[BIO 1306] Ch43_Lecture

[BIO 1306] Ch43_Lecture - 43 Animal Development: From Genes...

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43 Animal Development: From Genes to Organisms
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43 Animal Development: From Genes to Organisms 43.1 How Does Fertilization Activate Development? 43.2 How Does Gastrulation Generate Multiple Tissue Layers? 43.3 How Do Organs and Organ Systems Develop? 43.4 What Is the Origin of the Placenta? 43.5 What Are the Stages of Human Development?
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43.1 How Does Fertilization Activate Development? Different contributions to the zygote: Sperm: DNA and a centriole, in some species. Egg: DNA, organelles, nutrients, transcription factors, mRNAs.
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43.1 How Does Fertilization Activate Development? In an unfertilized frog egg: Vegetal hemisphere : the lower half of the egg, where nutrients are concentrated. Animal hemisphere : the opposite end of the egg, contains the nucleus.
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43.1 How Does Fertilization Activate Development? Cytoplasmic movement can be seen. The vegetal hemisphere is not pigmented while the animal hemisphere has two pigmented regions: Cortical cytoplasm: heavily pigmented Underlying cytoplasm: diffusely pigmented
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43.1 How Does Fertilization Activate Development? Egg cytoplasm is rearranged beginning with fertilization. Sperm enters the animal hemisphere: cortical cytoplasm rotates toward site of entry. The gray crescent : a band of pigmented cytoplasm opposite the site of sperm entry, important in development.
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Figure 43.1 The Gray Crescent
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43.1 How Does Fertilization Activate Development? Movement of cytoplasm establishes bilateral symmetry. Animal and vegetal hemispheres define anterior–posterior axis of embryo. Site of sperm entry becomes the ventral region and gray crescent becomes dorsal region of embryo.
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43.1 How Does Fertilization Activate Development? The centriole from the sperm initiates cytoplasmic reorganization. The centriole causes microtubules in the vegetal hemisphere to form a parallel array to guide cytoplasm. Microtubules also move organelles and proteins.
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43.1 How Does Fertilization Activate Development? As cytoplasm moves, developmental signals are distributed. β -catenin: a key transcription factor from maternal mRNA, throughout cytoplasm. GSK-3: phosphorylates and degrades β -catenin, throughout cytoplasm.
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43.1 How Does Fertilization Activate Development? GSK-3 inhibitor: found only in the vegetal cortex of the egg. After fertilization the inhibitor moves along microtubules to the gray crescent and prevents degradation of β -catenin. The result is a higher concentration of β -catenin in the dorsal region.
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Figure 43.2 Cytoplasmic Factors Set Up Signaling Cascades
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Cleavage : a rapid series of cell division, but no cell growth. Morula : the embryo as a solid ball of small cells. Blastocoel
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[BIO 1306] Ch43_Lecture - 43 Animal Development: From Genes...

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