Effect of heritable symbionts on maternally-derived embryo transcripts

Area of Science:

• Microbiology
• Genetics
• Evolutionary Biology

Background:

• Maternally-transmitted insect endosymbionts manipulate host reproduction via syndromes like male killing and cytoplasmic incompatibility (CI).
• The impact of these symbionts on early embryonic development, specifically maternally-loaded egg components, remains largely unexplored.

Purpose of the Study:

• To investigate whether endosymbionts influence the mRNA transcriptome of early Drosophila melanogaster embryos.
• To examine for evidence of Ribosome Inactivating Protein (RIP) activity in Spiroplasma-infected embryos.

Main Methods:

• mRNA sequencing (mRNA-seq) was used to compare gene expression in Drosophila embryos with and without endosymbionts (Spiroplasma poulsonii strains MSRO-Br and Hyd1, and Wolbachia strain wMel).
• Analysis of existing mRNA-seq datasets was performed to detect rRNA depurination signals indicative of RIP activity.

Main Results:

• No consistent symbiont-driven alterations in the mRNA transcriptome of early Drosophila embryos were observed.
• Statistically significant signals of rRNA depurination were detected in Spiroplasma-infected embryos, but not in symbiont-free or Wolbachia-infected controls.
• The depurination signal was stronger in embryos infected with the male-killing Spiroplasma strain.

Conclusions:

• Reproductive manipulation by these endosymbionts likely does not involve changes to maternally-loaded transcripts in early embryos.
• Spiroplasma poulsonii appears to utilize Ribosome Inactivating Proteins (RIPs) to damage host rRNA, potentially contributing to male-killing phenotypes.