Presentation on theme: "Group Quiz 6 Intro to Development"— Presentation transcript:
1 Group Quiz 6 Intro to Development Today:Group Quiz 6Intro to DevelopmentThursday: Review Paper Draft Due for Peer Review!
2 Backtracking: Advantages and Disadvantages of Sexual Reproduction?
3 Generalizations about Sexual Reproduction Offspring created by the fusion of haploid gametes to form a diploid zygote.The female gamete (ovum) is generally large and nonmotile.The male gamete (spermatozoan) is generally smaller and motile.
4 Generalizations about Sexual Reproduction Some animals are Hermaphrodites (single individual has both male and female reproductive systems)Common in sessile or burrowing animals, and in parasitesAdvantages? Does this generate genetic diversity?
5 Fertilization Overview Fertilization: the union of sperm and eggCan be EXTERNAL or INTERNAL
6 External Fertilization Photo by Scott Egan,; University of Rhode Island Dept. of Natural Resources; A pair of wood frogs, Rana sylvatica, in amplexus
7 Internal Fertilization Internal fertilization requires cooperative behaviorandSophisticated reproductive systems including organs to deliver sperm and receptacles for its storage and transport to eggs.
14 Fertilization: The Acrosomal Reaction External Fertilization in Sea UrchinsSperm exposed to molecules from the jelly coat surrounding an egg, the acrosome discharges its contents by Exocytosis= Acrosomal ReactionThe acrosomal process (elongating structure) then penetrates the jelly coat of the egg and adheres to a specific receptor molecule
15 Fertilization: The Acrosomal Reaction What needs to happen once one sperm nucleus has entered the egg?!
16 Fertilization: Fast Block to Polyspermy Fusion of the sperm and egg membrane causes ion channels in the egg’s membrane to openSodium ions flow into the cell, causing a membrane depolarization (change in membrane potential)Prevents more than 1 sperm from entering (1-3 seconds!)
17 Membrane potential is restored within 2 minutes! (Uh oh…)
18 Fertilization: Slow Block to Polyspermy The Cortical Reaction:Fusion of sperm and egg triggers release of calcium from the ER into the cytosolCalcium release begins at site of sperm entry and propagates across the fertilized egg
19 Fertilization: Slow Block to Polyspermy The Cortical Reaction:High calcium concentration causes the cortical granules to fuse with plasma membraneMouse oocyte stained to show cortical granules (small red dots). Genomic DNA in the metaphase plate of the secondary oocyte (top right) appears bluish-white. (From Biology of Reproduction 57: , 1997, Z. Xu, A. Abbott, G. Kopf, R. Schultz and T. Ducibella)
21 Fertilization: Slow Block to Polyspermy Enzymes from the cortical granules separate the vitelline layer from the plasma membraneWater is drawn into the perivitelline space by osmosis, swelling itThe swelling pushes the vitelline layer away from plasma membrane where it is hardened by enzymes to form the Fertilization Envelope
23 Fertilization: Activation Rise in Calcium also induces metabolic changes within the eggMetabolism increases rapidly!Nucleus of sperm starts to swellSperm nucleus merges with egg nucleus ~ 20 minutes)First division ~90 minutes
24 Sea Urchin Larva at 13 days Timing:Sea Urchin Larva at 13 days
25 Fertilization: Sea Urchins Vs. Mammals Internal Fertilization (terrestrial!)Key Initial Differences:1. Capacitation: molecules in mammalian female reproductive tract alter surface of sperm and increase the motility (~ 6 hrs)2. Mammalian egg cloaked by follicle cells- capacitated sperm cell must migrate through this layer to reach the zona pellucida
27 Fertilization: Sea Urchins Vs. Mammals The Zona Pellucida = filamentous network of glycoproteins (extracellular matrix)One of the glycoproteins, ZP3 functions as a sperm receptorBinding induces the acrosome to release its contents (as with sea urchins)Enzymes from acrosome help sperm penetrate the zona pellucida
28 Fertilization: Sea Urchins Vs. Mammals As with sea urchin, binding of egg triggers depolarization of egg membrane (fast block to polyspermy)A Cortical Reaction functions as the slow block (granules in cortex release contents; enzymes catalyze changes in the zona pellucida)
30 Unfertilized Star Fish Eggs Fertilization ReviewedUnfertilized Star Fish Eggs
31 Fertilized egg (zygote) - the nucleus is no longer visible; the fertilization envelope is present Let’s Watch:
32 Fertilization is followed by 3 stages: Stages of DevelopmentFertilization is followed by 3 stages:1. Cleavage2. Gastrulation3. Organogenesis
33 CLEAVAGE Succession of rapid cell divisions Partitions the cytoplasm into smaller cells, BLASTOMERES, each with its own nucleusEach region of cytoplasm contains different cytoplasmic components
34 2-cell and 4-cell stage of Sea Urchin Cleavage (Blastomeres) What happened to the size of each blastomere??2-cell and 4-cell stage of Sea Urchin Cleavage (Blastomeres)
35 Polarity of Zygote and Egg Most animals (except mammals) produce asymmetrical eggs and zygotesDistribution of yolk, mRNA and proteins is not uniformSets the stage for subsequent developmental events!
36 (Becomes the dorsal side) Yolk is concentrated at the vegetal pole.The opposite pole is the animal pole(Becomes the dorsal side)
37 Polarity of Frog EggsIn the final stage, a frog oocyte is pigmented dark brown in one hemisphere (animal pole).The other hemisphere (vegetal pole) shows the yellow color of the egg yolk.
38 The third division is horizontal, producing eight cells. CleavageThe first two cleavage divisions are vertical producing four cells extending from animal to vegetal pole.The third division is horizontal, producing eight cells.Continued divisions (16-64 cells) produce a solid ball of cells, the morula.
39 A fluid-filled cavity, the blastocoel forms within the morula, creating a hollow ball of cells, the blastula.Above right. Human- day 3-4Note the difference the presence of yolk makes!
41 Sea Urchin: Late Blastula - shows thickened layer of cells at one end, the vegetal pole
42 Morula (16-64 cells) Blastula (>128 cells) A fluid-filled cavity, the blastocoel, forms within the morula creating a hollow ballUrchinSource: courtesy of Dr. J. Hardin, Univ. of Wisconsin
43 ectoderm, endoderm and mesoderm Blastula GastrulaChanges in cell motility, shape and adhesion result in the spatial rearrangement of an embryoResults in three familiar embryonic tissue layers:ectoderm, endoderm and mesoderm
54 Fertilization is followed by 3 stages: Stages of DevelopmentFertilization is followed by 3 stages:1. Cleavage2. Gastrulation3. Organogenesis
55 In chordates, the neural tube and notocord form first 3. OrganogenesisMorphogenetic changes – folds, splits and clusterings (condensation) begin the process of organ buildingIn chordates, the neural tube and notocord form first
56 Sea Urchin: the bipinnaria larva (bilateral symmetry) develops into a brachiolaria larva; this larva undergoes metamorphosis to become the adult starfish, which has radial symmetry.
57 Earliest Organogenesis in Frog (Chordate) Embryos