title: Melanisation of Teladorsagia circumcincta larvae exposed to sunlight: a role for GTP-cyclohydrolase in nematode survival.
abstract: Trichostrongylid nematode parasites of livestock inhabit two very different niches during their life-cycle; within the host and free-living in the environment. UV radiation plays a significant role in the survival of free-living, pre-parasitic nematode larvae, with different species exhibiting differing levels of sensitivity. In many eukaryotes, melanisation is a key protective mechanism against UV damage, however there is little information about this process in parasitic nematodes. Caenorhabditis elegans cat-4 mutants, which are deficient in the enzyme guanosine triphosphate-cyclohydrolase I (GTP-CH), have both depleted levels of melanin in their cuticles and an increased sensitivity to anthelmintic drugs. Some parasitic nematodes have very high levels of GTP-CH transcript in their pre-parasitic stages, suggesting an important role for this biopterin synthetic enzyme. Here, we show that the Tci-cat-4 gene, which encodes GTP-CH in Teladorsagia circumcincta, has a role in melanisation and is also capable of rescuing C. elegans cat-4 mutants. In addition, following exposure of T. circumcincta L3s to sunlight, there is a 32% increase in GTP-CH enzyme activity (P=0.019), and a 21% increase in levels of melanin (P=0.031) compared with unexposed larvae. These data suggest that one explanation for the high level of GTP-CH present in pre-parasitic stages of trichostrongylid nematodes is to facilitate melanisation in response to UV exposure.
authors.affiliation: Moredun Research Institute, Pentlands Science Park, Bush Loan, Edinburgh, UK.
authors.forename: Rachael H
authors.initials: RH
authors.lastname: Baker
authors.forename: Collette
authors.initials: C
authors.lastname: Britton
authors.forename: Brett
authors.initials: B
authors.lastname: Roberts
authors.forename: Curtis M
authors.initials: CM
authors.lastname: Loer
authors.forename: Jacqueline B
authors.initials: JB
authors.lastname: Matthews
authors.forename: Alasdair J
authors.initials: AJ
authors.lastname: Nisbet
mesh_terms: D000818:Animals; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D006136:GTP Cyclohydrolase / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000528:radiation effects*; D007814:Larva / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects; D008543:Melanins / Q000378:metabolism*; D009154:Mutation; D013472:Sunlight; D014251:Trichostrongyloidea / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D008543:Melanins; D002374:Catalase; D006136:GTP Cyclohydrolase