Immunolocalization of a Gαq protein to the chemosensory organs of Dipolydora quadrilobata (Polychaeta: Spionidae)

Abstract

Chemoreception in marine invertebrates mediates a variety of ecologically important behaviors including defense, reproduction, larval settlement and recruitment, and feeding. The sensory pathways that regulate deposit-feeding activity by polychaetes living in sedimentary habitats are of particular interest because such feeding has profound effects on the physical and chemical properties of the habitat. Nevertheless, little is known concerning the molecular mechanisms of chemical signal transduction associated with deposit feeding and other behaviors in polychaetes. Chemosensory-based feeding behaviors are typically regulated by G-protein-coupled signal transduction pathways. However, the presence and role of such pathways have not been demonstrated in marine polychaetes. Methodologies involving degenerate primer-based reverse transcription with the polymerase chain reaction and rapid amplification of cDNA ends were used to identify and characterize a Galphaq subunit expressed in the feeding palps of the spionid polychaete Dipolydora quadrilobata. The D. quadrilobata Galphaq protein had high sequence similarity with previously reported Galphaq subunits from both invertebrate and vertebrate taxa. Immunhistochemistry and immunocytochemistry were used with confocal laser scanning microscopy and transmission electron microscopy to visualize the distribution of a Galphaq antibody in whole worms and in cilia of the feeding palps. Galphaq immunoreactivity was concentrated in the nuchal organs, food-groove cilia, and lateral/abfrontal cilia of the feeding palps. Because these structures are known to be involved in chemoreception, we propose that Galphaq isolated from D. quadrilobata is a key component of chemosensory signal transduction pathways in this species.

Proteomic analysis during larval development and metamorphosis of the spionid polychaete Pseudopolydora vexillosa

“…For instance, adenylate cyclase modulates larval settlement ability during the swimming cyprid stage in barnacles [33]. A putative chemosensory Gαq gene encoding a G protein has been recently localized on the palp sensory cells of another spionid Dipolydora quadrilobata [34]. However, in this study, we were unable to identify any sensory or receptor proteins using MS.…”

Whole-head recording of chemosensory activity in the marine annelidPlatynereis dumerilii

“…Our attempts to test this further were so far inconclusive. Palps, which are located close to the mouth and were more strongly activated by the amino acid and the sugar (Figure 3A,B), may be specialised in the detection of directly food-related chemical cues, as is hypothesised in spionid annelids [22,37,58]. These highly musculated appendages, which adult Platynereis use for prehension of food items (personal observations), could also serve in the contact chemoreception of hydrophobic compounds, whose importance is underestimated in marine animals [59,60].…”

<strong>Ecology and biology of chemoreception in polychaetes</strong>

“…The same chemical cue that elicited feeding behavior in Dipolydora quadrilobata (Riordan & Lindsay 2002) also activated sensory cells of the palps in activity-dependent celllabeling studies (Lindsay et al 2004). Although the signal transduction pathway has not been fully described, G-proteins may be involved (Tsie et al 2008).…”

“…Gα subunits are characterized into several classes, and among these, Gαq subunits have been demonstrated in the chemoreception signal transduction pathways of other invertebrates (Fadool et al 1995;Talluri et al 1995;McClintock et al 1997;Krieger & Breer 1999). Recently, Tsie et al (2008) isolated nearly full length sequence for a Gαq protein from the feeding palps of Dipolydora quadrilobata and observed Gαq immunoreactivity in nuchal organs, palp tissue, food groove cilia, lateral, and abfrontal palp cilia (Fig 2). Gαq immunoreactivity tended to be greater at the tips of feeding palps, suggesting the possibility of increased chemosensitivity in this region, which is also the region of the palps involved in "porewater sniffing" (Ferner & Jumars 1999).…”