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ppt 37

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Published on February 14, 2008

Author: Marcell

Source: authorstream.com

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Slide 1: “Cell-Cell interaction” during eye development in vertebrate. Beginning of life: Beginning of life While each organism starts off as a single cell, the progeny of that cell form complex structures that are Tissue and Organs. The tissue and organs are integrated into larger system. The Eye! And its precise arrangement: The Eye! And its precise arrangement The light enters through transparent cornea and is focused by the lens The light ray eventually makes an impression on the tissue of the retina and sends nerve impulses to the brain. Cell-Interactions : During organogenesis there is coordination among the different cells. One group of cell changes the behavior of the other group of cell. Changes include shape change, changes in mitotic rate, or changes in their fates. Cell-Interactions The EYE: The EYE Similar things happen in the case of eye development one group of cell “induce” other cell to develop in certain pattern. INDUCE?: INDUCE? Interaction at close range between two or more cells of different histories is called “proximate interaction or induction”. There are at least 2 components of every inductive interaction: An Inducer: a cell or tissue that produce signal and that changes cellular behavior of the other tissue. the Responder: cell or tissue which is responding to the signal; from the inducer. Eye Induction: Eye Induction In the case of vertebrate eye development the inducer is the optic vesicle; and the responder is head ectoderm. The responder performs under the influence of the signal from the inducer. Not all tissue can respond to the signal being produced by an inducer. Competence: Competence The ability to respond to a specific inductive signal is called competence (Wadington, 1940). The concept of competence can be studied during eye development in Xenopus laevis. The optic vesicle underneath head ectoderm will induce a part of head ectoderm to form lens tissue. Competence: Competence Competence: Hence, optic vesicle is acting as an inducer because it is sending signal to the head ectoderm to form lens Head ectoderm is responding by forming the lens. Competence Achieving the Competence: Achieving the Competence Pax6 protein in head ectoderm of a rat acts as competent factor to respond to the signal from optic vesicle. Pax6 protein is not seen in any other part of the surface ectoderm, its expression is only limited to lens forming region of head ectoderm. Importance of Pax6: Importance of Pax6 Figure: showing induction of optic and nasal structures by Pax6 in rat embryo. A. Histology of wild type homozygous for Pax6; rat embryo at 12 days of gestation, shows induction lenses and retinal development. B. Histology of Pax6 mutant rat embryo at 12 days of gestation; no lens, no nasal prominence and no nasal pit induction. Wild Type Pax6 Mutant Slide 13: Pax6-/Pax6-( homozygous mutant ). Pax6+/Pax6+( homozygous wild type). Homozygous mutant means that there is no production of Pax6 protein. Importance of Pax6 Slide 14: Importance of Pax6 The homozygous Pax6 mutant has phenotype lacking eye and nose. A. Wild type B. Pax6 mutant Figure: Newly born wild type rat show Newly born Pax6 mutant Prominent nose as well as eyes rats shows neither eyes (Closed). Nor nose. (From Fujiwara et al. 1994; photograph courtesy of M.Fujiwarw) Recombination Experiment: Recombination Experiment In the experiment conducted by Fujiwara et al. when head ectoderm from Pax6 mutant rat embryo was combined with a wild type optic vesicle; no lens is formed. It is because head ectoderm is Pax6 mutant thus Pax6 proteins are lacking in it, which is a competent factor. Recombination Experiment: Figure: recombination experiment show that the induction deficiency of Pax6-deficient rats is caused due to inability of surface ectoderm to respond to the optic vesicle. (Photograph courtesy M.Fujiwara). Recombination Experiment Expression of Pax6: Expression of Pax6 Experiments conclude that the anterior region of neural plate tissue induces expression of Pax6 in head ectoderm. (Henry and Grainger 1990; Li et al. 1994; Zygar et al. 1998). Other Inducers Involved: Other Inducers Involved In amphibian Taricha torosa, first inducer is the pharyngeal endoderm and then the heart forming mesoderm that lie beneath the lens forming ectoderm during early and mid gastrula stages. (Jacobson; 1966) The next inducer is optic vesicle. Other Inducers Involved: Other Inducers Involved Figure: lens induction in amphibians; Experiment done on newt Taricha torosa. The ability to produce lens tissue is first induced by pharyngeal endoderm, then by cardiac mesoderm, and finally by the optic vesicle. (After Jacobson; 1966). Nature of the Signal: Nature of the Signal optic vesicle appears to secrete two-induction factor; BMP4 (Furuta and Hogan; 1998), it is a protein by nature and induces the production of Sox2 and Sox3 transcription factor. FGF8, a signal that induces the appearance of L-Maf transcription factor.(Ogino and yasuda 1998; vogel-hopker et al.2000). Reciprocal Induction: Reciprocal Induction Once the lens is formed, now it induce the optic vesicle (studied in mouse). Means now, the inducer becomes the induced and the induced tissue becomes inducer. Under the influence lens secretions the optic vesicle differentiates into optic cup further the wall of optic cup differentiates into two layer that are prospective pigmented retina and prospective neural retina. Sequential Induction and Corneal Differentiation: Sequential Induction and Corneal Differentiation Sequential inductive events occur in corneal differentiation. Under the influence of lens inductive signal corneal ectoderm cell becomes columnar shaped and start secreting multiple layers of collagen. Mesenchymal cells from neural crest cells enter into cornea forming area using the collagen matrix. The hyaluronidase enzyme secreted by the mesenchymal cell further differentiates cornea. A third signal includes thyroxine hormone, It dehydrates the corneal tissue making it transparent,(Hay 1980; Bard 1990). Sequential Induction and Corneal Differentiation: Sequential Induction and Corneal Differentiation Retinal Differentiation: Retinal Differentiation The cells of outer layer of optic cup, - develops melanin pigment. - forms pigmented retina. The cell of inner layer of retina rapidly proliferates and generates a variety of glial, ganglion cell, inter-neurons and light sensitive photoreceptors neurons. Slide 25: Figure: development of neural retina (humans). A and B shows initial separation of neuroblast in retina. 3 layers of neurons retina of adult and the synaptic layer between them. Functional depiction of the major neuronal pathway in retina. (A and B after Mann1964; photograph courtesy of G. Grundwald). Retinal Differentiation CONCLUSION: CONCLUSION At last we can appreciate nature’s well maintained pathway for the development of this wonderful organ, because of which we can see the beautiful nature In the lecture we came to know about how signal transduction (by optic vesicle), signal reception (by lens forming ectoderm) cause differentiation of lens forming ectoderm in such a way that it has formed the lens and subsequently the eye for vision. Slide 27: S r i G u r u T e g h B a h a d u r K h a l s a c o l l e g e U n I v e r s I t y o f D e l h I Prepared by: Gaurav [Bsc.(H) physics III year] Ramanand [Bsc.(H) zoology II year] Hari Krishan [Bsc. (H) botany III year] Prashant [Bsc.(H) chemistry III year] :  THANK YOU

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