Early embryonic dev., patterning & twins

Question 1

Why do I need to know about early embryo patterning and development?

Answer 1

Failure of normal twin presentation or normal embryonic is a common cause of dystocia
Can result in:
Fetal mortality Maternal mortality Or both

Question 2

Why is dystocia important the animal industry?

Answer 2

Causes bird-losses in poultry & is leading cause of death in calves, post partum infection & death in heifers
- major cause of economic loss to beef industry

Question 3

What is gastrulation? (covered in detail in GIT dev. lec)

Answer 3

The process where the flattened pear-shaped bilaminar disc (developed from the ICM) undergoes reorganisation -> trilaminar disc
Forms the 3 distinct germinal layers: 1. Ectoderm 2. Mesoderm 3. Endoderm

Question 4

What process causes conjoined twins? (joined at the head)

Answer 4

Incomplete separation of two primitive streaks

Question 5

What is patterning? Earliest patterning event?

Answer 5

the process of defining a body or tissue plan during embryogenesis or organogenesis
Earliest event - creation of a ‘head’ from a ‘tail’

Question 6

What are the 2 major signalling centres required for patterning? ie. How do we make sure we develop one head/tail rather than two?

Answer 6

Anterior visceral endoderm - ‘head organiser’

Node - ‘rest of body organiser’

Question 7

Structures on the dorsal surface of embryo?

Answer 7

ectoderm in contact with the amniotic cavity (see slide 22)

Question 8

Structures on the ventral surface of embryo?

Answer 8

ectoderm is on outside of embryo

Question 9

Posterior protein ‘nodal’, activates expression of genes required for … formation?

Answer 9

posterior mesoderm formation

Question 10

Anterior visceral endoderm secretes 2 antagonists of the nodal protein. name them

Answer 10

Lefty1

Cerberus

Question 11

AVE expresses the dorsal factor…?

Answer 11

Oxt2

Question 12

What is the Hensen’s Node?

Answer 12

the ‘primitive node’ in birds

Question 13

Ectoderm gives rise to …?

Answer 13

epithelial & neural tissue

Question 14

Mesoderm gives rise to …?

Answer 14

cardiac muscle, skeletal muscle, kidney tubules, RBCs & smooth muscles in GIT

Question 15

Endoderm gives rise to…?

Answer 15

digestive & resp. tracts

Question 16

These fucking slides are so confusing, so i’m gonna ask, what are some factors involved in tissue-specific asymmetry?

Answer 16

• signalling molecules: Sonic hedgehog (Shh) & retinoic acid (RA)
• potassium ATPase
• Ca2+ ions

Question 17

In avian species other factors can affect patterning of the early embryo….what are they? Describe the process…

Answer 17

A/P axis formation determined by gravity
As the egg passes through the hen’s reproductive tract, it rotates for approx. 20 hours at 10/12 revolutions/hour.
This rotation concentrates the lighter components of the yolk to one side of the blastoderm which becomes posteriorised and will go on to form the primitive streak

Question 18

Why is patterning so important?

Answer 18

Because asymetry in the morulae contributes to normal development of the blastocoel cavity

Question 19

Describe the process that gives rise to twins

Answer 19

As well as implantation of more than one embryo, loss of asymetry in the in the early embryo (cleavage, morula or early blastocyst) -> twins

Question 20

Define ‘dizygotic’ twins

Answer 20

twins arise from two ova from two ovarian follicles fertilised by separate spermatazoa during a single breeding cycle

Question 21

Define ‘monozygotic’ twins. Which stage? spp? incidence?

Answer 21

two individuals developed from one fertilized oocyte; they have identical genomes

• primitive streak stage
• humans, sheep, pigs
• incidence <1%

Question 22

Give 2 examples of rates of twinning in domestic animals…

Answer 22

1. cattle: natural (dizygotic) twinning 2-3%; monozygotic 0.1%
2. sheep: natural (dizygotic) twinning 2-5%

Question 23

What are the 3 different twin timing processes?

Answer 23

1. pre-blastocyst - twins in 2 chorions & 2 amnions
2. early blastocyst - twins in 1 chorion & 2 amnions
3. late blastocyst - twins in 1 chorion & 1 amnion