PT  - JOURNAL ARTICLE
AU  - Leo Blondel
AU  - Savandara Besse
AU  - Cassandra G. Extavour
TI  - Evolution of a cytoplasmic determinant: evidence for the biochemical basis of functional evolution of a novel germ line regulator
AID  - 10.1101/2021.04.26.441385
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.04.26.441385
4099  - http://biorxiv.org/content/early/2021/04/27/2021.04.26.441385.short
4100  - http://biorxiv.org/content/early/2021/04/27/2021.04.26.441385.full
AB  - Germ line specification is essential in sexually reproducing organisms. Despite their critical role, the evolutionary history of the genes that specify animal germ cells is heterogeneous and dynamic. In many insects, the gene oskar is required for the specification of the germ line. However, the germ line role of oskar is thought to be a derived role resulting from co-option from an ancestral somatic role. To address how evolutionary changes in protein sequence could have led to changes in the function of Oskar protein that enabled it to regulate germ line specification, we searched for oskar orthologs in 1565 publicly available insect genomic and transcriptomic datasets. The earliest-diverging lineage in which we identified an oskar ortholog was the order Zygentoma (silverfish and firebrats), suggesting that oskar originated before the origin of winged insects. We noted some order-specific trends in oskar sequence evolution, including whole gene duplications, clade-specific losses, and rapid divergence. An alignment of all known 379 Oskar sequences revealed new highly conserved residues as candidates that promote dimerization of the LOTUS domain. Moreover, we identified regions of the OSK domain with conserved predicted RNA binding potential. Furthermore, we show that despite a low overall amino acid conservation, the LOTUS domain shows higher conservation of predicted secondary structure than the OSK domain. Finally, we suggest new key amino acids in the LOTUS domain that may be involved in the previously reported Oskar-Vasa physical interaction that is required for its germ line role.Competing Interest StatementThe authors have declared no competing interest.