Early Vertebrate Development Flashcards
What is the primary role of Pitx2 in biological development? Is there a specific function in humans?
Influencing left-right asymmetry. In humans: Pitx2 > leftness.
What are the characteristic symptoms of Reiger symptoms?
No left-right defects, but mild skull dysmorphism, eye socket and dental anomalies.
What is the relevance of Nodal signalling in asymmetry?
Loss of function leads to left-right patterning defects originating at the node.
What 2 theories have been used to try to decribe the asymmetrical mechanism of nodal flow?
- Leftward current carries “parcels” of signalling molecules
- Leftward current “mechanically” stimulates peripheral cilia
What 2 important things are present in the proposed nodal vesicular parcels responsible for left/ right asymmetry?
- Calcium ++
2. Sonic Hedgehog
How is left/right assymmetry affected when direction of nodal flow is reversed?
Left and right are then reversed during development.
How are nodal cilia involved in the development of left/right asymmetry in vertebrates?
They rotate clockwise to cause the flow of nearby molecules to travel from right to left.
What is KIF3B?
A microtubule motor protein in the same family as kinesin, responsible for development of cilia in the node.
What is meant by situs ambiguous?
Any deviation from normal internal organ orientation.
What is meant by situs inversus? What about situs inversus thoracalis and situs inversus abdominalis?
The inversion of internal organ orientation.
Thoracalis: inversion of thoracic organs
Abdominalis: inversion of abdominal organs
What is a morphogen?
A signalling molecule which organizes surrounding cells into a pattern/gradient. Acts on cells in a concentration-dependent manner.
How does a morphogen determine the fate of surrounding cells?
By arranging them according to differing concentrations of the morphogen.
Which TGF-beta family signalling molecule is active in the endoderm? What does this produce?
Xnr, active in the endoderm as a concentration gradient with the highest concentration at the dorsal side and the lowest at the ventral side.
Which TGF-beta family signalling molecule is active in the mesoderm? What does this produce?
BMP4, active in the mesoderm as a concentration gradient with the highest concentration at the ventral side and the lowest at the dorsal side.
What is the significance of Cerl and Lefty in biological development? What does it inhibit to accomplish this?
Both expressed in the AVE (anterior visceral endoderm), critical for correct anterior-posterior positioning. Acts as an antagonist for Nodal.
What important role does Nodal play in early vertebrate development?
Specifies the primitive streak formation.
BONUS: inhibited by Cerl and Lefty so it doesn’t just activate anywhere.
What does “Cerl” mean?
Cerberus-like.
Even if Cerl and Lefty are inhibited (activating Nodal), primitive streaks don’t pop up everywhere, why?
Because signalling from both Nodal and the Wnt pathway (Wnt3) are needed to induce formation of the primitive streak (redundancy).
What is the function of Gsc (Goosecoid)
Specifies the Spemann organizer fate.
What is the AVE? How does it form?
Anterior visceral endoderm. Extraembryonic, forms from the migration of cells from medial regions.
What structure in the mammal embryo is functionally equivalent to the Spemann organizer in frogs?
(Henson’s) node.
Cerl and Lefty inhibit Nodal (important for primitive streak formation alongside Wnt), but what signalling molecules inhibit Wnt?
Cerberus, Frzb and Dickkopf.
What structure in the mammal embryo is functionally equivalent to the anterior endomesoderm in frogs?
The anterior visceral endoderm (AVE).
Where in the mammalian embryo does involution occur?
Along the primitive groove.
What structure in the mammal embryo is functionally equivalent to the dorsal lip in frogs?
The node.
How do expression of Frzb and Dickkopf influence development?
Both inhibit Wnt
Frzb: increase head size
Dickkopf: decrease head size
Besides acting as an “off switch”, how can microRNA affect development?
By fine-tuning and stabilizing gene expression (dealing with concentration gradients).
What gradient is used for specializing the dorsal-ventral mesoderm?
The BMP gradient.
What gradient is used for specializing the anterior-posterior neural ectoderm?
The Wnt gradient.
Where is Wnt3 expressed in the mammalian embryo prior to gastrulation?
The posterior visceral embryo (PVE) and the posterior epiblast.
Where does gastrulation initiate in the embryo of amniotes?
At the posterior region of the epiblast.
Wnt signalling is required for _________ development and is inhibited during _________.
Required for posterior development, inhibited during anterior development.
When Cerberus functionality is lost why does head development still occur?
Because Frzb and Dickkopf have similar function as Cerberus in mediating head development (redundancy).
What 5 signalling molecules inhibit BMP?
- Chordin
- Noggin
- Follistatin
- Cerberus
- Xnr3
How does transplantation of a young frog gastrula dorsal lip influence the final tadpole form?
Tadpole develops with a second axis (TWO HEADS).
What is the function of siamois protein? What does it act alongside?
Acts with Smad 2/4 as a transcription factor for goosecoid protein (not strong enough alone).
What is the function of goosecoid protein?
Specifies the Spemann organizer.
Where is the Nieuwkoop center? What is it’s function?
Located in the dorsal endoderm, activates siamois protein to initiate transcription of goosecoid which specifies the Spemann organizer.
How is the dorsal-ventral axis defined in an embryo? What causes the uniform surface of the egg to differentiate?
The site of sperm entry defines the dorsal-ventral axis.
Where is dishevelled protein (+GBP+Wnt11 mRNA) located before sperm entry? What about after?
Located at the bottom of the vegetal pole, but migrates to the dorsal side upon sperm entry.
How is dishevelled protein able to migrate following sperm entry to the egg?
Microtubules form from the sperm and spread around the membrane to the opposite side of the embryo. Dishevelled is transported along these microtubules.
What is know to block microtubule formation in a fertilized egg, resulting in a ventralized embryo?
Blocked by UV.
Where in the fertilized embryo are Dsh and GBP enriched following cortical rotation?
Dsh and GBP are dorsally enriched.
Where is beta-catenin degraded in the embryo following cortical rotation? Where is it stable?
Degraded on the ventral side but dorsally stabilized.
What 6 steps outline the Wnt signalling pathway? Which of these components functions as an inhibitor?
- Wnt
- Frizzled
- Disheveled (inhibitor)
- GSK-3 (inhibitor)
- Beta-catenin
- Transcription
VegT is required for the formation of ______ and _______.
Endoderm and mesoderm.
The results of the animal/vegetal sandwich experiments show that ______ is able to induce _______,
Endoderm is able to induce mesoderm.
How can UV ventralized embryos be rescued?
By using the dorsal endoderm (Nieuwkoop center) to induce the dorsal mesoderm (Spemann’s organizer).
What is know to cause development of a dorsalized embryo?
Exposure to LiCl at the one-cell stage.
What is the default fate of the ectoderm? Why does it not become this when separated from the mesoderm?
Neural tissue. The mesoderm secretes BMP (induces epidermis) inhibitors (ex: Noggin) which cause ectoderm to become neural tissue.
What part of the BMP signalling pathway is inhibited by Noggin (or chordin, or follistatin)?
The inhibitors act on the BMP ligand to inhibit.
What developed structures arise from the dorsal mesoderm?
Notochord and neural tube.
What developed structures arise from the endoderm?
Pharynx, tongue, trachea, gall bladder, pancreas, bile duct, oesphagus, stomach, small intestine, proctodaeum.
What developed structures arise from the ventral mesoderm?
Blood and mesenchyme.
What developed structures arise from the somite?
Back muscles, vertebrae, dermis.
During what developmental stage do events occur which lead to neural fate determination?
Gastrulation.
What occurs when cells are translocated prior to determination?
Embryo develops according to the fate map.
What occurs when cells are translocated following determination.
Tissues develop into their determined fates regardless of where they have been moved to?
At what stage of development will cleavage no longer yield viable organisms?
After the 4-cell stage, cleavage does not result in viable organisms (b/c of asymmetry).
What is meant by “regulative” development?
Internal adjustment allows the embryo to maintain normal development despite disturbances.
What is meant by “mosaic” development?
All body regions spatially compartmentalized in the early embryo.
What 3 mechanisms are there for monozygous twinning?
- (25%) Each have own chorion and amnion
- (60-70%) Each have own amnion but share chorion
- (1-2%) Share chorion and amnion
What is meant by “polyembryony”?
The formation of more than one embryo from a single fertilized egg (ex: armadillos have identical quadruplets).
How does a chimeric organism arise?
A rare event (kinda the opposite of twinning) where 2 fertilized eggs fuse to become a single organism with 2 different sets of chromosomes depending on tissue.
What is the chorion? What about the amnion?
Chorion: outermost embryo membrane for exchange (mammals = placenta)
Amnion: secretes fluid
What occurs during the “compaction” event in early cleavage? What is important for this?
Flattening and joining of cell ball at 8-cell stage. E-caderin mediates formation of cell junctions.
What is the purpose of the yolk sac? What types of organisms have this?
Nourishes the developing organism, present in birds and reptiles.
What is discoidal cleavage? What organisms do this?
Only the upper cells divide, leaving large yolk sac below. Exhibited in fish, bird, and reptile development.
Which of the embryonic tissues arise from the embryo itself? Which are supplied by the mother?
Embryo: chorion (placenta), amnion, yolk sac
Mother: uterine epithelium, decidua (placenta)
What is the allantois?
One of the tissues supporting the developing embryo which does gas exchange and stores waste.
Localization of ___ establishes the future posterior in amphibians.
Par2
What is displaced radial cleavage? What organisms do this?
Initial 2 cleavages are vertical before the first horizontal cleavage. Occurs in amphibians.
What is the function of Par6?
Implicated in cytoskeletal rearrangement (particularly in humans).
Why are Par proteins important for animal early development?
Establishes asymmetry.
_______ localization specifies germ cell formation. What is essential for their specification?
P-granule. Ribonucleoprotein complexes are essential for specification.
What is the function of macho-1?
Specifies muscle development.
What differentiates meroblastic cleavage from holoblastic cleavage?
Meroblastic: partial cleavage of the embryo
Holoblastic: complete cleavage of the embryo
