A/P Patterning of the Neural Tube & Epidermis

Question 1

What are placodes?

Answer 1

Thickenings in the surface ectoderm that give rise to different tissue-specific epithelial and neuronal cell types.

Question 2

What are placodes and the epidermis formed from?

Answer 2

Non-neuronal ectoderm

Question 3

What is the optic vesicle?

Answer 3

An outgrowth of the neural tube

Question 4

What leads to retina and lens formation?

Answer 4

Reciprocal induction events between the optic vesicle and lens placode.

Question 5

What is the inducing signal in both directions of retina and lens formation process?

Answer 5

Fibroblast growth factor (FGF)

Question 6

What is the lens placode derived from?

Answer 6

Non-neuronal ectoderm

Question 7

Outline the general process of vertebrate eye development.

3

Answer 7

1. Optic vesicle evaginates from the brain and contacts overlying ectoderm
2. This induces the cells of the lens placode to be columnar
3. Lens placode differentiates into lens cells as the optic vesicle folds in on itself.
4. The lens placode becomes the lens vsicle
5. Lens is internalized and thre optic vesicle becomes the neural retina and retinal pigmented epithelium
6. Cell shape changes finalize invagination.
7. Lens vesicle induces overlying ectoderm to become the cornea.

Question 8

What gene is required for specification of the retina?

Answer 8

Retinal homeobox gene (Rx)

Question 9

What are the two functions of the Rx transcription factor?

Answer 9

Inhibits Otx2
Activates Pax6

Question 10

What is the major gene in forming the eye field in the anterior neural plate?

Answer 10

Pax6

Question 11

What is the result of being homozygous for LoF mutations in Pax6?

Answer 11

Lack of eyes

Question 12

What is the result of being heterozygous for LoF mutations in Pax6?

Answer 12

Small eyes

Question 13

What happens to Rx mutant mice and zebrafish?

Answer 13

Lack of eyes

Question 14

What gene is responsible for separating the optic field?

Answer 14

Shh

Question 15

How does Shh divide the field in two?

Answer 15

Suppresses Pax6 expression in center of neural tube.

Question 16

What happens if the Shh gene is mutated or if its processing is inhibited?

Answer 16

Cyclopia

Question 17

What happens if too much Shh is synthesized by the prechordal plate?

Answer 17

Too large of Pax6 inhibition leading to no eye formation

Question 18

Outline how excess Shh leads to no eye development.

4

Answer 18

Shh downregulates Pax6
Optic cup development is disrupted
Apoptosis of lens cells
Arrested eye development

Question 19

Where is Shh secreted from?

Answer 19

The prechordal plate

Question 20

How does Shh repress Pax6?

Answer 20

Shh activates Ptc2 and Pax2, which repress Pax6

Question 21

List the three major components of mammalian skin.

Answer 21

1. Stratified epidermis
2. Underlying dermis composed of loosely packed fibroblasts
3. Neural-crest derived melanocytes that reside in the basal epidermis and hair follicles

Question 22

What pathway positively regulates the differentiation of skin stem cells?

Answer 22

Notch pathway

Question 23

What is the origin of the dermis?

Answer 23

Mesoderm

Question 24

List the three types of immigrant cells in the epidermis.

Answer 24

1. Melanoblasts
2. Langerhans’ cells
3. Merkel cells

Question 25

Describe the immigration of melanoblasts.

Answer 25

Second month of development, produced in neural crest, migrate into embryonic dermis and then to epidermis.

Question 26

What is the purpose of melanoblasts?

Answer 26

Produce melanosomes at mid-pregnancy.

Question 27

Outline the migration of Langerhans' cells.

Answer 27

Late in first trimester arise from precursors in bone marrow.

Question 28

What is the function of Langerhans' cells?

Answer 28

Peripheral components of the immune system that interact with T-lymphocytes.

Question 29

Outline the migration of Merkel cells.

Answer 29

Derived from neural crest, move to palmar and plantar epidermis at 8-12 weeks gestation.

Question 30

What are Merkel cells associated with?

Answer 30

Free nerve terminals.

Question 31

In addition to neurons and skin, what else does the ectoderm give rise to?

Answer 31

Teeth, hair, mammary glands

Question 32

What does the development of epidermal appendages rely on?

Answer 32

Inductive signals between the ectoderm and mesoderm

Question 33

What determines the nature of ectodermal differentiation?

Answer 33

The dermis

Question 34

True or false: Ectodermal appendages go through their own unique placode and bud stages prior to diversification and epithelial morphogenesis.

Answer 34

False. Ectodermal appendages arise through shared placode and bud stages prior to diversification and epithelial morphogenesis.

Question 35

Give a general description of nail development.

Answer 35

Start at the end of third month as epidermal thickenings (primary nail field) on the dorsal surfaces of the digits.

Question 36

Outline the process of mammary gland development | 2

Answer 36

1. Ectodermal thickenings called milk lines develop and Wnts are expressed 2. Fragmentation and formation of the primordia of the mammary glands.