Exocrine glands of Lepeophtheirus salmonis (Copepoda: Caligidae): Distribution, developmental appearance, and site of secretion

Abstract

Exocrine glands of blood-feeding parasitic copepods are believed to be important in host immune response modulation and inhibition of host blood coagulation, but also in the production of substances for integument lubrication and antifouling. In this study, we aimed to characterize the distribution of different types of salmon louse (Lepeophtheirus salmonis) exocrine glands and their site of secretion. The developmental appearance of each gland type was mapped and genes specifically expressed by glands were identified. Three types of tegumental (teg 1-3) glands and one labial gland type were found. The first glands to appear during development were teg 1 and teg 2 glands. They have ducts extending both dorsally and ventrally suggested to be important in lubricating the integument. Teg 1 glands were found to express two astacin metallopeptidases and a gene with fibronectin II domains, while teg 2 glands express a heme peroxidase. The labial glands were first identified in planktonic copepodids, with reservoirs that allows for storage of glandular products. The last gland type to appear during development was named teg 3 and was not seen before the preadult I stage when the lice become more virulent. Teg 3 glands have ducts ending ventrally at the host-parasite contact area, and may secrete substances important for the salmon lice virulence. Salmon lice teg 3 and labial glands are thus likely to be especially important in the host-parasite interaction. Proteins secreted from the salmon louse glands to its salmonid host skin or blood represents a potential interface where the host immune system can meet and elicit effective responses to sea lice antigens. The present study thus represents a fundamental basis for further functional studies and identification of possible vaccine candidates. J. Morphol. 277:1616-1630, 2016. © 2016 Wiley Periodicals, Inc.

Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

“…It has been hypothesised that astacins have digestive and anticoagulation roles, also inactivating prey/host vasoactive peptides [76,81] to maintain hostparasite relationships [82][83][84][85]. However, sea lice astacin is expressed in tegument glands associated with probable roles in lubrication of integument as opposed to feeding [86]. Therefore, the presence of these proteases in Argulus SEPs may be associated with functional roles in haematophagy, but as the feeding activity is similar to L. salmonis, they may also be involved in preventing drag when infecting moving fish.…”

“…It has been hypothesised that to enable long term host contact and feeding, Argulus spp., like other ectoparasitic arthropods such as ticks and salmon lice (Lepeophtheirus salmonis (Krøyer, 1837)), must secrete a range of pharmacologically active components. These components have been suggested to be produced in the parasite's spinal, proboscis and labial glands and to be delivered through the preoral spine and the mouth tube to facilitate blood-feeding [7,8]. Argulus spp.…”

Histological and histochemical characterisation of glands associated with the feeding appendages of Argulus foliaceus (Linnaeus, 1758)

“…salmonis have highlighted the importance of secretions produced by a group of tegumental glands and labial glands to parasite virulence [22]. The similarity of the mode of parasitism expressed by Argulus spp.…”

“…These glands, which comprise five large gland cells on each side of the body, were observed to be closely associated with the labium, and thus here it is suggested that these glands be termed the "labial glands". Recently, Øvergård et al [22] found that sea lice, L. salmonis, have two labial glands, each made of two large secretory units connected to storage reservoirs accumulating the glandular products before secretion…”

“…through the ducts. The L. salmonis labial gland ducts extend ventrally into the mouth tube with openings in the oral cavity on the ventral surface of the labium and empty near the zone of activity of the mandibular teeth [22]. Caligid copepods such as Caligodes laciniatus (Krøyer, 1863) also have an intrabuccal pre-oral spine on the inner surface of the labrum [28] which may have a similar function to the tubular labial spine of Argulus spp.…”