Donovan 3

Question 1

What is the important role of Igf2?

Answer 1

Binds to Igf2 receptor (sink) and Igf1 receptor (uses this to signal growth)

• Igf2 receptor prevents binding to Igf1 thereby REDUCING growth
• was a correction from lec 2*

Question 2

What is the fate of germ cells?

Answer 2

Sperm and Ovum

Question 3

What are common developmental mechanisms?

Answer 3

1) Cell-cell interactions
Cell adhesion
Junction formation
Signaling centers
2) Morphogenetic movements
Migration of individual cells 
Coordinated movement of groups of cells
3) Cell growth and proliferation
Increase in size, number of cells
4) Cell death
Programmed cell death
5) Differential gene expression
Differentiation

Question 4

Where do germ cells first arise? What molecule signals it?

Answer 4

At the end of the epiblast that will become caudal end of embryo

-Appearance of PGDs is brought by signaling of bone morphogenetic family of growth factors (BMPs) which are part of transforming growth factor-beta (TGFb)

Question 5

What is the pathway of TGF-b?

Answer 5

Uses Smad pathway
1) TGFb (ligand) causes receptors to dimerize (heterodimer) which autophosphorylate each other 2) this dimer phosphorylates Smad, activating it so that i can enter the nucleus and activate target genes

**there are multiple Smads and BMPs

Question 6

How does BMP4 release to induce formation of PGCs?

Answer 6

• acts in paracrine fashion
• release of BMP4 acts on local cells that have the receptor for it
• those differentiate into PGCs
• cells too far away don’t have enough concentration and thus don’t follow the same pathway

Question 7

What is needed for germ cell specification?

Answer 7

1) active gene transcription: BMP signaling in PGCs

2) Active gene silencing or repression: Blimp suppresses somatic genes

Question 8

What is BLIMP1’s function?

Answer 8

• B lymphocyte maturation (B lymphocyte-induce maturation protein)
• BUT MORE IMPORTANTLY: blocks the somatic cell differentiation of PGCs

Question 9

From the caudal end where do the germ cells go?

Answer 9

Morphogenetic movement from caudal epiblast to gut tube (movement happens as new lineages form and the cells are “pushed” into the gut)

Question 10

From the gut where do the PGCs go?

Answer 10

They migrate out of the gut and into the hindgut mesentery (toward descending aorta) and towards the develop gonads.

PGCs are the “hotdog” in the “bun” (gonad)

Question 11

How do the cells migrate to gonad?

Answer 11

• Active cell migration
• Cell substrate adhesion (used to follow correct path; imagine ice skates for land vs. ice)
• Chemotaxis
• Regulated apoptosis (use to destroy cells that migrate to wrong place)

Question 12

What happens if a germ cell does not follow the right path?

Answer 12

If they don’t migrate to right place, they undergo programmed cell death (apoptosis)

Question 13

What is the role of integrins?

Answer 13

Allows for cell adhesion to fibronectin and laminin. Also allow for actin polymerization (lamellipodia). Without it, PGC make it to gonad in highly reduced numbers

-act through a phosporylation cascade involving Src and FAK

Question 14

What is the KIT signaling pathway?

Answer 14

KIT uses a tyrosine kinase to phosphorylate many different pathways.

-one of which is PI3K which in turn activates AKT. This is important in cell survival and proliferation and adhesion

Question 15

What happens in mutation of C-Kit?

Answer 15

No germ cell signaling so we get severely reduced number of germ cells.

-low germ cells numbers can stimulate the tissue more and can lead to ovarian or testicular cancer

Question 16

What is associated with Kit mutations?

Answer 16

Kit mutations affect neural crest cells and PGCs.

Question 17

If you encountered an infant with spotting and determined it was due to a C-Kit mutation what symptoms other than spotting might you expect ?

Answer 17

Can get defect of blood system (hematopoietic) system

Question 18

What does SDF-1 and CXCR4 do?

Answer 18

SDF-1 binds to CXCR4 receptor (GPCR family) and is used to guide migration (does not cause the migration itself)

• is a chemokine receptor
• not all or nothing in mutation, you have “backup” pathways

Question 19

Why is primordial germ cell development dependent on multiple extracellular ligands ?

Answer 19

provides key and lock mechanism; cells only survive at right time and right place. proliferate at right time to the right place. controls development. has backup as well so if you lose one pathway you don’t automatically die.

Question 20

What is BCL-2?

Answer 20

Very important ligand for controlling number of cells

• activation promotes cell survival
• Bax and Bad promote cell death
• act at surface of mitochondrial membrane

Question 21

How does PTEN affect the cell survival pathway?

Answer 21

In PI3K pathway, PTEN acts to inhibit signaling through AKT/PKB

• AKT/PKB signaling increases cell survival
• PTEN is a tumor suppressor (inhibits cell survival)

Question 22

What happens in PTEN knockouts with PGCs in the wrong locations?

Answer 22

They survive instead of undergoing apoptosis.

Question 23

What happens to a meiosis-competent germ cell with high retinoic acid (RA)? low RA?

Answer 23

High RA -> meitoic germ cell (female)

Low RA -> G0 germ cell (male)

Question 24

How do differentiated cells develop?

Answer 24

1) Early events of germ cell development are brought about by induction of transcriptional programs by growth factor signaling.
2) Repression of other transcriptional programs is also important for specification of the lineage.
3) Once germ cells are formed both morphogenetic movements of the embryo and their own active migration bring them to the gonad.
4) Germ cell numbers are regulated by multiple signals to ensure that the right numbers of cells arrive at the right place at the right time