691V Poster Online - Virtual Posters
Wednesday April 06, 4:00 PM - 7:00 PM

Authors:
Sarah Tomlin ²; Tristan Spain ¹; Harmit Malik ^2,3; Courtney Schroeder ¹

Affiliations:
1) UT Southwestern Medical Center; 2) Fred Hutchinson Cancer Research Center; 3) Howard Hughes Medical Institute

Keywords:
a. cytoskeleton; g. phylogenetics

The actin cytoskeleton, which is composed of force-generating polymers, often forms branched networks that are critical in many fundamental cellular processes, including cell motility, cell division and vesical movement. Branched actin networks are generated by the Arp2/3 complex, a 7-membered protein complex including actin-related proteins (Arps) 2 and 3. Similar to actin and most Arps, Arp2 is evolutionarily ancient among eukaryotes and under stringent sequence conservation, yet we surprisingly discovered two clade-specific gene duplications of Arp2 in Drosophila: Arp2D in the obscura clade and Arp2D2 in the montium clade. Our targeted sequencing and phylogenetic analyses of Arp2D and Arp2D2 show these duplicates have evolved independently and arose ~14 million years ago at the origin of their respective clades. The two duplicates exhibit distinct sequence diversification from canonical Arp2, and unlike the ubiquitously expressed Arp2, both duplicates are testis-enriched in expression. Why would evolution recurrently select for a divergent Arp2 for potential roles in the male germline? To elucidate the function of these duplicates, we investigated whether both duplicates can polymerize branched actin networks similar to canonical Arp2. We replaced canonical Arp2 in D. melanogaster with D. pseudoobscura Arp2D or D. auraria Arp2D2 and found they can both rescue the Arp2 knockout lethality phenotype, suggesting the duplicates can indeed polymerize branched actin networks despite their sequence divergence. Cytological analyses further confirmed the two duplicates localize to branched actin networks. Surprisingly, however, Arp2D-expressing flies have significantly reduced fertility unlike Arp2D2-expressing flies. Our findings suggest that canonical Arp2’s roles can largely be partitioned between somatic versus germline roles, and we hypothesize that while both Arp2 gene duplicates can polymerize branched actin in somatic cells, Arp2D fails to generate proper actin networks for germ cell development. We are currently investigating the integrity of germline actin in the transgenic flies and exploring how Arp2D’s sequence divergence has perhaps led to specialized actin polymerization for germline biology.