\di-ve-ləp-mənt\

1. \di-ve-ləp-mənt\ By James Kwan, Kai Orans, and Amy WAAHN

2. Different Forms of Development • Tadpoles and caterpillars are larval forms of adult forms • Larval form of sea urchin drifts in ocean surface waters until it develops into an adult • The zygotes of some animals (humans) develop into an infant that is much like the adult form.

3. Stages of Development • Fertilization • Cleavage • Gastrulation • Organogenesis

4. Fertilization • Internal and external fertilization • Gonads of the parents produces sperm and eggs • Contact of sperm with egg surface initiates metabolic reactions, activating egg • Main function: combining haploid sets of chromosomes into a single diploid zygote

5. The Acrosomal Reaction • Acrosomal reaction: specialized vesicle at tip of sperm (acrosome) discharges enzymes that digest the jelly coat surrounding the egg • Contact of the tip of acrosomal process (sperm structure) with egg membrane leads to fusion of plasma membranes • Fast block to polyspermy

6. The Corsical Reaction and Activation of Egg • Vesicules fuse with egg plasma membrane • Formation of fertilization envelope, resisting entry of additional sperm • Slow block to polyspermy • Activation of egg: substantial increase in the rates of cell respiration and protein synthesis

7. Acrosomal and Cortical Reactions

8. Fertilization shares many features in common with that of sea urchins. • Differences in timing among species • Example: in sea urchins, eggs have completed meiosis when released from female • Human eggs are arrested at metaphase of meiosis II

9. Mammalian Fertilization • Zona pellucida: extracellular matrix of the egg • Ensures moist environment for sperm • No fast block to polyspermy • Functions as sperm receptor: binding initiates acrosomal reaction and cortical reaction • Example: increase in sperm motility

10. Fertilization in Mammals

11. Cleavage • Succession of rapid cell division • Cells carry out S and M phases • Blastomeres: smaller cells that result from the partition of the zygote • Zygotes of sea urchins and other animals have definite polarity • Planes of division follow a pattern relative to poles of zygote • Establishment of three body axes

12. Cleavage cont’d • Polarity defined by uneven distribution of substances in cytoplasm • Yolk: stored nutrients • Vegetal pole (pole of egg where yolk is concentrated) and animal pole (pole where yolk concentration decreases) • Animal-vegetal axis of egg determines head-tail axis of embryo (ex: sea urchin eggs have a-v axis due to uneven distribution of substances

13. Cleavage cont’d • Holoblastic cleavage: blastocoel (fluid-filled cavity) centrally located, cleavage furrow passes all the way through the cells • Examples: animals whose eggs contain relatively little yolk, such as frogs, sea urchins, echinoderms, most chordates and deuterostomes • Meroblastic cleavage: incomplete division of egg • Example: bird eggs

14. Gastrulation • Morphogenetic process: groups of cells take up new locations that allow the formation of tissues and organs • For most animals, it is a rearrangement of blastula cells, producing 3-layered embryo with primitive digestive tube • Positioning allows cells to interact with each other, generating organs

15. Gastrulation cont’d • Three layers produced collectively called embryonic germ layers: • Ectoderm: outer layer • Endoderm: lines embryonic digestive tract • Mesoderm: fills space between ectoderm and endoderm

16. Gastrulation cont’d • Shallow invagination (cells buckle inward) transforms into archenteron • Blastopore: open end of archenteron • Gastrulation in sea urchins and frogs produces three-layered embryo (characteristic of most animal phyla, established early in development)

17. Gastrulation (chicken)

18. Regions of the three embryonic germ layers develop into rudimentary organs during organogenesis Cell migration, cell condensations, cell signaling, cell shape changes (similar mechanisms for vertebrates and invertebrates, but still differences because of different body plans) Condensation of dorsal mesoderm forms notochord Infolding of ectodermal neural plate forms neural tube, becomes central nervous system Neural Crest formed, a collection of cells that disperse throughout the body giving rise to teeth, bones, cartilage Organogenesis

19. Cell Differentiation Cells become specialized in structure and function Organized into tissues and organs in a 3-D arrangement Cytoplasm contains both RNA and proteins encoded by mother’s DNA Maternal substances in the egg that influence the courses of development are called cytoplasmic determinants Combination of these helps determine developmental fate by regulating expression of cell’s genes Another source of developmental info is the environment around a cell (induction)-signaling pathways Transcription regulates gene expression

20. Morphogenesis Major aspect of development, involve movement of cells Changes in cell shape involve reorganization of the cytoskeleton (ex. cells of neural plate into neural tube) Also drives cell migration Convergent extension, cells of a tissue become narrower while becoming longer, changes spherical shape of gastrula to rectangular shape of embryo

21. Extracellular Matrix (ECM) ECM= glycoproteins and macromolecules outside cell plasma membrane Cell membrane receptors bind to ECM Substances to inhibit migration Dialogue between cells as move on ECM

22. Territorial diagrams of embryonic development Combined with manipulation of test subject development Discoveries: 1) specific tissue of older embryo are of founder cells with unique factors b/c of asymmetrical division 2) older cells have less development potential Fate Mapping

23. Pattern Formation Cells influence fates through induction, switch on special genes to differentiate cell tissue Dorsal lip of blastopore = “organizer” Pattern formation Positional information (molecular cues) Apical ectodermal ridge (AER) – promote limb-bud outgrowth Zone of polarizing activity (ZPR) – limb bud organizer

24. Axes of the Body Plan Nonamniote vertebrates instructions for forming the body axes are established early (oogenesis or fertilization) Amniote body axes aren’t established until later Positional information is provided by cytoplasmic determinants and inductive signals Axes genes are encoded by genes from the mother, fittingly called maternal effect genes

25. Cell Movement Cell adhesion molecules (CAMs) –proteins that guide cell migration and stabilize tissue by binding to CAMs of other cells Cadherins (important group of CAMs)

26. Body Plan Overview Body plan is a set of morphological and developmental traits integrated into a whole Animals can be classified based on symmetry (radial, top and bottom, or bilateral) Bilateral animals have four sides and a central nervous system (brain) in the anterior end Symmetry fits lifestyle Number of germ layers can differentiate as well Cnidarians and comb jellies have only two: ectoderm and endoderm (diploblastic) while bilaterally symmetrical animals have three (triploblastic) Most triploblastic animals possess a body cavity, called coelom, which forms from tissue derived from mesoderm Coelom contains fluid that cushions suspended organs and enables organs to grow independently of outer body wall

27. Body Plan Illustrated

28. Specify anterior-posterior segment identity during embryonic development Play a role in limb pattern formation Mutations in regulatory sequences cause major changes in body form (Drosiphila growing legs in place of antennae) Differing patterns in insects and crustaceans can explain variation in number of leg bearing segments In arthropods changes in the sequence of existing Hox genes influenced increased body segment diversity, a hard exoskeleton, and jointed appendages Control development of the major regions of the vertebrate brain (similarities between anterior-posterior order in lancelets and vertebrates) Hox Genes

29. Three differences: cleavage, coelom formation, fate of blastopore Protostomes undergo spiral determinate cleavage, mesoderm splits and forms coelom Deuterostomes have radial indeterminate cleavage, folds of archenteron become coelom In protostomes, blastopore becomes head while in deuterostomes it becomes anus Protostome vs. Deuterostome

30. Cnidarians have diploblastic radial body, gastrovascular cavity, polyp and medusa form Cephalopods (octopus) feet evolved into a muscular siphon and part of the tenticle, well developed sense organs and complex brain, lost shell from mollusk ancestors Arthropods have a rigid exoskeleton, a variety of gas exchange organs, special appendages for specific tasks Crustaceans and Echinoderms (starfish) can regrow lost arms and legs Invertebrate Adaptations

31. Simple chordates Lancelets and tunicates show that ancestral chordates had genes related to the mammalian heart, thyroid gland, and brain Aquatic vertebrates developed fins, vertebrae, and a more extensive skull Mineralization allowed animals to become predators (started in the mouth and skull) Gnathostomes developed gills for gas exchange and jaws also underwent duplication of Hox genes Tetrapods developed legs in place of fins to walk on land Chordate-Vertebrate Adaptations

32. Vertebrate embryos require an aqueous environment to develop Movement of vertebrates onto land required shell and uteral adaptations, increased embryonic contact with fluid Amniotes include birds and mammals (amnions) Extraembryonic membranes include (chorion, amnion, yolk sac, allantois) provide life support system Amniote Adaptations

33. Mammalian Development Small eggs, store few nutrients, holoblastic cleavage Fertilization takes place in the oviduct Despite lack of yolk, mammalian gastrulation and organogenesis are similar to that of birds and other reptiles At completion of cleavage, embryo is in blastocyst stage Trophoblast initiates implantation and provides support Inner cell mass forms epiblast and hypoblast, homologous to those of birds When implantation is completed, gastrulation begins, invading trophoblast, mesodermal cells, and endometrial tissue contribute to forming a placenta By the end of gastrulation, embryonic germ layers have formed, as well as extraembryonic mesoderm and membranes Extra-embryonic membranes in mammals are homologous to those of birds and other reptiles

34. Developmental Disorders

35. Mental Retardation Top 3 causes: Down syndrome, fetal alcohol syndrome and Fragile X syndrome Include: epilepsy, autism, cerebral palsy and other disorders

36. Fetal Alcohol Syndrome • When the female ingests alcohol, it crosses the placental barrier and can stunt or modify growth, damage neurons and brain structure, and cause other physical or mental disorders • Amount, frequency, and timing of ingestion is currently not known. So when you get pregnant, do not drink alcohol.

37. Down Syndrome • Caused by an extra whole or part of the 21st chromosome • Inhibits cognitive ability, physical growth, and can cause facial anomalies • Lower than average mental capability • Family environment and vocal lessons can lesson the disadvantages, but currently, a cure is unknown

38. Cerebral Palsy • cerebral palsy often includes limitations of sensation, perception, cognition, communication, and behaviour, by epilepsy, and by secondary musculoskeletal problems • Occurs during pregnancy, birth, or rarely, after birth • Disturbance of the cerebrum is the area of cause, but specific cause is still debated • There is currently no known cure

39. Congenital Physical Anomalies • Did you know, most people have a congenital physical anomaly if examined enough? • Some Examples of these include… • Curved pinky (clinodactyly ) • Triple nipples (supernumerary nipples) • Short fourth toe • Sacral Dimples (dimple over the spine) • Extra fingers (polydactyly) • Indentations near the ear (preauricular pits ) • Webbed toes • Extremely long fingers (Arachnodactyly ) and can bend back 180 degrees • Genu Valgum (knees bend inwards and hit each other) • Flat feet • Genu Varum (knees bend outwards – bowlegged people) • Pectus Excavatum (caved in or sunken chest)

40. What Causes these Physical Anomalies? • Well, in general, we don’t know. They’re called “Sporadic” disorders • What can be some causes? • Some are genetic (polydactyly) • Some are environmental (mom drinks alcohol or mercury or other harmful substance during pregnancy) • Many are multifactorial (combination of genetic and environmental disorders)

41. What are some cures? • We don’t cure most of the Congenital Physical Anomalies. • For the ones that make us stick out in society, we sometimes chop them off (amputation) to hide them

42. References • "Fertilization." Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale Group, 2008. Student Resource Center - Bronze. Gale. PIEDMONT HIGH SCHOOL. 10 Apr. 2009 <http://find.galegroup.com/srcx/infomark.do?&co>. • Cobb, Bryan H., PhD. "Embryo and embryonic development." Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale Group, 2008. Student Resource Center - Bronze. Gale. PIEDMONT HIGH SCHOOL. 10 Apr. 2009 <http://find.galegroup.com/srcx/infomark.do>. • Campbell, Neil A., and Jane B. Reece. Biology. San Francisco: Pearson Education, Inc., 2008.