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Liu, Yang (2018) CHANGES THROUGHOUT A HOX REGULATED NETWORK DRIVE BODY PLAN EVOLUTION IN DROSOPHILA. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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A recurring discussion in evolution biology is how the anterior-posterior animal body axis organization was diversified throughout the animal kingdom. This question has been a major focus of the field of evolutionary-developmental biology. As this discipline grew, a general hypothesis was developed which speculated that cis-regulatory element (CRE) evolution is a major driver of the evolution of form by altering the expression patterns of developmentally important genes. Numerous classical studies revealed that differences in body segmental identity correlated with expression shifts in the developmentally important Hox transcription factor genes. However, the inaccessibility of genetic crosses between distantly related taxa, and the complexity of Hox regulatory mechanisms built a barrier to directly implicate and pinpoint the evolutionarily relevant cis changes underlying such body plan differences. One further complication is that Hox genes represent just one factor in vast regulatory networks, throughout which causative variation may have accumulated. To address these problems, I investigated an evolved Hox-regulated trait in Drosophila — differences in abdominal pigmentation that exist between two closely related crossable species, Drosophila (D.) yakuba and D. santomea. By applying analyses of introgression lines, gene expression, transgenic reporters, and CRISPR/Cas9-based complementation tests, I have elucidated evolutionary changes throughout a Hox-regulated network in D. santomea: The top level Hox transcription factor Abd-B has evolved a temporally and spatially restricted change in expression, which was accompanied by the gain of expression of another factor pdm3, which suppresses pigmentation. In three network terminal pigment-producing enzyme genes, the loss of yellow was attributed primarily to upstream changes, while the gain of ebony and the loss of tan resulted from changes in their CREs. I have identified most of these genes’ evolutionary relevant CREs, confirmed their contribution to the phenotype, and investigated their epistatic interactions. I propose that the picture I have derived illuminates the genetic basis of body plan evolution on macroevolutionary scales, in which Hox genes evolve in unison with other loci that span vast gene regulatory networks.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Liu, YangYAL68@pitt.eduyal68
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairRebeiz,
Committee MemberArndt,
Committee MemberCampbell,
Committee MemberBoyle,
Committee MemberAndolfatto,
Date: 26 September 2018
Date Type: Publication
Defense Date: 19 July 2018
Approval Date: 26 September 2018
Submission Date: 5 August 2018
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Number of Pages: 120
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: body plan evolution, Hox genes, gene regulatory network, cis regulatory elements, Transposon, Reciprocal hemizygosity test
Date Deposited: 26 Sep 2018 22:54
Last Modified: 26 Sep 2023 05:15


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