Lens Development and Differentiation (F) Flashcards
What is the first morphological sign of lens development?
lens placode
What is the process of secreted, signaling molecules derived from the optic vesicle crossing the extracellular matrix between the surface ectoderm and optic vesicle to trigger the formation of the lens placode and lens development?
lens induction
What are BMP proteins important for? 1. Where are they located? 2
- lens development
2. neural retina and lens ectoderm
What are BMP proteins important for? 1. Where are they located? 2
- lens development
2. neural retina and lens ectoderm
What molecules derived from the lens placode (future lens), cross the extracellular matrix between the surface ectoderm (future retina) and optic vesicle and facilitates neural retinal development?
FGF
What transcription factor triggers expression of a number of additional known transcription factors important for eye development?
PAX6
What processes require PAX6?
- Lens induction
- Lens fiber differentiation
- Corneal development
- Iris formation
- Retinal development
- Ciliary body
- Lacrimal gland
What is the molecule that, if not present, can lead to a lack of an eye?
PAX6
What direction does signaling for lens fiber differentiation come from?
posterior direction
What is required for lens fiber development?
Fgf: fibroblast growth factor
What is required for lens fiber development and differentiation embryonically and after maturation?
Fgf: fibroblast growth factor
What do secondary lens fibers differentiate from?
lens epithelial cells of the transitional zone
Where does mitosis of the epithelial lens cells take place?
the germinative zone
Where does the anterior meshwork of capillaries that surrounds the lens during embryonic development come from? 1. The posterior meshwork? 2
- iris stroma
2. hyaloid artery
When do the capillaries surrounding the lens during embryonic development regress? 1. What is this regression due to? 2
- second trimester
2. macrophage-derived signals triggering apoptosis of vessels
What are the three zones of epithelial cells?
- pregerminative zone
- germinative zone
- transition zone
What are the three zones of epithelial cells?
- pregerminative zone
- germinative zone
- transition zone
What cell cycle phase does a cell exit in order to be differentiated?
G1
What are required for cell cycle progression?
Cyclin dependent kinase (Cdks) and cyclin
What are the proteins that inhibit Cdk proteins and trigger G0 in the lens? 1. What zone do they then enter? 2
- p27 and p57
2. transition zone
What factors lead to more differentiated lens cells?
- increase age
2. closer relative distance to lens nucleus
Where is the index of refraction greater within the lens?
higher in center than periphery
Where does denucleation occur in the body?
- erythrocytes
- keratinocytes
- lens fibers
Where does denucleation occur in the body?
- erythrocytes
- keratinocytes
- lens fibers
What are the events that occur during lens cell denucleation?
1) Transcriptional activity ends
2) Gradual nuclear lamina break down
3) fusion of lysosomes with nuclear envelope
4) Dnase IIβ in nuclear compartment
5) chromatin condensation and breakdown
What are the intermediate filaments that become phosphorylated triggering disassembly of the nuclear envelope during denuleation?
lamins
What is the enzyme that breaks down DNA during denuleation?
Dnase IIβ
What are calcium dependent non-lysosomal proteases (breaks up organelle specific proteins) that mediate organelle breakdown?
Calpain
What target mitochondrial membrane proteins and facilitates mitochondrial degradation to mediate organelle breakdown?
Ubiquitin-proteasomes
What target mitochondrial membrane proteins and facilitates mitochondrial degradation to mediate organelle breakdown?
Ubiquitin-proteasomes
What are the functions of α-crystallin? 1. What triggers its expression? 2
- Contributes to refractive power and bind up proteins that have a tendancy to unfold (“chaperone” function)
- PAX6 and FGF
What makes up 50% of total protein in lens cells?
aquaporins
How are lens fibers held together?
- adherin junctional proteins (N-cadherin, catenins)
2. ball-and-socket junctions
What is required for some proteins to penetrate deeper layers within the lens with fiber cell fusions?
Lim2
What is required for some proteins to penetrate deeper layers within the lens with fiber cell fusions?
Lim2
What re the highly organized cytoskeletal structures that mediate the ordered arrangement of lens fibers?
- Actin filaments
2. Actin filament orgainizers (Tropomodulin and Spectrin)
What is required for some proteins to penetrate deeper layers within the lens with fiber cell fusions?
Lim1
