Post on 06-Apr-2018
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Induction and Morphogenesis
Readings
y Chapter 15 Section 15.1y Chapter 43 Section 43.3y Chapter 19 P.437-439
Introduction
y Cells in the organizer express and secrete proteins that influencethe behaviour (cell movement) and identities (commitment) of
nearby cells
y Induction is a mechanism for influencing the behaviour and/oridentity of nearby cells.
y A protein(s) is translated and secreted by some cells to inducenearby cells to change
Signals can be both paracrine and autocrine
Not all cells can respond to a particular signal. A cell must be competentto respond.
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General features of signal transduction pathways
Outside Cell Ligand (proteins, small
molecules)
Cytoplasm
Receptor
(proteins)
Transducer(s)
+ Second Messengers
(enzymes)
(small molecules)
Nucleus
Effector
(transcription factors)
Target
(genes)
Two Modes ofInductive Signaling
A relay mechanism induces multiple cell fates by using multiple signals
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Morphogens are special signaling proteins that are involved in patterning embryos via
gradient signaling
y Properties of morphogenso Induce different cell fates at different concentrationso Can act at a distanceo Have a direct effect on the target cell
Different cellular response at different morphogen concentrations
A morphogen acts directly on a distant target cell
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and cells respond differently depending upon the concentration of morphogen they
encounter
We cant distinguish between these different signaling modes on the basis of cell
behaviour
Cell Responses to Inductive Signals
y Animal cells:o Divideo Growo Change shapeo Stick togethero Moveo Differentiateo Die
Morphogenesis is driven by induce changes in cellular behaviour
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Cell Behaviour: Adhesion
The adhesive properties of individual cells keeps the embryo organized
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Neurulation: Making the Nervous System
y Neurulation begins during gastrulationy Cells that migrate early over the dorsal lip of the blastopore from
notochordy The notochord induces the overlying ectoderm to become neural
ectoderm and subsequently thicken, form parallel ridges, and fold in
on itself to form a neural tube below the epidermal ectoderm
y The central nervous system develops from the neural
Two Major Cell Arrangements
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Epithelial
y Regular cell shapey Tightly packedy Many cell-cell contactsy Simple or stacked sheets
Mesenchymal
y Irregular cell shapey Loosely packed withiny Extracellular matrixy Few cell-cell contact
Large scale changes in embryos and tissues result from small but coordinated changes
in cell shape
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Complex organs like the vertebrate eye from by a series of inductive events
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Somitogenesis: Segmenting the Vertebrate Body
y During neurulation, mesoderm along the sides of the notochordcondenses into blocks of cells called somites
Somites are patterned by signals from adjacent tissues
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Homeotic genes direct the morphogenesis of tissues that are appropriate to a specific
region of the body