Lecture 1 Flashcards
Recall the experiments carried out by Wilhelm Roux on frog embryos
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.
What is meant by a morphogen
A morphogen is a chemical (usually a diffusible signalling molecule) whose concentration varies forming a concentration gradient
What are the three requirements of a molecule for it to be a morphogen
Produced from a localised source, usually sensed through cell surface receptors and cells respond differently to difference concentrations of the morphogen
Give example(s) of paracrine/autocrine signalling mechanisms seen in development
Shh, Wnt, TGF?, BMP and FGF signalling
At what levels does the cell operate control on a gene program
Production of mRNA, processing and stability of mRNA, production of proteins and the activity of proteins
What other two methods are the of controlling the genetic program
miRNA, controls at the level of chromatin
Which type of cell-cell communication involves two cells communicating with each other by direct contact
Juxtacrine
Which type of cell-cell communication involves a factor acting on a receptor on a neighbouring cell
Paracrine
What are the two opposing theories of early development
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
What are the two ways in which the cell controls the genetic program at the level of gene transcription
Differential gene expression, enhancer-mediated control
What type of signal provides a favourable environment for a specific program
Permissive signals
How is asymmetric cell division achieved
Cytoplasmic, extracellular or membranal determinants are segregated/distributed unevenly in the precursor cells so that when it divides the daughters contain different levels
Give an example of a juxtacrine signalling mechanism seen in development
Delta-notch
What are the common features of signal transduction pathways
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
What type of signal initiates a new program
Instructive signals
Every cell has the potential to communicate with other cells, T or F
F - some cells dont
What are the four types of cell-cell communication
Paracrine, autocrine, Juxtacrine and endocrine
How does cell shape influence behaviour
Epithelial cells are fixed and immobile whereas mesenchymal cells allow migration. Thus epithelial to mesenchymal transitions (EMTs) are essential during development particularly in gastrulation.
What is meant by preformationism
The idea that organs develop from miniature versions of themselves as a homunculus (little human)
What are the two types of cell division seen during development and how do they differ
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
How do the experiments carried out by Hans Driesch differ to those of Roux
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.
Which types of cell signalling occur in development
Paracrine, autocrine and Juxtacrine
Cells need to be competent to respond to a signal by receiving and transmitting a signal to the nucleus, T or F
T
Gene content is identical in most cells and transcription/translation dictates the protein content of a cell, T or F
T
