genetic models self-organization how do genetic approaches help to understand development? how can...
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Genetic modelsSelf-organization
How do genetic approaches help to understand development?
How can equivalent cells organize themselves into a pattern?
Gene
Mutant Phenotype
To find out what a particular gene does during development:1) Make a targeted mutation in the gene (e.g. a knockout mouse).2) Examine the resulting phenotypes.3) Deduce the gene’s function.
DevelopmentalFunction
Gene
To identify genes that carry out a particular developmental process:1) Screen for mutants in which the process is altered (i.e. with mutant phenotypes).2) Identify the genes that have been mutated.3) Deduce function from phenotypes.
DevelopmentalFunction
Mutant Phenotype
DevelopmentalFunction
ProteinBiochemical
Function
Gene
Cloned genes can be used to analyze biochemical functions involved in a developmental process
Mutant Phenotype
To understand a developmental process, figure out relations among genes and proteins affecting the process.
DevelopmentalFunction
Protein BiochemicalFunction
Gene
DevelopmentalFunction
Protein BiochemicalFunction
Gene
DevelopmentalFunction
Protein BiochemicalFunction
Gene
Arabidopsis thaliana (Mouse-ear cress, Thale cress)
Small weed, related to mustard - can fit thousands of plants in a small area Short generation time: 6-8 weeks when pushed fast Diploid, self-pollinating, transformable
Small sequenced genome: About 125 Mb and 25,000 genes
Finding Arabidopsis mutants
EMS (ethylmethane
sulfonate)
3. Screen M2 plants for mutants having phenotypes of interest
2. Allow M1 plants to self-fertilize, collect M2 seed
1. Mutagenize seeds (M1)
~1000 somatic cellsTransparentEntire cell lineage describedGenome sequencedSelf-fertilizing hermaphrodite
Caenorhabditis elegans – a model genetic species
Ablate P6, another cell acquires vulval fate instead
An equivalence group – P3-P8 cells have the same potential
C. elegans vulva formation
Three cells give rise to the vulva because:1) They are close to the signal source2) They communicate with each other
(from Wilkinson et al. (1994), Cell 79: 1187-1198)
Anchor cell (AC) and Ventral uterine precursor cell (VU) – an equivalence group of 2 cells
lin12 or lag2 mutants:Both precursor cells become anchor cells
Signal = Lag2 (similar to Delta)
Receptor = Lin12 (similar to Notch)
Stochastic asymmetry
Positive feedback reinforcement
(from Wilkinson et al. (1994), Cell 79: 1187-1198)
Model for Anchor cell (AC) and Ventral uterine precursor cell (VU) specification
Drosophila neurogenic ectoderm:
Bristles are neural cells
Mutant sector with partial loss of Delta function