Chapter 52 - Patterning the Nervous System Flashcards
what are the 3 germ layers? what do they each develop into?
- ectoderm -> exoskeleton (skin + CNS)
- mesoderm -> organs
- endoderm -> inner linings of organs
what CNS precursor becomes regionalized early in embryogenesis?
the neural tube
what does the ectoderm give rise to?
the neural plate
what is the neural plate a precursor of?
the CNS and PNS
what gives rise to the neural plate?
the ectoderm
how does the neural tube form?
- the neural plate buckles at its midline
- closure of the dorsal neural folds
what does the neural tube lie over?
the notochord
what is the notochord?
- mesodermal tissues
- important organizational role
what does the notochord later become?
vertebral column
what is the neural tube flanked by?
somites
what are somites?
- mesodemral cells
- give rise to muscle + cartilage
what is the neural tube?
-ectodermal tissue that becomes the entire CNS
what is the first major stage of neural tube development?
the formation of 3 brain vesicles
why are 3 brain vesicles formed?
-differences in rate of the proliferation of cells in the rostral regions of the neural tube
what is the second major stage of neural tube development?
-3 brain vesicles elaborate into 5
what drives progressive patterning and subdivision of cells/tissues in the neural tube?
-a variety of secreted molecules
what is the organizer region?
-play an important “instructive” role in early differentiation
where does the entire nervous system derive from?
-a restricted region of of the ectoderm
what choice do ectodermal cells have early in development?
-whether to become neural or epidermal cells
what happened when Spemann and Mangold transplanted organizer cells? what does this show
- they followed their normal developmental program
- caused change in fate of the neighboring ventral ectodermal cells of the host embryo
- nervous system is induced by signals from a highly restricted organizing center
What is the default fate of ectodermal cells?
-neural differentiation
what is preventing ectodermal cells from becoming neural cells?
-signals from neighboring ectodermal cells
what are BMPs?
- group of growth factors
- play key roles in morphogenetic signaling
what do BMPs do in the absence of organizer cells?
- suppress the potential for neural differentiation
- promote epidermal differentiation
what do BMP inhibitors do?
-block BMP signaling and enable cells to become neurons
what are examples of BMP inhibitors?
- noggin
- chordin
- follistatin
how is the forebrain, midbrain, and hindbrain patterned?
signals from the mesoderm and endoderm
what is Wnt?
-proteins that create a gradient and pattern the mid/hindbrain boundary
where do Wnt signals come from?
-expressed by paraxial mesoderm
where are Wnt inhibitors secreted?
-secreted by endoderm
where are there more Wnt signaling activity?
lower at rostral levels of neural and higher at caudal direction
how is the forebrain, midbrain, hindbrain patterning further refined?
- 2 specialized cell groups
1. zona limitans intrathalamica
2. isthmic organizer
what do zona limitans intrathalamica do?
-secret sonic hedgehog
what does sonic hedgehog do?
- patterns nearby cells that give rise to nuclei of the thalamus
- also patterns spinal cord
what does the isthmic organizer region do?
-secretes FGF signals which work with shh gradients to specify serotonergic and dopaminergic cells
how do FGF signals work?
-express onto midbrain and hindbrain regions
which transcription factors do the midbrain and hindbrain have?
- midbrain (Otx2)
- hindbrain (Gbx2)
how does FGF act to pattern/differentiate midbrain/hindbrain?
- cells have already acquired Gbx2 or Otx2 transcriptional fate
- receive the same FGF signal
- but signal is interepreted differently
