title: Regulation of Life Cycle Checkpoints and Developmental Activation of Infective Larvae in Strongyloides stercoralis by Dafachronic Acid.
abstract: The complex life cycle of the parasitic nematode Strongyloides stercoralis leads to either developmental arrest of infectious third-stage larvae (iL3) or growth to reproductive adults. In the free-living nematode Caenorhabditis elegans, analogous determination between dauer arrest and reproductive growth is governed by dafachronic acids (DAs), a class of steroid hormones that are ligands for the nuclear hormone receptor DAF-12. Biosynthesis of DAs requires the cytochrome P450 (CYP) DAF-9. We tested the hypothesis that DAs also regulate S. stercoralis development via DAF-12 signaling at three points. First, we found that 1 μM Δ7-DA stimulated 100% of post-parasitic first-stage larvae (L1s) to develop to free-living adults instead of iL3 at 37°C, while 69.4±12.0% (SD) of post-parasitic L1s developed to iL3 in controls. Second, we found that 1 μM Δ7-DA prevented post-free-living iL3 arrest and stimulated 85.2±16.9% of larvae to develop to free-living rhabditiform third- and fourth-stages, compared to 0% in the control. This induction required 24-48 hours of Δ7-DA exposure. Third, we found that the CYP inhibitor ketoconazole prevented iL3 feeding in host-like conditions, with only 5.6±2.9% of iL3 feeding in 40 μM ketoconazole, compared to 98.8±0.4% in the positive control. This inhibition was partially rescued by Δ7-DA, with 71.2±16.4% of iL3 feeding in 400 nM Δ7-DA and 35 μM ketoconazole, providing the first evidence of endogenous DA production in S. stercoralis. We then characterized the 26 CYP-encoding genes in S. stercoralis and identified a homolog with sequence and developmental regulation similar to DAF-9. Overall, these data demonstrate that DAF-12 signaling regulates S. stercoralis development, showing that in the post-parasitic generation, loss of DAF-12 signaling favors iL3 arrest, while increased DAF-12 signaling favors reproductive development; that in the post-free-living generation, absence of DAF-12 signaling is crucial for iL3 arrest; and that endogenous DA production regulates iL3 activation.
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Biology, Hollins University, Roanoke, Virginia, United States of America.
authors.forename: Mennatallah M Y
authors.initials: MM
authors.lastname: Albarqi
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.|Department of Biology, Hollins University, Roanoke, Virginia, United States of America.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Stoltzfus
authors.affiliation: Department of Biology, Hollins University, Roanoke, Virginia, United States of America.
authors.forename: Adeiye A
authors.initials: AA
authors.lastname: Pilgrim
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Nolan
authors.affiliation: Department of Pharmacology, University of Texas Southwest Medical Center, Dallas, Texas, United States of America.
authors.forename: Zhu
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Pharmacology, University of Texas Southwest Medical Center, Dallas, Texas, United States of America.|Department of Molecular Biology, University of Texas Southwest Medical Center, Dallas, Texas, United States of America.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Kliewer
authors.affiliation: Department of Pharmacology, University of Texas Southwest Medical Center, Dallas, Texas, United States of America.|Howard Hughes Medical Institute, University of Texas Southwest Medical Center, Dallas, Texas, United States of America.
authors.forename: David J
authors.initials: DJ
authors.lastname: Mangelsdorf
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: James B
authors.initials: JB
authors.lastname: Lok
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002782:Cholestenes / Q000378:metabolism*; D004195:Disease Models, Animal; D004285:Dogs; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D017238:Genes, Helminth; D005849:Gerbillinae; D015801:Helminth Proteins / Q000235:genetics / Q000378:metabolism*; D007814:Larva / Q000378:metabolism; D008018:Life Cycle Stages; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D017171:Strongyloides stercoralis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D013322:Strongyloidiasis / Q000378:metabolism
chemical_list: D002782:Cholestenes; D015801:Helminth Proteins; D018160:Receptors, Cytoplasmic and Nuclear; C533800:dafachronic acid