|CABRERA, ANA - University Of Florida|
Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2014
Publication Date: 12/8/2014
Citation: Cabrera, A.R., Shirk, P.D., Evans, J.D., Hung, K., Sims, J.W., Alborn, H.T., Teal, P.E. 2014. Three halloween genes from the varroa mite, varroa destructor (Anderson & Trueman) and their expression during reproduction. Insect Molecular Biology. doi: 10.1111/imb.12155.
Interpretive Summary: The varroa mite is the major ectoparasite pest of the honey bee in North America and is one of the central factors in colony collapse disorder. A mite infestation weakens the colonies not only by feeding on the bees but by vectoring pathogens. Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology identified the genes for 3 proteins in the varroa mites that are central to the production of steroid hormones in insects. The 3 genes were DNA sequenced and the transcripts characterized. The transcript level for first gene in the steroid pathway increased when the female mite transitioned from a feeding stage to the reproductive stage. These genes provide significant targets for control using molecular techniques to disrupt hormone production and reproduction of the pest varroa mites.
Technical Abstract: Ecdysteroid biosynthesis involves sequential enzymatic hydroxylations by two microsomal enzymes plus five cytochrome P450’s, collectively known as Halloween genes. Complete sequences for three Halloween genes, spook (Vdspo), disembodied (Vddib) and shade (Vdshd), were identified in varroa mites and sequenced. Genomic sequence comparisons showed Vdspo contained 5 introns as opposed to a maximum of 2 introns in other arthropods while Vddib and Vdshd were similar to their arthropod orthologs. Phylogenetic analyses of predicted amino acid sequences for Halloween orthologs showed that the acarine orthologs were distantly associated with insect and crustacean clades indicating acarine genes were more ancestral. The lack of orthologs or pseudogenes for remaining genes suggests these pathway elements had not evolved in ancestral arthropods. Vdspo transcript levels were highest in gut tissues, while Vddib transcript levels were highest in ovary-lyrate organs. In contrast, Vdshd transcript levels were lower overall but present in both gut and ovary-lyrate organs. Vddib and Vdshd transcripts were both elevated in eggs removed from gravid female mites. Vdspo transcript levels were significantly higher in reproductive mites than in phoretic mites while Vddib and Vdshd were not significantly different. A brood cell invasion assay was developed for acquiring synchronously staged mites. Mites within 4 hrs of entering a brood cell had transcript levels of all three that were not significantly different from mites on adult bees. These analyses suggest that varroa mites are capable of modifying 7-dehydro-cholesterol precursor and can complete other hydroxylations but whether the mite needs to produce ecdysteroid products is undetermined.