For the first time, scientists have edited the genes of cockroaches using CRISPR-Cas9, a technology that can target and change parts of an organism’s DNA, reports a new study.
The breakthrough not only produced the first so-called “knockout cockroaches” in history, a term that refers to cockroaches with artificially inactivated genes, it could also dramatically simplify gene-editing in numerous other insects, opening up applications for pest control, evolutionary biology, and other entomological fields.
CRISPR-Cas9, often referred to simply as CRISPR, is a technique of artificially introducing DNA sequences into an organism to precisely manipulate selected locations in an organism’s genome. This technology has revolutionized genetics by enabling a host of new insights into evolutionary biology and pathways to disease treatments, earning it the 2020 Nobel Prize in Chemistry.
Scientists have already edited the genes of some insects by performing microinjection of CRISPR materials into embryos as they develop. However, this technique has been off limits to a large number of species, including cockroaches, that have inaccessible embryos—until now.
Researchers led by Yu Shirai, a scientist at Kyoto University, have overcome this constraint by injecting genetic materials into adult female cockroaches, an approach that the team calls “direct parental’’ CRISPR (DIPA-CRISPR), according to a study published on Monday in Cell Reports Methods.
The researchers successfully demonstrated that both cockroach and beetle offspring contained artificially edited genes when their mothers were subjected to the injections, and that the “mutant” cockroach offspring also passed the artificial mutations onto the next generation after they mated.
“With over a million species described, insects are a treasure trove of diversity and represent boundless possibilities as research tools for answering fundamental questions in biology,” Shirai’s team said in the study. “Current approaches for insect gene editing require microinjection of materials into early embryos, which is highly challenging in most species. In this work, we established and optimized a simple and efficient method for insect gene editing by adult injection, which can be readily implemented in any laboratory and directly applied to a great diversity of non-model insect species.”
Scientists have struggled to apply CRISPR to cockroaches because these insects shield their fertilized eggs in hard cases for days or weeks until the offspring hatch. As a result of this “unique reproduction system, it is impracticable to inject materials into very early embryos” and so “genetic manipulation of cockroaches (i.e., transgenesis or gene editing) has not been achieved so far,” according to the study.
Shirai’s team was inspired to try injecting genetic materials into mature female cockroaches, as opposed to embryos, by similar studies that achieved this technique in mosquitoes and wasps. After running several experiments that introduced genes for eye color into the cockroach species Blattella germanica, the team found that up 21.8 percent of offspring inherited the artificial mutations, “which easily enabled the first establishment of knockout cockroach lines,” reports the study.
Moreover, the researchers discovered that when DIPA-CRISPR was applied to the red flour beetle Tribolium castaneum, as much as 50 percent of the offspring inherited the mutant genes. The team also produced “knockin” beetles, meaning offspring that carried genes that were artificially inserted into their DNA, in contrast to knockout organisms that carry artificially inactivated genes.
The results provide a roadmap for future trials in other insects, which could yield new information about the complex evolutionary backstories of these invertebrates as well as applications for pest management.
“The successful application of DIPA-CRISPR in the two evolutionarily distant insect species gives an idea of its generalizability,” concluded Shirai’s team in the study. “Due to its simplicity and accessibility, DIPA-CRISPR will greatly extend the application of gene editing technology to a wide variety of model and non-model insects, including global/ local agricultural and medical pests whose genomes have not been manipulated in any way.”