Pupal and Adult Injections for RNAi and CRISPR Gene Editing in Nasonia vitripennis

Here, we describe methods for efficient pupal and adult injections in Nasonia vitripennis as accessible alternatives to embryo microinjection, enabling functional analysis of genes of interest using either RNA-silencing via RNA interference (RNAi) or gene knockout via CRISPR/Cas9 genome editing.

Research on non-canonical insect model, like parasitoid wasp, is limited because embryonic microinjection is very challenging. Our method bypasses this problem, enabling site-specific and heritable germline mutations. Injecting pupae or adult females is fast and removes the requirement for expensive equipment or specialized training required to achieve successful embryonic microinjections.

This technique will allow no specialized labs that do not have access to expensive equipment to do functional studies in any insect species they are using as a model. After the optimization, this method can be used to study functional genetics of many other genes in Nasonia. We also think this method may be used to deliver nucleic acids for genetic transformation of Nasonia or other insects.

Begin by setting up approximately 20 mated females singularly in small glass test tubes plugged with cotton. Add two S.bullata hosts per tube and maintain the wasps at 25 degrees Celsius and 30%relative humidity with a 12:12 light dark cycle for two to three days. After two to three days, gently remove the females using a fine tipped brush to avoid continuous over position and a synchrony in offspring development.

Removed females can optionally be re-hosted or stored at five degrees Celsius for up to a month. Maintain the parasitized host at 25 degrees Celsius and 30%relative humidity with a 12:12 light dark cycle for seven days if the desired injection stage requires white pupae, for 13 days, if the required developmental stage is black pupae, or 14 days for young, newly emerged adults. When the desired stage is reached, crack open the host puparium with a dissecting needle to recover N.vitripennis pupae and adults.

Prepare a glass slide by applying a line of school glue at the center. Spread the glue with the dissecting needle to obtain a thick layer, which will be used to align the pupae. Let the glue dry for approximately two minutes before transferring the pupae.

Under a dissecting microscope, use a dissecting needle to apply glue on the back of the head of the pupa. Attach the pupa to the glue layer on the slide with its abdomen facing up. Align 20 to 30 pupae side-by-side on the slide.

Place the slide with the pupae and a Petri dish to let the glue drive for approximately 10 minutes. Before starting the injections, test the adherence of the pupae to the glue by pushing them gently with the dissecting needle. If most of the pupae are loosened, prepare a new slide.

Alternatively, remove all loose pupae and proceed to inject those that are properly attached to the slide. Load one capillary glass tube into a needle puller and pull needles following the manufacturer's instructions. Load the needle with five microliters of the prepared injection mixture using microloader pipette tips.

Open the needle, sliding the tip on a surface made from two overlapping slides. Alternatively, open the tip of the needle with a pair of fine forceps to create a sharp edge. Place the slide with the aligned pupae under a dissecting microscope, then insert the needle into the femtojet's injection tube and tighten the grip head.

Looking at the needle under the microscope, turn on the femtojet and set the compensation pressure and injection pressure parameters by rotating the rotary knobs. Carefully insert the needle between the second and third visible abdominal segments with a vertical angle of about 30 degrees. Inject with a continuous flow until the whole abdomen turns green in the case of white stage pupae or until the abdomen increases in size in the case of black pupae.

Stop injecting when it is clear that the abdomen cannot take any more liquid or when the liquid starts flowing out of the body. Move carefully to the next pupa and repeat these steps. Transfer the slide with the injected pupae to a Petri dish.

Cover the dish with its lid and place it at 25 degrees Celsius until wasp emergence. For adult preparation, separate groups of 20 virgin females in a clean small test tube with a fine paint brush. Place a glass slide on top of ice and align the female side by side on the cold slide with abdomens facing up under a dissecting scope.

Load one needle with the ribonucleoprotein solution using a microloading tip and insert the needle into the connector pack of the aspirator tube assembly. Support the females from the opposite side with blunted dissecting needles, while injecting slowly into the abdomen. Avoid touching the ovipositor.

This will severely damage this critical reproductive structure. Carefully insert the needle between the second and third visible abdominal segments with a vertical angle of about 30 degrees. Inject the solution into the female abdomen, stopping when no more liquid can enter or when leaking of surplus solution is observed.

Move carefully to the next female and repeat these steps. When finished, gently transfer a single injected females to a new tube with one host using a paintbrush. Leave them to recover at room temperature for approximately one hour, confirm survival, and return the tubes to the rearing incubator.

After adult eclosion from the injected pupae, place single wasps into a glass to plugged with cotton and insert one S.bullata host. For CRISPR/Cas9 knockout experiments, allow females to parasitize the host for one day and replace the host each day for three consecutive days. Place the parasitized host, set 25 degrees Celsius until emergence of the G0 male offspring, approximately 13 to 14 days.

Under a dissecting microscope, screen G0 males for the mutated phenotypes. The cinnabar gene is responsible for eye pigmentation. Wasps with brown eyes are wild-type and wasps with bright red eyes or variations between red and brown eyes are mutants.

This protocol can be used for either pupal or adult microinjection. Survival rates of this procedure range from 15 to 100%The efficiency of achieving the desired phenotype via RNAi or CRISPR without requiring laborious egg injections is shown here. When injecting pupae or adult females, the needle should be sharp and be introduced in a way that liquid should not leak immediately after injecting.

If this happens, remove the needle, ensure that the tip is fine and sharp, change it if necessary or inject in a different location. Function analysis can be performed on the gene of interest targeted from this procedure. This will answer a question about the gene function and if the gene is necessary for the specific phenotype studied.