Abstract
Rearranged chromosomes have been applied to construct genetic balancers to manipulate essential genes in C. elegans Although much effort has been put into constructing balancer chromosomes, approximately 6% (map units) of the C. elegans genome has not been covered, and this area lies mostly in pairing centers (PCs). Here, we developed a method for conditional chromosomal engineering through combinatorial use of the CRISPR/Cas9 and Cre/LoxP technologies. Functional DNA fragments containing LoxP sequences were inserted into designated genomic loci using a modified counterselection (cs)-CRISPR method. Then, heat-shock-induced Cre recombinase induced an inversion of the chromosomal region between the two LoxP sites. The chromosomal inversions were subsequently detected by the appearance of pharyngeal GFP. Through this method, we have successfully generated several chromosomal inversion lines, providing valuable resources for studying essential genes in pairing centers.