Lipoprotein mediated lipid uptake in oocytes of polychaetes (Annelida)

Abstract

The uptake of the 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-labeled sex-unspecific Nereis lipoprotein was investigated in oocytes of the nereidid polychaetes Nereis virens and Platynereis dumerilii. The fluorescence label was first observed in endocytic vesicles (<1 microm diameter), which later fused to larger vesicles (2-3 microm); these were finally incorporated into existing unlabeled yolk granules (5-6 microm). In Platynereis oocytes, the fusion of endocytic vesicles was delayed in oocytes at their final stage of development compared with those at an early stage of development. Lipoprotein double-labeled with fluorescein isothiocyanate (FITC) and DiI revealed that both the protein and the lipid moiety remained co-localized during incorporation into the yolk granules of the oocyte. No labeling of the cytoplasmic lipid droplets was observed. In N. virens, unlabeled Nereis lipoprotein was effective as a competitive inhibitor of DiI-labeled Nereis lipoprotein. Ligand blot experiments demonstrated the presence of a lipoprotein receptor with an apparent molecular mass of 120 kDa, which is different from that of the known yolk protein receptor. This indicates the presence, in the polychaete oocyte, of two distinct receptors mediating yolk protein and lipoprotein uptake, respectively. Thus, the sex-unspecific lipoprotein contributes to the lipid supply of the growing oocyte in addition to the known uptake of the yolk-protein-associated lipids. The absence of label in the cytoplasmic lipid droplets, even after prolonged incubation with labeled lipoprotein, suggests that these lipids arise either by the breakdown and resynthesis of lipoprotein-derived lipids and/or by de novo synthesis within the oocyte.

Lipid accumulation and metabolism in polychaete spermatogenesis: Role of the large discoidal lipoprotein

“…The main lipids transported by this lipoprotein were found to be phospholipids, especially phosphatidylcholine (Schenk et al, 2006). A recent study (Schenk and Hoeger, 2009) has shown that polychaete oocytes possess—in addition to the known vitellogenin receptor (Hafer et al, 1992)—a second lipoprotein receptor for the sex unspecific lipoprotein, a situation also reported for insect oocytes (Cheon et al, 2001). This receptor has been characterized as a membrane protein with an apparent molecular mass of ∼120 kDa (Schenk and Hoeger, 2009).…”

“…A recent study (Schenk and Hoeger, 2009) has shown that polychaete oocytes possess—in addition to the known vitellogenin receptor (Hafer et al, 1992)—a second lipoprotein receptor for the sex unspecific lipoprotein, a situation also reported for insect oocytes (Cheon et al, 2001). This receptor has been characterized as a membrane protein with an apparent molecular mass of ∼120 kDa (Schenk and Hoeger, 2009). This finding has raised the question as to the importance of lipoprotein‐mediated lipid supply in the growth and development of male germ cells which is presently unknown in invertebrates including polychaetes.…”

“…The oocytes of most oviparous animals store large amounts of a yolk protein, vitellin, which is taken up as a precursor—vitellogenin—and enters the oocyte by receptor‐mediated endocytosis (Fischer and Dhainaut, 1985; Kunkel and Nordin, 1985; Röhrkasten and Ferenz, 1985; Steyrer et al, 1990; Hafer et al, 1992). However, the sex‐independent lipoproteins have also been shown to contribute to the egg yolk and are considered to be the main source of exogenous lipids at least in insect and polychaete eggs (Kawooya and Law, 1988; Kawooya et al, 1988; Hayashi et al, 1989; Kulakosky and Telfer, 1990; Telfer et al, 1991; Ziegler and Van Antwerpen, 2006; Schenk and Hoeger, 2009). However, in the light of the large male gamete biomass generated by nereidid polychaetes, similar nutrient supply of the male gametes seems likewise required.…”

The Pandinus imperator haemolymph lipoprotein, an unusual phosphatidylserine carrying lipoprotein

“…The flow was 1 ml/ min and the eluate was monitored at 280 nm. The eluate was collected in 10 s-fractions (170 ml) and the proteins precipitated after making up the sample to 50% in acetone (ice-cold) and incubation at 0 C for 20 min as described (Schenk and Hoeger, 2009). The supernatant was discarded and the pellets washed in 500 ml 50% ice-cold acetone as described above.…”

“…The vertebrate, especially the mammalian lipoproteins have received most attention due to their role in cardiovascular diseases (Hevonoja et al, 2000;Khovidhunkit et al, 2004). Among the invertebrates, the lipoproteins of the insects, termed lipophorins, have received most attention (Soulages and Wells, 1994; Van der Horst et al, 2002;Rodenburg and van der Horst, 2005), but also on other arthropod and invertebrate lipoproteins, such as crustaceans (Puppione et al, 1986;Hall et al, 1995;YepizPlascencia et al, 1995;Stieb et al, 2008), chelicerates Bowers, 1987, 1989;Cunningham et al, 1994Cunningham et al, , 2000Rehn and Lee, 1994), molluscs (Pollero et al, 1992;Heras and Pollero, 2002) and recently polychaetes (Schenk et al, 2006;Schenk and Hoeger, 2009) studies are available.…”