| Summary: | The salmon louse (Lepeophtheirus salmonis) is an obligate, hematophagous ectoparasite infecting salmonid fish such as the Atlantic salmon (Salmo salar). The parasite is at present the number one threat to the Norwegian salmon farming industry. There is a high density of hosts in salmon farms, and due to the high mutation rate and fecundity of the parasite, the salmon louse is currently ahead of the development of effective pest controls. Resistance has been reported against several available chemotherapeutants, and non-therapeutic interventions are as per now not sufficient to treat salmon louse infestations. Particularly adult female lice have blood as a major dietary component. This is a high-risk, high-reward strategy which the parasite is well-adapted to. Blood is highly nutritious and constantly renewed in the vertebrate host, but also contains toxic, yet necessary, compounds such as iron and heme (iron protoporphyrin IX). The salmon louse is likely a heme auxotroph, as many homologous enzymes of the conserved heme biosynthetic pathway are not found within its genome. As such, the salmon louse is innately dependent on its host for iron and heme supply. Blood-feeding and subsequent iron and heme trafficking are thus essential to study in the salmon louse, and could potentially reveal candidate proteins for pest management by e.g. vaccination or nutritional deprivation. Ferritin is a well-conserved multi-subunit iron storage and distribution protein that can be either cytosolic or secreted. In the present study, several ferritin-encoding genes were identified in the salmon louse genome (LsFer1, 2, 3 and 4). Secreted heavy chain homolog (LsFer1) and secreted light chain homolog (LsFer2) transcripts were found to be expressed in the salmon louse intestine, where the precursor protein is probably loaded with iron intracellularly before it is secreted to the hemolymph. RNA interference-mediated knockdown of these two transcripts resulted in severe phenotype alterations for the adult female salmon louse. In both ...
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