Female insects may, on rare occasions, give birth only to females. One cause of this is the manipulation of reproduction by symbiotic bacteria. For example, the symbiotic bacterium Spiroplasma infects female Drosophila fruit flies, causing 'male killing' that kills only the next generation of males at the egg stage. This is an advantageous strategy for the symbiotic bacterium for spreading the infection, as they are transmitted to the next generation only through the female parent.
A research group led by Program-Specific Assistant Professor Toshiyuki Harumoto of the Hakubi Center for Advanced Research/Graduate School of Biostudies at Kyoto University was the first in the world to discover the causative male-killing toxin in 2018 and named it Spiroplasma poulsonii androcidin (Spaid). However, the detailed function and action mechanism of Spaid was yet to be clarified.
In response to this, the research group focused on the "OTU domain," one of the eukaryotic-like domains within the Spaid protein. The addition of ubiquitin (a small protein consisting of 76 residues) to target proteins is a process that is involved in various biological phenomena, such as the degradation of target proteins. The OTU domain acts to remove ubiquitin. The research group found that the removal of the OTU domain led to Spaid degradation in Drosophila cells and significantly attenuated male killing. They also found that OTU-deficient Spaid is degraded by Spaid in Drosophila cells which leads to the loss of the ubiquitination signal. This suggests that the same domain acts between Spaid molecules to stabilize each other.
With this discovery, much can be learned from the reproductive manipulation of insects. Expectations are high for the creation of a new pest control technology that is cost effective and environmentally friendly.
Mechanism of stabilization of the 'male-killing' toxin in the symbiotic bacterium Spiroplasma