1. Genetic models Self-organization How do genetic approaches help to understand development? How can equivalent cells organize themselves into a pattern?

2. GeneFunction Phenotype

3. 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. Developmental Function

4. 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. Developmental Function Mutant Phenotype

5. Developmental Function Protein Biochemical Function Gene Cloned genes can be used to analyze biochemical functions involved in a developmental process Mutant Phenotype

6. To understand a developmental process, figure out relations among genes and proteins affecting the process. Developmental Function Protein Biochemical Function Gene Developmental Function Protein Biochemical Function Gene Developmental Function Protein Biochemical Function Gene

7. Carrying out a mutant screen in a non- hermaphodite species

8. ~1000 somatic cells Transparent Entire cell lineage described Genome sequenced Self-fertilizing hermaphrodite Caenorhabditis elegans – a model genetic species

10. Cell lineage of C. elegans

11. Full somatic cell lineage of C. elegans

12. C. elegans vulva formation

13. Ablate P6, another cell acquires vulval fate instead An equivalence group – P3-P8 cells have the same potential

14. Ablate anchor cell, no vulva forms

15. C. elegans vulva formation Three cells give rise to the vulva because: 1)They are close to the signal source 2)They communicate with each other

16. Where does the Anchor Cell (AC) come from?

17. (from Wilkinson et al. (1994), Cell 79: 1187-1198) Anchor cell (AC) and Ventral uterine precursor cell (VU) – an equivalence group of 2 cells

18. 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

19. (from Wilkinson et al. (1994), Cell 79: 1187- 1198) Model for Anchor cell (AC) and Ventral uterine precursor cell (VU) specification

20. Delta - Notch signaling pathway

21. Lateral inhibition in a field of cells (such as Drosophila neurogenic ectoderm)

22. Drosophila neurogenic ectoderm: Bristles are neural cells Mutant sector with partial loss of Delta function

23. Action of Delta and Notch in Drosophila neurogenic ectoderm Neuroblast Epidermis

24. Action of Delta and Notch in Xenopus neural plate

25. Dominant-negative Delta mRNA injected into Xenopus embryo (Normally, other cells differentiate as neural tissue later)

27. Red blood cell homeostasis through a negative feedback loop Low O 2 EPO production in kidney Red blood cell production EPO High O 2 CFU-E precursor cells

28. Effect of having a hypersensitive erythropoietin (EPO) receptor Low O 2 EPO production in kidney Increased Red blood cell production EPO More O 2 delivery to muscles High O 2 CFU-E precursor cells

29. Effect of having a hypersensitive EPO receptor - Resets the homeostasis at a different level Low O 2 Reduced EPO production in kidney Increased Red blood cell production Less EPO More O 2 delivery to muscles High O 2 CFU-E precursor cells

30. Friday, April 8 th – Class will be in 101 Greenlaw