Week 6 Cell Differentiation & Stem Cells- Holy

Question 1

Mosaic development

Answer 1

cell fate is already assigned during cleavage, strict developmental plan in place

• removal of one of more cells will result in a INCOMPLETE EMBRYO
• not in mammals, only happens in “lower level” animals

Question 2

Regulative development

Answer 2

blastomere initally has similar developmental potencies, each capable of giving rise to a complete embryo. Differentiation responsive to enviornmental siganls

*removal of cells will still give you COMPLETE individual, fate not determine early on

Question 3

Monozygotic twins

Answer 3

cells fail to adhere together normally and fall apart into two masses, each mass is able to give rise to an entire individual if it occurs early enough

Question 4

Totipotent
Pluripotent
Multipotent
Unipotent

Answer 4

Totipotent- can give rise to all embryonic, and extra embryonic cell types and structures

Pluripotent- can give rise to all embryonic cell types and structures

Multipotent- can give rise to multiple (but not al cell types)

Unipotent- can give rise to just one type of cell

Question 5

Define Induction

Answer 5

ability of one cell to influence the development of another cell. How cell fate is specified during cell differentiation in humans

Question 6

What is a morphogen?

Answer 6

signal that alters cell fate

Question 7

Types of Signaling
Paracrine
Juxtacrine
Autocrine
Gradient

Answer 7

Paracrine- involves diffusible molecules

Juxtacrine- involves cell-cell contact

Autocrine- cells stimulate themselves

Gradients- important in embryonic developmen, responds to gradients of morphogens, depends on “amount” of morphogen

Question 8

How is trophoblast (outer) and inner cell mass fates decided?

Answer 8

Hippo signaling pathway

Cdx2 becomes expressed ONLY in trophoblast cells via hippo signaling

Hippo pathway remains active in inner cells (expresses Oct4, Nanog and Gata)

Question 9

Epiblast and hypoblast formation is decided by

Answer 9

differential expression of transcription factors!

Oct4/Nanog OR Gata (but not both)
Nanog/Oct4 = epiblast
Gata= hypoblast

Question 10

How is Dorsal-ventral determined?

Answer 10

Neural tube differentiation
Notochord induced ventral floor of neural tube to secrete SONICE HEDGEHOG

Overlaying ectoderm induces dorsal roof plate to secret BMP

Question 11

How is left-right axis determine?

Answer 11

Ciliary cells of primitive node establish directional fluid flow from left to right

leftward flow increases expression of Nodal on left side (some nodal still expressed on right), nodal stimulates production of Lefty

Lefty inhibits Nodal on Left side but not on right

nodal on right stimulates Pitx2

Question 12

How is anterior-posterior axis determined?

Answer 12

Hox (homeobox genes)- DNA binding protein that acts as a transcription factor

organized on gene complex in same general order as ant-post axis

Retinoic Acid regulates Hox expression

Question 13

Differentiating of specialized cells types and tissues in the body is due to…

Answer 13

instructed by a HANDFUL of signaling pathways. The big 5

TGF pathways
Hedgehog pathway
FGF pathway
Wnt pathway
Notch pathway

Question 14

What are cadherins?

Answer 14

mediate selective cell-cell adhesion in tissues specific patterns. Cadherins only bind to similar types –> differential cell adhesion

Question 15

What induces cell migration and adhesion?

Answer 15

Handful of signaling pathways activate transcription factors such as SNAIL which regulates genes involved in motility and adhesion

Question 16

Two essential features of stem cells

Answer 16

• Stem cells are not terminally differentiated, but can give rise to daughter cells that can terminally differentiate
• Stem cells can self-renew by dividing and producing two daughter cells, at least one of which does not enter the differentiation pathway but remains a stem cell.

Question 17

When do we carrying out epigenetic reprogramming?

Answer 17

• shortly after fertilization (preimplantation reprogamming)- demethylation is incomplete
• During primordial germ cell determination, demethylation is complete to allow earsing of imprinted regions according to the sex of the embryo

Question 18

Multiple mechanisms promote stem cell DNA health

Answer 18

-because they are the reserve cells that are used to replenish tissues and organs need to protect them from genomic damgage

1. use of progenitor cells as an amplifying system (reduce number of divisions stem cells need to complete)
2. stem cells have the ability to specifically segregate their replicated chromosomes, so one daughter strand gets all of the template = “immortal strand hypothesis”.