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#lens development

5 public questions tagged with this topic.

Eye Lens Induction -l

Which factor is NOT involved in vertebrate lens formation?

Vertebrate lens regulatory network centers on Pax6, Sox2, Six3, Prox1, FoxE3 and L-Maf/c-Maf factors that directly control crystallin genes. Sox2 partners Pax6 on enhancers, L-Maf drives delta-crystallin, FoxE3 maintains anterior epithelium. HoxB1 belongs to posterior patterning Hox cluster controlling rhombomere identity in hindbrain and spinal cord via retinoic acid collinear expression. It does not express in anterior preplacodal ectoderm, never binds lens enhancers, and knockout shows hindbrain but not eye defects. Therefore Hox genes generally excluded from anterior sense placode development, distinguishing lens program from axial patterning modules.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: Lens transcription factors Pax6 Sox2 L-Maf versus Hox genes.

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Eye Lens Induction -l

Which of the following factors is activated by FGF8 in eye lens induction?

FGF8 secreted by optic vesicle neuroepithelium acts as second-phase inducer after BMP priming. Vogel-Hopker experiments demonstrated FGF8 transcripts localize to distal optic vesicle, and beads soaked in FGF8 implanted under head ectoderm ectopically activate L-Maf, a large Maf bZIP transcription factor specific to lens. L-Maf directly binds LCE enhancer of delta-crystallin and transactivates lens fiber differentiation genes including Prox1 and connexins. Inhibiting FGFR signaling with dominant-negative receptor abolishes L-Maf expression, proving FGF8 initiates transcriptional cascade for fiber elongation and crystallin accumulation.

Ref: PMCID PMC article: The Function of FGF Signaling in the Lens Placode - FGF8 induction of L-Maf expression.

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Eye Lens Induction -l

Which of the following best describes the role of Pax6 in lens development?

Competence describes tissue ability to respond to an inducer. In presumptive lens ectoderm, Pax6 is expressed well before optic vesicle contact as part of preplacodal region specification by Six1, Eya1. It remodels chromatin and directly binds to enhancers of FoxE3, Sox2 and crystallins, keeping them poised. Upon arrival of BMP4 and FGF signals from optic vesicle, Pax6-positive ectoderm rapidly transcribes lens genes. Pax6 does not itself provide inductive signal nor inhibit BMP, but creates responsive state. Conditional removal from surface ectoderm blocks lens despite intact signaling center.

Ref: Gilbert, Developmental Biology, 11th ed., Chapter 12: Role of Pax6 in conferring lens-forming competence to ectoderm.

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Eye Lens Induction -ll

What is the role of L-Maf in lens formation?

L-Maf, a large Maf bZIP transcription factor expressed in lens placode downstream of Pax6, Sox2, and FGF-BMP signaling, directly regulates crystallin genes essential for transparency. L-Maf binds Maf recognition elements in delta-crystallin enhancer in chick and alphaA-crystallin promoter in mammals, activating high-level expression during fiber cell elongation and organelle loss. It does not induce optic vesicle formation, inhibit Sox2, or prevent corneal differentiation. L-Maf knockout lenses show severe deficiency in crystallin accumulation and fiber elongation arrest, confirming its central role in regulating structural lens genes and differentiation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: L-Maf regulation of delta-crystallin and lens fiber genes.

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Eye Lens Induction -ll

What happens when FGF8 beads are implanted near ectoderm in lens development?

Implantation of fibroblast growth factor 8-soaked beads near competent head ectoderm mimics optic vesicle signal and triggers lens transcriptional program. FGF8 activates MAPK signaling inducing L-Maf expression in ectoderm, which directly transactivates delta-crystallin and beta-crystallin enhancers driving lens fiber differentiation. Implantation experiments in chick demonstrated bead-induced ectopic lens placodes expressing Sox2 and crystallins, whereas inhibition of Pax6, suppression of Six3, or activation of Wnt blocks not observed. This bead assay evidences sufficiency of FGF8 as lens inducer upstream of L-Maf-crystallin cascade and Sox2 activation.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 12: FGF8 beads inducing L-Maf and crystallin expression.

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