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ANAT 381 Experimental Embryology > Epigenetics IV: X-chromosome inactivation > Flashcards

Epigenetics IV: X-chromosome inactivation Flashcards

1
Q

What lead to dosage imbalances between homogametic and heterogametic sexes?

A

Dimorphic sex chromosomes

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2
Q

What are some properties of the inactive X chromosome (Xi)?

A

Compact structure, nuclear periphery, epigenetically inherited, H3K27me, H3K9me, hypoacetylation of histones, DNA methylation and Xist non-coding RNA

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3
Q

When does X-chromosome inactivation occur?

A

It randomly occurs in the embryo and is coincident with onset of differentiation

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4
Q

XCI occurs first specifically in the _____________ and affects the paternal X

A

Trophectoderm

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5
Q

Choice of which X is inactivated appears to be (chosen/random)

A

Random

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6
Q

Where does X-chromosome reactivation occur?

A

PGCs

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7
Q

Mosaicism is (epigenetic/genetic)

A

Epigenetic

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8
Q

What region of the chromosome allows X inactivation?

A

X inactivation center (Xic)

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9
Q

What is the role of Xist?

A

Coats the Xi and causes silencing in cis

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10
Q

Which cells can be used to study XCI?

A

Embryonic stem cells

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11
Q

How is Xist regulated?

A

Cis factors on the X chromosome and trans factors on the autosomes

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12
Q

Xist is regulated by (sense/antisense) transcription

A

Antisense

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13
Q

What is the negative regulator of Xist?

A

Tsix

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14
Q

Xist is detected by (sense/antisense) probes and Tsix is detected by (sense/antisense) probes

A

Sense; antisense

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15
Q

Removal of Tsix promoter from one X causes what effect for Xist?

A

Xist is activated in that X chromosome

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16
Q

X lacking Tsix is always (activated/inactivated)

A

Inactivated

17
Q

In males only (Xist/Tsix) is expressed

A

Tsix

18
Q

What represses the action of Xist?

A

Pluripotency transcription factors

19
Q

Rnf12 is an enzyme that is encoded on the X chromosome and causes the degradation of which trans transcription factor?

A

Rex1

20
Q

True or false: Degradation of Rex1 by Rnf12 causes X inactivation

A

True

21
Q

What are the general approaches for defining functions of Xist RNA?

A

Genetics and biochemistry

22
Q

Identify the results to the deletion of a Xist RNA repeat
a. No repression of transcription, but Xist can still localize to the X chromosome, recruitment of SPEN
b. No Xist localization to inactive X, repression compromised
c. No PRC association or H3K27me on inactive X but repression can still happen

A

a. Delete A repeat
b. Delete E repeat
c. Delete C repeat

23
Q

True or false: XCI requires Xist for maintenance

A

False

24
Q

What does stable maintenance of XCI in the embryo require?

A

DNA methylation by DNMT1 and DNMT3B and hypoacetylation of histones

25
Q

CGI is (unmethylated/methylated) at promoters on inactive X

A

Methylated

26
Q

Where does reactivation of the inactive X occur?

A

PGCs

ANAT 381 Experimental Embryology (24 decks)

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