Lecture 1

Question 1

Recall the experiments carried out by Wilhelm Roux on frog embryos

Answer 1

Roux killed half of the cells at the 2 and 4-cell stage and looked at this effect on the developing embryo. It was noticed that ablation of these cells lead to the production of half embryos. This lead him to believe that at that stage each cell contributes uniquely to the development of the embryo and that the cell that wasn’t killed is only capable of adopting its primary fate.

Question 2

What is meant by a morphogen

Answer 2

A morphogen is a chemical (usually a diffusible signalling molecule) whose concentration varies forming a concentration gradient

Question 3

What are the three requirements of a molecule for it to be a morphogen

Answer 3

Produced from a localised source, usually sensed through cell surface receptors and cells respond differently to difference concentrations of the morphogen

Question 4

Give example(s) of paracrine/autocrine signalling mechanisms seen in development

Answer 4

Shh, Wnt, TGF?, BMP and FGF signalling

Question 5

At what levels does the cell operate control on a gene program

Answer 5

Production of mRNA, processing and stability of mRNA, production of proteins and the activity of proteins

Question 6

What other two methods are the of controlling the genetic program

Answer 6

miRNA, controls at the level of chromatin

Question 7

Which type of cell-cell communication involves two cells communicating with each other by direct contact

Answer 7

Juxtacrine

Question 8

Which type of cell-cell communication involves a factor acting on a receptor on a neighbouring cell

Answer 8

Paracrine

Question 9

What are the two opposing theories of early development

Answer 9

Epigenesis - Aristotle belief that development is a gradual process, stage by stage, whereby new functions and characteristics are added on top of others. The other theory is that everything is already present and pre-established in the fertilised egg and all is required is amplification

Question 10

What are the two ways in which the cell controls the genetic program at the level of gene transcription

Answer 10

Differential gene expression, enhancer-mediated control

Question 11

What type of signal provides a favourable environment for a specific program

Answer 11

Permissive signals

Question 12

How is asymmetric cell division achieved

Answer 12

Cytoplasmic, extracellular or membranal determinants are segregated/distributed unevenly in the precursor cells so that when it divides the daughters contain different levels

Question 13

Give an example of a juxtacrine signalling mechanism seen in development

Answer 13

Delta-notch

Question 14

What are the common features of signal transduction pathways

Answer 14

Ligand binding to a receptor causes its activation which leads to the transduction of the signal to the nucleus via a cascade if secondary messenger activation. This in-turn leads to the activation of a transcription factor which induces the transcription of specific target genes

Question 15

What type of signal initiates a new program

Answer 15

Instructive signals

Question 16

Every cell has the potential to communicate with other cells, T or F

Answer 16

F - some cells dont

Question 17

What are the four types of cell-cell communication

Answer 17

Paracrine, autocrine, Juxtacrine and endocrine

Question 18

How does cell shape influence behaviour

Answer 18

Epithelial cells are fixed and immobile whereas mesenchymal cells allow migration. Thus epithelial to mesenchymal transitions (EMTs) are essential during development particularly in gastrulation.

Question 19

What is meant by preformationism

Answer 19

The idea that organs develop from miniature versions of themselves as a homunculus (little human)

Question 20

What are the two types of cell division seen during development and how do they differ

Answer 20

Symmetric cell division - progeny divide and give rise to two identical daughter cells. Asymmetric cell division – progeny divide and give rise to two daughters with different characteristics

Question 21

How do the experiments carried out by Hans Driesch differ to those of Roux

Answer 21

Hans Driesch carried out similar experiments on sea urchin embryos. He divided the embryos up at the 2 and 4 cell stage and allowed them to develop, each cell in isolation from the others. He believed that these cells would give rise to the relevant part of the body plan already decided on. However each of the separated cells gave rise to a separate sea urchin proving that these cells were totipotent and could give rise to any of the cells of the body.

Question 22

Which types of cell signalling occur in development

Answer 22

Paracrine, autocrine and Juxtacrine

Question 23

Cells need to be competent to respond to a signal by receiving and transmitting a signal to the nucleus, T or F

Answer 23

T

Question 24

Gene content is identical in most cells and transcription/translation dictates the protein content of a cell, T or F

Answer 24

T

Question 25

Explain Wissman’s theory of how cells become different

Answer 25

Two types of cells exist, somatic and germ cells. Germ cells contain determinants (germ plasm) whereas somatic cells only contain a subset of these determinants which define its particular set of characteristics

Question 26

Which type of cell-cell communication involves a factor acting on receptors on the same cell that produced it

Answer 26

Autocrine