Single-step generation of homozygous knockout/knock-in individuals in an extremotolerant parthenogenetic tardigrade using DIPA-CRISPR

クマムシ類で初めてゲノム編集個体の作出法を確立しました。ノックアウト・ノックイン（ssODNを用いたもの）が可能で、成体雌に Cas9 complex を注入するだけで、子個体としてホモ変異体が直接得られることがわかりました。クマムシの耐性に関わる非ドメイン型タンパク質の機能解析に役立つと期待しています。

Tardigrades are small aquatic invertebrates known for their remarkable tolerance to diverse extreme stresses. To elucidate the in vivo mechanisms underlying this extraordinary resilience, methods for genetically manipulating tardigrades have long been desired. Despite our prior success in somatic cell gene editing by microinjecting Cas9 ribonucleoproteins (RNPs) into the body cavity of tardigrades, the generation of gene-edited individuals remained elusive. In this study, employing an extremotolerant parthenogenetic tardigrade species, Ramazzottius varieornatus, we established conditions that led to the generation of gene-edited tardigrade individuals. Drawing inspiration from the direct parental CRISPR (DIPA-CRISPR) technique employed in several insects, we simply injected a concentrated Cas9 RNP solution into the body cavity of parental females shortly before their initial oviposition. This approach yielded gene-edited G0 progeny. Notably, only a single allele was predominantly detected at the target locus for each G0 individual, indicative of homozygous mutations. By co-injecting single-stranded oligodeoxynucleotides (ssODNs) with Cas9 RNPs, we achieved the generation of homozygously knocked-in G0 progeny, and these edited alleles were inherited by G1/G2 progeny. This is the first example of heritable gene editing in the entire phylum of Tardigrada. This establishment of a straightforward method for generating homozygous knockout/knock-in individuals not only facilitates in vivo analyses of the molecular mechanisms underpinning extreme tolerance, but also opens up avenues for exploring various topics, including Evo-Devo, in tardigrades.

Authors: Koyuki Kondo, Akihiro Tanaka & Takekazu Kunieda

Journal: PLOS Genetics

DOI: https://doi.org/10.1371/journal.pgen.1011298