Signalling pathways in development Flashcards
What is cell-cell signalling is essential for?
induction, regulation, patterning, cell division etc
What are the different modes of sending and receiving signals?
Cell-cell or cell-substratum contact, diffusible/paracrine signals
Signal transduction pathways via cytoplasm or cytoskeleton
What do responses to signals include?
alteration of gene expression
alteration of cell behaviour
Why can we study signalling pathways in different species?
The same signalling mechanisms perform the same/similar functions in different species
What does signal transduction often involve?
phosphorylation of proteins
mediated by kinases
only on Ser/Thr/Tyr
What regulates the signal?
Feedback mechanisms: positive and negative feedback loops exist
Different pathways interact with one another to achieve, or modify, their effects
Name major classes of signalling molecules?
Receptor Tyrosine Kinases Hedgehog Wnts Transforming Growth Factor b superfamily Cytokines (Thyroid Hormone, Retinoids) Notch/Delta Eph/ephrins Semaphorins Extracellular matrix
What diseases associated with connexin mutation?
Eye defects - cataracts, micropthalmia Cx 26, 45, 50
Skin disorders Cx 26, 30, 31
Deafness Cx 26, 30, 31
Mouse models similar, also heart defects, embryonic lethality
What occurs during EMT?
- dissolution of cell-cell junctions
- cytoskeletal rearragnements
- increased motility
- synthesis of ECM
When is EMT involved in development?
-Gastrulation; formation of the mesoderm by EMT produces the third embryonic cell layer
Neural crest delamination- EMT of neuroepithelial cells in the key step for induction of the neural crest
What causes induction of EMT?
EC signals e.g. BMP/TFGbeta/Wnet/FGF/MMPs–> causes cytoplasmic effectors (SMADs, GSK-3beta, NK-kappaB, MAPK, cytoskeleton, ROS)–>= nuclear regulators of transcription
Describe actin-integrin linkage
Single pass transmembrane proteins
Alpha/beta heterodimers in various combinations confer binding specificity
Signalling can occur in both directions
Link to actin cytoskeleton
FAK links to intracellular kinases
The actin-integrin linkage. The linkage between the extracellular matrix and the actin cytoskeleton is depicted. Integrins can bind directly to the talin head domain. Through its tail domain, talin can bind directly to actin as well as to other components of the linkage, such as vinculin. Vinculin can also bind to actin directly, as well as to the actin cross-linker α-actinin. Both vinculin and α-actinin are anchored to the membrane, and their activity is modulated by interactions with phosphatidylinositol (4,5)-bisphosphate (PIP2). Finally, vinculin and FAK can bind to the actin nucleator Arp2/3
Give examples of nuclear hormone receptors
E2, RA
What are Receptor Tyrosine kinases?
Single pass, trans-membrane receptors Specific tyrosine residues phosphorylated upon ligand binding Autophosphorylation Ligands are dimers, receptors dimerise PDGF, EGF, FGF, VEGF
What pathways can the EGF receptor activate?
- PLC (Pip2/Dag-IP3)
- JAK/STAT
- Ras/Raf
What causes achondroplasia?
FGFR3
Autosomal dominant mutation affecting endochondral bone formation
80% of patients have activating mutations in FGFR-3 (G380R, within the trans-membrane region)
Constitutive ERK (MAPK) activation
inhibits chondrocyte differentiation to hypertrophic form
inhibits PTHrP/PTHR, required for chondrocyte proliferation
What is achondroplasia?
(most common cause of dwarfism) - shortening of long bones of limbs, short stature, macrocephaly
What does Dominant negative PDGFR- blocks ?
Xenopus gastrulation
What can act as mesoderm inducer in xenopus mesoderm induction?
Activin
What family is activin part of?
TGF-beta superfamily
Describe xenopus activin gradients
100 ng Activin= heart and cartilage
10-50ng= notochord
5-10= muscle
0.1-1= lymphocyte/erythrocyte/vascular tissue
What do morphogens do?
A morphogen is an inducing factor that can induce different cell fates depending on its concentration
A morphogen gradient requires a source and a sink
Describe the TGF beta superfamily
Single-pass transmembrane Serine / Threonine kinases
Ligands include TGF, activins, BMPs, myostatin
Receptor phosphorylation leads to SMAD activation
sma - small
MAD - mothers against decapentaplegic
What SMADs respond to BMPS?
Smad 1,5,8
respond to BMPs
What SMADs respond to TGF-beta?
Smad 2,3
respond to TGF
What SMADs are inhibitory?
Smad 6,7
are inhibitory and compete with Smad 4
How do we know SMAD2 and 4 dimerise?
Visualising protein interactions using bi-molecular fluorescence: Use GFP protein (Venus)- chop it in half
