Lecture 1- Introduction

• How do cells acquire different characteristics? • How do cells organise themselves into organs? • What controls the behaviour of cells will underpin how the organism will form and be maintained • How do cells communicate with each other and provide precision and accuracy?

The population is aging faster than its growth

• Cell behaviour • Genetic programme • Cell-cell communication

• Epigenesis: organisms develop progressively over time through the generation of new structures and forms • Preformationism: organisms develop from miniature versions of themselves

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

• Suggests the nucleus of the zygote contains special factors called determinants • Whilst the fertilised egg underwent rapid cycles the cell division cleavages, the determinants would be distributed unevenly to the discrete cells and would control the cells future development • The fate of each cell was predetermined in the egg by the factors it received during cleavage • These unequal distributions make daughter cells different from each other

• Experiment with frog embryos • Concluded the development of the frog is based on mosaic mechanisms, the cells having their character and fate determined at each cleavage

• Aristotle’s epigenesis theory 2. Weismann’s germ plasm theory

• All cells have the same DNA so will all have the same genes present • However the gene will only be expressed in certain cells and therefore the proteins will only be expressed in certain cells • The presence of certain proteins in a cell under pins it’s identify and function

• A mutated gene will mean every cell in the body will carry the mutation • However, the gene is only transcribed and translated (expressed) into proteins in certain cells/tissues • So, mutations will only be ‘visable’ in the tissues where the protein is needed and therefore normally expressed

Intrinsic cues: a cell differentiates into another Extrinsic cues: a cell is influenced/instructed by another cell when differentiating

• Cell differentiation • Cell survival • Cell division • Cell adhesion • Cell shape • Cell migration • Cell death

Through cell-cell communication

• Paracrine signalling • Autocrine signalling • Juxtacrine signalling

• Communication through the release of chemical messengers over a relatively short distance • Cell A may make a secrete protein which is released and binds to receptor on cell B (telling cell B to become different/change)

• Cell signals to itself my releasing a ligand which binds to its own receptor • Cell A makes a signal which is released and stimulates its own receptors on its own cell to change/differentiate itself

• Cell signal is directly passed from ine cell to another that is in direct or close contact with another cell • The signal does not freely diffuse

• Signal reception require cells to be competent to allow signalling pathway to operate/activate • Signals can be instructive or permissive • Signals can acts a morphogens • Transmission of the signal to the nucleus involves a signal transduction cascade

Instructive: signal which initiated a new programme Permissive: signal which provides a favourable environment for a specific programme

Instructs district cell fates according to the concentration of the signal/morphogen

• Reception: the ligand binds to a cell surface receptor and activates it • Transduction: receptor activation induced the transduction of the signal from the membrane to the nucleus via a cascade of secondary messenger activation • Response: transcription factor is activated and induces the transcription of specific target genes

• The production of mRNA • The processing/stability of mRNA • The production of proteins • The activity of proteins

• Differential gene expression • Enhancer-mediates control of gene expression • Control at the level of chromatin and miRNAs can regulate enhancer control elements

Changes operate mainly at the level of mRNA synthesis through the activity of specific transcription factors