Genes and Development

1. Genes and Development

2. Development of an organism • Organisms contain many types of cells specialized both structurally and metabolically • All descend from a single zygote • Development is all changes that occur in life • Cell determination • Groups of cells become committed • Leads to cell differentiation • Differences among cell types due to differential gene expression

3. Nuclear equivalence • Nuclei of all differentiated cells are genetically identical • Different cells express different subsets of genes • Somatic cells • Germ line cells • Totipotency • Capability of cells to direct development of entire organism

4. Vertebratecell lineages

5. Cell totipotency

6. Nuclear totipotency

7. Mouse models to study disease • Ethically researchers often cannot use humans as test subjects • Animal model is used instead • An example is cystic fibrosis, a genetic disease • Gene targeting is used to produce mice homozygous or heterozygous for cystic fibrosis

8. First cloned mammal • 1997 • Cloned sheep “Dolly” was born in Scotland • Genetic material derived from • Cultured adult sheep’s mammary gland cell • Fused with enucleated sheep’s egg • Cultured in vitro and transferred to host mother

9. Mammaliancloning

10. Stem cells • Undifferentiated cells • Can produce differentiated descendants • Also retain ability to reproduce themselves • Totipotent stem cells • Give rise to all cell types • Pluripotent stem cells • More specialized

11. Exceptions to nuclear equivalence • Genomic rearrangements • Physical changes in gene structure • Gene amplification • More copies of certain genes for transcription

12. Gene amplification

13. Choice of organisms for research in developmental genetics • Fruit fly, Drosophila melanogaster • Abundance of mutant alleles and ease of mapping new mutations on the chromosomes • Roundworm, Caenorhabditiselegans • Lineage of every somatic cell is known • Laboratory mouse, Mus musculus • Used in studies of mammalian development

14. Life cycleof Drosophila

15. Location of imaginal discs in Drosophila

16. Maternal effect genes • Genes that organize structure of egg cells • Genes in maternal tissues transcribed to produce mRNA molecules that are transported in egg • Analysis of mutant Drosophila revealed that these genes involved in polarity of embryo

17. Early development in Drosophila

18. Classes of genes involved in pattern formation of embryonic segments in Drosophila

19. Segmentation genes • Genes that generate a repeating pattern of body segments within embryo • Gap genes • Pair-rule genes • Segment polarity genes • Homeotic genes

20. Comparison ofmutations in Drosophila segmented genes

21. Antennapedia Locus

22. Hox gene clusters

23. Induction and apoptosis • Induction in C. elegans • Developmental interactions with neighboring cells • Anchor cell induces surface cells to form vulva • Apoptosis in humans • During development, hand forms a webbed structure • Fingers become individualized when cells between them die

24. Caenorhabditiselegans

25. Cell lineages of C.elegans

26. Inductionin C.elegans

27. Mouse model for mammalian development • Transgenic mice studied • Early development of mice and other mammals similar • Almost all research in stages leading to implantation • Chimera • Organism containing two or more kinds of genetically dissimilar cells from two zygotes

28. Chimeric mice

29. Producingatransgenicmouse

30. Cancer and cell development • Cancer-causing oncogenes • Proto-oncogenes • Code for various growth factors or growth factor receptors • Respond to stimulation by growth factors • Cell may misinterpret signal and grow and divide inappropriately • Tumor suppressor gene mutation

31. Cell growth control cascade