Introduction

Question 1

What question does developmental biology try to answer?

Answer 1

How do we get from a single cell to a multicellular organism?

Question 2

Does development stop with birth?

Answer 2

NO

It is a lifelong process

Question 3

What challenges does aging put on our society?

Answer 3

Strain on resources and money

Question 4

What changes cell behvaiour?

Answer 4

Change in the genetic programme (gene expression)

Question 5

Why are animal models used in developmental biology?

Answer 5

Most of the concepts that drive developmental processes are evolutionarily conserved

Understand what goes on in animal model - can help to understand what goes on in human

Question 6

What are the 2 opposing theories of developmental biology?

Answer 6

1) Epigenesis

2) Preformation

Question 7

What is the epigenesis model of developmental biology?

Answer 7

• Embryo develops in a step-wise process

- PROGRESSIVELY acquires new structures and function

Question 8

Who proposed the theory of epigenesis?

Answer 8

Aristotle

Question 9

Why was the theory of epigenesis not widely accepted?

Answer 9

Scientists struggled to understand how the generation of new structures and tissues were formed

Question 10

What is the preformation theory of developmental biology?

Answer 10

• Start from a mass of cells which are a predetermination of something that will exist later on
• Organism develops from a miniature version of themselves (homunculus)
• Homunculus sits inside the sperm head
• Just needs to be allowed to grow

Question 11

What discovery lead back to the epigenesis theory?

Answer 11

The discovery of the cell by Robert Hooke (1655)

Question 12

How did Robert Hooke discover the cell?

Answer 12

• Placed thin sections of cork underneath the microscope

- Saw compartments, which he called cells - stated that these were the basic structure of life

Question 13

What did the discovery of the cell produce?

Answer 13

• A tool to understand how you could get progressive development
• Have a basic unit with can be studied and manipulated

Question 14

What did the discovery of the cell lead to?

Answer 14

The END of the preformation theory

Question 15

From the theories of developmental biology, what 3 conclusions were made?

Answer 15

1) All organisms are composed of one or more cells
2) The cell is the most basic unit of structure, function and organisation in all organisms
3) All cells arise from pre-existing living cells

Question 16

What are the 2 theories that describe how cells become different to each other, in order to generate an embryo?

Answer 16

1) ‘Germ plasm determinants’ theory

2) ‘Induction theory’

Question 17

Who proposed the ‘germ plasm determinants’ theory?

Answer 17

Weismann

Question 18

What did Weismann suggest?

Answer 18

• Germ cells have a set of determinants
• All germ cells have the SAME SET of determinants
• Somatic cells only have a SUBSET of these determinants: this is what determines the structure and behaviour of the cell

Question 19

Who performed an experimental demonstration of Weismann’s theory?

What did he do?

Answer 19

William Roux:

• Took a fertilised xenopus egg at the 2-cell stage and killed one cell using a burning needle
• Saw that only HALF the embryo developed
• This supports Weismann’s theory

Question 20

Who proposed the ‘induction theory’?

Answer 20

Hans Driesch

Question 21

What experiment did Hans Driesch perform?

Answer 21

• Sea urchin eggs at the 2 or 4 cell stage
• Separated the cells from each other and allowed them to develop
• Lead to the formation of a FULL embryo

Question 22

What was the difference between Roux and Drieschs experiment?

What does this show?

Answer 22

Driesch disrupted cell-cell communication

Shows that NORMAL development is dependant on cell-cell communication

Question 23

What did Driesch prove about Weismanns theory?

How?

Answer 23

Proved it not to be entirely true:

• Each somatic cell does have the full set of determinants
• BUT, only choose to execute a subset of the programme

Question 24

How does the cell choose what subset of determinants it is going to express? How?

Who proved this? How?

Answer 24

Cell-cell communication

• Cells INSTRUCT neighbouring cells to carry out a certain genetic programme or PREVENT from carrying out a certain genetic programme

Proved by Hans Driesch - when the cells were separate, there was no positive or negative signals - allowing to form the whole embryo

Question 25

What drives the differences between cells?

Answer 25

Differenced in genes that are transcribed and translated

Question 26

Describe the protein content in cells

Answer 26

- Some proteins are ubiquitous (the same in every cell) | - Some proteins are SPECIFIC to different cells

Question 27

What does the REPERTOIRE of proteins in a cell determine?

Answer 27

The IDENTITY and FUNCTION of the cell

Question 28

What 2 things determine the repertoire of proteins in a cell?

Answer 28

1) Intrinsic cues | 2) Extrinsic cues

Question 29

What are intrinsic cues?

Answer 29

Cell directly differentiates into another cell Driven by transcription factors becoming active

Question 30

What are extrinsic cues?

Answer 30

External cells in the environment which instruct another cell when there is NO RELATIONSHIP between these 2 cells (no lineage)

Question 31

How do cells acquire new properties that make them different to each other?

Answer 31

1) Cell division - symmetric, asymmetric 2) Cell adhesion - dispersal, condensation 3) Cell shape - Epithelial or mesenchymal 4) Cell migration 5) Cell death

Question 32

What is symmetric cell division?

Answer 32

Formation of IDENTICAL daughter cells

Question 33

What does symmetrical division allow?

Answer 33

The growth of a tissue

Question 34

What is asymmetric cell division?

Answer 34

Formation of 2 daughter cells that are different to each other

Question 35

What gives rise to asymmetrical cell division?

Answer 35

Differential segregation of cell determinants

Question 36

What does asymmetric cell division lead to?

Answer 36

Diversity

Question 37

Which type of cell division is widely used in stem cell biology? Why?

Answer 37

Asymmetrical cell division: - Leads to the generation of a new cell type from the mother cell - Whilst continuing to propagate another cell type (maintain the stem cell)

Question 38

What 3 ways does cell-cell communication occur?

Answer 38

1) Paracrine 2) Autocrine 3) Juxtacrine

Question 39

What is paracrine signalling?

Answer 39

Secreted ligand which recognises a receptor on a NEIGHBOURING cell

Question 40

What is autocrine signalling?

Answer 40

Secreted ligand which recognises a receptor on the SAME cell

Question 41

What is juxtacrine signalling?

Answer 41

Ligand and receptor are both MEMBRANE bound

Question 42

What does juxtacrine signalling require?

Answer 42

Very close interactions between different cells

Question 43

What is an example of juxtacrine signalling?

Answer 43

Notch signalling

Question 44

What does signal reception require cells to be? What does this mean?

Answer 44

COMPETENT: - Permissive environment, receptor and transduction components must be present

Question 45

What does signal reception require signals to be?

Answer 45

INSTRUCTIVE or PERMISSIVE

Question 46

What do instructive signals do?

Answer 46

Initiate a new programme

Question 47

What do permissive signals do?

Answer 47

Provide a favourable environment for a specific programme

Question 48

What can signals act as? What do these do?

Answer 48

Morphogens Instruct distinct cell fates according to their concentration

Question 49

What does transmission of a signal to the nucleus involve? What does this lead to?

Answer 49

A signalling transduction cascade - cell surface, cytoplasmic and nuclear proteins that relay the signal Leads to changes in gene expression

Question 50

What are 3 common features in signal transduction cascades?

Answer 50

1) Reception 2) Transduction 3) Response

Question 51

What modulates receptor activity?

Answer 51

Series of proteins: - Co-receptors - Inhibitors

Question 52

How is a signal transduced from the receptor to the nucleus?

Answer 52

Signalling cascade of secondary messengers

Question 53

What is the response of signal transduction pathway?

Answer 53

- Transcription factor activated - Induction of the expression of specific target genes - Change in the gene expression of a cell (mRNA)

Question 54

What are the levels at which a cell can operate to control a gene programme? (As transcription/translation determines the protein content of a cell, which determines the structure/function)

Answer 54

1) Production of mRNA 2) Processing/stability of mRNA 3) Production RATE of proteins 4) Activity of proteins (eg. phosphorylation)

Question 55

Does the presence of a protein/expression of a gene imply the function of the gene is present? Why?

Answer 55

NO Gene expression/translation/transcription can be modulated at many different stages

Question 56

What might the product of the gene that is newly transcribed do?

Answer 56

Activate or repress another gene from being transcribed (which may drive the identity of another cell)

Question 57

How can the control of a genetic programme occur at the level of gene transcription?

Answer 57

- Enhancer-mediated control of gene expression - miRNAs - Control at the level of chromatin