Sumitani and colleagues have recently published an interesting paper on a cell ablation system they developed in Bombyx mori that is likely to be widely applicable in insect systems.
Conditional cell death systems can have a variety of uses in basic and applied insect science.
On the basic side, conditional cell death systems can be used to selectively ablate certain cells and tissues when used in combination with transgene regulatory systems that give one good temporal and spatial control of transgene expression. Cell and tissue ablation is a powerful tool for exploring functional questions in developmental and neurobiology, for example.
On the applied side, conditional cell death systems can be used to selective sterilize or kill insects and these capabilities can be useful in the context of genetics-based population control strategies like the Sterile Insect Technique (SIT) or Release of Insects with Dominant Lethality (RIDL).
Previous conditional cell death systems have used misexpression of pro-apoptotic genes like hid or reaper. Sumitani et al. have used the mammalian pro-apoptotic factor Bax, B-cell leukaemia/lymphoma 2-associated X protein or Bcl-2-associated protein. In mammals this protein results in mitochondrial damage that triggers apoptosis.
Sumitani et al. show that expression of Bax from the mouse (mBax) seemed to have similar effects when express in Bombyx mori cell lines and subsequently constructed transgenic B. mori that enabled them to selectively express mBax in certain tissues.
Sumitani et al. used the Gal4/UAS system, which has been shown to be very effective in B. mori. The created transgenic B. mori with UAS:mBax. Although successful, many of the transgenics initially recovered could not be established as lines and it was speculated that this may have been due to leaky expression from the transgene resulting in lethality.
Using preexisting Gal4 lines that were capable of driving gene expression in different parts of the silk gland, the authors showed convincingly that they were getting tissue specific cell ablation.
Interestingly they selectively expressed UAS:mBax in bombykol-sensitive olfactory receptor neurons. Bombykol is the female pheromone. Male reactivity to the pheromone was correlated with the presence of UAS:mBax. Response was not completely eliminated but significantly reduced.
The mechanism by which mBax expression is leading to cell death by apoptosis in insects is not known but it seems likely, as the authors note, that this system will likely be functional in other insects and this could be useful for a variety of applications.
Sumitani, M., Sakurai, T., Kasashima, K., Kobayashi, S., Uchino, K. et al., 2015 Establishment of a specific cell death induction system in Bombyx mori by a transgene with the conserved apoptotic regulator, mouse Bcl-2-associated X protein (mouse Bax). Insect Mol Biol 24: 671-680doi: 10.1111/imb.12192