Transposon insertion sequencing (TIS) is an emerging technique which utilizes a massive transposon mutant library to screen specific phenotype and determine the conditional essential genetic requirements for bacterial fitness under distinct conditions combined with high-throughput parallel sequencing technology. Compared with a massive mutant library in traditional TIS, the defined mutant library sequencing (DML-Seq) has advantages as: 1) efficient mutagenesis; 2) low bottleneck effects; 3) avoid hotpots caused by screening; 4) can be directly used in the following experiments. Here, we described an optimized procedure of DML-Seq for fitness screen to supply classical TIS using the marine pathogenic bacterium Edwardsiella piscicida as an example.

Loss of function studies shed significant light on the involvement of a gene or gene product in different cellular processes. Short hairpin RNA (shRNA) mediated RNA interference (RNAi) is a classical yet straightforward technique frequently used to knock down a gene for assessing its function. Similar perturbations in gene expression can be achieved by siRNA, microRNA, or CRISPR-Cas9 methods also. In Drosophila genetics, the UAS-GAL4 system is utilized to express RNAi and make ubiquitous and tissue-specific knockdowns possible. The UAS-GAL4 system borrows genetic components of S. cerevisiae, hence rule out the possibility of accidental expression of the system. In particular, this technique uses a target-specific shRNA, and the expression of the same is governed by the upstream activating