Spaink et al (2013) describe their use of a robotic injection system as a high throughput screening tool in zebra fish, Danio rerio, embryos. Automated and semi-automated injection systems for zebra fish embryos as well as other systems are not new and they have been evolving over the last decade. Spaink et al (2013) make improvements on a system they have reported on earlier that allows them to inject 2000 zebra fish embryos per hour. Wang et al. (2007) have reported manual injection rates of zebra fish embyros of 600-1200 per hour. To say that the system of Spaink et al is cool is not an understatement.
Embryos are aligned using a honeycombed agarose grid, described in Carvalho et al. (2011), which holds 1024 embryos. The grid with embryos is loaded into a stage coupled to a controller and a motorized micro-manipulator while the loaded needle is inserted into an Injectman II (Spaink et. al 2013). Before starting to inject the needles z-position needs to be calibrated, this is achieved by using a prism device which, allows the user to calibrate the 3D position of the needle to an accuracy of 10 μm in 3D (Spaink et. al 2013). At this point the system is ready to inject. The injection system uses a computer to control the movments of the stage to align each egg and the movement of the needle, through-microscope imaging permits visualizing the egg and the user determines the optimum position within the embryo to inject by moving the pointer to this position and clicking to initiate injection. Once the injection is complete the stage is automatically moved to the next embryo and the system now completes all movements and injections automatically. Here’s a video from Spaink et al (2013).
Recent advances in the technology for automated microinjections in zebra fish embryos whet the appetite of insect researchers for similar technology. Is the technology at the point where it can be used for insect embryo microinjection? With a bit of work – maybe.
Here at the University of Maryland Insect Transformation Facility (UM-IFT) we manually inject thousands of non-Drosophila embryos per week, in the support of researchers utilizing various genetic modification technologies. It would be nice to speed up our efforts through the use of a system similar to that used by Spaink et al. Automated injection systems for insect embryos have been reported. Zappe et al (2006) describe a MEMs-based system for injecting Drosophila embryos – although not designed for creating transgenics.
What issues would need to be overcome to make automated injection of insect embryos a reality? In thinking about automating insect microinjection for, let’s say, mosquitoes I think there are three major hurtles to overcome: desiccating the embryos, piercing the embryos and needle clogging.
Insect eggs generally need to be desiccated slightly before injection and controlling this process in an automated system will be challenging, too little desiccation and the embryo explodes during injection and too much desiccation can kill the embryo and also make it difficult for the needle to piece the egg.
When injecting mosquito embryos you need to probe the embryo’s surface with the tip of the needle before finding an area where the needle will slip into the embryo. It is not always the same location and while I am not sure why one area of the surface would be more amenable to injection than another, it is something I have noticed after injecting mosquito embryos for nearly 15 years.
Although perhaps not a problem with zebra fish embryos, needle clogging is a significant problem while injecting many insect embryos. This is often a result of ooplasm and yolk clogging needles from the outside.
Can these hurtles be overcome? Probably.
As genetic technologies are developed for various insects high throughput delivery systems could become important not just for creating transgenic insects but for other purposes as well.
Spaink HP, Cui C, Wiweger MI, Jansen HJ, Veneman WJ, Mar√≠n-Juez Rn, de Sonneville J, Ordas A, Torraca V, van der Ent W, Leenders WP, Meijer AH, Snaar-Jagalska BE, Dirks RP (2013) Robotic injection of zebrafish embryos for high-throughput screening in disease models. Methods 62: 246-254 doi 10.1016/j.ymeth.2013.06.002
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