standard Water Fleas and Insects – Common Challenges for Genetic Modification – Shared Solutions?

The water flea, Daphnia pulex, is a microcrustacean that has become a model for biomedical research and, perhaps more significantly, a model for probing G x E (Genetics x Environment) interactions. Some genetic modification methods have been developed for Daphnia magna, mainly RNAi.

There are a number of species of Daphnia for which genetic technologies are also needed. Like insects there are subtle and not so subtle differences in species morphology and biology that makes transferring  technologies from one species to another a challenge.

In a paper from 2013 by Hiruta et al, the authors describe their successful efforts to develop a microinjection system for RNA interference for Daphnia pulex.

In reading the paper it was interesting to see how the technical issues mirrored perfectly those encountered with insects.

Hiruta et al say:
“There are two major technical problems for microinjection in daphnid species. One is the rapid hardening of egg membrane (sic) and the other is a considerable difference between the internal and external osmotic pressures of the egg. The former prevents egg membrane penetration by a needle, and the latter produces leaking of internal contents (yolk, oil droplets, and so on) when the needle is withdrawn”

This should sound very familiar to any insect biologist who has attempted to apply some of the currently available genetic technologies to “their” species of insect.  Most genetic platforms require embryo microinjection.

Methods developed for Daphnia magna were not directly transferable, and new protocols needed to be developed.

The solutions to the problems Hiruta et al describe are potentially applicable to some insects and arthropods (ticks?). They employ sucrose solutions to manipulate the osmotic pressure surrounding the eggs to relieve internal pressure and enable the introduction of small volumes of liquid (dsRNA).

Pulex embryo in situ following RNAi injection.  From Hiruta (2013)

Pulex embryo in situ following RNAi injection. From Hiruta (2013)

This short paper nicely illustrates how problems need to be addressed in order to develop genetic technologies and is worth a look by insect biologists interested in technology development and transfer to a species of interest.

Development of a microinjection system for RNA interference in the water flea Daphnia pulex
Chizue Hiruta, Kenji Toyota, Hitoshi Miyakawa, Yukiko Ogino, Shinichi Miyagawa, Norihisa Tatarazako, Joseph R Shaw and Taisen Iguchi
BMC Biotechnology 2013, 13:96


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