Friday, May 9, 2025
5/9/2025
Evolutionary Diversification of Cytoskeletal Proteins for Tissue-Specialized Roles - Project Summary/Abstract Cytoskeletal proteins perform essential roles in cell biology, and they generally evolve under stringent sequence conservation across phyla for these functions. One cytoskeletal family known as the actin-related protein (Arp) superfamily evolved before the last common ancestor of eukaryotes and plays many fundamental roles in the cytoplasm and nucleus, including nucleating actin, transporting cargo, repairing DNA damage, and chromatin remodeling. Most studies of Arps are motivated by their ubiquity and stringent conservation. However, we have discovered that the Arp superfamily displays unexpected diversification via the rapid expansion of paralogs and accelerated amino-acid substitutions in Drosophila and mammals. Interestingly, this genetic diversification across phyla has acquired tissue-specific expression and is often enriched in the male germline, a striking contrast to the ubiquitously expressed canonical Arps. Arp diversification is largely unexplored relative to studies of almost universally conserved Arps, most likely due to the lack of deep evolutionary roots. However, rapid sequence divergence suggests functional innovation that provides a fitness advantage and raises questions regarding how Arp diversification has specialized for tissue-specific roles. All Arps share the canonical actin fold, and accumulating evidence indicates that recent Arp adaptation has repurposed the actin fold for critical functions in fertility and development and may play unique roles in actin biology. We will gain molecular insight into this unexpected diversification of Arps in Drosophila and mammals to reveal how it specializes cytoskeletal networks for specific cellular contexts. Here, we outline our research program over the next five years, focusing on three distinct projects investigating Arp diversification in insects and mammals. We will determine how evolution alters the canonical Arp2/3 complex, an essential actin nucleator found in most eukaryotes, and tailors actin polymerization kinetics, stability, and structure for tissue- and species-specific actin networks. Additionally, we will investigate a young, non-canonical Arp that arose in flies and plays a role in fertility. Studying this Drosophila Arp provides a unique opportunity to genetically dissect how evolution modified the actin fold for novel functions without comprising actin’s essential roles. Lastly, we will focus on several non-canonical, rapidly evolving Arps in mammals that form a complex, localize to actin in the testis, and are critical in shaping the sperm head. We will identify how these divergent Arps adapted for complex assembly and gain structural insight, which will shed light on how mutations in these Arps lead to human infertility. Overall, this proposal uses an interdisciplinary approach, including cell biology, genetics, and biochemistry, to understand from a molecular to an organismal level how Arps across phyla evolve and functionally innovate for specialized roles. Our long-term goal is to extend our analyses to other cytoskeletal families that display unique evolutionary diversification to broadly study the roles of cytoskeletal proteins beyond core “housekeeping functions” and reveal how these proteins unexpectedly adapt and fulfill roles their canonical counterparts fail to accomplish.
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