Gastrulation and Neurulation

Question 1

What is gastrulation?

Answer 1

1- Process in early(ish) embryology

2- Bilaminar disc becomes trilaminar disc

Question 2

What are the three layers of the trilaminar disc?

Answer 2

1- Endoderm
2- Mesoderm
3- Ectoderm

Question 3

What is the notochord?

Answer 3

1- Structure in blastocyst
2- Lies along anteroposterior axis
3- Closer to dorsal than ventral
4- Induces neurulation
5- Later on forms spinal cord
6- Formed when epiblast cells burrow in between epiblast and hypoblast, forming notochord and mesoderm

Question 4

How is the mesodorm formed?

Answer 4

Epiblast cells migrate through the primitive streak to form the mesoderm between epiblast and hypoblast

Question 5

What is neurulation?

Answer 5

1- Folding of tri-laminar disc
2- Neural plate becomes neural tube
3- Induced by notochord

Question 6

What induces the beginning of neurulation?

Answer 6

Notochord

Question 7

What factors do the notochord and primitive node secrete at the beginning of neurulation?

Answer 7

1- Chordin
2- Noggin
3- Follistatin

Question 8

Why do the notochord and primitive node release factors at the beginning of neurulation?

Answer 8

1- Block BMP effects (bone morphogenetic proteins)

2- Determine back and neural tissue development instead

Question 9

Describe the formation of the neural tube.

Answer 9

1- Notochord induces neurulation
2- Ectoderm epithelial cells become columnar
3- Edges of neural plate thicken and migrate towards midline of embryo, fusing on the dorsal side to form a tube
4- Neural groove and neural fold become apparent
5- Folding begins at level of ~4th somite and continues cranially and caudally

Question 10

When does the midline groove become apparent?

Answer 10

19+ days

Question 11

When does closure at the cranial region of the neural plate occur?

Answer 11

~25 days

Question 12

When does closure at the caudal region of the neural plate occur?

Answer 12

~28 days

Question 13

What happens if cranial closure does not occur?

Answer 13

Anecephaly

Question 14

What happens is caudal closure does not occur?

Answer 14

Spina bifida

Question 15

What are neural crest cells?

Answer 15

1- Temporary group of cells
2- Arise from ectoderm
3- Produce a variety of cells e.g. melanocytes
4- Found at the border between neural tube and epidermis

Question 16

What are examples of cells derived from neural crest cells?

Answer 16

1- Ganglia (cranial nerve, dorsal root, autonomic)
2- Adrenal medulla
3- Schwann cells
4- Peripheral glial cells
5- Smooth cardiac muscle
6- Odontoblasts
7- Thyroid parafollicular C cells
8- Melanocytes

Question 17

What disorders can arise from defective neural crest development?

Answer 17

1- Pigment anomalies, may come with deafness and/or GI motility issues
2- Waardenburg’s syndrome
3- Treacher Collins syndrome

Question 18

What is the cause of Waardenburg’s syndrome?

Answer 18

1- Defective neural crest development
2- Pax-3 gene deletion
3- SOX10 gene may be affected

Question 19

What are the signs of Waardenburg’s syndrome?

Answer 19

1- Pigment abnormalities
2- Albinism
3- Deafness
4- Heterochromia
5- Telecanthus (wide-set eyes)
6- If SOX10 gene is affected, constipation

Question 20

What is the cause of Treacher Collins syndrome?

Answer 20

1- Defective apoptosis of neural crest cells

2- Defective TCOF1 gene leading to defective Treacle protein

Question 21

What are the signs of Treacher Collins syndrome?

Answer 21

1- Abnormal eye shape
2- Micrognathia (undersized jaw)
3- Conductive hearing loss
4- Underdeveloped zygomes
5- Malformed ears

Question 22

What are somites?

Answer 22

1- Bilateral divisions

2- Along head-to-tail axis

Question 23

How are somites formed?

Answer 23

1- Segmentation clock pathway
2- Wave of fibroblast growth factor FGF travels along head to tail end, creating somites
3- Cycle happens every 90 minutes

Question 24

How often does the somite formation cycle go through?

Answer 24

Every 90 minutes

Question 25

What are homebox genes?

Answer 25

1- ~160 bp long
2- Detemine body axes
3- Directly contributes to formation of body structures

Question 26

What are the four topographical types of mesoderm?

Answer 26

1- Paraxial mesoderm
2- Intermediate mesoderm
3- Lateral plate mesoderm
4- Midline mesoderm (under neural tube)

Question 27

What does the paraxial mesoderm derive into?

Answer 27

1- Head

2- Somite

Question 28

What are the three layers/segments of the somite?

Answer 28

1- Sclerotome
2- Myotome
3- Dermatome

Question 29

What does the intermediate mesoderm eventually give?

Answer 29

1- Kidney

2- Gonads

Question 30

What are the two layers of the lateral plate mesoderm?

Answer 30

1- Splanchnic (cardiovascular system)

2- Somatic (body wall)

Question 31

What are the two derivatives of the midline mesoderm?

Answer 31

1- Prechordal plate which forms

2- Notochord

Question 32

What does the yolk sac become?

Answer 32

Gut tube

Question 33

Where is the gut tube derived from?

Answer 33

Yolk sac

Question 34

How is the gut cut off from the yolk sac?

Answer 34

1- Amniotic cavity

2- Enwraps the embryo, almost completely cutting off gut from yolk sac

Question 35

What are the derivatives of the ectoderm?

Answer 35

1- Epidermis
2- Lens and retina
3- Olfactory epithelium
4- Oral cavity epithelium
5- Sensory organs of ear
6- Salivary gland
7- Sweat glands
8- Mammary gland
9- Adenohypophysis (anterior pituitary)

Question 36

When is the vitelline duct obliterated?

Answer 36

~5-6 weeks