Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Epigenetics of human development wikipedia , lookup
Genetic engineering wikipedia , lookup
Gene therapy of the human retina wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Genome (book) wikipedia , lookup
History of genetic engineering wikipedia , lookup
Designer baby wikipedia , lookup
Epigenetics in stem-cell differentiation wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Ch. 21: The Genetic Basis of Development The application of genetic analysis and DNA technology has changed our understanding of how a complex multicellular organism develops from a single cell. In 1995, Swiss researchers demonstrated that a particular gene functions as a master switch that triggers the development of the eye in Drosophila. A similar gene triggers eye development in mammals. Developmental biologists are discovering remarkable similarities in the mechanisms that shape diverse organisms. Chapter 21: The Genetic Basis of Development 1. How do we study development in the genetics-based lab? -Model organisms -fruit fly, nematode worm, mouse, etc. Figure 21.2 Model Organisms for Genetic Studies of Development DROSOPHILA MELANOGASTER (FRUIT FLY) Drosophila - small, easy & cheap to culture - 2 week generation time - 4 chromosomes - LARGE literature of info CAENORHABDITIS ELEGANS (NEMATODE) C elegans - easy to culture - transparent body with few cell types - zygote to mature adult in 3 days 0.25 mm ARABIDOPSIS THAMANA (COMMON WALL CRESS) MUS MUSCULUS (MOUSE) Zebra fish - vertebrate - external fertilization - external development Mouse - mammalian vertebrate - LARGE literature - transgenics & knock-outs - internal fertilization - internal development DANIO RERIO (ZEBRAFISH) Chapter 21: The Genetic Basis of Development 2. How does a zygote transform into an organism? 1) Cell division – early cell divisions are called cleavage – no cytokinesis 2) Morphogenesis—”creation of form/shape” 3) Cell differentiation – process by which cells become specialized differential gene expression!!! Figure 21.3a, b (a) Fertilized eggs of a frog (b) Tadpole hatching from egg (a) Animal development. Most animals go through some variation of the blastula and gastrula stages. The blastula is a sphere of cells surrounding a fluid-filled cavity. The gastrula forms when a region of the blastula folds inward, creating a tube—a rudimentary gut. Once the animal is mature, differentiation occurs in only a limited way—for the replacement of damaged or lost cells. Cell movement Zygote (fertilized egg) Eight cells Blastula (cross section) Gut Gastrula (cross section) Adult animal (sea star) Cell division Morphogenesis (b) Plant development. In plants with seeds, a complete embryo develops within the seed. Morphogenesis, which involves cell division and cell wall expansion rather than cell or tissue movement, occurs throughout the plant’s lifetime. Apical meristems (purple) continuously arise and develop into the various plant organs as the plant grows to an indeterminate size. Observable cell differentiation Seed leaves Shoot apical meristem Zygote (fertilized egg) Root apical meristem Two cells Figure 21.4a, b Embryo inside seed Plant Chapter 47: Animal Development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? - Cytoplasmic determinants – mRNA & proteins in egg cytoplasm - Cleavage pattern – divides cytoplasmic determinants - Induction – cellular peer pressure—responses to signals from nearby cells Figure 21.11 Sources of developmental information for the early embryo Unfertilized egg cell Molecules of another cytoplasmic determinant Sperm Molecules of a a cytoplasmic determinant Fertilization Nucleus Zygote (fertilized egg) Mitotic cell division Two-celled embryo (a) Cytoplasmic determinants in the egg. The unfertilized egg cell has molecules in its cytoplasm, encoded by the mother’s genes, that influence development. Many of these cytoplasmic determinants, like the two shown here, are unevenly distributed in the egg. After fertilization and mitotic division, the cell nuclei of the embryo are exposed to different sets of cytoplasmic determinants and, as a result, express different genes. Figure 21.11b Early embryo (32 cells) NUCLEUS Signal transduction pathway Signal receptor Signal molecule (inducer) (b) Induction by nearby cells. The cells at the bottom of the early embryo depicted here are releasing chemicals that signal nearby cells to change their gene expression. Cellular peer pressure Figure 47.24 How does distribution of the gray crescent at the first cleavage affect the potency of the two daughter cells? EXPERIMENT 1 Left (control): Fertilized salamander eggs were allowed to divide normally, resulting in the gray crescent being evenly divided between the two blastomeres. Gray crescent Right (experimental): Fertilized eggs were constricted by a thread so that the first cleavage plane restricted the gray crescent to one blastomere. Gray crescent 2 The two blastomeres were then separated and allowed to develop. Normal Belly piece Normal RESULTS Blastomeres that receive half or all of the gray crescent develop into normal embryos, but a blastomere that receives none of the gray crescent gives rise to an abnormal embryo without dorsal structures. Spemann called it a “belly piece.” CONCLUSION The totipotency of the two blastomeres normally formed during the first cleavage division depends on cytoplasmic determinants localized in the gray crescent. Now let’s look at induction…. Figure 47.25 Can the dorsal lip of the blastopore induce cells in another part of the amphibian embryo to change their developmental fate? EXPERIMENT Spemann and Mangold transplanted a piece of the dorsal lip of a pigmented newt gastrula to the ventral side of the early gastrula of a nonpigmented newt. Pigmented gastrula (donor embryo) Dorsal lip of blastopore Nonpigmented gastrula (recipient embryo) RESULTS During subsequent development, the recipient embryo formed a second notochord and neural tube in the region of the transplant, and eventually most of a second embryo. Examination of the interior of the double embryo revealed that the secondary structures were formed in part from host tissue. Primary embryo Secondary structures: Notochord (pigmented cells) Neural tube (mostly nonpigmented cells) Primary structures: Secondary (induced) embryo Neural tube Notochord CONCLUSION The transplanted dorsal lip was able to induce cells in a different region of the recipient to form structures different from their normal fate. In effect, the dorsal lip “organized” the later development of an entire embryo. Chapter 47: Animal Development 1. 2. 3. 4. How do we study development in the genetics-based lab? How does a zygote transform into an organism? What three things influence cell fate? Once cells have differentiated can they de-differentiate? - Plant cuttings - Animal cells???? Transverse section of carrot root EXPERIMENT 2-mg fragments Fragments cultured in nutrient medium; stirring 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 cultured on agar medium. Later it is planted in soil. A single RESULTS Somatic (nonreproductive) carrot cell developed into a mature carrot plant. The new plant was a genetic duplicate (clone) of the parent plant. Adult plant CONCLUSION At least some differentiated (somatic) cells in plants are toipotent, able to reverse their differentiation and then give rise to all the cell types in a mature plant. Figure 21.5 Figure 21.6 Can the nucleus from a differentiated animal cell direct development of an organism? EXPERIMENT Researchers enucleated frog egg cells by exposing them to ultraviolet light, which destroyed the nucleus. Nuclei from cells of embryos up to the tadpole stage were transplanted into the enucleated egg cells. Frog embryo Frog egg cell Fully differentiated (intestinal) cell Less differentiated cell Donor nucleus transplanted Most develop into tadpoles Frog tadpole Enucleated egg cell Donor nucleus transplanted <2% develop into tadpoles Permanent (epigenetic) changes had occurred to the differentiated nucleus -Methylation of DNA to turn off non-intestinal genes -Only intestinal activators available Chapter 21: Genetic basis of development 1. 2. 3. 4. 5. How do we study development in the genetics-based lab? How does a zygote transform into an organism? What three things influence cell fate? Once cells have differentiated can they de-differentiate? How was Dolly cloned? - nuclear transplantation Fig. 21.7 Reproductive Cloning of a Mammal by Nuclear Transplantation APPLICATION This method is used to produce cloned animals whose nuclear genes are identical to the donor animal supplying the nucleus. 1 RESULTS The cloned animal is identical in appearance and genetic makeup to the donor animal supplying the nucleus, but differs from the egg cell donor and surrogate mother. 2 Egg cell from ovary Nucleus Nucleus removed 3 Cells fused removed TECHNIQUE Shown here is the procedure used to produce Dolly, the first reported case of a mammal cloned using the nucleus of a differentiated cell. Egg cell donor Mammary cell donor Cultured mammary cells are semistarved, arresting the cell cycle and causing dedifferentiation Nucleus from mammary cell 4 Grown in culture Early embryo Dolly only lived 6 yrs. Premature signs of aging…no telomerase! 5 Implanted in uterus of a third sheep 6 Embryonic development Surrogate mother Lamb (“Dolly”) genetically identical to mammary cell donor Chapter 21: Genetic basis of development 1. 2. 3. 4. 5. 6. How do we study development in the genetics-based lab? How does a zygote transform into an organism? What three things influence cell fate? Once cells have differentiated can they de-differentiate? How was Dolly cloned? What is a stem cell? - a relatively unspecialized cell - can differentiate into different cell types under specific conditions Figure 21.9 Working with stem cells Embryonic stem cells Adult stem cells Early human embryo at blastocyst stage (mammalian equivalent of blastula) From bone marrow in this example Totipotent cells Pluripotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cells Nerve cells Blood cells Chapter 21: Genetic basis of development 1. 2. 3. 4. 5. 6. How do we study development in the genetics-based lab? How does a zygote transform into an organism? What three things influence cell fate? Can cells de-differentiate? How was Dolly cloned? What is a stem cell? - Embryonic – totipotent - Adult – pluripotent - iPS – induced pluripotent stem cell - differentiated cells get re-programmed - retroviruses used to introduce extra cloned copies of 4 stem cell master regulator genes in differentiated cells - some “kinks” still exist - WFIRM – WF Institute of Regenerative Medicine 7. When is a cell “determined” (fated)? - Master regulator gene(s) turned “on” - Muscle cells – MyoD transcription factor – activator turns on all muscle genes Figure 21.10 Determination and differentiation of muscle cells Nucleus Master control gene myoD Other muscle-specific genes DNA Embryonic precursor cell OFF OFF Figure 21.10 Determination and differentiation of muscle cells Nucleus Master control gene myoD Other muscle-specific genes DNA OFF Embryonic precursor cell 1 Myoblast (determined) Determination. Signals from other cells lead to activation of a master regulatory gene called myoD, and the cell makes MyoD protein, a transcription factor. The cell, now called a myoblast, is irreversibly committed to becoming a skeletal muscle cell. OFF OFF mRNA MyoD protein (transcription factor) Figure 21.10 Determination and differentiation of muscle cells Nucleus Master control gene myoD Other muscle-specific genes DNA OFF Embryonic precursor cell 1 Myoblast (determined) 2 Determination. Signals from other cells lead to activation of a master regulatory gene called myoD, and the cell makes MyoD protein, a transcription factor. The cell, now called a myoblast, is irreversibly committed to becoming a skeletal muscle cell. Differentiation. MyoD protein stimulates the myoD gene further, and activates genes encoding other muscle-specific transcription factors, which in turn activate genes for muscle proteins. MyoD also turns on genes that block the cell cycle, thus stopping cell division. The nondividing myoblasts fuse to become mature multinucleate muscle cells, also called muscle fibers. OFF OFF mRNA MyoD protein (transcription factor) mRNA MyoD Muscle cell (fully differentiated) mRNA Another transcription factor mRNA mRNA Myosin, other muscle proteins, and cell-cycle blocking proteins Chapter 21: Genetic basis of development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? 4. Once cells differentiate can they de-differentiate? 5. How was Dolly cloned? 6. What is a stem cell? 7. When is a cell “determined” (fated)? 8. How does morphogenesis (pattern formation) occur in animals? - development of spatial organization of tissues & organs - mostly occurs in embryonic & juvenile stages of animals - occurs continually in plants - consists of molecular cues that direct formation – differential gene expression Figure 21.12 Key developmental events in the life of Drosophila Follicle cell Nucleus Egg cell developing within Egg cell ovarian Nurse follicle cell Fertilization Laying of egg Fertilized egg Egg shell Nucleus 1 Embryo Multinucleate single cell 2 Early blastoderm Plasma membrane formation 3 Yolk Late blastoderm Cells of embryo 4 Segmented embryo Body segments 0.1 mm 5 Hatching Larval stages (3) 6 Pupa Metamorphosis Head Thorax 7 Abdomen Adult fly 0.5 mm Dorsal BODY AXES Anterior Posterior Ventral Chapter 21: Genetic basis of development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? 4. Once cells differentiate can they de-differentiate? 5. How was Dolly cloned? 6. What is a stem cell? 7. When is a cell “determined” (fated)? 8. How does morphogenesis (pattern formation) occur in animals? 9. How can gene function be determined (ch 20)? - study mutants & knock-outs - helped us understand animal development Chapter 21: The Genetic Basis of Development Eye Antenna Leg Wild type Mutant Chapter 21: Genetic basis of development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? 4. Once cells differentiate can they de-differentiate? 5. How was Dolly cloned? 6. What is a stem cell? 7. When is a cell “determined” (fated)? 8. How does morphogenesis (pattern formation) occur in animals? 9. How can gene function be determined (ch 20)? 10. How do flies go from zygote to organism? - cytoplasmic determinants in egg produced by maternal effect genes - establish axes (anterior & posterior, left & right) - bicoid Chapter 21: The Genetic Basis of Development Maternal effect genes are aka egg-polarity genes bicoid – determines anterior end – transcription factor Tail Head T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8 Wild-type larva Tail Tail A8 A7 Mutant larva (bicoid) A8 A6 A7 (a) Drosophila larvae with wild-type and bicoid mutant phenotypes. A mutation Figure 21.14a in the mother’s bicoid gene leads to tail structures at both ends (bottom larva). The numbers refer to the thoracic and abdominal segments that are present. Egg cell Nurse cells 1 Developing egg cell bicoid mRNA 2 Bicoid mRNA in mature unfertilized egg Fertilization Translation of bicoid mRNA 100 µm 3 Bicoid protein in early embryo Anterior end (b) Gradients of bicoid mRNA and Bicoid protein in normal egg and early embryo. Figure 21.14b Chapter 21: The Genetic Basis of Development In flies, after the body’s axes are determined…. - segmentation genes produce proteins that direct formation of body segments - identity of body segments is directed by homeotic genes (many) - all have 180 nucleotide (60 aa) homeobox domain common to many invertebrates & vertebrates - suggests that they developed early in history of life on Earth - Hox genes Hierarchy of Gene Activity in Early Drosophila Development Maternal effect genes (egg-polarity genes) Gap genes Pair-rule genes Segment polarity genes Homeotic genes of the embryo Other genes of the embryo Segmentation genes of the embryo Chapter 21: Genetic basis of development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? 4. Once cells have differentiated can they de-differentiate? 5. How was Dolly cloned? 6. What is a stem cell? 7. When is a cell “determined” (fated)? 8. How does morphogenesis (pattern formation) occur in animals? 9. How can gene function be determined (ch 20)? 10. How do flies go from zygote to organism? 11. What have we learned from C elegans? Chapter 21: The Genetic Basis of Development -Cell lineage (cell history) of the C. elegans nematode is known… Zygote 0 Time after fertilization (hours) First cell division Nervous system, outer skin, musculature Outer skin, nervous system Musculature, gonads Germ line (future gametes) Musculature 10 Hatching Intestine Intestine Eggs Vulva ANTERIOR POSTERIOR 1.2 mm Induction leads to many developmental changes in C elegans Figure 21.16 Cell signaling & induction during development of C elegans a. Induction of cell 3 by cell 4 causes….. -posterior daughter cell to form intestines -anterior daughter cell to form muscle & gonads b. The anchor cell induces the 6 cells of the vulva Chapter 21: Genetic basis of development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? 4. Once cells have differentiated can they de-differentiate? 5. How was Dolly cloned? 6. What is a stem cell? 7. When is a cell “determined” (fated)? 8. How does morphogenesis (pattern formation) occur in animals? 9. How can gene function be determined (ch 20)? 10. How do flies go from zygote to organism? 11. What have we learned from C elegans? 12. What is apoptosis? -programmed cell death – cell suicide -involves ced genes – cell death genes – stimulates production of proteases and nucleases Figure 21.18 Molecular basis of apoptosis in C. elegans Ced-9 protein (active) inhibits Ced-4 activity Death signal receptor Mitochondrion Ced-4 Ced-3 Inactive proteins Cell forms blebs (a) No death signal Ced-9 (inactive) Death signal Active Active Ced-4 Ced-3 Activation cascade (b) Death signal Other proteases Nucleases Figure 21.19 Effect of apoptosis during paw development in mice Interdigital tissue 1 mm Figure 21.19 Chapter 21: Genetic basis of development 1. How do we study development in the genetics-based lab? 2. How does a zygote transform into an organism? 3. What three things influence cell fate? 4. Once cells have differentiated can they de-differentiate? 5. How was Dolly cloned? 6. What is a stem cell? 7. When is a cell “determined” (fated)? 8. How does morphogenesis (pattern formation) occur in animals? 9. How can gene function be determined (ch 20)? 10. How do flies go from zygote to organism? 11. What have we learned from C elegans? 12. What is apoptosis? 13. What is the relationship among the genetic basis of development across organisms? - Molecular analysis of the homeotic genes in Drosophila has shown that they all include a sequence called a homeobox – Hox genes - An identical (or very similar) DNA sequence has been discovered in the homeotic genes of vertebrates and invertebrates Figure 21.23 Conservation of fruit fly homeotic genes in fruit fly & mouse Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome Mouse chromosomes Mouse embryo (12 days) Adult mouse