Chapter 52 - Patterning the Nervous System

Question 1

what are the 3 germ layers? what do they each develop into?

Answer 1

1. ectoderm -> exoskeleton (skin + CNS)
2. mesoderm -> organs
3. endoderm -> inner linings of organs

Question 2

what CNS precursor becomes regionalized early in embryogenesis?

Answer 2

the neural tube

Question 3

what does the ectoderm give rise to?

Answer 3

the neural plate

Question 4

what is the neural plate a precursor of?

Answer 4

the CNS and PNS

Question 5

what gives rise to the neural plate?

Answer 5

the ectoderm

Question 6

how does the neural tube form?

Answer 6

• the neural plate buckles at its midline

- closure of the dorsal neural folds

Question 7

what does the neural tube lie over?

Answer 7

the notochord

Question 8

what is the notochord?

Answer 8

• mesodermal tissues

- important organizational role

Question 9

what does the notochord later become?

Answer 9

vertebral column

Question 10

what is the neural tube flanked by?

Answer 10

somites

Question 11

what are somites?

Answer 11

• mesodemral cells

- give rise to muscle + cartilage

Question 12

what is the neural tube?

Answer 12

-ectodermal tissue that becomes the entire CNS

Question 13

what is the first major stage of neural tube development?

Answer 13

the formation of 3 brain vesicles

Question 14

why are 3 brain vesicles formed?

Answer 14

-differences in rate of the proliferation of cells in the rostral regions of the neural tube

Question 15

what is the second major stage of neural tube development?

Answer 15

-3 brain vesicles elaborate into 5

Question 16

what drives progressive patterning and subdivision of cells/tissues in the neural tube?

Answer 16

-a variety of secreted molecules

Question 17

what is the organizer region?

Answer 17

-play an important “instructive” role in early differentiation

Question 18

where does the entire nervous system derive from?

Answer 18

-a restricted region of of the ectoderm

Question 19

what choice do ectodermal cells have early in development?

Answer 19

-whether to become neural or epidermal cells

Question 20

what happened when Spemann and Mangold transplanted organizer cells? what does this show

Answer 20

• 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

Question 21

What is the default fate of ectodermal cells?

Answer 21

-neural differentiation

Question 22

what is preventing ectodermal cells from becoming neural cells?

Answer 22

-signals from neighboring ectodermal cells

Question 23

what are BMPs?

Answer 23

• group of growth factors

- play key roles in morphogenetic signaling

Question 24

what do BMPs do in the absence of organizer cells?

Answer 24

• suppress the potential for neural differentiation

- promote epidermal differentiation

Question 25

what do BMP inhibitors do?

Answer 25

-block BMP signaling and enable cells to become neurons

Question 26

what are examples of BMP inhibitors?

Answer 26

- noggin - chordin - follistatin

Question 27

how is the forebrain, midbrain, and hindbrain patterned?

Answer 27

signals from the mesoderm and endoderm

Question 28

what is Wnt?

Answer 28

-proteins that create a gradient and pattern the mid/hindbrain boundary

Question 29

where do Wnt signals come from?

Answer 29

-expressed by paraxial mesoderm

Question 30

where are Wnt inhibitors secreted?

Answer 30

-secreted by endoderm

Question 31

where are there more Wnt signaling activity?

Answer 31

lower at rostral levels of neural and higher at caudal direction

Question 32

how is the forebrain, midbrain, hindbrain patterning further refined?

Answer 32

- 2 specialized cell groups 1. zona limitans intrathalamica 2. isthmic organizer

Question 33

what do zona limitans intrathalamica do?

Answer 33

-secret sonic hedgehog

Question 34

what does sonic hedgehog do?

Answer 34

- patterns nearby cells that give rise to nuclei of the thalamus - also patterns spinal cord

Question 35

what does the isthmic organizer region do?

Answer 35

-secretes FGF signals which work with shh gradients to specify serotonergic and dopaminergic cells

Question 36

how do FGF signals work?

Answer 36

-express onto midbrain and hindbrain regions

Question 37

which transcription factors do the midbrain and hindbrain have?

Answer 37

- midbrain (Otx2) | - hindbrain (Gbx2)

Question 38

how does FGF act to pattern/differentiate midbrain/hindbrain?

Answer 38

- cells have already acquired Gbx2 or Otx2 transcriptional fate - receive the same FGF signal - but signal is interepreted differently