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Inducer. Responder. Types of signals. Setting up a signaling gradient: the role of the wingless gene. Anterior. A- Hair. segment. P- Bare Skin. Cells know their positions within the body and differentiate accordingly. Posterior.
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Inducer Responder Types of signals
Setting up a signaling gradient: the role of the wingless gene
Anterior A- Hair segment P- Bare Skin Cells know their positions within the body and differentiate accordingly Posterior
To set up this pattern, flies use the secreted protein Wingless to specify a posterior fate A = hair P = bare skin segment wild type
Anterior: Low Wingless, Hairs Posterior: High Wingless, Naked Cuticle
Signals can also act in a graded fashion
Wingless diffuses away from the cells that secrete it Wingless-expressing cells
Wingless signaling specifies posterior cell fates in the ventral epidermis A = hair P = bare skin wild type arm mutant ALL cells have anterior (hair) fate
Therefore, all cells can see wingless, and the concentration of wingless itself is what determines cell fate Setting up a signal gradient
Signal transduction moves information from the cell surface to the nucleus and other cellular targets
Genetics revealed the ligand and proteins in this signal transduction pathway
Genetics can also position proteins within the signaling pathway
An example of the conservation of key developmental regulatory machinery across animal phyla flies mammals See also Figure 6.20A
Colon cancer, the second leading cause of cancer deaths in the U.S., results from inappropriate Wnt signaling Polyps, the first stage In tumor development
Long range signaling Insects: A model system to study hormonal control of postembryonic development Figure 18.9
Vincent B. Wigglesworth Discovered that blood-borne hormones control insect metamorphosis through experiments with a blood-sucking bug, Rhodnius prolixus
Experiment #1 Blood-borne hormones regulate the timing of metamorphosis induces 1st instar larva to molt into very small adult
Other hormones prevent metamorphosis Experiment #2
Other hormones prevent metamorphosis Experiment #3 Transplant corpus allatum from 4th to 5th instar larva Adult Result: blocks metamorphosis, instead get “6th instar larva”
PTTH The cascade of hormones regulating insect metamophosis 20E Figure 18.16
Steroid hormones (ie 20E): hydrophobic signaling molecules that can pass through the plasma membrane 20E
Most signals Steroid hormones (ie. 20E)
An insecticide produced by plants cause premature metamorphosis