A/P Patterning of the Neural Tube & Epidermis Flashcards
What are placodes?
Thickenings in the surface ectoderm that give rise to different tissue-specific epithelial and neuronal cell types.
What are placodes and the epidermis formed from?
Non-neuronal ectoderm
What is the optic vesicle?
An outgrowth of the neural tube
What leads to retina and lens formation?
Reciprocal induction events between the optic vesicle and lens placode.
What is the inducing signal in both directions of retina and lens formation process?
Fibroblast growth factor (FGF)
What is the lens placode derived from?
Non-neuronal ectoderm
Outline the general process of vertebrate eye development.
3
- Optic vesicle evaginates from the brain and contacts overlying ectoderm
- This induces the cells of the lens placode to be columnar
- Lens placode differentiates into lens cells as the optic vesicle folds in on itself.
- The lens placode becomes the lens vsicle
- Lens is internalized and thre optic vesicle becomes the neural retina and retinal pigmented epithelium
- Cell shape changes finalize invagination.
- Lens vesicle induces overlying ectoderm to become the cornea.
What gene is required for specification of the retina?
Retinal homeobox gene (Rx)
What are the two functions of the Rx transcription factor?
Inhibits Otx2
Activates Pax6
What is the major gene in forming the eye field in the anterior neural plate?
Pax6
What is the result of being homozygous for LoF mutations in Pax6?
Lack of eyes
What is the result of being heterozygous for LoF mutations in Pax6?
Small eyes
What happens to Rx mutant mice and zebrafish?
Lack of eyes
What gene is responsible for separating the optic field?
Shh
How does Shh divide the field in two?
Suppresses Pax6 expression in center of neural tube.
What happens if the Shh gene is mutated or if its processing is inhibited?
Cyclopia
What happens if too much Shh is synthesized by the prechordal plate?
Too large of Pax6 inhibition leading to no eye formation
Outline how excess Shh leads to no eye development.
4
Shh downregulates Pax6
Optic cup development is disrupted
Apoptosis of lens cells
Arrested eye development
Where is Shh secreted from?
The prechordal plate
How does Shh repress Pax6?
Shh activates Ptc2 and Pax2, which repress Pax6
List the three major components of mammalian skin.
- Stratified epidermis
- Underlying dermis composed of loosely packed fibroblasts
- Neural-crest derived melanocytes that reside in the basal epidermis and hair follicles
What pathway positively regulates the differentiation of skin stem cells?
Notch pathway
What is the origin of the dermis?
Mesoderm
List the three types of immigrant cells in the epidermis.
- Melanoblasts
- Langerhans’ cells
- Merkel cells
Describe the immigration of melanoblasts.
Second month of development, produced in neural crest, migrate into embryonic dermis and then to epidermis.
What is the purpose of melanoblasts?
Produce melanosomes at mid-pregnancy.
Outline the migration of Langerhans’ cells.
Late in first trimester arise from precursors in bone marrow.
What is the function of Langerhans’ cells?
Peripheral components of the immune system that interact with T-lymphocytes.
Outline the migration of Merkel cells.
Derived from neural crest, move to palmar and plantar epidermis at 8-12 weeks gestation.
What are Merkel cells associated with?
Free nerve terminals.
In addition to neurons and skin, what else does the ectoderm give rise to?
Teeth, hair, mammary glands
What does the development of epidermal appendages rely on?
Inductive signals between the ectoderm and mesoderm
What determines the nature of ectodermal differentiation?
The dermis
True or false: Ectodermal appendages go through their own unique placode and bud stages prior to diversification and epithelial morphogenesis.
False. Ectodermal appendages arise through shared placode and bud stages prior to diversification and epithelial morphogenesis.
Give a general description of nail development.
Start at the end of third month as epidermal thickenings (primary nail field) on the dorsal surfaces of the digits.
Outline the process of mammary gland development
2
- Ectodermal thickenings called milk lines develop and Wnts are expressed
- Fragmentation and formation of the primordia of the mammary glands.
