LENS INDUCTION IN XENOPUS.pptx

lens induction in xenopus

1. LENS INDUCTION IN XENOPUS Presented by: BARUN SAHU Sambalpur University

2. SOME IMPORTANT TERMS Induction Inducer Responder Competence Reciprocal induction

3. SIGNAL FOR EYE LENS INDUCTION Induction : between optic vesicle and head ectoderm Lead to differentiation of outer ectoderm cell to form lens placode Need inducer and responder(who will be competent) Signal-1 Signal-2 Reciprocal Induction : Inducer get induced and responder become inducer Gastrulation : 3-germ layer form Endoderm, mesoderm, and ectoderm

4. SIGNALLING OF LENS INDUCTION AT EARLY GASTRULA STAGE AT EARLY NEURAL STAGE

5. SIGNALLING OF LENS INDUCTION OPTIC VESICLE BMP-4 FGF-8 SOX-2 L- Maf Pax6 & SOX-2 Expression of δ -crystalline gene Pax6 + SOX-2 + L- Maf Develop lens placode Transparency of lens Lens placode Optical Vesicle (reciprocal induction) Optical Vesicle to form bilayer structure-inner and outer layer Inner layer- give rise to retina Outer layer give rise to optic nerves and pigmented layer 1. 2. 3. AT LATE NEURAL STAGE

6. STEPS OF EYE LENS DEVELOPMENT A. Eye field and optic vesicle(OV) formation B. Lens placode(LP) formation C. Interaction between optic vesicle(OV) and lens placode(LP)

7. MUTATION CASE IN PAX-6 Shh(Sonic hedgehog) mutation- one eye in the center of face (cyclopia) Pax6 deficient- Aniridia(condition) (Iris is reduced or lacking) Wild type Mutant

8. OPTIC VESICLES SURFACE ECTODERM LENS FORMATION WILD TYPE WILD TYPE YES Pax6 mutant(Pax6-) WILD TYPE YES WILD TYPE Pax6 mutant(Pax6-) No Pax6 mutant(Pax6-) Pax6 mutant(Pax6-) No MUTATION CASE WILD TYPE MUTANT TYPE Xenopus

9. SUMMARY Only head ectoderm is competent to respond to this signal from optic vesicle by producing a lens. Pax-6 is important in providing the competence to respond to the inducers from the optic cup. Optic vesicle appear to be the inducer. Optic vesicle appears to secrete two paracrine factors, one of which may be BMP-4, a protein that is received by lens cell and induces the production of Sox 2 transcription factors. The other paracrine factor is FGF-8 ,a signal that induces the appearance of the L- maf transcription factors . The combination of the Pax-6,Sox-2,and L- maf in the ectoderm is needed for the productions of the lens and the activation of lens specific genes such as δ crystallin. Optic cup is formed due the reciprocal induction and cup differentiated into two layers,the pigmented layer and the retina. If Pax -6 is lost, whether it is in fruit flies, frogs, rats or human, it results in a complete loss or reduction of the eyes