Lecture 1: Intro Flashcards
What is epigenesis?
The theory that an embryo develops progressively from an undifferentiated egg cell. Gradual unfolding of a process that becomes progressively more complex over time, leading to an embryo.
What is the cell theory?
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 cells
All cells contain all genes but they are selectively expressed in different cell types.
What are the different types of cellular ques? How do cells respond?
Intrinsic ques already present in the cell e.g., in asymmetric division.
Extrinsic cues from another cell. These could be secreted proteins or small molecules.
Cells respond with changes in behaviour i.e., differentiation, migration, adhesion, apoptosis etc.
Discuss the different types of extrinsic signals.
Extrinsic signalling can be paracrine (act on nearby cells), autocrine (acting on itself) or juxtracrine (through connecting cell surface receptors). They can also be instructive (directly inducing a change in cell fate) or permissive (reveals a latent signal). For example, a permissive signal may stop a cell from dying meaning it can respond to an instructive signal. An example of an instructive secreted extrinsic signal is a morphogen which provokes different cell responses depending on the concentration it receives.
Discuss the principles of signal transduction to the nucleus.
Gene expression determines a cells characteristics and function. Nuclear signalling involves a transduction cascade. A ligand binds and activates a cell surface receptor. Transduction of the signal from the membrane to the nucleus via second messengers, where TF are activated inducing transcription or repression of specific target genes. mRNA is synthesises, splicing and polyadenylating occurs, and then the protein is produced.
State the key steps in cell signalling.
1) reception of signal
2) transduction of signal
3) cell response to signal
Define gastrulation.
Endodermal and mesodermal cells move from the outer surface of the embryo to the inside where they become organs.
Define morphogenesis.
Changes in the form/shape of an embryo
Define neurulation.
The future brain and spinal cord formation from ectodermal neural plate
What is most of what we know today about developmental biology based on?
Animal models, especially drosophila, zebrafish and mice.
Genetic studies i.e., LOF and GOF.
Define cell determination
A stable change in the state of a cell such that its fate is fixed. So it will follow its normal fate when grafted in a different region of the embryo.
Define cell specification.
When transplanted to a different region of the embryo the new environment could direct it to acquire a different fate.
Explain the difference between a TF and a signalling ligand.
A signalling ligand is (in most cases) non autonomous i.e., the gene is transcribed and the protein translated in one cell which is then secreted and the product exerts its action on a second, responding cell. E.g., Wnt, Shh, BMP, Nodal, Notch, FGFs.
A TF is cell-autonomous i.e., the protein functions in the nucleus of the cell in which the gene that encodes it is transcribed and its mRNA translated. It then binds to control elements of other genes within the cell to either activate or repress transcription.
What is the consequence of mitotic division on gene inheritance patterns?
All somatic cells inherit the entire genome which remains constant in all cell types apart from B and T lymphocytes which rearrange their immunoglobulin and T cell receptor genes respectively in response to antigen stimulation.
Why is development a dynamic process?
Cell states are created by distinct populations of mRNA transcripts and proteins which are synthesised at a particular rate and broken down by enzymes. The rate of mRNA and protein turnover and abundance can change rapidly in dividing populations as the rate of proliferation changes. As cells move to different microenvironments, different molecular signals modulate gene expression.
