvey Flashcards
generally paternal alleles want offspring to be what?
big
generally maternal alleles want offspring to be what
equal size and manageable
how was it shown that both maternal and paternal genes are essential for embryo development
gynogenetic diploid were inviable and androgenetic diploids were inviable
as even the XX individuals did not survive what could the authors conclude
that inviability was not caused by the sex chromosomes
imprinting is essential for normal development in mammals T/F
T
Imprinting is important for development of what animals
development of long lived animals with placenta
what is a classic example of an imprinted gene
IGF-II
what is IGF-II
insulin like growth factor II gene
what kind of imprinting does IGF-II go under
maternal imprinting
if IGF-II is knocked out what size mice
small mice
when the IGF-II mutation is transmitted through which germline does it result in heterozygous progeny that are growth deficient
male
- When the disrupted IGF-2 gene is transmitted maternally, the heterozygous off-spring are
phenotypically normal
how was it concluded that inheritance of Igf-2 and phenotpye was not a dosage effect
Homozyous mutants are indistinguishable in appearance from growth-deficient heterozygous siblings
in mice the paternal and maternal members of some autosomal gene pairs are functionally…
non equivalent
- Only the paternal allele of IGF-2 is expressed in embryos, while the maternal allele is silent
T
what is maternal imprinting
allele of a particular gene inherited from mother is transcriptionally silent (not expressed
direct observation of phenotype is governed by paternal allele
what is paternal imprinting
allele of a particular gene inherited from father is transcriptionally silent
direct observation of the phenotype is governed by maternal allele
usually in diploid species, if a defective copy of a gene is inherited there is a second functioning copy from the other parent that can compensate for this loss. what is this not true for
imprinted genes
in imprinted genes - Even though there are two copies of the gene, as only one copy is expressed, mutations affecting this copy will result in disease. T/F
T
- Situations that result in both copies of a gene being silenced will also lead to expression of the disease. this is known as …
uniparental disomy (UPD)
- An imprinted region of the human genome that contains Ifg2 (the human homologue of IGF-II mouse gene) causes a paternally inherited disease called what
Beckwith-Weidemann syndrome
what is beckwith weidemann syndrome?
pediatric overgrowth disorder involving a predisposition to tumour development
- mutation in dad germline results in hypermethylation of IC1
- daughter now has active copy of IGFR2 from dad. the maternal copy is silenced
- has child that has active copies from both parents so has BWS
T
what is prader willi syndrome characterised by
obesity, behaviour and cognitive problems. deficiencies in sexual development
in the gene that causes preader willi and angelmans which copy of the gene normally gets expressed and which is normally silenced
dad -expressed
mums - silent
what happens in prader willi syndrome
paternal gene doesnt get expressed so no forms of the gene are expressed
how is the paternal gene not expressed in prader willi
deletion of PW genes maternal UPD (silent) mutation in imprinting centre leading to methylation of paternal gene epimutation - wrong methylation (not erased from mother) translocation to move the genes away from imprinting centre
which gene causes angelmans syndrome and where is it usually expressed
UBE3A - only expressed on maternal
paternal mutations in chromsome 15 lead to what
prader willi
maternal mutations in chromosome 15 leads to what
angelmans
what can angelmans syndrome be caused by
maternal deletion of praderwilli region
mutation of UBE3A
UPD (father)
what are the symptoms of angelmans
developmental deficiencies
sleep disorders
seizures
happy diposition
what are the symptoms of temple syndrome
small stature
developmental delay
small hands and feet
central obesity developing with age.
what imprinted region is involved in temple syndrome
14q32
what causes temple syndrome
UPD - maternal
deletion of region
mutation in imprinting region
when can UPD occur
after trisomy rescue due to a nondisjunction event
what enzyme is involved with marking euchromatin
histone acetyl transferase - targets H3 tail. this is then a docking site for bromo-domain proteins which stimulate nucleosome assembly
which enzymes are involved in repressing chromatin
histone lysine methyltransferases - methylate the H3 tail and provides docking site for heterochromatin protein 1 (HP1). this impairs nucleosome accessibility
demethylation of CpG islands at promoter sequences is associated with what?
active genes
methylation at CpG islands is associated with what?
silencing of the gene
at a maternally imprinted locus, the promoter would be …
methylated
the entire genome is methylated and demethylated how many times during gamete development and fertilisation
2 once during gamete development and once after fertilisation
imprinted genes always exhibit the methylation pattern of the parent in eggs and sperm regardless of whether they came from maternal or paternal genome. resetting is done when?
primordial germ cell to gametes stage
imprinted genes are reset in the developing gamete and bypass the epigenetic reprogramming when
in early embryo
what is the purpose of genome wide epigenetic reprogramming in gamete
reset imprinted 1.genes for sex of embryo
- erases parental or acquired epigenetic memories
- facilitates gametogenesis
- maintain the silencing of transposable elements
- reduces mutation rate in germline
what is the purpose of genome wide epigenetic reprogramming in pre-implantation embryo (2)
resets zygotic epigenetic genome for naive pluripotency
some evidence of maternal vs paternal wars
during gamete formation imprinting genes change their status. in preimplantation embryo imprinted genes….
are protected
imprinted genes act like the rest of the genome in gamete formation. Do not act like the rest of the genome in pre-implantation embryo T/F
T
during migration of PGCs somatic epigenetic memories are erased by what techniques
- global DNA demethylation
- genomic imprint erasure
- X-chromosome reactivation
- reorganisation of chromosome
remethylation occurs first in males/females
males
remethylation begins when in males
spermatogonial stem cells E13.5
remethylation begins when in growing oocytes
after birth
vast majority of ecapees from global demethylation are associated with what
retrotransposable elements
in preimplantation embryos the paternal genome is demethylated by what kind of mechanism
active mechanism
in preimplantation embryos the female genome is demethylated by what kind of mechanism
passive mechanism that requires DNA replication
the waves of demethylation and remethylation in the early embryo are essential for what
normal development and totipotency
- The mechanism by which some genes bypass the reprogramming is not known, but …… are a candidate mechanism
long noncoding RNAs
When does genome-wide demethylation occur during mammalian
development?
in gamete formation (primordial germ cells) and in preimplantation embryos
What would happen to an imprinted gene (e.g. UBE3 (causes
Angelman’s syndrome)) in the germline?
demethylated and maybe remethylated. reprogrammed
which enzyme carries out reacquisation of methylation
DNA methyltransferase
3A (DNMT3A)
what maintains methylation status
imprinted genes carry multiple motifs of 6 to 7 nucleotides (TGCCGC exactly), which will recruit a specific protein called ZFP57 only when this motif is methylated
how does ZFP57 maintain methylation status
Through its KRAB domain, ZFP57 brings its cofactor KAP1 to the chromatin, which in turn leads to the recruitment of repressive chromatin modifiers, including ESET/SETB1, which controls H3K9 trimethylation
mutations in ZFP57 causes hypomethylation at multiple imprinted loci
what are imprinted loci a barrier to (4)
cloning mammals
engineering reproductive cells
production of bimaternal and bipaternal mammals
generation of artificial gametes from somatic tissues
what was the first cloned mammal and how was the procedure carried out
Dolly the sheep
somatic cell nuclear transfer
what was the problem with dolly the sheep
there was no opportunity for resetting of methylation so the cell was not pluripotent
marks have been copied many times and copying of epigenetic marks is error prone
what are the steps to artificial gametes as a fertility treatment
- take somatic cell
- perform SCNT and induce embryo development in vitro
- extract embryonic stem cells from blastocyst
- induce gametogenesis in vitro
- use functional gamete to fertilise partners egg or sperm
- develop into embryo
- implant in mother
what were the man made mouse eggs made from
- embryonic stem cells
2. adult tail tip fibroblast
how do you make a man made mouse egg
- Fully in vitro method, primordial germ cell like cells are co-cultured with female gonadal somatic cells and hormones, inhibitors and other factors are administrated at key stages to stimulate the development of a follicular environment and to coordinate stages of egg cells maturation
how did they make bimaternal mice
oocyte activation and isolation of haploid ESCs
loss of maternal imprints in culture
genome editing of paternally imprinted regions - deleted 3 ICRs
injection of the haploid ESC into a mature oocyte
how did they make bipaternal mice
sperm injected into an enucleated oocyte
isolation of androgenetic haploid ESCs
loss of paternal imprints in culture
genome editing of maternally imprinted region - deleted 7 ICRs
coinkection of haploid ESC and sperm into an enucleated oocyte
it is thought that there is about how many imprinted loci in the mouse genome
100
what is the impact of the work of bipaternal/bimaternal mice in imprinting disoeders
- Could be used to model regulation of imprinting genes
- A technique for accurate reversible epigenetic switch between maternal and paternal imprinting
- Offspring from same sex parents
- Explore the feasibility of altering the regulation of imprinting genes might offer an approach to treat imprinting disorders
