Week 4 - Signalling and cell death

• Why cell communication important for development?


  cells make a multicellular organism, instruct tissues when to divide, differentiate, die.
• Key elements of cell signalling?


  extracelluoar signalling molecules, receptor, intracellular pathways; effector proteins
• Factors affecting how cell responds to signal?


  Proteins expressed, level of receptor expression, type of receptor. extracellullar signals can act rapidly (changes in cell movement, secretion, metabolism) or slowly (increased cell growth and division gene expression)
• What different ways can a cell respond to a signal?


  Phosphorylation of proteins to alter cytoskeleton, cell metabolism, open ion channels, change rate and force of contraction, secretion, contraction
• Key features and differences between signalling typesparacunre, endocrine, synaptic, contact-dependent

  
• Morphogenic gradient


  Inductive signal making cells on either side direct to new development pathway. Paracrine signalling. Patterning tissues so closer cells differentiate into something then further cells differentiate into something else. Depends on concentration of growth factors
• How is apoptosis used in development and homeostasis?

  Hand and digit development
• Key events in apoptosis, how different from to necrosis. 


  Necrosis: by tissue injury. cells burst, damaged of surrounding cells

  
• ECM


  all protein and other molecules outside and around cells
• What is in connective tissue?


  one type of primary tissue: cells like fibroblasts and certain immune cells and ECM with fibres and ground substance
• Main classifications of connective tissues?


  Loose, dense: regular and irregular, loose: blood, cartilage, bone
• Functions of epithelial tissues


  protection, absorption, secretion
• How do epithelial and mesenchymal tissues differ


  epithelial cells are tightly connected together to form a layer while mesenchymal cells are loosely connected,’cells can switch between these states
• 5 major characteristics of epithelial tissues


  polarity, supported by connective tissue layer, tight contacts between cells, not vascularised but is innervated, able to regenerate.
• How epithelial tissues are classified 


  cell shape (columnar, cuboidal, squamous), layers (simple, strategies, pseudo stratified, transitional, germinal: germ cells) and specialisations (goblet cells, microvilli, cilia, keratin)
• Changes in cell adhesion can lead to what shape and tissue changes in embryo development?


  required From the 2 cell stage: creating layers require epithelia, changing shape of layers require myosin actin adhesion belt, cell aggregating requires increased cell cell adhesion, cell dispersion requires decreasing cell cell adhesion, delaminating (separating from basal lamina) requires loss of cell matrix adhesion, migration requires dynamic change in cell matrix interaction.
• Thermodynamic model of cell interactions 


  cells with different cell cell adhesion sort out using strength of adhesion. Cells trade weaker bonds for stronger bonds, hierarchy of cell sorting: cells with strongest adhesion segregate to the middle.
• Cell junctions

  • Tight junctions
  • Adherens junctions
  • Desmosomes
  • Gap junctions
  • Cell matrix junctions
• Tight junctions (zonula occluden)


  Block passage of molecules and ions through space between cells, block movement of integral membrane proteins between apical and basolateral surfaces of cell
• Adherens junction

  Encircles cell, provide adhesion including actin filaments inserting into dense plaques on cytoplasmic surfaces, Cadherins connect cells at adherents junctions
• Desmosome (macula adherens)


  Plaque like thickenings hold cells tightly together, intermediate filaments converge on plaque, site of attachment between cells and cytoskeleton
• Gap junction (nexus)


  Made of connected transmembrane proteins, permit free movement of ions and small molecules and change in membrane potential passing between cells, Connexins make up the gap junction channel called connexon
• Focal adhesions


  Actin filaments insert into dense plaques on cytoplasmic surfaces connecting to transmembrane proteins integrins which binds to ECM molecules like collagen and fibrinectin
• Hemidesmosomes

  Connects basal surface of epithelial cell to basal lamina, extra cellular domains of integrins bind to laminin in basal lamina, intracellular domain binds via anchor protein plectin to intermediate filaments
• paracrine signalling molecule feature?

  Water soluble molecule
• Where is the signalling molecule for contact dependent signalling?

  Surface of cell
• gastrulation, invagination changing shape, letting go cells on either side for ingression


  Examples of changes in cell adhesion
• Examples of simple squamous epithelium

  Air sacs of lungs, lining of heart blood vessels and lymphatic vessels: allow secretion and material to pass through difusion and filtration
• Simple cuboidal epithelium examples

  Ducts of small glands and kidney tubules for secretion and ansorptoon
• Simple columnar epithelium


  absorbs and secretes llike bronchi, uterus, GI tract, bladder
• Pseudostratified columnar epithelium?

  Respiratory tract Upper
• Stratified squamous epithelium

  Protect against abrasion in esophagus, mouth, vagina
• stratified cuboidal epithelium

  Protective tissue on sweat glands, salivary glands, mammary glands
• Stratified columnar epithelium

  Secretes and protects in make urethra and ducts of some goands
• Transitional epithelium

  Bladder urethra ureters
• The signalling molecule is typically bound in the ECM by collagen fibres in paracrine signalling yes or no?

  No.