BIOL 426_ 3 - Polarity and Segmentation

BIOL 426_ 3 - Polarity and Segmentation - Polarity and...

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Polarity and Segmentation Part I
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Topics: Hox genes and segmentation Midbrain-hindbrain signaling center Forebrain development Spinal cord development
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Vertebrate Brain and Spinal Cord CNS polarity Neural tube swells to form Brain structures Curvatures bring brain areas together
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Drosophila Brain and Spinal Cord Adult Embryo Compound eyes CNS segmentation resembles Body segmentation
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Programmed Gene Expression Controls Anterior-Posterior Axis Anterior: Bicoid Hunchback Posterior: Nanos Caudal A P Drosophila as a model system Hox genes control the anterior-posterior axis Bicoid: transcription factor, DNA-binding protein Nanos: RNA-binding protein Maternal effect: mRNAs of bicoid and Nanos are distributed in anterior and posterior regions prior to fertilization of the egg! Bicoid and Nanos genes control Gap genes Gap genes control Pair-rule genes Pair-rule genes control segment polarity genes Segment polarity genes control homeotic genes Each segment of body is under strict Control of a sequential hierarchy genes
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Homeobox-Containing Genes Homeobox: short conserved DNA sequence that encodes a DNA-binding protein motif (homeodomain) famous for its presence in genes that are involved in orchestrating development in a wide range of organisms. Hox genes are clustered homeobox-containing genes present in all metazoans, with an evolutionary conserved function in conferring positional identity along the main body axis in bilaterians. Edward Lewis first identified Hox genes in Drosophila in 1978. Hox proteins are transcription factors.
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Hox Gene Clusters Conserved in Drosophila and Mouse Hox genes are arranged sequentially In the order of their expression along The anterior-posterior axis of animal. 2 Hox gene clusters in Drosophila: Antennapedia complex Bithorax complex Hox genes are highly conserved Among animals Drosophila Mouse embryo Hox gene organization along chromosome: Anterior gene at 3’ Posterior gene at 5’ Mouse has four separate Hox gene clusters On four different chromosomes, controling more complicated developmental process
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Hox Gene in Morphology Development FIGURE 2.4 Elimination of the Hox gene cluster in the Tribolium beetle results in all segments developing an identical morphology. A shows the normal appearance of the beetle, and B shows an animal without a Hox gene cluster. The normal number of segments develop, but all of the segments acquire the morphology of the antennal segment , showing the importance of the Hox genes in the development of positional identity in animals. (Reproduced from Stuart et al., 1993, with permission) Wild type beetle Hox gene mutant, all antenna
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Hindbrain: Example for Hox Gene in Vertebrate Nervous System Rhombomeres are repeated morphological subdivisions of the hindbrain. Each rhombomere expresses a
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BIOL 426_ 3 - Polarity and Segmentation - Polarity and...

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