Animal Development

Animal Development

1. Life Cycle

   • the sequence of events from one generation to the next Includes *production of gametes *fertilization *repeated mitotic divisions of the fertilized egg to produce a mass of cells *movement of cells into a hollow ball *more movement of sheets of cells inward to form a tube inside the embryo. This tube will become the gut *establishment of anterior/posterior and dorsal ventral body orientation *development of organs *larval stage-larvae have all body systems except for mature sexual organs *metamorphorsis in which body is remodeled to form an adult (reptiles, birds, and mammals, do not undergo metamorphosis and some other mammals)
   • 1) Gametes and Fertilizatoin
     • Gametes formed by meiosis
       • sperm
         • Structure
           • Head
             • acrosome
               • specialized vesicle at the tip of the sperm that holds hydrolytic enzymes that dissolve the zone pellucida
             • Nucleus
               • Contains 23chromosomes that hold the DNA 
             • Cell Membrane
           • Neck
             • helps sperm swim in fluids and push through the follicle cell layer and zona pellucida
             • Connecting Piece
           • Mitochondrial Sheath
             • mitochondria
               • Used to create ATP
           • Flagellum
             • helps sperm swim in fluids and push through the follicle cell layer and zona pellucida
             • Axial Filament
               • structure
                 • Axial filament that contains typical 9 + 2  microtubules
           • End Piece
       • Eggs
         • Structure
           • Jelley Layer
           • Nucleus
             • Holds 23 chromosomes which hold DNA
           • Cortical Granules
             • Enzymes that block polyspermy
           • Yolk Granule
             • nourish cell during development
           • Vitelline envelope
             • Called zona pellucida in mammals When the sperm binds with the sperm receptors of the vitelline evelope (zona pellucida in mammal) a cortical reaction occurs that prevents polyspermy
     • Fertilization
       • The union of eggs and sperm.   Combines information from female and male into a single diploid Initiates Development
   • 2) Cleavage and Blastulation
     • Cleavage
       • Transforms a zygote into a multicellular embryo 
       • Cell Division
         • by mitosis
         • blastomeres
           • smaller cells created by cleavage 
           • Cytoplasm
             • cytoplasms of large fertilized egg is distributed in smaller cells called blastomeres
           • Blastulation
             • Blastula
               • After a specific amount of blastomeres are created a blastula will form. Blastula is a hollow ball. 
               • blastocoel
                 • fluid filled space in the middle of a blastula 
               • Function
                 • Increases cells exposure to extracellular fluid which also exposes the cell to nutrients. Increases surface area to volume ratio. and allows cells to excrete waste and gases with the external environment. (as opposed to a solid ball) 
               • Single Layered
               • Called Blastocyt for humans
   • 3, Gastrulation
     • Invagination
       • Invagination of the blastula in which a sheet of cells in infolded  into the embryo. It forms cell layers called germ layers and a grastula
       • Grastula
         • Embryonic Gut or archenteron
           • Importance
             • Allows animal to eat larger pieces of food. Digest food without losing enzymes In contrast other animals have to ingest food by phagocytosis or secrete digestive enzymes to digest large food items externally 
         • blastopore
           • Initial opening of the gut
         • Sponges and Cnidarians
           • 2 embryonic layers
             • ectoderm
               • inner layer of cells
               • single layered
             • endoderm
               • outer layer of cell
               • single layerd
         • All other animals
           • 3 embryonic tissues
             • ectoderm
               • Single layerd
               • Forms
                 • Surface structures *epidermis *nervous and sensory systems
             • mesoderm
               • 2 Ways its Develops
                 • 1) cells wander in from into blastocoel from the ectoderm and endoderm boundaries *sea urchins and humans 2) Develop from endoderm cells often forming pouches off the archenteron *worms and snails  
               • Forms
                 • muscle, circulatory, and osmo-regulatory tissues
             • endoderm
               • single layerd
               • Forms
                 • digestive tissues
             • Advantages
               • Larger body size isolation of middle tissue layer from the external environemnt allowing control of its chemical composition *greatly advantagous for nervous and muscle tissue allows for numerous of cells for development of specialized muscles, circulatory and other organs
       • Body Axes
         • anterior-posterior
         • dorsal-ventral
         • proximal-distal
   • Body Cavities
     • A fluid or liquid space located beween the digestive tract and outer body walla
     • Animals with 1 tube
       • acoelomates
         • animals with 3 embryonic tissue and no body cavity
       • hydra
         • 2 embryonic tissue
       • Flat worms
     • Coelomates
       • animals with body cavities
       • true coelom
         • a body cavity or fluid-filled cavity between the gut and the body wall that is lined by tissue derived from embryonic mesoderm
     • pseudocoelmate
       • pseudocoelom
         • A body cavity which is lined by tissues derived from the endoderm and mesoderm.
     • Development
       • Protostomes
         • schizocoely
           • Cells from the ectoderm and mesoderm boundary migrate inward. The mesoderm then splits and forms a cavity within the mesoderm. The blastocoel shrinks and disappears as the mesoderm increases and moves outward.
       • Deuterostomes
         • Pouch of mesoderm develops from the archenteron. Each pouch has a small opening. as the mesoderm grows these spaces enlarge and become mesoderm
         • Enterocoely

2. How organizaiotn of developmentoccurs

   • Mechanisms
     • Cell proliferation
       • Increase in cell # not cell size
     • Cell Specialization
       • differentiate
         • acquire distinct characterization
         • Gene have to be turned on and off
     • cell movement
       • cell shape
       • cell adhesion
       • cell motility
     • cell-cell interaction
       • cells regulate development of neighbor cells
     • programmed cell death
       • forms structures deletes structures controls cell numbers eliminates abnormal cells
   • Genes Coordinate Development
     • Such as  *body axes *body segements *identify of segments *build structures corresponding to each segment
     • Regulatory Genes
       • sequential activity of regulatory genes progressively specifies patterns
       • Regulatory Cascade
         • Maternally supplied mRNA control  Segmentation Genes control  Hox genes control Effector genes Segments in developing embryo differentiate
         • 1) Maternally Supplied mRNA
           • controls segmentation genes *transcribed before fertilization
           • 2) Segmentation genes
             • Define position and edges of segments 
             • Gap genes
               • define general position of segment
             • Pair Rule Genes
               • define edges of segments
             • Polarity Genes
               • define anterior-posterior axis of segments
             • 3) Homeotic Genes
               • Define identity of segments Trigger development of structures especially outgrowths such as *tentacles *wings *legs *eyes
               • Clusters
                 • Homeotic genes are located in ordered clusters on chromosomes *action in embryo corrseponds spatially and temporally to order
               • Effector Genes
                 • Build Structures of body by controlling  *cell growth *cell shape *cell proliferation *cell death *cell Movement

3. Evolution and Development

   • Homeotic genes
     • The order of homeotic clusters on chromosomes is consereved across bilateral animal phyla * as orgasnisms are more diverse or complex there is more homeotic clusters, but the onces they share in common tend to be in similar order on chromosomes
   • Bilateral Animals
     • Have the same set of developmental genes

4. Organogenesis

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