CYP18A1 regulates molting in Macrobrachium nipponense by mediating 20E inactivation

The pulsatile fluctuations of the steroid hormone 20-hydroxyecdysone (20E) in crustaceans involve both its biosynthesis and subsequent inactivation. Although the regulatory mechanisms of 20E biosynthesis have been extensively studied, the physiological significance of its inactivation in crustaceans is far less clear. This study reports the identification of the cytochrome P450 enzyme gene Mn-CYP18A1 from Macrobrachium nipponense . Structural analysis confirmed the presence of conserved cytochrome P450 motifs in Mn-CYP18A1 , notably the heme binding domain. Phylogenetic analysis indicates that CYP18A1 orthologs are widely distributed in most major groups of insects and crustaceans. Expression analysis revealed that Mn-CYP18A1 expression was highest in the eyestalk compared to other tissues and peaked during the postmolt stage. RNA interference mediated knockdown of Mn-CYP18A1 prompted the upregulation of 20E biosynthetic genes ( CYP306A1 , CYP307A1 ) and the nuclear receptor FTZ-F1 , consequently elevating 20E titers. This consequently led to molting impairment and a significant reduction in the molting rate. Our study demonstrates that 20E inactivation, mediated by Mn-CYP18A1 , is essential for normal molting in M. nipponense . • Mn-CYP18A1 contains typical conserved structural domains of the cytochrome P450 family. • Mn-CYP18A1 has its highest expression in the eyestalk, peaking in the postmolt stage. • Knockdown of Mn-CYP18A1 upregulates CYP306A1 , CYP307A1 , and FTZ-F1 . • Silencing Mn-CYP18A1 elevates 20E titers and impairs molting in Macrobrachium nipponense .