Rapidly Evolving Toll-3/4 Genes Encode Male-Specific Toll-Like Receptors in Drosophila
| Autor: | Harmit S. Malik, Tera C. Levin |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
0301 basic medicine
Lineage (genetic) Receptors Cell Surface Ligands Germline Evolution Molecular 03 medical and health sciences positive selection Gene duplication Genetics Melanogaster Animals Drosophila Proteins Amino Acid Sequence Binding site Molecular Biology Gene Ecology Evolution Behavior and Systematics Discoveries Phylogeny Sex Characteristics biology Toll-Like Receptors gene duplication phylogenomics biology.organism_classification gene gain and loss Toll Toll-like receptor TLR immunity Immunity Innate Toll-Like Receptor 3 Toll-Like Receptor 4 030104 developmental biology Drosophila melanogaster Drosophila Drosophila Protein Signal Transduction |
| Zdroj: | Molecular Biology and Evolution |
| ISSN: | 1537-1719 0737-4038 |
| Popis: | Animal Toll-like receptors (TLRs) have evolved through a pattern of duplication and divergence. Whereas mammalian TLRs directly recognize microbial ligands, Drosophila Tolls bind endogenous ligands downstream of both developmental and immune signaling cascades. Here, we find that most Toll genes in Drosophila evolve slowly with little gene turnover (gains/losses), consistent with their important roles in development and indirect roles in microbial recognition. In contrast, we find that the Toll-3/4 genes have experienced an unusually rapid rate of gene gains and losses, resulting in lineage-specific Toll-3/4s and vastly different gene repertoires among Drosophila species, from zero copies (e.g., D. mojavensis) to nineteen copies (e.g., D. willistoni). In D. willistoni, we find strong evidence for positive selection in Toll-3/4 genes, localized specifically to an extracellular region predicted to overlap with the binding site of Spätzle, the only known ligand of insect Tolls. However, because Spätzle genes are not experiencing similar selective pressures, we hypothesize that Toll-3/4s may be rapidly evolving because they bind to a different ligand, akin to TLRs outside of insects. We further find that most Drosophila Toll-3/4 genes are either weakly expressed or expressed exclusively in males, specifically in the germline. Unlike other Toll genes in D. melanogaster, Toll-3, and Toll-4 have apparently escaped from essential developmental roles, as knockdowns have no substantial effects on viability or male fertility. Based on these findings, we propose that the Toll-3/4 genes represent an exceptionally rapidly evolving lineage of Drosophila Toll genes, which play an unusual, as-yet-undiscovered role in the male germline. |
| Databáze: | OpenAIRE |
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