1. Neurulation (see slides posted at end of DB5 ppt) Inducer Responder

2. Signaling Inducer Responder

3. Signals can act in a graded fashion

4. Setting up a signaling gradient: the role of the wingless gene

5. Cells know their positions within the body and differentiate accordingly Anterior Posterior A- Hair P- Bare Skin segment

6. wild type A = hair P = bare skin To set up this pattern, flies use the secreted protein Wingless to specify a posterior fate segment

9. Anterior: Low Wingless, Hairs Posterior: High Wingless, Naked Cuticle

10. Wingless-expressing cells Wingless diffuses away from the cells that secrete it

11. Wingless signaling specifies posterior cell fates in the ventral epidermis arm mutantwild type ALL cells have anterior (hair) fate A = hair P = bare skin

12. Therefore, all cells can see wingless, and the concentration of wingless itself is what determines cell fate Setting up a signal gradient

13. Signal transduction moves information from the cell surface to the nucleus and other cellular targets

15. Genetics revealed the ligand and proteins in this signal transduction pathway

16. Genetics can also position proteins within the signaling pathway

17. An example of the conservation of key developmental regulatory machinery across animal phyla fliesmammals  See Figure 3.28

18. 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

19. Insects: A model system to study hormonal control of postembryonic development Figure 15.9 Long range signaling

20. Vincent B. Wigglesworth Discovered that blood-borne hormones control insect metamorphosis through experiments with a blood-sucking bug, Rhodnius prolixus

21. Blood-borne hormones regulate the timing of metamorphosis Experiment #1 induces 1st instar larva to molt into very small adult

22. Experiment #2 Other hormones prevent metamorphosis

23. Experiment #3 Other hormones prevent metamorphosis Transplant corpus allatum from 4th to 5th instar larva Result: blocks metamorphosis, instead get “ 6th instar larva ” Adult

24. The cascade of hormones regulating insect metamophosis Figure 15.16 PTTH 20E

25. Steroid hormones (ie 20E): hydrophobic signaling molecules that can pass through the plasma membrane 20E Figure 15.16

26. Most signals Steroid hormones (ie. 20E)

27. An insecticide produced by plants cause premature metamorphosis