1 animal embryology

8/11/2019 1 Animal Embryology

1/49

ANIMAL EMBRYOLOGY

INTRODUCTION to


2/49


3/49

Grading system

40% midterm exam

40% quizzes and long exams

10% written report

10% project


4/49

Written Report

Select two or more related journalarticles on any new embryology topic

Make a summary/synthesis Make a reaction


5/49


6/49

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.


7/49

Phylogenetic development

Historical development of species ortaxon

Evolutionary development orevolution


8/49

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


9/49

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.


10/49

Two major functions of

Development Generates cellular diversity and

order within each generation.

Ensures the continuity of life

from one generation to the next


11/49

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


12/49

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.


13/49

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


multicellular organisms


multicellular organisms


14/49

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


15/49

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


16/49

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


17/49

Zygote

Adult

Regulated growth

and differentiation

Interactions of genome

With internal cellular andExternal environment


18/49

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


19/49

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


20/49

Central dogma of life

DNA RNA PROTEIN

REPLICATION

TRANSCRIPTION TRANSLATION


21/49

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


22/49

Pattern regulating genes in Drosophila(fruit fly)

Tissue-specific

genes

Homeotic orselector genes

Segment polarity

gene

Pair rule gene

Gap gene

Maternaleffectgenes

(MEG)


23/49

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


24/49

Theory of

preformation

Two camps:

Spermists

ovists


25/49

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


26/49

Kaspar Friedrich Wolff

(German) Epigenesis (1759)

Embryonic development occurs through

progressive remodelling and growth.


27/49

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)


28/49

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).


29/49

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).


30/49

Matthias Schleiden and

Theodor Schwann (1839) Cell theory

Then the foundation of modern

embryology was laid down and

embryology as a science began


31/49


32/49

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.


33/49

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.


34/49

Experimental embryology

Roux (1850-1924):

Schmidt (1933)

Defectiveembryo

2 normalembryos


35/49

Some striking results of

experimental embryology


36/49

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


37/49

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


38/49

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


39/49

Genomic equivalence in

plants Differentiated somatic cells in plants

can be triggered in a culture mediumto produce a whole plant


40/49

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


41/49

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


42/49

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


43/49

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


44/49

Cell lineage


45/49

Patterns of gene expression

is self-sustaining1. Cytoplasmic memory

2. Nuclear memory or genomeimprinting


46/49


47/49

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


48/49

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


49/49

1 animal embryology

Documents