17. Body plans Flashcards
(26 cards)
What defines the structural organization of an organism?
A body plan
A body plan includes morphological features such as shape, size, and arrangement of organs.
What is a key defining feature of vertebrates?
The backbone
What type of symmetry do vertebrates exhibit?
Bilateral symmetry
What are the defined axes in vertebrate body plans?
- Anterior-posterior (AP) axis
- Dorsal-ventral (DV) axis
- Left-right axis
Where is the head located in vertebrates?
At the anterior end with brain and sensory organs
What is the phylotypic stage?
The middle of developmental ‘hourglass’ where vertebrate embryos look most similar
What establishes the animal-vegetal axis in Xenopus?
Maternal factors before fertilization
What is the role of VegT mRNA in Xenopus development?
Localized to the vegetal pole to become the future AP axis
How is the dorsal-ventral axis established in Xenopus?
By the sperm entry point and cortical rotation
What does the Nieuwkoop center lead to in Xenopus?
Spemann-Mangold organizer
What are the functions of the organizer in Xenopus?
- Self-differentiate into dorsal mesoderm
- Dorsalizes surrounding mesoderm
- Dorsalizes ectoderm
- Initiates neural tube formation
- Initiates gastrulation movements
- Secretes BMP inhibitors (Noggin, Chordin, Follistatin)
What are the key molecular signals in Xenopus development?
- Beta-catenin (dorsal signaling)
- TGF-β/Smad2 signaling (mesodermal fate)
What causes initial symmetry breaking in chick development?
Gravity due to egg rotation in the hen’s reproductive tract
What is the primitive streak in amniotes?
A structure that arises from Koller’s sickle in the posterior marginal zone
What key signals induce Nodal expression in amniotes?
- Vg1
- Wnt
How does Hensen’s node relate to the organizer function in amniotes?
It forms at the tip of the primitive streak and is equivalent to the Spemann-Mangold organizer
What specifies the left side in chick development?
Pitx2
What role does Sonic hedgehog play in chick left-right axis formation?
Secreted by Hensen’s node
What is the significance of motile cilia in mouse left-right axis formation?
They create directional fluid flow
What do Hox genes encode?
Transcription factors that confer segment identity
What is collinearity in Hox genes?
The order on chromosome matches spatial expression pattern
What experimental evidence supports the role of Hox genes?
- Hox10 knockout causes ectopic ribs in lumbar region
- Hox11 knockout disrupts sacral patterning
What are conserved signaling pathways involved in comparative development?
- Wnt
- TGF-β
- BMP
What is a structural difference in early embryos of different species?
- Zebrafish/chick: yolk eggs
- Xenopus: spherical structure
- Mouse: cup structure
- Human: disk structure similar to chick
