Flashcards in Eye Development Deck (21)
What are the major placoderms and what do they form?
-hypophyseal placode: primordium for Ratheke's pouch -> adenohypophysis
-olfactory placode: primordium for olfactory epithelium
-lens placode: primordium for lens
-trigeminal placode: primordium for CN V
-otic placode: primordium for inner ear
-epibrachial placode:primordium for sensory neurons supplying visceral structures (CN VII, IX, X)
What is the preplacodal region?
-encircles cranial plate
-induced by cranial mesoderm and neural tube
-involves activation of FGF pathway and inhibition of Wnt and BMP
What is the optic stalk?
-lateral evaginations of the diencephalon which enlarges distally to form the optic vesicle
What does the optic vesicle do?
-optic vesicle asymmetrically invaginate a to form a cup-like structure with a groove along one side of it
-the groove is the choroid fissure and it is continuous with the groove in the optic stalk
-the groove in the optic stalk is continuous with the posterior chamber of the eye
-the hyaloid artery uses the choroid fissure and optic stalk to pass into the posterior chamber of the eye
What does the initial expression of Pax6 produce?
What does Pax6 do in Drosophilia?
-turns of gene sequence needed for eye development
-absence of gene leads to eyeless mutant
What does Pax6 do in mammals?
-absences of gene results in early optic vesicle formation, but the rest of eye formation does not occur
-prospective lens ectoderm does not respond to induction by optic vesicle
How does Pax6 affect the optic stalk?
-high conc of Shh inhibit expression of Pax6
-low conc of Shh in distal optic stalk permits expression of Pax6 and development of optic vesicle -> leads to formation of retina
-high conc of Shh in proximal optic stalk decreases expression of Pax6 and induces expression of Pax2 -> this will provide guidance of axons of ganglion cells from retina
Explain how the lens is form.
-formed by lens. Fibers derived from inner pole of lens vesicle
-lens fiber cells are postmitotic, elongated cells made up mostly of crystalline proteins alpha, beta, and gamma
-rest of lens fiber cells are derived from mitotic activity of cuboidal cells of anterior lens epithelium
-retinal secretions, esp FGF, accumulate in the vitreous humor and stimulate formation of lens fibers
Explain how the cornea is formed.
-Pax6 is necessary for corneal induction
-underlying lens vesicle induces overlying ectoderm to transform from bilayered epithelium (simple cuboidal basal layer +flattened periderm) to transport multilayered structure
The invaginate optic cup forms both the _________ and ________ ____________.
-pigmented and neural retina
What is the pigmented retina?
-outer thin layer of the optic cup after invagination occurs
What is necessary for the differentiation of the pigmented retina?
-Otx2 stimulated by Shh
In terms of the fixation of retinal polarity, what is formed first?
-nasotemoral (anterior-posterior) axis is fixed first
How is the nasotemoral axis produced?
-established by gradients composed of ephrins and receptors
-ganglion cells differentiate first and bipolar neurons and cones differentiate last
-the spread of the gradient is from the center to the periphery
-Notch gene expression keeps cells from differentiating too early
What retinal axis is fixed second?
How is he dorsoventral axis fixed?
-established by the antagonistic actions of Shh and BMP, along with V entropic, Tbx-5, Pax2, and Vax2
What is anophthalmos?
-the absence of one of both eyes
What is microphthalamos?
-birth defect where one of both of the eyes are abnormally small, eye may be missing but tissue is still there
What is a coloboma?
-a hole in one of the structures of the eye, such as the iris, retina, choroid, or optic disc