embryology cellular and molecular mechanisms involved in fertilization and development
TRANSCRIPT
EmbryologyEmbryology
Cellular and Molecular Cellular and Molecular Mechanisms Involved in Mechanisms Involved in
FertilizationFertilizationand Developmentand Development
Sea Urchin Sea Urchin FertilizationFertilization
Contains digestive enzymes
unfertilized sea urchin egg
fertilized sea urchin egg
Vitelline envelopeEgg plasma membrane
Animation Animation 43-0143-01
Sea Urchin FertilizationSea Urchin Fertilization
Acrosomal enzymes digest
jelly coat
Bindin on acrosomal process contacts
receptors on vitelline envelope
Acrosomal process forms
by actin polymerization
Egg plasma membrane forms
fertilization cone to engulf sperm head
Preventing PolyspermyPreventing Polyspermy
• Polyspermy = fertilization of egg by more Polyspermy = fertilization of egg by more than one spermthan one sperm
• Blocked in two waysBlocked in two ways– Fast block to polyspermy: Change in Fast block to polyspermy: Change in
charge across the egg plasma membrane, charge across the egg plasma membrane, mediated by influx of sodium ionsmediated by influx of sodium ions
– Slow block to polyspermy: cortical Slow block to polyspermy: cortical granules release enzymes and water-granules release enzymes and water-absorbing materials to form fertilization absorbing materials to form fertilization envelope around egg, mediated by envelope around egg, mediated by release of stored calcium from release of stored calcium from endoplasmic reticulumendoplasmic reticulum
Sea Urchin FertilizationSea Urchin Fertilization Cortical granules Cortical granules
fuse with plasma fuse with plasma membrane and membrane and releaserelease– Enzymes to catalyze Enzymes to catalyze
reactions thatreactions that• break bonds between break bonds between
vitelline envelope and vitelline envelope and plasma membraneplasma membrane
• remove bindin remove bindin receptorsreceptors
• harden vitelline harden vitelline envelopeenvelope fertilization envelopefertilization envelope
– Substances that Substances that absorb water and absorb water and raise vitelline raise vitelline envelopeenvelope
Applying Your KnowledgeApplying Your Knowledge
A.A. Which structure of the egg has a receptor for Which structure of the egg has a receptor for sperm?sperm?
B.B. Which structure is directly responsible for Which structure is directly responsible for bringing the sperm head into the egg ?bringing the sperm head into the egg ?
C.C. Which part of the sperm contains enzymes Which part of the sperm contains enzymes for digesting through the jelly coat for digesting through the jelly coat surrounding the egg? surrounding the egg?
1.1. BindinBindin2.2. Cortical GranuleCortical Granule3.3. AcrosomeAcrosome4.4. Vitelline envelopeVitelline envelope5.5. Fertilization coneFertilization cone
DevelopmentDevelopment• A series of progressive changes that A series of progressive changes that
generates the structures of the generates the structures of the organism throughout its life cycleorganism throughout its life cycle
• IncludesIncludes– growth: change in size due to increase in growth: change in size due to increase in
cell number and/or cell size cell number and/or cell size – differentiation: cellular specializationdifferentiation: cellular specialization– morphogenesis: establishing body and morphogenesis: establishing body and
organ shapesorgan shapes
Determination Precedes DifferentiationDetermination Precedes Differentiation
• Determination: commitment Determination: commitment of a cell to a particular fate, of a cell to a particular fate, occurs by the activation of occurs by the activation of specific genesspecific genes
• Affected by Affected by – Cytoplasmic Cytoplasmic
segregationsegregation– InductionInduction
• Differentiation isDifferentiation isthe result of the result of determinationdetermination
Induction: process in which a substance or tissue Induction: process in which a substance or tissue influences the fate of a group of adjacent cellsinfluences the fate of a group of adjacent cells
Optic vesicle induces lens placode
Optic cup induces lens
Lens induces cornea
Transplant of tissue from dorsal lip of blastopore induces second invagination
and formation of secondary embryo.
Embryonic StagesEmbryonic Stages
• Cleavage: series of rapid cell Cleavage: series of rapid cell divisions following fertilization, divisions following fertilization, leading to leading to – morula: ball of cellsmorula: ball of cells
– blastula: hollow sphere of cellsblastula: hollow sphere of cells
MorulaMorula BlastulaBlastula
Blastocoel = fluid-filled
space
Blastomere = individual cell
of blastula
Yolk Content Affects Cleavage PatternsYolk Content Affects Cleavage Patterns
Blastodisc= layer of cells on top of yolk
Cytoplasmic Determinants Influence Cleavage PatternsCytoplasmic Determinants Influence Cleavage Patterns
Mosaic Development
Regulative Development
Orientation of mitotic spindles in early cleavage is dependent on the organization
of cytoplasmic determinants in the egg
Cell Adhesion Molecules Cell Adhesion Molecules Influence Blastula OrganizationInfluence Blastula Organization
• Cell Adhesion Molecules (CAMs) are trans-Cell Adhesion Molecules (CAMs) are trans-membrane cell surface proteins that bind to CAMs membrane cell surface proteins that bind to CAMs on other cells.on other cells.
• CAMs are involved in cell migration and producing CAMs are involved in cell migration and producing stable tissue structure.stable tissue structure.
• Experiments have shown that cadherin (one type of Experiments have shown that cadherin (one type of CAM) stabilizes the frog blastula.CAM) stabilizes the frog blastula.
Embryonic StagesEmbryonic Stages Gastrulation: cellular movements Gastrulation: cellular movements
forming three tissue layers and distinct forming three tissue layers and distinct body axesbody axes
primitive gut
linings of digestive and respiratory tracts
nervous system, skin
mesoderm
blood vessels, muscle, bone, liver and heart
Sea Urchin
Invagination
Migration
Neurulation in the FrogNeurulation in the Frog Notochord, derived from Notochord, derived from
mesoderm, induces the mesoderm, induces the overlying ectoderm to form overlying ectoderm to form the neural tubethe neural tube
Applying Your KnowledgeApplying Your Knowledge
A.A. Which one represents a hollow ball of cells?Which one represents a hollow ball of cells?
B.B. Which tissue induces formation of neural Which tissue induces formation of neural structures?structures?
C.C. Which one involves invagination or involution Which one involves invagination or involution of cells? of cells?
1.1. GastrulaGastrula2.2. NeurulaNeurula3.3. BlastulaBlastula4.4. EctodermEctoderm5.5. MesodermMesoderm
MorphogenesisMorphogenesis
• Pattern Formation: organization of Pattern Formation: organization of differentiated tissues into specific differentiated tissues into specific structuresstructures– Body segmentation in fruit flies is Body segmentation in fruit flies is
controlled by controlled by • gradients of materials established in the gradients of materials established in the
egg egg • actions of a series of embryonic genesactions of a series of embryonic genes
Animation Animation 19-0319-03
Genes Affecting Body SegmentationGenes Affecting Body Segmentation Products of Maternal Effect Genes establish gradients in the egg
Gap genes define broad areas and regulate Pair-rule genes
Pair-rule genes refine segment locations and regulate Segment Polarity genes
Segment Polarity genes determine segment boundaries and orientations
Homeotic genes define the role of each segment
Mutation in a Homeotic Gene Causes Mutation in a Homeotic Gene Causes Legs to Grow Where Antenna Should BeLegs to Grow Where Antenna Should Be
Homology between Homology between Genes Controlling Genes Controlling
Segmentation in Fruit Segmentation in Fruit Flies and MiceFlies and Mice
Morphogenesis May Require ApoptosisMorphogenesis May Require Apoptosis
Apoptosis = Programmed Cell DeathApoptosis = Programmed Cell Death
Cellular and Molecular Mechanisms Cellular and Molecular Mechanisms Essential to DevelopmentEssential to Development
• Specificity of receptors and enzymes Specificity of receptors and enzymes
• Cytoplasmic organizationCytoplasmic organization
• Cell movement through the action of Cell movement through the action of cytoskeletal elements and cell adhesion cytoskeletal elements and cell adhesion moleculesmolecules
• Orientation of tissue layers leading to Orientation of tissue layers leading to InductionInduction
• Differential Gene Expression Differential Gene Expression
Applying Your KnowledgeApplying Your Knowledge
A.A. Which process leads to a morula?Which process leads to a morula?B.B. Which process leads to the formation of Which process leads to the formation of
somites, the precursors to vertebrae?somites, the precursors to vertebrae?C.C. Which process is directly preceded by Which process is directly preceded by
determination? determination?
1.1. DifferentiationDifferentiation
2.2. GrowthGrowth
3.3. MorphogenesisMorphogenesis