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Ectoderm
One of the three germ layers that will turn into the epidermis and the nervous system.
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Mesoderm
Middle of the three germ layers that will go on to create muscle, connective tissue, the skeleton, blood, and blood vessels.
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Endoderm
One of the three germ layers that will go on to create the gut and the respiratory tract, among other things.
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Morula
- A ball of cells formed following zygote formation during fertilization
- No cavity is present.
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Blastula
- A hollow sphere of cells formed from the morula.
- Defined from a morula into a blastula upon the formation of the blastocoel.
- Both the blastula and morula will contain cells that are dividing without increasing the overall size of the entire ball of cells.
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Blastocoel
- The cell-less region of the blastula.
- The first cavity of the organism.
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Gastrula/gastrulation
- Caused by an invagination of the blastula at the blastopore.
- It goes from a single layer (more or less) of cells into a trilaminar (three cell layers) structure.
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Archenteron
- Second cavity of the gastrula.
- This will develop into the digestive tract/gut.
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Neurulation
- The formation of the neural tube.
- The neural plate, part of the ectoderm, will fold into itself (invagination) forming a neural tube, and neural crest cells.
- This happens when signaled on from the notochord.
- The neural tube will go on to form the central nervous system.
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Neural crest cells
- Cells formed at the dorsal part of the neural tube
- These will reposition themselves to form the peripheral nervous system.
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Notochord
Part of the mesoderm, but is responsible for driving the induction of epidermis and neural tissue.
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Induction
- When a cell is instructed to adopt a certain fate or characteristic by signals in its environment.
- Essentially, one cell telling another cell what to do
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Competence
- The ability of a cell to respond to a signal
- A function of the receptors, signaling molecules, transcription factors, expressed by the cell.
- Cell must want to respond to signal
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Determination/specification
When a cell is restricted in its developmental potential (to become a specific type of cell).
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Differentiation
- When a cell elaborates a specific developmental program (to become a cell type from a precursor cell)
- Cells become different from each other and acquire specific functions and characteristics
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What does neural development depend on?
Interactions between environmental cues and genetic factors
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Environmental cues
Inductive events
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Genetic factors
- Cell lineages
- Competence to respond to other genetic factors or environmental cues
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Whats special about the human (and other species) brain?
Its a highly ordered and complex structure
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How are cells of the ectoderm induced to become neural?
Well?
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What are the milestones in development?
- Fertilization
- Cell proliferation/cleavage
- Patterning
- Differentiation
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Fertilization
Haploid egg and sperm
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Cell proliferation/cleavage
Zygote goes through series of cleavages
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Patterning
- Cells arranged/specified in the proper positions
- Establishment of the body plan (head vs. toes)
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Whats the main problem?
- How do things go from simple to complex
- What are the initial steps in the development of the nervous system?
- Fertilization
- Cleavage
- Gastrulation
- Neuralation
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Real morphological growth starts at what stage?
Neurula stage
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What is the preferred model for studying early development? Why?
- Xenopus laevis (African clawed frog)
- Embryos are big
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What happens during the blastula stage?
Cells differentiate from each other
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What happens during gastrula stage?
Movement goes through blastopore into blastocoel
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Blastopore
Dent at dorsal lip thatll go into blastocoel
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Where is the notochord?
On the dorsal side, right under the neural plate in between the somites
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What is the notochord important for?
Induction
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What two parts does the neural tube split into?
- Rostral- anterior/head
- Caudal- posterior/butt
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What does the rostral part of the neural tube lead to?
Formation of the brain
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What does the caudal part of the neural tube lead to?
Formation of the spinal cord
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What did Spemann and Mangold demonstrate?
Inductive signals are responsible for specifying the nervous system from ectoderm
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What happened to early ectoderm if cultured alone, without the dorsal lip?
Became epidermal tissue
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What happened to early ectoderm when cultured with the dorsal lip?
Turns into neural tissue
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What does DLB stand for?
Dorsal lip of the blastopore
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What was the DLB named? Why?
- The organizer
- Transplanted DLB induces host ectoderm to adopt neural fate
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What did the early scientists think because of the observations they saw with the dorsal lip and ectoderm? Why were they wrong?
- There had to be some sort of message from the dorsal lip to tell the ectoderm to become neural tissue
- Wasnt exactly telling it to be nervous, it was telling it NOT to be epidermal tissue
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What is the animal cap?
Essentially the dorsal part of the blastocyst that is almost completely ectoderm
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What experiment was done with the animal cap?
They compared cultured animal cap when it was clumped together, or dissociated
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What is a dissociated animal cap?
Single cells
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What happens to the dissociated cells from the animal cap?
Turns into neurons
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What happens to intact animal cap?
Turns into epidermal tissue
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What did the experiment with the animal caps tell the researchers? Why?
- The default state is neural tissue
- The dissociated cells werent able to efficiently receive any signals when dissociated
- Without any signals, they became neurons
- Meaning, its their default state
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What does BMP stand for?
Bone morphogenetic protein
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What does BMP bind to?
BMP receptors (BMPRs) ...
(-__-)
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What happens when BMP binds to BMPRs?
Sends signaling cascade that induces a cell to NOT become neural tissue, and become epidermal
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What is the competing signal for BMP?
Noggin, it binds to BMP
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What is noggin?
A BMP antagonist
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What happens when noggin binds to BMP?
- Prevents it from binding to BMPRs, kinda makes it a weird shape so it doesnt fit into the receptors
- BMPRs are empty
- No induction to epidermal tissue
- Turns into default neural tissue
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What other proteins are similar to noggin?
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Where is most BMP secreted?
Ventral side
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Where is noggin most secreted?
At DLB (organizer)
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