Characterized cantharidin distribution and related gene expression patterns in tissues of blister beetles, Epicauta chinensis

Abstract

Cantharidin (CTD), a terpenoid defensive toxin mainly produced by blister beetles, is widely known by its toxicity to both cancer cells and pests. However, little information is known about its biosynthesis in blister beetles. In this study, first we determined the CTD content in various tissues of adult blister beetles on different days after mating, and then detected the temporal and spatial expression patterns of genes related to CTD biosynthesis in Epicauta chinensis. Results revealed that the accessory gland is the source of the highest CTD production. The second highest level was in the fat body in male blister beetles after mating. In females, the highest CTD content was in the reproductive system except the ovary after mating. As revealed by messenger RNA expression level analysis, the highest levels of 3-hydroxy-3-methylglutary-CoA reductase (HMGR) and juvenile hormone epoxide hydrolase (JHEH) transcripts of E. chinensis were observed in the fat body in males after mating. However, the highest transcript level of EcHMGR was in the ovary and EcJHEH was maintained at a nearly similar level in females. The transcript level of methyl-farnesoate epoxide was significantly higher in the head and that of CYP4BM1 in the midgut in both male and female E. chinensis. We speculate that the fat body may play a more important role than other tissues on the CTD biosynthesis in male E. chinensis after mating. There may be multiple tissues involved in the process of CTD biosynthesis. These four genes probably play regulatory roles in different tissues in males.

Unraveling the role of male reproductive tract and haemolymph in cantharidin-exuding Lydus trimaculatus and Mylabris variabilis (Coleoptera: Meloidae): a comparative transcriptomics approach

“…The concentration of the secreted CA vary from 0.03 to 0.79 mg for each gram of exuded haemolymph [ 9 , 10 ], but largely depends on species, environmental and physiological conditions. Males produce more CA than females [ 9 – 15 ] and accumulate large amounts of this terpene in their reproductive organs and, particularly, in male accessory glands (MAG) [ 13 , 16 – 19 ]. During mating, males transfer large quantities of CA to females [ 6 , 20 – 23 ] which, in turn, use the received compound for protecting eggs from potential predators or parasites [ 13 , 16 , 21 , 24 ].…”

“…Such a renewed interest has led to a growing literature devoted to reveal the molecular basis of CA de novo biosynthesis in blister beetles, focusing on species belonging to the (species-rich) Meloinae subfamily. Both gene-expression analyses of key-enzymes in different organs of Epicauta sibirica Pallas, 1773 (tribe Epicautini; all reported as chinensis Laporte, 1849) [ 18 , 19 , 34 , 35 ] and a de novo transcriptomic approach comparing the relative abundance of transcripts in males vs. females in Hycleus cichorii (Linnaeus, 1767) (tribe Mylabrini; reported as Mylabris ) [ 36 ] were coherent with previous studies indicating that: (i) CA may be synthetized via the mevalonate (MVA) pathway [ 37 ], (ii) farnesol may act as an intermediate [ 38 – 40 ], and (iii) a juvenile hormone (JH) metabolite could be involved in one of the latest biosynthetic steps [ 35 , 37 , 41 ].…”

“…However, there is still a gap of knowledge on some crucial steps of the CA biosynthetic pathway, as well as the specific site of its in vivo production. At first, the third pair of MAG was designated as the production site [ 16 , 42 ], but recently, both high CA content and transcriptional level of the 3-hydroxy-3-methylglutary-CoA reductase (HMGCR, an essential enzyme of the MVA pathway) observed in the fat body of E. sibirica suggested that CA biosynthesis may more likely occur in this tissue [ 19 ].…”

Draft Genome of a Blister Beetle Mylabris aulica

“…Cantharidin (C 10 H 12 O 4 , CTD) is a monoterpene chemical compound produced by some species of the Meloidae family from Coleoptera, commonly known as blister beetles or Spanish flies (Crowson, 1970;Carrel et al, 1993;Karras et al, 1996;Tagwireyi et al, 2000;Jiang et al, 2019). CTD is antiinflammatory, antiviral, and increases immune-regulating activities (Moed et al, 2001); therefore, it has been widely used to treat a variety of diseases including skin-related diseases (furuncles and piles) (Su et al, 2016), tuberculous scrofuloderma (Silverberg et al, 2000;Moed et al, 2001;Richard et al, 2014) and erectile dysfunction (Wang, 1989;Liu and Chen, 2009).…”

The Inhibition of Serine/Threonine Protein Phosphatase Type 5 Mediates Cantharidin Toxicity to Control Periplaneta americana (L.)

“…Cantharidin (CTD) comes from blister beetles, where it is a defensive toxin and protects blister beetles from attack [ 21 , 22 ]. More recently, its application in plant protection has attracted increasing attention.…”