Discussion5Synopsis - Discussion 5 Synopsis: How insects...

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Discussion 5 Synopsis: How insects lose their limbs Margaret Emerson, Connie Tran and Krisopher Wold The first article by Mike Levine, “How insects lose their limbs” is a summary article about the evolution of the insect hexapod (six-legged) body plan. Levine focuses on the comparison of the insect and crustacean group to understand how functional changes in Ultrabithorax (Ubx) protein have resulted in insects losing limbs in the abdominal region and thus, only possessing their six limbs in the thoracic region. Ubx is a Hox protein encoded by a Hox gene that, in insects, represses the expression of Distalless (Dll) which is required for limb formation. However, Ubx is also expressed in the limbs of crustaceans and onychophorans but does not repress the formation of limbs in these groups. The functional differences of Ubx in these groups give rise to important morphological differences in how these groups look. These studies are relevant to evolution and development, because they show different mechanisms for the evolution of different body plans; changes in Hox genes, changes in Hox protein function and new activities of Hox proteins. The second article, “Evolution of a transcriptional repression domain in an insect Hox protein” by Galant & Carroll identified the specific repression domain in Drosophila Ubx most likely responsible for the insect hexapod body plan. This specific domain is found in insects but absent in Ubx of other arthropods and onychophrans. Their study compared Drosophila ( insecta ) and a closely related sister group, onychophoran – the velvet worm. Drosophila Ubx (DUbx) and onychophoran Ubx (OUbx) had similar functions when misexpressed in Drosophila . Both proteins were able to transform antennae to leg and wing to haltere. However, unlike DUbx, OUbx is unable to change thoracic to abdominal identity or repress Distalless – important distinguishing functions of insect Ubx. This important difference prompted further study. These differences were either due to a collection of differences in their sequences or due to one or more discrete functional motifs (a specific segment of amino acids). Therefore, Ubx from Drosophila , onychophoran and two intermediate taxa – the red flour beetle and the butterfly were sequenced. Although there were some conserved amino-acid sequences, there were also sequences unique only to
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This note was uploaded on 10/24/2010 for the course BIOL 514 taught by Professor Goldstein during the Fall '10 term at UNC.

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Discussion5Synopsis - Discussion 5 Synopsis: How insects...

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