vrIs121 [let-607(fosmid)::GFP + unc-119(+)]. let-607 locus in fosmid tagged at the carboxy-terminus with GFP. Derived by crossing the LET-607::GFP transgenic strain (YL529) to let-607(tm1423) mutants. vrIs121 transgene rescues the lethal mutant phenotype of let-607(tm1423) homozygous mutants. Reference: Weicksel SE, et al. Development. 2016 Oct 1;143(19):3540-3548.