PROJECT SUMMARY
Cytoskeletal proteins are fundamental in many biological processes among all eukaryotes. Given their
essentiality, they are conventionally thought to be highly conserved. However, signatures of genetic innovation
in the form of gene-family expansions and accelerated amino-acid substitutions are found among key
cytoskeletal family members. Rapid molecular divergence between closely related species is unexpected in
conserved protein families and is indicative of an adaptive advantage for sequence innovation. This proposal
will investigate the causes and consequences of this dramatic diversification of cytoskeletal proteins. Actin-
related proteins (Arps) are one cytoskeletal family that has ancient evolutionary origins yet exhibits recurrent
genetic innovation in both mammals and insects. Unlike the well-conserved members of the Arp superfamily,
divergent Arps are testis-specific in expression, suggesting they have acquired specialized roles for male
reproduction. Yet the biological process that drives their innovation is unknown. The localization of gametic
Arps in Drosophila suggests they play roles at germline-specific actin structures. This proposal will address the
hypothesis that gametic Arps facilitate the generation of actin structures that are critical for male reproductive
fitness. Aim 1 will uncover the function of one gametic Arp found in all Drosophila species, Arp53D, which
localizes to two germline actin structures during late spermatogenesis. D. melanogaster, which has many well-
established genetic tools and only one gametic Arp, provides an advantageous system in which to investigate
the function of a divergent Arp at actin and probe how its structural diversification allows for novel roles. Aim 2
will extend the analysis to mammalian gametic Arps to gain a deeper understanding of the potentially shared
biological processes that are driving Arp innovation among multiple phyla. A few pieces of evidence suggest
that mammalian gametic Arps play actin regulatory roles, much like Arp53D. Aim 2 will take a comprehensive
approach to elucidate their evolutionary histories and localization with respect to actin, while characterizing the
male infertility phenotype of one Arp with an established mouse knockout model. Finally, preliminary findings
suggest additional cases of rapidly evolving cytoskeletal proteins, beyond Arps, are present in the male
germline. Aim 3 will systematically search Drosophila and mammalian genomes for rapid evolution and gene
duplications among cytoskeletal proteins that are testis-enriched in expression. This aim will yield additional
cases of genetic innovation that will serve as projects in the applicant’s future lab to broadly understand the
adaptive sequence plasticity of cytoskeletal proteins and what drives their specialization for male reproduction.
To launch this project, the applicant requires training in fertility assays, mouse testis histology and additional
evolutionary analyses. She will ultimately use her background in biochemistry to study diversifying cytoskeletal
proteins at a mechanistic level.