06 Genes and Development

06 Genes and Development - 1. Determination and...

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Unformatted text preview: 1. Determination and Differentiation Genomic Equivalence Activation and I nactivation of Specific Genes 2. Signals that Regulate Gene Expression Cytoplasmic Determinants Cell-Cell I nduction 3. Pattern Formation and Gene Expression Axes Determination Morphogens Segmentation Segmentation Genes Formation of Body Parts Homeotic (Hox) Genes Apoptosis - Cell Death Genes Some Key Stages of Development in Animals The Concept of Genomic Equivalence All cells within the individual contain the same DNA (Genomic Equivalence) Different cell types arise as a result differential gene expression Thus to understand development it is necessary to understand how genes are turned on and off Mutant Drosophila with an extra small eye on its antenna The mutation alters gene expression in the course of development of the antennae. As a result the fly ends up with an extra eye. One experimental approach for testing genomic equivalence is to see whether a differentiated cell can generate a whole organism Can the nucleus from a differentiated animal cell direct development of an organism? EXPERIMENT Researchers enucleated frog egg cel ls by exposing them to ul traviolet light, which destroyed the nucleus. Nuclei from cells of embryos up to the tadpole stage were transplanted into the enucleated egg cells. Frog embryo Frog egg cell Frog tadpole Less differ- entiated cell Donor nucleus trans- planted Enucleated egg cell Fully differ- entiated (intestinal) cell Donor nucleus trans- planted Most develop into tadpoles <2% develop into tadpoles Early experimental demonstration of genomic equivalence Reproductive Cloning in Mammals (1997) I n most nuclear transplantation studies, only a small percentage of cloned embryos have developed normally to birth. Many epigenetic changes, such as acetylation of histones or methylation of DNA, must be reversed in the nucleus from a donor animal in order for genes to be expressed or repressed appropriately for early stages of development Dolly Copy Cat, the first cloned cat 2002 Gene Savings and Clone $50,000 Stem Cells : Completely or Partially Undifferentiated Cells Embryonic stem cells Adult stem cells Early human embryo at blastocyst stage (mammalian equiva- lent of blastula) From bone marrow in this example Totipotent cells Pluripotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cells Nerve cells Blood cells Totipotent: completely undifferentiated and can give rise to any cell type Pluripotent: can give rise to multiple, but not all, cell types A stem cell is a relatively unspecialized cell that can reproduce itself indefinitely and differentiate into specialized cells of one or more types Determination and Differentiation involve transcriptional regulation of gene expression which, in...
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06 Genes and Development - 1. Determination and...

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