báo cáo nghiên cứu Amphibian embryology

Cleavage in Amphibians • Unequal radially symmetrical and holoblastic • Mesolecithal STAGE 1 Two cells stage 1 hour: The first division begins at the animal pole and slowly extends dow

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1 Nguyễn Anh Tuấn

2 Vũ Duy Long

3 Trịnh Kiều Anh

4 Nguyễn Phương Anh

5 Phạm Thị Thúy

6 Nguyễn Thị Hương

7 Nguyễn Thị Miên

8 Phạm Ngọc Sơn

Amphibian embryology

Brief Content

1 Early Amphibian Development

a Cleavage in Amphibians

b Amphibian Gastrulation

2 Axis Formation in Amphibians

c Organogenesis

1 Early Amphibian Development

a Cleavage in Amphibians

• Unequal radially symmetrical and holoblastic

• Mesolecithal

STAGE 1 Two cells stage ( 1 hour): The first division begins at the animal pole and slowly extends down into the vegetal region

Fertilized egg Stage 1

STAGE 3 Sixteen cells stage (2 - 3 hours):

- at the eight cell stage , the third cleavage occurred horizontally and just above the equatorial pane

=> a difference in largeness of the blastomeres (micromeres and macromeres)

- at the sixteen cell stage, the cleavage furrows are completed and the macromeres are fully separated

micromeres < macromeres ( about the size and color)

=> morula

STAGE 2 Four cells stage (2 hours):

- at right angles to the first one

- largeness and color of four formed blastomeres can differ

- not always complete (the higher concentration of yolk at the vegetal pole)

STAGE 128-cell stage (3-7 hours):

the blastocoel becomes apparent, and the embryo is considered a blastula

blastocoel

=> It prevents the cel ls beneath it from interacting prematurely

with the cel ls abov e it

= > It permits cell migration during gastrulation

EP-cadherin

Keep the blastomeres together

Supplied in the oocyte cytoplasm

Non EP-cadherin

b Amphibian Gastrulation

Early Gastrulation stage (10 hours):

- The blastopore becomes visible

- The cells at the surface of the dorsal side

move inside (invaginate) at the dorsal

blastopore lip.

Late gastrulation/yolk plug stage (12 hours)

- process of involution and epiboly

⇒ the circular blastopore is formed

− at the end this opening is completely filled with a dense mass of yolk rich cells

=> the yolk plug

Bottle cells

contact with the outer surface of the embryo appear at time of neurulation

Is process that rearranges the cells of the blastula

Provides cells with new position and new neighbors

Modified by the presence of large yolk cells in the vegetal pole

Move surface cell inward to establish new layers called germ layers

The involution creates and destroys the blastocoel

Gastrulation: arrangement of embryonic cells

Neural groove/ Neural Tube (15 - 24 hours):

- formation of the nervous system

- the ectoderm at the dorsal side forms the neural plate (after fertilization 14 hours)

- neural plate moves inwards in the median region of the plate (15 hours after

fertilization)

⇒ form the neural groove

− the neural walls develop to form the neural tube (24 hours after fertilization)

Neural tube (After 24 hours)

The anterior-posterior body axis growth and becomes forebrain, eye vesicles and gill plates are developing

c Organogenesis

Tail bud (1 day and 7 hours)

The rudimentary eyes are clearly distinguishable Furthermore, the place of the stomoderm (presumptive mouth) and the first external shape of the gills and tail are visible

gray crescent:

• equally into the two blastomeres

• only the blastomere containing the gray crescent develops normally

2 Axis Formation in Amphibians

Fibronectin and the Pathways for Mesodermal Migration

• before gastrulation, the presumptive ectoderm of the blastocoel roof secretes an extracellular matrix that contains fibrils of fibronectin

• The involuting mesoderm appears to travel along these fibronectin fibers

• Boucaut and co-workers injected large amounts of a small peptide containing this sequence into the blastocoels of salamander embryos shortly before gastrulation began

=> No migrating cells were seen along the underside of the ectoderm

β-catenin localized to the future dorsal cells of the blastula

an anchor for cell membrane cadherins

a nuclear transcription factor

necessary for forming the dorsal axis

=> Recognize dorsal and ventral side

The left-right axis

crucial event is the expression of a nodal gene in the lateral plate mesoderm on the left side of the embryo

initiated at fertilization through the Vg1 protein

=> activate a Nodal protein solely on the left side of the body

=> activate expression of Pitx2 (on the left side of the embryo)

anterior-posterior axis

If the embryo is first injected

with Xwnt3a RNA, the anterior markers are lost

the BMP inhibitors bone morphogenetic proteins

contribute to the ventral mesoderm

Chordin localized in the dorsal blastopore lip and later in the dorsal mesoderm of the

notochord

Follistatin activin receptor normally functioned to bind an inhibitor of neurulation

the Wnt inhibitors

Cerberus secreted protein that accomplishes the induction of the most anterior head structures

promotes the formation of the cement gland, eyes, and olfactory (nasal) placodes

Frzb and Dickkopf

http://www.vcbio.science.ru.nl/en/virtuallessons/embryology/amphibian/

Developmental Biology - ninth edition-SCOTTF.GILBERT

http://worms.zoology.wisc.edu/frogs/gastxen/BC_summary.html

Giáo án sinh học phát triển- TS Nguyễn Lai Thành