week 1 summary

• How did the study of developmental biology originate?

  Embryology (descriptive study of embryonic development), cytology (study of cellular structure and function) and genetics
• What is the overriding question of dev bio?


  How does a single cell develop into a multi-cellular, functional adult?
• What are the fundamental processes of development?

  - Cleavage division

  - Pattern formation

  - Morphogenesis

  - Growth

  - Cell differentiation
• What processes are required during development?

  - Cell to cell communication

  - Cell shape changes

  - Cell movement

  - Cell proliferation

  - Cell death
• Original Cell Theory components

  - All organisms are composed of cells

  - Cell is the basic unit of life

  - Cells are produced by the division of pre-existing cells
• Modern cell theory


  - Cells contain hereditary information that can be passed on

  - All cells are essentially comprised of the same chemical mix

  - Cells can carry out all the basic chemical and physiological processes within themselves

  - Cellular activity depends on the activities of sub-cellular structure
• Why are we made up of individual cells?

  Efficiency (as SA increases, better for nutrient/oxygen supply and waste disposal)

  
  

  Specialisation (numerous small cells allow for specialisation)
• Plasma membrane


  Fluid mosaic

  Incorporates receptors that allow the cell to respond to signals from outside

  Selectively permeable
• What is key for the cell-cell communication?

  The plasma membrane, through having receptors on the cell

  
  

  This allows it to receive messages such as differentiate, grow and divide, survive or die
• How a single signal works

  An extracellular signal molecule binds to a receptor protein the plasma membrane.

  
  

  Intracellular signalling proteins occur, acting on effector proteins.

  
  

  Effector proteins downstream can lead to many alterations in cellular behaviour (e.g. gene regulatory proteins, metabolic enzyme)
• Cillia


  Protrusions from the cell surface

  
  

  Can be motile - which helps respiratory surfaces, fallopian tubes

  
  

  Can be immotile - cell signalling
• Flagella


  Involved in cellular movement, and moving materials along the outside of the cell

  
  

  E.g. sperm tail
• Difference between cillia and flagella

  Flagella is longer and there are fewer of them compared to cilia
• Issue when cilia doesn't work

  Called a ciliopathies

  
  

  Can cause things like carniofacial abnormalities, toes fused together
• Mitochondria-rich cell types


  Skeletal and cardiac muscle

  Sperm tail

  Renal tubular cells
• Mitochondrial defects


  Usually if something is wrong, if is not compatible with life

  
  

  Sometimes defects can be minor, causing 'exercise intolerance'.

  
  

  Can also result in disorders with vision is lost
• An issue in the ER function


  Can cause disorders with sleep, Alzheimer's disease, MS, prion diseases etc.

  
  

  The disease states is when there is a decrease in normal protein folding
• Vacuole


  Cellular space for water/other storage
• Lysosome


  Produced by the Golgi, contains digestive enzymes that can kill the cell
• Peroxisome


  Bud off from the endoplasmic reticulum that can get of toxins and break down long chain fatty acids
• Heterochromatin


  Dark regions

  
  

  Tightly packed DNA, indicative of transcriptionally INACTIVE regions of DNA

  
  

  Nothing can access this part of the DNA to switch on these genes
• Euchromatin


  Light regions

  
  

  Loose, open chromatin

  
  

  Allows ACTIVE transcription and therefore gene expression
• Where are heterochromatin and euchromatn found?

  In non-dividing cells, as the chromatin is not formed into chromosomes
• Totipotent


  Stem cells with the potential to differentiate into any type of cell.
• Pluripotent


  Cells that are capable of developing into most, but not all, of the body's cell types
• Multipotent


  cell with limited potential to develop into many types of differentiated cells
• Nullipotent


  Cannot differentiate any more, fully functional cell types
• Cellular differentiation pathway


  Totipotent

  Pluripotent

  Multipotent

  Nullipotent
• What causes cellular differentiations?

  Result of differences in gene expression

  
  

  Some genes are expressed in all cells, some genes are active only in select specialised cells
• Transcription factors


  Proteins that directly regulate and drive gene expression by interacting with the promoter of a gene
• Master regulator transcription factors

  Certain points in development that require the presence of a 'master regulator'

  
  

  E.g. SRY, found on the Y chromosome. When activated, switches on a cascade of genes encoding other transcription factor
• Master regulator in Drosophila example

  Eyeless (ey)

  
  

  It is present as a TF in mouse and humans, and when mutated leads to eye defects.

  
  

  But in Drosophila, it is a master regulator and will causes it to be eyeless
• Special features of RBC

  - Flexible, flattened (for better oxygen diffusion)

  - Disk shaped cells

  - Don't have a nucleus

  - Flexibility allows it fit through tiny capillaries
• Specialised features of spermatozoon

  Sperm cells have three regions,

  - the head (acrosome and nucleus)

  - the mid-piece (mitochondria)

  - tail (flagellum)
• How were flaws in human developmental biology originally detected?

  Ultrasound

  
  

  It has enhanced a lot to give a 3D image.
• Early diagnosis of developmental abnormalities


  In some cases, a diagnosis can allow for surgical treatment of the fetus

  
  

  E.g. cleft palete
• Optical projection tomography (OPT)

  Passes visible light through an embryo - which has been rendered semi-transparent by chemical treatment

  
  

  It records how much light passes through, so darker regions are thicker. Looks at a particular protein

  
  

  A 3D embryo model is produced
• Why doesn't OPT work with humans?

  You have to pass the light through an embryo, can't do that with humans as unethical. So do it with mice
• 3D morphometric analysis


  Combines different information (e.g. from ultrasound, MRI, OPT) and collect the data to make 3D images

  
  

  Then use this image to measure and see if the individual is developing normally or not

  
  

  Used for down syndrome detection
• Resolution


  Defined as the ability to distinguish two very small and closely-spaced objects as separate entities