Gene regulation in eukaryotes II: Epigenetics - Heterochromatin: function, structure, formation, and maintenance
44 important questions on Gene regulation in eukaryotes II: Epigenetics - Heterochromatin: function, structure, formation, and maintenance
In which two general forms does chromatin occur?
What are the differences between euchromatin and heterochromatin?
- Heterochromatin is more compact;
- Heterochromatin has an inhibitory effect on gene expression.
What are the three different functional roles of heterochromatin?
- Prevention of transposable element movement;
- Prevention of viral proliferation.
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How does heterochromatin silence genes?
What are transposable elements?
How does heterochromatin inhibit TE movement?
How does heterochromatin prevent viral proliferation?
Which two types of heterochromatin are there?
- Constitutive heterochromatin.
What is the difference between facultative and constitutive heterochromatin?
Where is constitutive often located within a chromsome?
What kind of sequences within the constitutive heterochromatin may have an important role in the formation of the compact structure?
How is constitutive chromatin remodeled in some species?
What is a hallmark characteristic of constitutive chromatin in yeast and animal cells?
What is the modification H3K9me3 an example of?
How do specific proteins bind to particular PTMs in nucleosomes?
What domains on the same protein as the reader domains modify chromatin?
What kind of domains remove PTMs?
How can reader domains contribute to the formation of heterochromatin?
What kind of histone PTM can cause transcription to be inhibited?
What is a difference in the stability of facultative and constitutive chromatin?
On what depends the heterochromatic state of facultative heterochromatin?
Where is facultative heterochromatin located within the chromosome?
What kind of repeat sequences does the DNA of facultative heterochromatin contain?
To what extent is facultative heterochromatin methylated?
What kind of PTMs are found in facultative chromatin?
What happens to the constitutive and facultative heterochromatin in the daughter cell after cell division?
What is higher-order structure?
Which 5 molecular events does heterochromatin formation involve?
- Binding of proteins to nucleosomes;
- Chromatin remodeling;
- DNA methylation;
- Binding of non-coding RNAs-
What are two consequences of those 2 molecular events?
- Higher-order structures, in which heterochromatin has the following characteristics:
- Closer, more stable contacts of nucleosomes with each other;
- Formation of loop domains;
- Binding of heterochromatin to the nuclear lamina.
Reader domains in which kind of proteins recognize the H3K9me3 modification?
How does HP1 contribute to a closer and more stable contact between nucleosomes?
What kind of proteins play a role in promoting the formation of loop domains, and how do they do that?
- condensin, which promotes chromosome compaction via loop domain formation;
- cohesin, which facilitates the formation of loop domains during interphase;
- CTCFs, which bind to sites containing three copie of a CCCTC sequence and then bind to each other. This promotes loop formation.
What are the nuclear lamina (NL)?
How are the chromosomal regions that are in contact with the NL called?
What are the 2 important roles of LADs?
- The genes in LADs are expressed at low levels, which suggests a role for LADs in gene repression.
What are the three phases of heterochromatin formation?
- Spreading;
- Barriers.
How does heterochromatin formation spread?
How is the spreading phase stopped, so that a euchromatic region is protected from heterochromatin?
- The barrier contains antisilencing protiens that counteract the effects of proteins required for heterochromatin formation (for example, enzymes that catalyze acetylation of histones).
What happens with epigenetic changes after cell division?
What kind of chromatin is established in embryonic development?
How are PTMs on histones transmitted from cell to cell during cell division (steps)?
- The original histones recruit chromatin-modifying and chromatin-remodeling complexes, which lead to changes in chromatin structure.
How does DNA polymerase contribute to the maintenance of heterochromatin structure in the daughter cells of cell division?
How do higher-order structures of chromatin play a role in maintaining heterochromatin structure after cell division?
Name 2 diseases that are due to abnormalities in heterochromatin formation, and tell what the problem in this disease is.
- Roberts syndrome: a loss-of-function mutation in a gene that encodes an acetyltransferase.
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