This single amino acid deletion mutation, which blocked PC1/G protein mediated activation of promoter-reporter activity as well as PC1/PC2 channel activity in cellular assays, also resulted in a severe loss of PC1 function as evidenced by a cystic embryonic kidney phenotype and embryonic lethality in Pkd1ΔL/ΔL embryos, and rapid cyst formation in newborn Pkd1ΔL/fl following Hoxb7 Cre-mediated excision of the floxed allele. This evidence concerns the gene PKD1 and cyst.