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Cell and Embryology

Textbook: Wolpert L, Beddington R, Jessell T, Lawrence P, Meyerowitz E, Smith J. (2007) Principles of Development. 3th ed. London: Oxford university press.

Gilbert SF. (2003) Development Biology. 7th ed. Sunderland: Sinaure Associates Inc.

introductionBasic conceptExam I FertilizationExam II

Schedule

Model systemsExam IIIPatterning the vertebrate body plan I: Axes and germ layerExam VIPatterning the vertebrate body plan II: the mesoderm and early nervousExam VDevelopment of nematodes, fish, sea urchins ascidians and slime moldExam VIHuman embryology or development biologyFinal exam VII

http://www2.nsysu.edu.tw/MR-embryology/index.htm

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Why Study Development?• development

I am fearfully and wonderfully made. (Psalm 139)

There are a Handful of Major Model Organisms Overview of basic embryonic development

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Zebrafish (Zebrafish (Danio rerioDanio rerio) ) ---- A Vertebrate ModelA Vertebrate Model

•It is 3 cm long

•Short generation time

•Large clutch size

•External fertilization

•Transparent embryos

•Rapid development

http://zfin.org/ and http://www.nih.gov/science/models/zebrafish/

Zebrafish as a High-throughput Model for biomedical Research and Therapeutic Development

Large number of offspringOptically clear embryosShort generation timeS ll SiForward Genetics: Reverse Genetics:Small SizeForward Genetics:

ENU mutagenesisInsertional mutagenesis

Transgenic fishTilling with ENUMorpholino injection

Genomics:Sequenced GenomecDNA projectsMicroarrays

Small Molecule Screens:Predictive of higher vertebratesDelivery by injection or soaking

Carcinogenesis: Aqueous deliverySimilar to human tumors

Model organism

The organism chosen for understand broad biological principles is called a model organism.

DROSOPHILA MELANOGASTER(FRUIT FLY)

MUS MUSCULUS(MOUSE)

ARABIDOPSIS THAMAN(COMMON WALL CRES

(FRUIT FLY)

CAENORHABDITIS ELEGANS(NEMATODE) DANIO RERIO

Figure 21.2

(NEMATODE)

0.25 mm

DANIO RERIO(ZEBRAFISH)

No human, why?

once fertilization is completed, a succession of rapid cleavage

cleavage

ensues the cells undergo the 1) S (DNA synthesis) 2) M (mitosis) phases of the cell cycle but often no G1 and G2 phases G1 and G2 phases

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cleavage in echinoderm embryo

the embryo does not enlarge during this period but simply partitions the cytoplasm of the zygote into many smaller cells, called blastomeresand each with its own nucleus

Cleavage to neurulation

Gastrulation: External view Gastrulation: Internal view

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Caenorhabditis elegans

Drosophila

Xenopus

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Experimental Approaches

• What causes cell differentiation: cytoplasm or nucleus?

• Defect experiments• Isolation experiments• Recombination experiments• Transplantation experiments

– Defect experiment:

Isolation experiment

Conditional specification?

Spemann and Mangold’s Discovery of Induction (1924)

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• Many different structures– Are derived from the three embryonic germ layers during y g y g

organogenesisECTODERM MESODERM ENDODERM

• Epidermis of skin and itsderivatives (including sweatglands, hair follicles)

• Epithelial lining of mouthand rectum

• Sense receptors inepidermis

• Notochord• Skeletal system• Muscular system• Muscular layer ofstomach, intestine, etc.

• Excretory system• Circulatory and lymphatic

• Epithelial lining ofdigestive tract

• Epithelial lining ofrespiratory system

• Lining of urethra, urinarybladder, and reproductivesystem

Figure 47.16

• Cornea and lens of eye• Nervous system• Adrenal medulla• Tooth enamel• Epithelium or pineal and

pituitary glands

systems• Reproductive system

(except germ cells)• Dermis of skin• Lining of body cavity• Adrenal cortex

• Liver• Pancreas• Thymus• Thyroid and parathyroid

glands

after fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis

fertilization in sea urchin model

fig 47.3

cortical reaction: sperm binding activate a signal transduction pathway involving 2 second

IP d

fertilization in sea urchin model

messengers, IP3 and DAG, that

cause Ca2+ to be released from the egg’s endoplasmic reticulum (ER) into the cytosol a surge in Ca2+ levels in the cytoplasmthe cytoplasm

fig 11.12

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cortical reaction: the Ca2+ release from the ER begins at the site of sperm entry and then propagates in a wave across the fertilized egg

fertilization in sea urchin model

fig 47.4

fertilization in sea urchin model

fig 47.5

once fertilization is completed, a succession of rapid cleavage

ensues the cells undergo the

cleavage

the cells undergo the 1) S (DNA synthesis) 2) M (mitosis) phases of the cell cycle but often no G1 and G2 phases

cleavage in echinoderm embryo

fig 47.7

the embryo does not enlarge during this period but simply partitions the cytoplasm of the zygote into many smaller cells, called blastomeresand each with its own nucleus

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morula: the first 5 to 7 divisions form a cluster of embryonic cells

blastocoel a fluid-filled cavity of the early

cleavage in frog embryo

embryobegins to form within the morula and is fully formed in the blastula

blastula: a hollow ball of embryonic cells

the body axes has been determined before fertilization and been i t i l t di i fintensively studies in many frog spppolarity of the zygote

except the egg of mammals, the eggs and zygotes of animals have a definite polarity

is due to uneven distributions of mRNAs, proteins, and yolk

cleavage in frog embryo

meroblastic cleavage: the incomplete division of a yolk-rich egg, i.e. cleavage of the fertilized egg is restricted to the small disk of yolk free cytoplasm and

cleavage in bird embryo

fig 47.10

small disk of yolk-free cytoplasm and cannot penetrate through the dense yolk the yolk remains uncleaved

holoblastic cleavage: the complete division of eggs having little yolk (as in sea urchins) or a moderate amount of yolk (as in frogs)

blastoderm the avian equivalent of the blastula blastomeres devidedinto 2 layers

)

cleavage in bird embryo

1) epiblast: upper2) hypoblast: lowerblastocoelthe cavity between epiblast andhypoblast layers

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gastrula: some of the cells at or near the surface of the blastula move to an interior location and the embryo becomes 3-germ-layerembryo

gastrulation

allows cells to interact with each other in new ways ectoderm: forms the outer layer of the gastrula endoderm: the embryonic digestive tract mesoderm: partly fills the space between the ectoderm and

the endoderm eventually, these 3 cell layers develop into all the tissues and organs

of the adult animalof the adult animal

gastrulation in sea urchin embryo

• involution: a process along the blastopore, future endoderm and mesoderm cells on the

f ll th d f th

gastrulation in frog embryo

surface roll over the edge of the lip into the interior of the embryo

• blastocoel collapses and displaced by archenteron which is formed by the tube of endoderm

fig 47 12fig 47.12

gastrulation in bird embryo

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organogenesis in frog embryo

somites: condensations occur in strips of mesoderm lateral to the notochord, which separate into

f

organogenesis in frog embryo

blocks of somites, being arranged serially on both sides along the notochord

parts of the somites dissociate into individual mesenchymalcells, which migrate to new locations

t b th t h d vertebrae: the notochord functions as a core around mesodermal cells

fig 47.14

inductive signals and the cell fateorganizer region

Spemann and Mangold

fig 47.25

dorsal lip of the blastopore functions as an organizer by initiating a chain of inductions

gin 1920s

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formation of the limb in chick model formation of the limb in chick model

fig 47.27

homeotic genes and pattern formation in the development of the body segments of Drosophila and Mus

homeotic genes and pattern formation

adult derivatives of the three embryonic germ layers in vertebrates

organogenesis

fig 47.16

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cytoskeleton in morphogenesis

tab 6.1