Genetic models Self-organization

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

2. Gene Function Phenotype

3. 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 Gene Mutant Phenotype

4. 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 Gene Mutant Phenotype

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

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

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

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

9. 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: • They are close to the signal source • They communicate with each other

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

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

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

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 High O2 CFU-E precursor cells Red blood cell production Low O2 EPO EPO production in kidney

28. Effect of having a hypersensitive erythropoietin (EPO) receptor More O2 delivery to muscles High O2 Increased Red blood cell production CFU-E precursor cells Low O2 EPO EPO production in kidney

29. Effect of having a hypersensitive EPO receptor - Resets the homeostasis at a different level More O2 delivery to muscles High O2 Increased Red blood cell production CFU-E precursor cells Low O2 Less EPO Reduced EPO production in kidney

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