1. Chapter 21 The Genetic Basis of Development

2. Model Organisms

3. Embryonic Development Cell Division Cell differentiation Morphogenesis –Body plan and body axes –Animals: Movements of cells and tissues –Plants: Apical meristems

4. LE 21-4 Animal development Zygote (fertilized egg) Eight cellsBlastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell movement Gut Cell division Morphogenesis Observable cell differentiation Seed leaves Shoot apical meristem Root apical meristem Plant Embryo inside seed Two cells Zygote (fertilized egg) Plant development

5. Differential Gene Expression Genomic equivalence? Totipotency in plants – Fig, 21.5 –Cells dedifferentiated Dedifferentiation in animal cells? –Cloning

6. LE 21-5 Transverse section of carrot root 2-mg fragments Fragments cul- tured in nutrient medium; stir- ring causes single cells to shear off into liquid. Single cells free in suspension begin to divide. Embryonic plant develops from a cultured single cell. Plantlet is cul- tured on agar medium. Later it is planted in soil. A single somatic (nonreproductive) carrot cell developed into a mature carrot plant. The new plant was a genetic duplicate (clone) of the parent plant. Adult plant

7. LE 21-6 Frog embryoFrog egg cellFrog tadpole UV Less differ- entiated cell Donor nucleus trans- planted Enucleated egg cell Most develop into tadpoles <2% develop into tadpoles Donor nucleus trans- planted Fully differ- entiated (intestinal) cell

8. LE 21-7 Mammary cell donor Egg cell donor Egg cell from ovary Nucleus removed Cells fused Cultured mammary cells are semistarved, arresting the cell cycle and causing dedifferentiation Nucleus from mammary cell Early embryo Grown in culture Implanted in uterus of a third sheep Surrogate mother Embryonic development Lamb (“Dolly”) genetically identical to mammary cell donor

9. Stem Cells in Animals Stem cells Embryonic –Totipotent Adult –Pluripotent stem cells

10. LE 21-9 Embryonic stem cellsAdult stem cells Pluripotent cells Totipotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cellsNerve cellsBlood cells

11. Differentiation Transcriptional regulation of gene expression during development –Determination and tissue-specific proteins –Master regulatory genes Cytoplasmic determinants and cell-cell signals –Cytoplasmic determinants –Induction

12. LE 21-10_3 Nucleus Embryonic precursor cell DNA OFF Master control gene myoDOther muscle-specific genes mRNAOFF Determination Myoblast (determined) MyoD protein (transcription factor) Differentiation Muscle cell (fully differentiated) mRNA MyoD mRNA Another transcription factor Myosin, other muscle proteins, and cell-cycle blocking proteins

13. LE 21-11a Sperm Molecules of a cytoplasmic determinant Fertilization Nucleus Molecules of another cytoplasmic determinant Unfertilized egg cell Zygote (fertilized egg) Mitotic cell division Two-celled embryo Cytoplasmic determinants in the egg

14. LE 21-11b Early embryo (32 cells) Signal transduction pathway Signal receptor Signal molecule (inducer) NUCLEUS Induction by nearby cells

15. Pattern Formation Pattern formation – the body plan Positional information –Cytoplasmic determinants –Induction

16. LE 21-12a Egg cell developing within ovarian follicle Follicle cell Nucleus Egg cell Fertilization Nurse cell Fertilized egg Embryo Nucleus Laying of egg Egg shell Multinucleate single cell Early blastoderm Plasma membrane formation Late blastoderm Yolk Body segments Cells of embryo Segmented embryo 0.1 mm

17. LE 21-12b Hatching Larval stages (3) Pupa Metamorphosis Adult fly Head Thorax Abdomen 0.5 mm BODY AXES Dorsal Ventral PosteriorAnterior

18. LE 21-13 Eye Antenna Leg Wild typeMutant

19. Cell Signaling: Body Plan Axis establishment –Maternal effect genes (aka, egg-polarity genes) –Morphogens Segmentation pattern – genes Identity of body parts –Homeotic genes (Hox genes) Apoptosis

20. LE 21-14 Head Tail Wild-type larva Mutant larva (bicoid) Drosophila larvae with wild-type and bicoid mutant phenotypes Developing egg cell Bicoid mRNA in mature unfertilized egg Nurse cells Egg cell bicoid mRNA Bicoid protein in early embryo Fertilization Translation of bicoid mRNA 100  Gradients of bicoid mRNA and Bicoid protein in Normal egg and early embryo Anterior end m

21. Table 21-UN425

22. LE 21-18 Ced-9 protein (active) inhibits Ced-4 activity Mitochondrion Ced-4Ced-3 Inactive proteins Death signal receptor No death signal Death signal Ced-9 (inactive) Cell forms blebs Active Ced-4 Active Ced-3 Other proteases Nucleases Activation cascade Death signal

23. Morphological Diversity Widespread conservation of developmental genes among animals –Homeobox  homeodomain –Not only present in Hox genes

24. LE 21-23a Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome

25. LE 21-23b Mouse chromosomes Mouse embryo (12 days) Adult mouse