Steroid hormones in Acari, their functions and synthesis

Abstract

Acari are arthropods with the conserved features of an exoskeleton that require the shedding of cuticle for growth. Steroid hormones, ecdysteroids, regulate the mechanisms necessary for growth and development. Acari lack juvenile hormones, so they utilize ecdysteroids as the solo lipophilic hormone throughout their life for molting as well as for reproduction. Although some research on ecdysteroidogenesis has been conducted in the Acari, two important questions remain unclear: the active form of ecdysteroid and sites for ecdysteroidogenesis. The active form of ecdysteroids in Acari is controversial. Analysis by mass spectrometry confirms that most Acari use 20-hydroxyecdysone (20E), but the spider mite Tetranychus urticae (Koch) (Acari: Tetranychidae) uses Ponasterone A (25-deoxy-20-hydroxyecdysone). Analyses of ecdysteoridogenic genes provide clear evidence that the ovary is the primary site of ecdysteroidogenesis in both immature and mature ticks. In this review, the known functions of ecdysteroids are summarized and recent progress on ecdysteroidogenesis is introduced.