Early embryonic dev., patterning & twins Flashcards
Why do I need to know about early embryo patterning and development?
Failure of normal twin presentation or normal embryonic is a common cause of dystocia
Can result in:
Fetal mortality Maternal mortality Or both
Why is dystocia important the animal industry?
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
What is gastrulation? (covered in detail in GIT dev. lec)
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
What process causes conjoined twins? (joined at the head)
Incomplete separation of two primitive streaks
What is patterning? Earliest patterning event?
the process of defining a body or tissue plan during embryogenesis or organogenesis
Earliest event - creation of a ‘head’ from a ‘tail’
What are the 2 major signalling centres required for patterning? ie. How do we make sure we develop one head/tail rather than two?
Anterior visceral endoderm - ‘head organiser’
Node - ‘rest of body organiser’
Structures on the dorsal surface of embryo?
ectoderm in contact with the amniotic cavity (see slide 22)
Structures on the ventral surface of embryo?
ectoderm is on outside of embryo
Posterior protein ‘nodal’, activates expression of genes required for … formation?
posterior mesoderm formation
Anterior visceral endoderm secretes 2 antagonists of the nodal protein. name them
Lefty1
Cerberus
AVE expresses the dorsal factor…?
Oxt2
What is the Hensen’s Node?
the ‘primitive node’ in birds
Ectoderm gives rise to …?
epithelial & neural tissue
Mesoderm gives rise to …?
cardiac muscle, skeletal muscle, kidney tubules, RBCs & smooth muscles in GIT
Endoderm gives rise to…?
digestive & resp. tracts
These fucking slides are so confusing, so i’m gonna ask, what are some factors involved in tissue-specific asymmetry?
- signalling molecules: Sonic hedgehog (Shh) & retinoic acid (RA)
- potassium ATPase
- Ca2+ ions
In avian species other factors can affect patterning of the early embryo….what are they? Describe the process…
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
Why is patterning so important?
Because asymetry in the morulae contributes to normal development of the blastocoel cavity
Describe the process that gives rise to twins
As well as implantation of more than one embryo, loss of asymetry in the in the early embryo (cleavage, morula or early blastocyst) -> twins
Define ‘dizygotic’ twins
twins arise from two ova from two ovarian follicles fertilised by separate spermatazoa during a single breeding cycle
Define ‘monozygotic’ twins. Which stage? spp? incidence?
two individuals developed from one fertilized oocyte; they have identical genomes
- primitive streak stage
- humans, sheep, pigs
- incidence <1%
Give 2 examples of rates of twinning in domestic animals…
- cattle: natural (dizygotic) twinning 2-3%; monozygotic 0.1%
- sheep: natural (dizygotic) twinning 2-5%
What are the 3 different twin timing processes?
- pre-blastocyst - twins in 2 chorions & 2 amnions
- early blastocyst - twins in 1 chorion & 2 amnions
- late blastocyst - twins in 1 chorion & 1 amnion
