Plays an essential role for patterning the left-right axis. Requires solely on the left side, downstream of the leftward flow, but upstream of dand5, a nodal inhibitor involved in left-right patterning. Binds 1 zinc ion per subunit. Expressed specifically in dorsal forerunner cells (DFCs) that form a ciliated Kupffer's vesicle later. Embryos with CRISPR-induced cirop null are fertile but the developing heart at 48 h post-fertilization (hpf) show cardiac looping randomization. Only 25% of cirop deficient embryos show a normal positioning of brain, heart and pancreas at 72 hpf. No other ciliopathy-related phenotypes such as body curvature, kidney cysts or hydrocephalus are observed in cirop mutant embryos at 72 hpf. When dand5 is depleted on the left side of cirop null zebrafish embryos, the phenotype is rescued. Belongs to the peptidase M8 family.