Chapter 5: Stem Cell Niches I

Question 1

Pluripotent stem cells in embryos can be found in

Answer 1

the inner cell mass of the blastula stage

Question 2

A blastula is __ cells

Answer 2

128 cells. contains a blastocoele and ICM, surrounded by trophectoderm. Before the blastula stage, at 8(still zygote)-16-64 cells, the embryo is a morula and it is totipotent.

Question 3

In a blastula, the trophectoderm cells surround the ____ ___ __ and ___

Answer 3

inner cell mass and blastocoele cavity.

Question 4

ICM gives rise to ___ and ___. what do these structures do/give rise to?

Answer 4

ICM gives rise to epiblast and primitive endoderm.

epiblast: gives rise to all cell types of a mammal by producing embryonic stem cells. ESCs retain their pluripotency and are continuously/infinitely dividing in lab conditions
primitive endoderm: form the yolk sac, chorion, and embryonic side of the placenta (extaembryonic) and creates a barrier between blasocoele cavity and trophoblast cells.

Question 5

Embryonic stem cells (ESCS) come from the ___ of ICM

Answer 5

epiblast of the ICM.

Question 6

what three TFs are needed for ICM cells to give rise to the epiblast and all the associated derived cell types

Answer 6

Nanog, Oct4, Sox2 required to maintain pluripotency (stem cells from epiblast). Ensures no differentiation will occur.

-expression of the 3TFs is lost as the epiblast begins to differentiate.

Question 7

the transcription factor ____ gets upregulated in the outer cells of the morula, which promotes trophectoderm differentiation and represses epiblast development.

Answer 7

the transcription factor CDX2 gets upregulated in the outer cells of the morula, which promotes trophectoderm differentiation and represses epiblast development.

Question 8

How is the ICM created from the trophectoderm.

Answer 8

usually, the trophectoderm divides meridionally to create more trophectoderm.

• if trophectoderm divides equatorially, one cell becomes ICM/epiblast and the other starts as a trophectoderm.

in trophectoderm cells there is a cellular polarity around the apico-basal axis. There is already a TF/protein gradient in the pre-blastocyst stage.

Question 9

in trophectoderm cells there is a cellular polarity around the ___-___axis which allows for trophectoderm to create ICM through equatorial division around the ____-___ axis.

Answer 9

in trophectoderm cells there is a cellular polarity around the apico-basal axis which allows for trophectoderm to create ICM through equatorial division around the apricobasal axis.

Question 10

In the morula, how is the trophectoderm and ICM formed?

Answer 10

there is an asymmetric factor (aPFC) localization around the apicobasal axis of a morula that is formed in the cells that will become the trophectoderm.

• partitioning protein factors recruits E-cadherin to the basolateral membrane where the outer cells contact the future ICM cells.
• E-cadherin is involved with cell segregation and proper cell-sheet formation

-Ecadherin recruitment to basolateral membrane of morula cells trigger formation of cell mass and induces partitioning between trophectoderm and ICM.

Question 11

What would happen if you removed Ecadherin/prevented Ecadherin formation in the morula

Answer 11

removing Ecadherin results in disrupted apicobasal polarity and specification of both ICM and trophectoderm cells.

Question 12

How is Ecadherin implicated in induced pluripotency in ICM cells?

Answer 12

Ecad binding between trophectoderm and ICM cell’s AMOT activates Hippo pathway in the ICM cell. Activated Hippo pathway INHIBITS Yap-Taz-TEAD TF complex. Causes induced pluripotency in ICM cells through Oct 4 activation

Question 13

Induced pluripotency of cells in ICM: Ecad activates ___ pathway. Activated ___ pathway INHIBITS ___-___-___TF complex. Causes induced pluripotency in ICM cells through ____ activation. Allows for epiblast (ESCs from ICM) formation

Answer 13

Ecad activates Hippo pathway. Activated Hippo pathway INHIBITS Yap-Taz-TEAD TF complex. Causes induced pluripotency in ICM cells through Oct 4 activation

Question 14

Usually, Yap-Taz activates ___ and ___ paracrine factor. What does this do?

Answer 14

Usually, Yap-Taz activates Wnt and TGFBETA paracrine factor. Shuts off ability for cell to keep proliferating.

Question 15

Yap/taz inhibition via hippo pathway activation allows for pluripotency maintenance in ICM cells through Oct 4 activation. Usually, Yap/taz associated with ___ to promote the expression of ____, which promotes trophectoderm differentiation

Answer 15

Yap/taz inhibition via hippo pathway activation allows for pluripotency maintenance in ICM cells through Oct 4 activation. Usually, Yap/taz associated with TEAD to promote the expression of CDX2, which promotes trophectoderm differentiation

Question 16

In order to activate the Hippo pathway and activate Oct 4 via repression of Yap/taz, which usually regulates the expression of CDx2-tead, what does Ecadherin of the trophoblast cell bind do in the ICM cell?

Answer 16

Ecadherin binds to Amot to induce the hippo pathway. Hippo pathway inhibit Yap/Taz. Yap/Taz inhibition prevents CDX2 expression, and activates OCt 4 to maintain pluripotency.

Question 17

If there was no Ecadherin-induced Hippo activation in an ICM cell, What would happen

Answer 17

no hippoactivation = yap/taz/tead complex activation. Results in upregulation of Cdx2 expression. Directs cells to trophectoderm.

Question 18

Hippo signaling represses the Yap-Taz-Tead transcriptional complex, IN THE ICM, the result is THE _____________________________

In the outer cells, the apically positioned partitioning proteins inhibit Hippo signaling, leading to an active Yap-Taz-Tead tran- scriptional complex, an upregulation of cdx2, and THUS THE ______

Answer 18

Hippo signaling represses the Yap-Taz-Tead transcriptional complex, and in the ICM, the result is the maintenance of pluripotent ICM development through Oct4.

In the outer cells, the apically positioned partitioning proteins inhibit Hippo signaling, leading to an active Yap-Taz-Tead tranScriptional complex, an upregulation of cdx2, and the trophectoderm fate

Question 19

Ovary in adults contain what kind of stem cells

Answer 19

germ stem cells. GSCs

Question 20

in drosophila, egg production occurs in ___, which house GSCs as well as ___ cells that make the niche.

Answer 20

in drosophila, egg production occurs in 12 tubes of ovarioles, which house GSCs as well as germanium cells that make the niche.

Question 21

As a GSC divides, it renews to form a ____ that matures as it moves farther out of the stem cell niche. As it moves out of the way of the niche’s regulatory signals, it comes an ___.

Answer 21

cytoblast. As it moves far away, it becomes the mature oocyte that can be fertilized.

Question 22

Binding of a GSC to a ___ cell via ___ (type of segregation and organization protein) prevents GSC differentation.

Answer 22

Binding of a GSC to a CAP cell via ECADHERIN (type of segregation and organization protein) prevents GSC differentation.

-when GSCs divide beside CAP cells, one daughter cell will become tethered to the CAp cell via ecadherin, and the others form an oocyte as it moves away from the cap cell. therefore, binding to the ecad prevents GSC differentiation.

Question 23

Binding of a GSC to a ___ cell via ___ (type of segregation and organization protein) prevents GSC differentation.

Answer 23

Binding of a GSC to a CAP cell via ECADHERIN (type of segregation and organization protein) prevents GSC differentation.

-when GSCs divide beside CAP cells, one daughter cell will become tethered to the CAp cell via ecadherin, and the others form an oocyte as it moves away from the cap cell. therefore, binding to the ecad prevents GSC differentiation.

Question 24

Explain the maintenance and proliferation of GSCs in drosophila ovary

Answer 24

• CAP cells secrete TGFbeta
• TGFbeta exerts effects on GSC by binding to receptors, resulting in BMP activation in GSC
• BMP activation in GSC results in the activation of MAD/MED, which inhibits BAM genes.
• BAM genes usually promote differentiation into oocyte.
• if BAM is inhibited because of BMP signal transduction and MAD/MED recruitment, the GSC stays in proliferative stage and does not turn into an oocyte.

Question 25

in drosophila ovary, how is it ensured that only GSCs near CAP cells remain proliferative while GSCs further away from CAP can differentiate?

Answer 25

Collagen, ECM and heparan sulphate proteoglycans prevent TGFbeta proteins from travelling far from source cells.
-ensures that only cells close to the cap proliferate. If far away from the Cap cells, Bam is expressed and the GSC cells can form an oocyte

Question 26

cell generation occurs in the ___ of the adult digestive system

Answer 26

crypts

Question 27

ISCs (intestinal stem cells) can give rise to three main types of digestive system cells. waht are they?

Answer 27

1) enterocytes (absorption)
2) goblet (secretion)
3) enteroendocrine (secretion)

Question 28

division of cells in the crypt of a villi force cells to move up the crypt towards the villli. As they move further up the base of the crypt, they

Answer 28

differentiate into enterocytes, goblet cells or neteroendocrine cells when they move closer to the tip of the villi. At the very tip, they get shed off.

Question 29

intestinal stem cells with __ protein can generate all the differentiated cells of the intestinal epithelium. What are these stem cells called.

Answer 29

LGR protein. LGR+ stem cells = CBCCs = crypt base columnar cells.

Question 30

CBCCs are located in the crypt near __ cells

Answer 30

paneth cell

Question 31

when CBCCs are near paneth cells, they :

Answer 31

remain as stem cells. Daughter cells that drift away from paneth cells will move away from the base and undergo differentiation and become a progenitor cell.

Question 32

In order to keep CBCCs in proliferative state and prevent differentiation, Paneth cells produce ___ and __-, an activator of __

Answer 32

In order to keep CBCCs in proliferative state and prevent differentiation, Paneth cells produce WNT3A AND DII4, an activator of NOTCH.

• recall, notch binds to delta and causes gene expression by getting cleaved by a protease and acting on CSL TF and displacing a repressing factor. Also recruits P300 to activate target genes.

Question 33

DII4 binding to Notch on CBCC induces proliferation and differentiation by inducing gene expression in the CBCC, which preferentially turns the cell into __ or ____

Answer 33

DII4 binding to Notch turns the CBCC into goblet or enteroendocrine cells rather than enterocytes.

Question 34

in the digestive tract, __ cells are found just below the crypt cells. What does it secrete?

Answer 34

Stromal cells are loated just below the crypt cells. Secretes Wnt2b with HIGH LEVELS at crypt base.

Question 35

Wnt2b is secreted by stromal cells with high levels at the crypt base, but what gradient is opposing it?

Answer 35

There is an opposing BMP4 gradient with high concentrations at the top of the crypt.

Question 36

CBCCs expressing ___ and ____ can bind to Wnt2b and BMP4. What does this induce?

Answer 36

CBCCs expressing Frizzled7 and BMPR1a can bind to Wnt2b (secreted by stromal cells underneath the crypt cells) and BMP4.

• Wnt signalling promotes survival and proliferation of CBCCs and progenitor cells, whereas BMP (top of villi) promotes differentiation.

Question 37

IN INTESTINAL STEM CELLS: Wnt signalling promotes _______ of CBCCs and progenitor cells, whereas BMP (top of villi) promotes _____.

Answer 37

• Wnt signalling promotes survival and proliferation of CBCCs and progenitor cells, whereas BMP (top of villi) promotes differentiation.

Question 38

in addition to CBCCs, what other cells are found in the crypt regions of villi

Answer 38

1) paneth: aids in proliferation/stem cell maintenance. via Wnt3a and DII4-notch interactions. DII4-notch also promotes the formation of goblet/endocrine cells rather than enterocytes when the CBCCS later drift away too.
2) Stromal cells. Secretes Wnt2b which binds to Frizzled7 on the receptors of CBCCs, promotes proliferation of CBCCs
3) +4 Cells.located near the paneth cells from the base of the crypt. +4 cells can also generate all the cell types of hte intestine. They just divide way slower, basically they are quiescent.