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Bios375_Test2Objectives

Bios375_Test2Objectives - C HAPTER 3 Learning Objectives...

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CHAPTER 3 Learning Objectives Define Induction. Explain what is involved in the process of induction. Induction - The process by which one cell population influences the development of neighboring cells via interactions at a close range. o There are at least 2 components to every inductive interaction. 1) Inducer : the tissue that produces a signal (or signals) that changes the cellular behavior of the other tissue. Often this signal is a secreted protein called a paracrine factor. Paracrine factors are proteins made by a cell or group of cells that alter the behavior or differentiation of adjacent cells. Paracrine factors are secreted into the extracellular space and influence their close neighbors 2) Responder: the tissue being induced. Cells of the responding tissue must have both a receptor protein for the inducing factor and the ability to respond to the signal. Define Competence. Explain how competence is acquired in development. Competence - the ability to respond to a specific inductive signal. 1
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o Even if the receptor proteins are present, not every tissue type is competent to respond to an inducer’s signal. Figure 3.13 Ectodermal competence and the ability to respond to the optic vesicle inducer in Xenopus . The optic vesicle is able to induce lens formation in the anterior portion of the ectoderm (1) but not in the presumptive trunk and abdomen (2). If the optic vesicle is removed (3), the surface ectoderm forms either an abnormal lens or no lens at all. (4) Most other tissues are not able to substitute for the optic vesicle. Explain the experimental evidence for induction based on the following experimental approaches: Manipulation of tissues in an embryo (Figure 3.13), recombination experiments in tissue culture (Figure 3.17). For Figure 3.13 see above picture. If the optic vesicle (presumptive retina) of a Xenopus laveis embryo is placed in an ectopic location underneath the head ectoderm (i.e., in a different part of the head from where the frog’s optic vesicle normally occurs), it will induce that ectoderm to produce lens tissue. Only the optic vesicle appears to be able to do this; therefore, it is an inducer. However, if the optic vesicle is placed beneath 2
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the ectoderm in the flank or abdomen in the same organism, that ectoderm will not be able to form lens tissue. Only head ectoderm is competent to respond to the signals from the optic vesicle by producing a lens Figure 3.17 Regional specificity of induction in the chick. When cells from different regions of the dermis (mesenchyme) are recombined with the epidermis (epithelium), the type of cutaneous structure made by the epidermal epithelium is determined by the original source of the mesenchyme. -The dermal mesenchyme is responsible for the regional specificity of induction in the competent epidermal epithelium. Researchers can separate the embryonic epithelium and mesenchyme from each other and recombine then in different ways. The same epithelium develops
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