Signalling Flashcards
How to measure cell signalling capacity?
- number of signalling proteins encoded by genome
Compare signalling capacity between unicellular vs multicellular
multicellular organisms devote 10x more genes to signalling
Name the forms of signal
- Proteins (insulin, fibroblast growth factors)
- Small hydrophobic molecules (animal steroid hormones)
- Small hydrophillic molecules (plant auxins)
- Gas (ethylene, nitric oxide)
- Electrical (nerve impulses)
What is signalling range and list the 3 types and how far the distance is.
The distance between the signalling cell and the target cell defines the ‘signalling range’
- Long range signalling 1000mm
- Intermediate range signalling 1mm
- Short range signalling 0
What are the proper names for long/medium/short range signalling and how do they travel to their appropriate sites?
long range = endocrine, travels by bloodstream
intermediate range = paracrine, travels through diffusion
short range/contact dependent = juxtacrine, no distance so no traveling required
give examples of long range signalling
- male and female hormones in sexual dimorphism
- flowering in plants triggered by day length (so all flowers come out at same time to maximise pollination)
- nervous system
Explain flowering im plants triggered by daylight in detail:
Long range signalling enables some plants to time their flowering according to the daylength
- This allows plants of the same species to synchronise their flowering
- This is important for cross pollination
- A flower that comes out by itself will not get pollinated by another flower!
CO is a TF and when day is long (lots of sunlight) CO is expressed at a high level. binds to promotor and causes transcription and translation of CO protein.
- long days = high CO protein = high FT protein = moves through sap from leaf to shoot and slower forms
What does incompetent cells mean?
Many more cells exposed to signal than respond to it. This describes the ability of a cell or tissue to respond to a signal. conversely other cells or tissues cannot respond so
are described as ‘incompetent
Growth cones can bear receptors that interact with axon guidance molecules via paracrine or juxtacrine signalling mechanisms. describe these in detail.
1. Paracrine = short range (examples Slit/Robo + Netrin/DCC)
- The growth cone reacts to these signals as it approaches the cell expressing them.
- Juxtacrine = contact dependent (examples Eph/Ephrin + Semaphorin/plexin)
- The growth cone reacts to these signals when it comes into contact with the cell expressing them
How does nerve signal travel long distances between cells?
- over a short range at synapse
- Nerve impulse causes pre-synaptic cell to release neurotransmitter
- Neurotransmitter travels short distance across the synapse and binds to receptors on post-synaptic cell
- Triggers nerve impulse in post-synaptic cell
Is the knee jerk reflex long/intermediate/short range signalling?
intermediate
- long distance covered by signal travelling along axons
- signalling between cells involve intermediate distance by neurotransmitter
- not short range as neurotransmitter has to travel
Signalling in sex determination. what is primary and secondary sex characteristics?
Primary sex characteristics = capacity of the reproductive gland
- Gonads = ovaries or testes
- Gametes = eggs or sperm
Secondary sex characteristics = sexual dimorphism
- distinct difference in size or appearance between the sexes of an animal in addition to the sexual organs themselves
Explain how the formation of Conrad’s determination secondary sex characteristics
Sry [sex determing region Y chromosome] is a transcription factor only expressed from the Y chromosome. If gonad cells are XY they will express Sry which regulates gene expression leading to testes differentiation.
During sex neutral development the mammalian XX or XY embryo have both male and female structures true/false?
True
How does XY lead to male determination?
Sry signal from Y chromosome causes the gonads to become testes and male structures persists whilst female disappears
XY testes secretes male hormones such as MUllerian-inhibiting substance and testosterone. what do they each do?
- inhibits mullein duct (oviduct)
- signals wolffish duct to develop into vas deferent to carry sperm and signals secondary male sex character
What kind of signalling does testosterone undergo?
long range bc steroid hormone
how does XX undergo female determination?
absence of Sry signal from Y chromosome so gonad becomes ovaries. no mullarian inhibiting substance and no testosterone. ovaries secrete female hormones which signal to instruct female phenotype.
What does default mean in signalling?
what happens unless a signal instructs an alternative fate
CAIS-complete androgen insensitivity syndrome people lack receptors. how does this prove the ‘default’ theory
develop female at puberty because of the absence of ‘male’ signals. although signals are produced they don’t respond.
List the 2 mechanisms that could’ve led to Gynandromorph in chicken
- mosaic = genetic change in cell lineage derived from single zygote
- chimera = fusion of genetically distinct embryos
how does the gynadromorph chicken shows that endocrine signalling cannot be sufficient to determine secondary sex characteristics in chickens
The female and male sides of the same chicken are exposed to the same hormones in the bloodstream.
Male (ZZ) and female (ZW) cells must have ___ sex identity
- Hormone signalling from the gonads are important but the ___of the signal by target cells is also critical.
- This is an example of cell ______
- intrinsic
- interpretation
- autonomous sex determination
What is not the primary component driving sexual dimorphism in chicken
long range signalling
What is cell autonomous
cell autonomous = cells develop either male or female secondary sex character determined by genotype
What is cell non-autonomous
cell non-autonomous = cells competent to develop male or female secondary sex character in response to endocrine signals whatever their genotype.
What is temperature-dependent sex determination?
Egg incubation temperature determines sex phenotype
How many cells does paracrine signalling operate over?
100 cells
Why is the development of the vertebrate ‘pentadactyl’ limb has provided a useful model system to study paracrine signalling during development
The basic 5 digit structure is conserved between tetrapods (amphibians, reptiles, birds, and mammals)
Describe the limb axis nomenature.
proximal (wrist), distal (fingertips)
thumb (anterior), pinky (posterior)
How does the vertebrate limb develop along proximal-distal axis?
- AER on the winged expressed protein called FGF4
- Fibroblast growth factors (FGFs) are a family of secreted signalling proteins
- FGF4 is expressed in the AER so is in the right place at the right time
- A source of FGF4 can rescue limb truncation caused by AER removal
What is dachshund short leg phenotype due to?
ectopic expression of FGF4 in developing limbs
How does the vertebrate limb develop along anterior-posterior axis
- A source of morphogen on one edge of the developing limb anterior-posterior axis.
- A resulting anterior-posterior concentration gradient.
- A specific range of morphogen concentration would specify each digit along the anterior-posterior axis.
This result makes sense if the donor ZPA creates an posterior High to anterior Low morphogen concentration gradient mirroring that created by the host ZPA
- Posterior digits form next to grafted ZPA
- More anterior digits form far from grafted ZPA
What is a morphogen?
A morphogen is an substance active in pattern formation whose spatial concentration varies and to which cells respond differently at different threshold concentrations
What is an organiser? Example?
signalling center that directs the development of the whole embryo or part of the embryo.
The ZPA is an example of an organiser because it signals to the developing limb and directs differentiation between digits along the anterior-posterior axis
Shh protein also creates mirror image of limbs when grafted. What does this show?
Shh protein is sufficient to provide the ZPA morphogen activity
What is lateral inhibition?
Organising cell structures by inhibitory signalling at very close range
How do trichomes come about
initially the epidermal precursor cells are indistinguishable (grey) and then one cell becomes selected as a trichome precursor and develops into mature trichome
how is trichome spacing regulated?
- Once a cell decides to become a trichome it normally inhibit neighbours from becoming trichomes
- Triptychon normally essential for this lateral inhibition as neighbouring cells can become trichomes when Triptychon mutated.
How does signalling by cell:cell contact helps in the development of the inwardly buckled structure of the crypt?
- specifically repulsive signalling between EphB and ephrinB proteins.
- Proliferating stem cells in the crypt express EphB
- Flanking cells express EphrinB
- As stem cells proliferate their numbers increase BUT they cannot escape from the crypt as this would involve mixing with the flanking EphinB expressing cells
Endocrine vs autocrine
endocrine = signalling + target cell
autocrine = signalling cell responds to its own signals
