Identification and Characterization of 24-Dehydrocholesterol Reductase (DHCR24) in the Two-Spotted Cricket, Gryllus bimaculatus
1
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Chiba 277-8562, Japan
2
Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371-8512, Japan
*
Author to whom correspondence should be addressed.
Insects 2021, 12(9), 782; https://doi.org/10.3390/insects12090782
Submission received: 29 July 2021
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Revised: 27 August 2021
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Accepted: 27 August 2021
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Published: 1 September 2021
(This article belongs to the Collection Insect Signals)
Simple Summary
DHCR24 (24-dehydrocholesterol reductase) is a key enzyme for producing cholesterol from desmosterol and that is also involved in the conversion of plant sterols to cholesterol in most plant-feeding insects. This study extensively examined the possibility of DHCR24 involved in the sterol conversion in omnivorous insects, which feed on multiple food origins. Homologs of DHCR24 (GbDHCR24-1 and -2) were identified and characterized by using the two-spotted cricket, Gryllus bimaculatus, as an experimental model. The quantitative expression analyses and RNA interference experiments revealed that GbDHCR24-1 rather than GbDHCR24-2 facilitates the desmosterol-to-cholesterol conversion in crickets. Our data suggested that the omnivorous species produced cholesterol from desmosterol in the same manner as the plant-feeding species do.
Abstract
Arthropods, including insects, convert sterols into cholesterol due to the inability to synthesise cholesterol de novo. 24-dehydrocholesterol reductase (DHCR24) plays an important role in the conversion. Not only involving the cholesterol biosynthesis in vertebrates, DHCR24 is required for the conversion of desmosterol into cholesterol in phytophagous insects. The current study extensively examined DHCR24 in omnivorous insects, which feed on both plants and animals, using Gryllus bimaculatus as the experimental model. We identified cDNAs encoding two homologues of DHCR24 from G. bimaculatus, which were designated as GbDHCR24-1 and GbDHCR24-2. Both homologues contained the flavin adenine dinucleotide binding domain, which is a feature of DHCR24. Quantitative polymerase chain reaction revealed that among tissues of adult crickets, fat body and anterior midgut expressed high levels of GbDHCR24s. Both fat body and anterior midgut demonstrated DHCR24 activities in which one of the functions is the conversion of desmosterol into cholesterol in vitro. Knockdown of GbDHCR24-1 significantly reduced the conversion activity in the anterior midgut while knockdown of the GbDHCR24-2 did not. Additionally, the accumulation of desmosterol was detected in a feeding experiment with a specific DHCR24 inhibitor, azacosterol. We finally concluded that GbDHCR24-1 is the major enzyme that facilitates the desmosterol-to-cholesterol-conversion in crickets.
Keywords:
DHCR24; desmosterol; cholesterol; phytosterols; cricket; omnivorous insects; RNAi
