Aldehyde dehydrogenase 3 converts farnesal into farnesoic acid in the corpora allata of mosquitoes

Abstract

The juvenile hormones (JHs) play a central role in insect reproduction, development and behavior. Interrupting JH biosynthesis has long been considered a promising strategy for the development of target-specific insecticides. Using a combination of RNAi, in vivo and in vitro studies we characterized the last unknown biosynthetic enzyme of the JH pathway, a fatty aldehyde dehydrogenase (AaALDH3) that oxidizes farnesal into farnesoic acid (FA) in the corpora allata (CA) of mosquitoes. The AaALDH3 is structurally and functionally a NAD+-dependent class 3 ALDH showing tissue and developmental-stage-specific splice variants. Members of the ALDH3 family play critical roles in the development of cancer and Sjögren-Larsson syndrome in humans, but have not been studies in groups other than mammals. Using a newly developed assay utilizing fluorescent tags, we demonstrated that AaALDH3 activity, as well as the concentrations of farnesol, farnesal and FA were different in CA of sugar and blood-fed females. In CA of blood-fed females the low catalytic activity of AaALDH3 limited the flux of precursors and caused a remarkable increase in the pool of farnesal with a decrease in FA and JH synthesis. The accumulation of the potentially toxic farnesal stimulated the activity of a reductase that converted farnesal back into farnesol, resulting in farnesol leaking out of the CA. Our studies indicated AaALDH3 plays a key role in the regulation of JH synthesis in blood-fed females and mosquitoes seem to have developed a “trade-off” system to balance the key role of farnesal as a JH precursor with its potential toxicity.

Metabolic analysis reveals changes in the mevalonate and juvenile hormone synthesis pathways linked to the mosquito reproductive physiology

“…In all these instances, the rate of JH biosynthesis is controlled by the rate of flux of isoprenoids in the pathway, which is the outcome of a complex interplay of changes in precursor pools, enzyme levels and external regulators (Li et al, 2004; Li et al, 2003a, 2003b; Li et al, 2006; Nouzova et al, 2011; Nyati et al, 2013; Rivera-Perez et al, 2013). A coordinated expression of most JH biosynthetic enzymes has been previously described in mosquitoes and silkworm (Kinjoh et al, 2007; Nouzova et al, 2011; Ueda et al, 2009).…”

“…A coordinated expression of most JH biosynthetic enzymes has been previously described in mosquitoes and silkworm (Kinjoh et al, 2007; Nouzova et al, 2011; Ueda et al, 2009). Increases or decreases in transcript levels for all the enzymes are generally concurrent with increases or decreases in JH synthesis (Kinjoh et al, 2007; Nouzova et al, 2011; Rivera-Perez et al, 2013; Ueda et al, 2009). Previous studies have proposed that regulation of JH synthesis occurs upstream of the acetyl-CoA pool (Sutherland and Feyereisen, 1996), as well as by rate limiting bottlenecks at different enzymatic steps in the pathway, including the activities of HMG-CoA reductase (Kramer and Law, 1980; Monger and Law, 1982), farnesol dehydrogenase (Mayoral et al, 2009), farnesal dehydrogenase (Rivera-Perez et al, 2013) or juvenile hormone acid methyltransferase (Shinoda and Itoyama, 2003; Minakuchi et al, 2008; Sheng et al, 2008).…”

“…Increases or decreases in transcript levels for all the enzymes are generally concurrent with increases or decreases in JH synthesis (Kinjoh et al, 2007; Nouzova et al, 2011; Rivera-Perez et al, 2013; Ueda et al, 2009). Previous studies have proposed that regulation of JH synthesis occurs upstream of the acetyl-CoA pool (Sutherland and Feyereisen, 1996), as well as by rate limiting bottlenecks at different enzymatic steps in the pathway, including the activities of HMG-CoA reductase (Kramer and Law, 1980; Monger and Law, 1982), farnesol dehydrogenase (Mayoral et al, 2009), farnesal dehydrogenase (Rivera-Perez et al, 2013) or juvenile hormone acid methyltransferase (Shinoda and Itoyama, 2003; Minakuchi et al, 2008; Sheng et al, 2008). Studies in several insects demonstrated that exogenous additions of precursors stimulate JH biosynthesis in a developmental-dependent mode (Feyereisen et al, 1981a; Feyereisen et al, 1981b; Nouzova et al, 2011), indicating that as a general rule, enzymes of the JH pathway are in excess.…”

“…However, studies evaluating how changes in metabolite levels and enzyme activities influence the flux of precursors on the JH synthesis pathway and how these changes relate to the different stages of reproductive physiology are lacking. With the development of new strategies that facilitate the analysis of transcripts, enzymatic activities and metabolites in the minuscule CA of insects (Nouzova et al, 2011; Nyati et al, 2013; Rivera-Perez et al, 2012; Rivera-Perez et al, 2013); it is now possible to provide comprehensive descriptions of the MVA and JH pathways by integrating information on changes in the three basic components of those pathways. In the present studies, we integrated the analysis of changes in mRNA levels for the 13 enzymes of the MVA and JH-branch pathways at 10 different developmental or physiological states during pupae and adult female mosquito, with studies of the catalytic activities of 8 of the enzymes at 5 critical times in pupae and adult female and finally, we measured changes in all the intermediates of the MVAP from acetyl-CoA to FPP, as well as all metabolites of the JH-branch during 9 distinct physiologically-relevant time points in female pupal and adult stages.…”

Allatotropin inhibits juvenile hormone biosynthesis by the corpora allata of adult Bombyx mori

“…The regulatory mechanisms of JH biosynthesis in the adult stage have also been well studied in several insect species, in particular, cockroaches (reviewed by Stay and Tobe, 2007;Marchal et al, 2013) and mosquitoes (Noriega, 2004;Mayoral et al, 2009;Nouzova et al, 2011Nouzova et al, , 2012Pérez-Hedo et al, 2013;Nyati et al, 2013;Rivera-Perez et al, 2013). Allatotropin (AT) and allatostatin (AST) are two major neuropeptide hormones that control JH synthesis during the adult stage (Weaver and Audsley, 2009;Goodman and Granger, 2005).…”