Genomic exicision of positive selection markers using Cre recombinase mRNA. (A) A schematic overview of Cre-mediated excision. Cre recombinase mRNA was microinjected into the gonads of P0 hermaphrodites carrying homozygous vps-45 mini genes flanked by LoxP sites. F1 hermaphrodites were examined by PCR#1 in which Cre-LoxP excision resulted in 410-bp products. Self-progenies (F2 hermaphrodites) were examined by PCR#1 and PCR#2 to confirm that vps-45 mini genes were successfully excised. (B) Frequency of excision (PCR#1 positive/total F1) by microinjection of Cre mRNA. (C) Cre-excision was detected by PCR#1(upper, 410 bp). Unexcised regions were detected by PCR#2 (lower, 1060 bp).