heIs105 [rps-27::loxP::NLS::mCherry::let858 UTR::loxP::NLS::GFP::let-858 UTR + unc-119(+)] IV. heSi164 [rps-27::loxN::NLS::mCherry::let858 UTR::swsn-1p::swsn-1::unc-54 UTR::loxN::NLS::GFP::let-858 UTR + unc-119(+)] V. heSi141 [hlh-8(short)::FLAG::CRE::tbb-2 + unc-119(+)] X. Maintain the line at 15C and shift to 25C for mutant analysis. Expression of CRE recombinase in the mesoblast lineage driven by the hlh-8 promoter. heSi164 carries a swsn-1 rescue construct which ensures rescue of the temperature-sensitive swsn-1(os22) mutation. Upon expression of CRE (in this case in the mesoblast lineage) the swsn-1 gene will be excised, creating a mesoblast specific mutant of swsn-1. This recombination event can be visualized by a switch from red to green in those mesoblast cells in which swsn-1 was lost. The animals are healthy at 15C, but embryonic lethal and larval arrested at 23-25C. swsn-1(os22) causes mild overproliferation in the mesoblast lineage. The swsn-1 rescuing transgene is unable to rescue germline development of swsn-1(os22) mutants. Reference: Ruijtenberg S & van den Heuvel S. Cell. 2015 Jul 16;162(2):300-13.