Investigating the regulation and evolution of tartan during Drosophila male genital diversification

Male genital structures have evolved rapidly in many animal groups and in some cases are the only features that can distinguish species that have recently diverged. However, we still lack knowledge about the genetic mechanisms responsible for the divergence of this trait. The Drosophila melanogaster species subgroup has been used to investigate this and recent studies between D. simulans and D. mauritiana have identified that the gene tartan (trn) is involved in the evolution of the surstyli (claspers) which form part of the external male genitalia. trn encodes a leucine-rich repeat transmembrane protein and contributes to the difference in surstyli size and the bristle number between D. simulans and D. mauritiana. trn is differentially expressed (spatially and temporarily) between the developing surstyli of these two species. This indicates that changes in the regulation of trn rather than the coding sequence underlie its contribution to surstyli divergence. In my PhD project I have investigated the regulation of trn. First, I characterised the endogenous trn expression using a Trn tagged protein, and then I screened the trn locus to search for enhancers. I identified nine regions that are active during pupal development, three of which are active in the male genitalia, U4, U8 and D6. U4 was the most promising region because its activity overlaps with endogenous trn expression in the developing genitalia, and therefore I investigated which transcription factors were candidates to bind to this enhancer. I identified caudal (cad) as a likely candidate to be regulating U4. I then used RNAi to further characterise the function of cad during genitalia development. My results showed that the anal plates are lost upon cad RNAi knockdown and that this gene may regulate trn expression around anal plates to delimit their specification. Additionally, I investigated the evolution of the U4 enhancer sequence and activity. Analysis of the D. mauritiana U4 activity shows it has expanded expression compared to the D. melanogaster U4. This result suggests that there has been evolution of this enhancer in D. mauritiana that may contribute to the larger surstyli of this species, but this remains to be directly tested. Taken together, my investigation has characterised most of the regulatory landscape of trn and has identified an enhancer that is active in the genitalia and that may have evolved between species. My investigation will allow us to further understand the compartmentalization and regulation of male genitalia development and the evolution of these structures.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2022

Author dc:creator

• Figueras Jimenez, Javier

Contributors dc:contributor

• McGregor, Alistair

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/GHVC-7C52

OAI identifier oai:identifier

tle:77e269f3-fb72-4f3a-99bd-cffaa38b25fe:d6bd9758-527a-46cd-bfe2-c433766e8fca:1