| Summary: | <p>Abstract</p> <p>Background</p> <p>A method for inhibiting the expression of particular genes using external guide sequences (EGSs) has been developed in bacteria, mammalian cells and maize cells.</p> <p>Results</p> <p>To examine whether EGS technology can be used to down-regulate gene expression in <it>Caenorhabditis elegans </it>(<it>C. elegans</it>), we generated EGS-Ngfp-lacZ and EGS-Mtgfp that are targeted against <it>Ngfp-lacZ </it>and <it>Mtgfp </it>mRNA, respectively. These EGSs were introduced, both separately and together, into the <it>C. elegans </it>strain PD4251, which contains <it>Ngfp-lacZ </it>and <it>Mtgfp</it>. Consequently, the expression levels of <it>Ngfp-lacZ </it>and <it>Mtgfp </it>were affected by EGS-Ngfp-lacZ and EGS-Mtgfp, respectively. We further generated an EGS library that contains a randomized antisense domain of tRNA-derived EGS ("3/4 EGS"). Examination of the composition of the EGS library showed that there was no obvious bias in the cloning of certain EGSs. A subset of EGSs was randomly chosen for screening in the <it>C. elegans </it>strain N2. About 6% of these EGSs induced abnormal phenotypes such as P0 slow postembryonic growth, P0 larval arrest, P0 larval lethality and P0 sterility. Of these, EGS-35 and EGS-83 caused the greatest phenotype changes, and their target mRNAs were identified as ZK858.7 mRNA and <it>Lin-13 </it>mRNA, respectively.</p> <p>Conclusion</p> <p>EGS technology can be used to down-regulate gene expression in <it>C. elegans</it>. The EGS library is a research tool for reverse genetic screening in <it>C. elegans</it>. These observations are potentially of great importance to further our understanding and use of <it>C. elegans </it>genomics.</p>
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