PgmNr D1488: Rapidly Evolving Stonewall maintains Germline Stem Cells and regulates Transposons.

Authors:
Daniel Zinshteyn; Daniel Barbash


Institutes
Cornell University, Ithaca, NY.


Keyword: heterochromatin

Abstract:

Germline stem cells (GSCs) are the progenitor cells for the entire population of an organism’s germline. In Drosophila, these cells reside in a well-defined cellular niche that is required for both their maintenance (self-renewal) and differentiation (asymmetric division resulting in a daughter cell that differs from the GSC). Dozens of genes have been implicated in both maintenance and differentiation and most of them are required for production of viable gametes. The critical function of these genes suggests that they should be highly conserved across Drosophila taxa. However, population genetic analyses have shown that many of them have undergone adaptive evolution within the D. melanogaster lineage. One possible cause of this evolutionary signature is the critical role that many of these genes play in regulating genomic parasites, particularly transposons.  It may be that some of these genes are locked in a dynamic arms-race with rapidly evolving selfish elements.

The stem-cell maintenance factor Stonewall (Stwl) is a particularly intriguing candidate, as it has undergone adaptive evolution and has been implicated in heterochromatin maintenance. We hypothesized that Stwl is required for regulating transposons in D. melanogaster. We performed RNA-seq on stwl mutant ovaries and testes to assay the transcript abundance of transposable elements in the absence of a functional Stwl. We find that mutant stwl ovaries show significant de-repression of many transposon families. Surprisingly, heterochromatic genes are not preferentially misregulated relative to euchromatic genes. These data suggest that Stwl may be required for regulation of transposons via a mechanism other than general heterochromatin maintenance. Our findings support the hypothesis that Stwl is a target of positive selection as a response to rapidly evolving TEs.



Flybase Genetic Index:
1. FlyBase gene symbol: stwl; FBgn: FBgn0003459