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Parasites flicking the NPY gene on the host's switchboard: why NPY?

MARIJKE DE JONG-BRINK¹, CHERITH N. REID^*, CORNELIS P. TENSEN and ANDRIES TER MAAT

Department of Developmental Neurobiology, Faculty of Biology, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands;
^* Queen's University, Belfast, School of Biology and Biochemistry, Medical Biology Centre, N. Ireland; and
Department of Dermatology, Amsterdam Leiden Institute for Immunology (ALIFI) Academisch Ziekenhuis Vrije Universiteit, Amsterdam, The Netherlands

¹Correspondence: Faculty of Biology, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands. E-mail: mdejong{at}bio.vu.nl

It was investigated whether up-regulation of the NPY gene by the schistosome Trichobilharzia ocellata in its snail host Lymnaea stagnalis redirects the host's energy flows. We cloned the cDNA encoding Lymnaea NPY (LyNPY), purified and sequenced the peptide, and used synthesized peptide for physiological and morphological studies. Increasing the LyNPY titer in nonparasitized snails (mimicking parasitosis) by 1) implantation of slow-release pellets and 2) injections suppressed reproductive activity and reduced growth in a dose- and time-dependent manner without affecting food intake. When the LyNPY titer was back to normal, reproduction and growth were resumed, coinciding with a transient increase of food intake serving to replenish glycogen stores. Observations on double-immunostained whole mount preparations of brains support these data. A close association was found between LyNPY-positive axons and axons both from ovulation hormone-producing neurons and molluscan insulin-like peptide-producing neurons involved in regulation of growth. As no synaptic(-like) contacts were observed, it is supposed that LyNPY acts nonsynaptically. No morphological interaction was found between LyNPY-positive axons and motoneurons innervating the feeding apparatus. Our data explain why it is an advantageous strategy for endoparasites to up-regulate the highly conserved NPY gene in their host.—de Jong-Brink, M., Reid, C. N., Tensen, C. P., Ter Maat, A. Parasites flicking the NPY gene on the host's switchboard: why NPY?

Key Words: host interaction • LyNPY • reproduction • food intake • glycogen storage