Neurulation

Question 1

derivatives of ectoderm

Answer 1

• results from neurulation and subsequent development

Question 2

ectoderm structures : surface ectoderm

Answer 2

• epidermis
• lens, cornea
• anterior pituitary

Question 3

ectoderm structures: neural crest

Answer 3

• peripheral nervous system
• facial cartilage

Question 4

ectoderm structures: neural tube

Answer 4

• brain
• neural pituitary
• spinal cord
• retina

Question 5

draw neural tube formation

Answer 5

–

Question 6

neural tube formation

Answer 6

• cell shape and adhesion changes
• see figure

Question 7

early shaping of neural tube

Answer 7

• morphological manifestation of segmentation in the development of the CNS
• 3 part to 5 part brain
• prosencephalon divides into telencephalon and diencephalon
• mesencephalon divides into myelen, meten and mesen.

Question 8

telencephalon

Answer 8

• cerebrum

Question 9

diencephalon

Answer 9

• optic vesicle

Question 10

mesencephalon

Answer 10

• midbrain

Question 11

metencephalon

Answer 11

• cerebellum

Question 12

myelencephalon

Answer 12

• medulla

Question 13

neuromeres

Answer 13

• the segments of the neural tube that establish the embryonic brain during development

Question 14

neural tube formation and patterning

Answer 14

• gradient of BMP determines if ectoderm will be neural or not…
• low BMP = neural plate
• medium = neural border
• high BMP = non neural ectoderm

Question 15

Neural induction

Answer 15

• BMP gradient
• BMP inhibits neural formation
• BMP antagonists inhibit BMP (chordin, noggin)
• draw figure

Question 16

what does BMP do?

Answer 16

• blocks dorsal/neural development
• allows for ventral development

Question 17

1st step to neural tube patterning

Answer 17

• wnt/ant-wnt gradient
• see figure (draw)

Question 18

patterning AP axis

Answer 18

• AP identity of broad regions of CNS is specified during gastrulation and neural plate formation
• two signaling centers:
  1: head organizing regions: Anterior visceral endoderm, prechordal plate
  2: notochord

Question 19

first step of patterning AP axis

Answer 19

• following neural induction, vertical inductions from signaling centers produce first subdivision
• defines midbrain-hindbrain borders

Question 20

forebrain/midbrain region

Answer 20

• Otx2 TF is expressed

Question 21

hindbrain/spinal cord region

Answer 21

Gbx2 TF is expressed

Question 22

second step of patterning AP axis

Answer 22

• isthmic organizer (isthmus)
• expression boundary between otx2 and gbx2
• midbrain/hindbrain border
• controls regional specification of neural tissue
• FGF8 synthesized posterior to isthmus
• wnt1 synthesized anterior to isthmus
• leads to expression of engrailed

Question 23

Third step patterning AP axis

Answer 23

• FGF8 and Wnt induce a gradient of expression of certain transcription factors on both sides of the isthmic organizer
• induces engrailed, which expresses Pax2 and Pax5

Question 24

fourth step patterning AP axis

Answer 24

• Pax2/5 and pax6 TFs subdivide early neural tube into 3 divisions
• pax2 and 5 expressed in midbrain and rhombomere 1 region
• pax6 expressed in forebrain and hindbrain
• SEE FIGURE

Question 25

Pax6

Answer 25

• master control gene
• development of eyes and sensory organs

Question 26

fifth step of patterning AP axis

Answer 26

• forebrain/midbrain development

Question 27

combo of patterning AP axis steps

Answer 27

• 1) vertical inductions produce 1st subdivisions
• 2) Isthmic organizer
• 3) FGF and Wnt induce TF gradient
• 4) Pax 2,5 and 6 divide early neural tube into 3 parts
• 5) Forebrain/ midbrain development

Question 28

Posterior neural development

Answer 28

• caudal to the isthmic organizer; hindbrain and spinal cord

Question 29

3 signaling pathways of posterior neural development

Answer 29

• Wnt
• FGF
• retinoic acid

Question 30

Regulation of Posterior neural development

Answer 30

• response to graded signal
• differential thresholds of response to constant signal
• interactions of different pathways
• see figure

Question 31

role of Wnt/B-catenin activity in posterior neural developement?

Answer 31

• caudalizes the embryonic nervous system

Question 32

cascade gene expression, posterior neural development

Answer 32

• wnt activates cdx and meis
• cdx inhibits PG14 Hox (hindbrain), activates another hox (spinal cord)
• meis activates PG14 hox
• spinal cord hox inhibits hindbrain hox
• see figure

Question 33

segmentation of hindbrain

Answer 33

• rhombomere formation
• involved expression of several categories of genes
• similar to drosophilia

Question 34

segmentation of spinal cord

Answer 34

• defined by signals from paraxial mesoderm (somites)
• see figure

Question 35

How do hox genes specify segmental identity

Answer 35

• Regulated by:
  TFs acting on gene specific regulatory regions
  gene position
  miRNAs
• not expressed in forebrain/midbrain
• important in hindbrain through spinal cord
• segmental identity of individual neuromeres

Question 36

How are hox genes expressed

Answer 36

• temporal and spatial order
• reflects order on chromo
• sharp anterior border, less sharp posterior border
• 3’ genes required for production of anterior structures
• almost every region of AP axis characterized by Hox genes