Chapter 10:Animal Growth and Development 1 Fetus by Leonardo da Vinci
Chapter Objectives • Describe basic stages of embryonic development • Memorize human extra-embryonic membranes; their functions and significance • Explain the influence of cytoplasm and cell-cell interactions
Haploid Sperm Egg 2 1 Meiosis Fertilization Zygote (fertilized egg) Adult 3 Diploid Blastula (cross section) 7 Metamorphosis Digestive tract Outer cell layer (ectoderm) 4 Primitive gut 6 5 Early gastrula Larva Inner cell layer (endoderm) Later gastrula Opening • Most animals reproduce sexually and then proceed through a series of developmental stages
This electron micrograph (courtesy of Dr. Don W. Fawcett and Susumu Ito) shows the sperm cell of a bat. Note the orderly arrangement of the mitochondria. They supply the ATP to power the whip-like motion of the tail. It all begins with fertilization when a sperm... Sperm:male gamete; generally small and motile Gametes: reproductive cells of plants or animals; each has ½ the number of chromosomes required for an adult Check out all those mitochondria!
Egg:female gamete; larger, with protein/fat rich yolk, mitochondria, etc. …fuses with an egg. Zygote = cell formed by fertilization, earliest stage of embryo 22 21 • Plasma membrane changes to prevent any more sperm from entering • The sperm and egg nuclei fuse • The egg becomes “activated,” and metabolism/protein synthesis begins • Zygote cytoplasm moves various chemicals around in the cell that help control development
Sea Urchin Fertilization Membrane2 Unfertilized Sea Urchin Egg Fertilized Sea Urchin Egg The exact changes look different in different organisms… But keeping other sperm out is part of normal animal development! 47-06-SeaUrchinTimeLapse-B.mov
Fertilization The union of egg and sperm give rise to the fetus through this general scheme of events… 1. ZygoteSingle cell made from egg and sperm 2. Growth Increase size and # of cells 3.Differentiation Cells specialize 4.MorphogenesisTissues and organs form Higher levels of organization (tissue, system) Cellular Level
Some Differentiated Cells3 Cytoskeletal Proteins Form follows function! See also p. 265 Transport Proteins Alveolar macrophage 950x Intestinal cell with microvilli 6840x Neurotransmitters Actin and Myosin Heart muscle cell 5050x Neuron 635x
Each kind of cell makes specific proteins… Which give it special shape and abilities, 14
But how to get there from a zygote?And make it all work together?! Step 1.Start first with setting the stage for development… Egg + Sperm = Zygote 7 24 Xenopus laevis & fertilized eggs9
Xenopus Eggs26 Then, which is back, front, etc… ? 7 This part is controlled by chemicals in the cytoplasm! 8
Step 2: Cleavage Where the zygote grows through many rounds of mitosis… The cells get smaller each time… Producing a Morula! 16-64 cells 9
Step 3: Blastulation The morula turns into fairly simple ball of cells called a Blastula, often with a hollow blastocoel in the middle 9 Different animals have blastulae of different shapes and forms. See P. 266 The growth stage now ends, and differentiation/morphogenesis begins…
Infolding of cells Step 4: Gastrulation8 Some cells move from the surface of the blastula to the middle ~ Producing3 Primary Germ Layers. Ectoderm: Skin, nervous system, sense receptors Endoderm : Digestive system lining Mesoderm : Skeleton, muscles, heart, internal organs, blood This is very complex--- Cells change shape, location, and their connections to each other. Xenpus Movies\lotscleavmov2.mov
So far… Gastrulation Cleavage Ectoderm Mesoderm Endoderm Zygote 2-cell embryo Gastrula (cross section) Blastocyst (cross section) Many-celled solid ball
Step 5: Neurulation8 The Gastrula morphs into a Neurula ~ • The first mesoderm becomes the Notochord which will become the backbone. The body plan becomes clear – dorsal, ventral, etc. • The dorsal ectoderm folds up to form the Neural Tube which will develop into the brain, spinal cord, and nerves. See Figure 10.8 on P. 268
9 Neurulation in Xenopus laevis C/D B A Ectoderm 10 Xenpus Movies\gastmov.mov
Further Differentiation and Morphogenesis9 In Xenopus, this happens in about a week!
… Surprised?5 Zebrafish Chicken Dog Human Skink
Developmental Patterns and Evolutionary Relationships11 All vertebrates evolved from a common ancestor and develop in similar ways! See P. 270
Homeotic Genes Genes which determine what body parts are made where… Segmentation:dividing the body into functional sections Turn other genes on or off as needed Homeotic Genes and Morphogenesis Homeotic (Hox) Gene Homeobox: (60 aa) makes the protein product bind to DNA Development Gene Transcription regulated by the Hox protein 23 Homeodomain: DNA binding site 23 Polydactyly: A mutation in Homo sapiens in the Hoxd13 gene 12 A mutation in Drosophila melanogasterin the Antennapedia gene ~ 4 min
The amazing thing is that the fly and mouse genes have really similar DNA sequences… What does that mean? Think Ch. 9 10
The Journey of the Human Zygote10 In humans, the blastula is called a Blastocyst. The inner cell mass goes through Gastrulation.
1. The inner cell mass goes through gastrulation like other vertebrates 2. The rest of the blastocyst develops into the embryonic membranes Amnion: Surrounds embryo Chorion: encloses all other membranes 3. The Chorion extends villi into the uterine wall Chorionic villi + Uterine lining = Placenta Gastrulation in Humans15 Blastocyst (Blastula Stage) Cavity Outer Cell Layer (Future Chorion) Inner Cell Mass Uterine Lining (Endometrium)
Maternal - Fetal Circulation10 Chorion Placenta Amnion
6 At 8 weeks, we start calling the embryo a Fetus.
www.w-cpc.org/fetal1.htmlhttp://www.med.unc.edu/embryo_images/unit-welcome/welcome_htms/contents.htmhttp://www.visembryo.com/baby/stage5.htmlhttp://anatomy.med.unsw.edu.au/cbl/embryo/Embryo.htmwww.w-cpc.org/fetal1.htmlhttp://www.med.unc.edu/embryo_images/unit-welcome/welcome_htms/contents.htmhttp://www.visembryo.com/baby/stage5.htmlhttp://anatomy.med.unsw.edu.au/cbl/embryo/Embryo.htm These sites are linked on our course web page. They provide fantastic animations and greater in depth detail regarding human embryological development. The pictures in your book are cool, too!
Birth Defects can be caused by defective genes or environmental factors. Neural Tube Defects--- caused by problems at the neurulation stage… Eg. Spina bifida and Anencephaly Many can be prevented with Folic Acid and Vitamin B-12 but there are also 3 genes involved. See P. 275 17 16
The Nucleus contains all genes needed by an adult organism…20 But other factors in the cell matter, too. Just having all the genes isn’t enough… Differentiation turns some genes off! Look at P. 279
The later in development we get the DNA, the less likely it is to produce a viable tadpole.25 So, what’s going on?
What causes determination and differentiation? • Determination: the commitment of a cell to its “fate” or course of development Point of No Return • Differentiation: when the cell changes to fulfill its determined function. • How do we even ask the questions? • Surgical techniques moving cells around • Moving cell nuclei into new cells • DNA-RNA Hybridization – to see what mRNA is being transcribed in specific cells.
The Overall Picture26 2. Differentiation 1. Determination
What’s going on with differentiation?? They all have the same genes, but… What’s the green mean? 27
Determination & Differentiation 1. Cytoplasmic Determination Different concentrations of regulatory molecules in the cytoplasm of the zygote can activate different genes causing early Determination. Some animals are more flexible than others… See P. 281 See P. 283 for a specific example
Gene Expression in Drosophila18 Regulatory proteins in early development determine regions of the embryo where different genes are transcribed and translated (Expressed).
DNA-RNA Hybridization25 Use a labeled (tagged) piece of DNA to find out which cells are making mRNA. Then, you know which proteins are being made where.
Determination & Differentiation2. Cell-Cell Interactions (Embryonic Induction) Embryonic cells interact with each other, affecting each other’s developmental fate. See P. 284 This doesn’t happen if you transplant cells from early gastrula stages. You just get skin.So there’s a critical period where a cell’s fate can still be changed.
More specifically, the inducing signal is coming from the developing notochord. 10 See P. 285
Further Discoveries 1. Cells do NOT have to be touching to induce a response --- So some diffusable molecule is the signal. 2.The notochord produces 2 proteins that signal for neural induction (production of neural tissues) -- Chordin and Noggin 3. Chordin and Noggin control the synthesis of other proteins that then regulate transcription of nerve specific proteins. Over 10 proteins have been identified. And there is still so much we don’t know….
Sources Cited 1. www.ana.sote.hu/fejl1.htm 2. smccd.net/accounts/snitovsky/ watertest.htm 3. www.denniskunkel.com with permission 4. http://www.snv.jussieu.fr/vie/dossiers/XenopeSegm/segmxen.html 5. http://www.exploratorium.edu/exhibits/embryo/embryo.html# 6. http://embryo.soad.umich.edu/carnStages/carnStages.html 7. http://anthro.palomar.edu/animal/glossary.htm 8. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html 9. http://www.snv.jussieu.fr/bmedia/xenope1/xenope3.html 10. BioCD. From Biology, Fifth Edition. Campbell, Reece, Mitchell. Addison, Wesley, Longman. 1999. 11. laxmi.nuc.ucla.edu:8888/.../Basic_Embryology_I/ Pindex.html 12. http://zygote.swarthmore.edu/droso4.html 13. http://www.eatonhand.com/img/img00040.htm 14. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AnimalTissues.html 15. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookREPROD.html 16. http://medgen.genetics.utah.edu/photographs/pages/neural_tube_defects.htm 17. http://www.surgical-tutor.org.uk/default-home.htm?system/hnep/neural_tube.htm~right 18. http://www.mpibpc.gwdg.de/inform/MpiNews/cientif/jahrg8/1.02/fig6.html 19. http://www.biology.arizona.edu/developmental_bio/problem_sets/Developmental_Mechanisms/06t.html 20. http://www.usask.ca/biology/biol316/316questions/development.html 21. www.bbc.co.uk/health/genes/ basics/what_4.shtml 22. www.stanford.edu/dept/news/report/ news/august9/sperm-89.htm 23. http://www.eatonhand.com/img/img00040.htm 24. batraciens.net/ xenopus.htm 25. BSCS Biology Blue, 8th Edition 26. http://www.micromacro.co.uk/natural_history/html/amphib/nh6003.htm 27. w3.dwm.ks.edu.tw/bio/ activelearner/16/ch16c3.html 28. Bioshow: for Biology: Concepts and Connections, Second Edition. Campbell, Mitchell, and Reece