1 animal embryology
TRANSCRIPT
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ANIMAL EMBRYOLOGY
INTRODUCTION to
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Grading system
40% midterm exam
40% quizzes and long exams
10% written report
10% project
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Written Report
Select two or more related journalarticles on any new embryology topic
Make a summary/synthesis Make a reaction
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Ontogenetic development
Individual development
Used to denote the processes that are
involved in the transformation of thefertilized egg, or some other rudimentderived from a parent organism, into
a new adult individual.
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Phylogenetic development
Historical development of species ortaxon
Evolutionary development orevolution
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Development
Orderly sequence of change leadingto increase in complexity that occurs
during the growth of an organism Involved a series of complex
biochemical pathways whose steps
are under gene control Fertilized eggmulticellular organism
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We Develop from a Single Cell
One initial cell, the fertilized egg(zygote), generates hundreds ofdifferent kinds of cells that differin contents, shape, size, color,mobility, and surface composition.
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Two major functions of
Development Generates cellular diversity and
order within each generation.
Ensures the continuity of life
from one generation to the next
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Developmental programs in
plants and animals differ ANIMALS
there is movement of cells and tissues
Growth is limited to embryo and juvenileperiods
PLANTS
Presence of perpetual embryonic tissues( apical meristems)
Continuous growth of new organs
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What particles are
responsible for development?
All the properties of any organism are
determined in the last instance by thesequence of base triplets (codon) inthe DNA molecules.
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Differences among cells in
multicellular organisms Due to different patterns of gene
expression
Not from differences in the genomeof cells
All cells have the same genes(genomic equivalence) because theseare all derived from a single-celledzygote
Differences among cells in
multicellular organisms
Differences among cells in
multicellular organisms
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Three processes that can
overlap during development Cell Division
Cell Differentiation cell selectively activates genes and synthesizes
proteins not found in other cell types Cells become specialized in structure and function
e.g. erythrocytes has hemoglobinbeta cells of pancrease - synthesize insulinmesophyll cells in leaves synthesize
chlorophyll
Morphogenesis = processes that organizedifferent cells into tissues and organs
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Initial aspects of
morphogenesis Establishment of initial/basic body
plan Requires cell division, differentiation
and selective cell death (apoptosis)
Initial aspects of
morphogenesis
Initial aspects of
morphogenesis
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Developmental genetics
Study of relationships between generegulation and cell differentiation
during development Deals with coordinated expression of
genes from fertilization to adult
formation
Developmental geneticsDevelopmental geneticsDevelopmental geneticsDevelopmental geneticsDevelopmental genetics
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Zygote
Adult
Regulated growth
and differentiation
Interactions of genome
With internal cellular andExternal environment
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Genetic Basis of Development
Differential gene action or
Differential gene expression
Turning ON or OFF of genes at the rightplace and time
Production of gene product in the right
form and right amount
Genetic Basis of DevelopmentGenetic Basis of DevelopmentGenetic Basis of Development
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Differential gene
expression Involves a cascade of regulatory genesthat are activated and act at the propertime and place
Product (i.e. protein) of one set of genestrigger the expression of next set ofgenes
Regulatory genes encode transcriptionactivator proteins that bind to thepromoter of next set of genes
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Central dogma of life
DNA RNA PROTEIN
REPLICATION
TRANSCRIPTION TRANSLATION
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Intriguing questions
How are genes to be expressed activatedin a coordinated manner?
How is expression of other genessilenced?
How are developmental decisions fr0zen?
Is differentiation accompanied bysecondary qualitative and quantitativechanges in structure and accessibility ofthe genome?
Intriguing questions
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Pattern regulating genes in Drosophila(fruit fly)
Tissue-specific
genes
Homeotic orselector genes
Segment polarity
gene
Pair rule gene
Gap gene
Maternaleffectgenes
(MEG)
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Historical Review
Aristotle (384-322 B.C.) described thedevelopment of the chick in the egg
Galen (130-200 A.D.) learned muchabout the structure of relativelyadvanced fetuses
Hamm and Leeuwenhoek (1677) first
observed human sperm De Graaf (1672) = discovered ovarian
follicle
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Theory of
preformation
Two camps:
Spermists
ovists
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Bonnet (1745) = discoveredparthenogenesis in eggs of some insects
Strengthened ovistscause Spallanzani (1722-1799) = demonstrated
that in normal circumstances both male
and female sex products are necessaryfor the initiation of development
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Kaspar Friedrich Wolff
(German) Epigenesis (1759)
Embryonic development occurs through
progressive remodelling and growth.
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Karl Ernst von Baer
(1828) More general basic features of any
animal group appear earlier in
development than do special featuresthat are peculiar to different
members of the group (von Baers
Law)
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Biogenetic Law or Baers
law Features that characterize all
vertebrate animals (brain and spinal
cord, notochord, segmented muscles,aortic arches) are developed earlier
than the features distinguishing the
various classes of vertebrates (hair inmammals, feather in birds).
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Biogenetic Law or Baers
law Ontogeny is a recapitulation of
phylogeny.
Events that happened in thousands ofmillions of years (phylogeny) is nowperformed in a matter of days and weeks
(ontogeny).
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Matthias Schleiden and
Theodor Schwann (1839) Cell theory
Then the foundation of modern
embryology was laid down and
embryology as a science began
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Developmental biology
Not only embryonic development butalso postnatal processes such as
normal or neoplastic growth,metamorphosis, regeneration and
tissue repair at levels of complexity
ranging from molecular toorganismal.
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Differential gene expression can bedetected in early fly embryos before
cells are morphologically different.
Developmental Biology Reveals Changes in theProperties of Cells as They Specialize.
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Experimental embryology
Roux (1850-1924):
Schmidt (1933)
Defectiveembryo
2 normalembryos
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Some striking results of
experimental embryology
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Methods in Experimental embryology
Extirpation/ablation removal ofsmall parts of embryos and careful
analyses of the development effectsthat resulted
Parabiosis transplantation of
various parts of embryos from placeand place within the embryo or even
the conjoining of two entire embryos
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Methods in Experimental embryology
Transplantation
Autografting same embryo
Heterografting different species Xenografting different order
Explantation
excising small sample of embryonic tissueand growing it in an artificial environment.
Also called microsurgical methods
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New biotechnologies
Sperm sorting
Selectivefertilization
In vitro fertilization
http://localhost/var/www/apps/conversion/tmp/scratch_7/PICSI%20%20%20human%20egg%20fertilization%20by%20selected%20spermatozoonAVI.wmvhttp://localhost/var/www/apps/conversion/tmp/scratch_7/PICSI%20%20%20human%20egg%20fertilization%20by%20selected%20spermatozoonAVI.wmv -
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Genomic equivalence in
plants Differentiated somatic cells in plants
can be triggered in a culture mediumto produce a whole plant
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Genomic equivalence in
animals Animals will not often divide in culture
NUCLEAR TRANSPLANTATION can bedone: nucleus of a differentiated cell is
transplanted into enucleated egg cellsnormal development
Source of nucleus should beundifferentiated cells of an embryobecause these cells are totipotent
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Totipotency
Cells that retain the ability of thezygote to give rise to all specialized
cells of a mature organism Totipotent cells retain the ability to
proceed through all stages of
development and thus produce anormal adult
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Stages in cell type
formation Cell determination
Stage when the cell becomes committed to
perform a specialized function Involves cell memory that is self
perpetuating
Pre-requisite to differentiation
Cell differentiation
Expression of the cells predeterminedspecialized role
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The path a cell takes is
influenced by:1. Environment (cytoplasmic)
Influences which genes turn on or off2. Cell lineage
Activity of progeny cells affected by
progenitor cells Progenitor cell gene activity pattern is
passed on to progeny cell
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Cell lineage
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Patterns of gene expression
is self-sustaining1. Cytoplasmic memory
2. Nuclear memory or genomeimprinting
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Patterns of gene expression
is self-sustaining2. Nuclear memory or genomeimprinting
Self-sustaining changesoccurring/intrinsic to the chromosome
Selection of genes to be expressed
Condensation-decondensation patternof chromatin
Pattern of methylation of DNA
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Natural test for Nuclear
Memory1. Obtain egg and sperm cells have identical set of genes but
different state of differentiation Question: Do sperm and egg-derived
chromosomes remain functionally
different in zygote? Yes, because of nuclear memory
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