Review: Hemolymph lipoproteins of crustaceans and chelicerates

The hemolymph of crustaceans (decapods, isopods, amphipods, copepods, branchiopods, cirripedes) and chelicerates (ticks, mites, spiders, scorpions, horseshoe crabs) contain female-specific and sex-independent lipoproteins in the high-density lipoprotein (HDL, density: 1.063-1.21 g/ml) and very high-density lipoprotein (VHDL, density>1.21 g/ml) classes. The first part of this review includes the history of the important developments in the study of hemolymph lipoproteins, synthesis by different tissues, important functions and synthesis/utilization by developing embryos. The sex-independent and female-specific lipoprotein have very different functions. The sex-independent lipoprotein functions include clotting, pattern recognition and transport of lipids, hormones, vitamins, heme and pheromones. Female-specific lipoproteins primarily serve as a source of energy and nutrition for developing embryos. Female-specific lipoproteins are assembled in the ovary, hepatopancreas, fat body or mid-gut and after the peptide is cleaved into subunits the lipoproteins are secreted into the hemolymph with subsequent uptake into the developing oocytes by receptor-mediated endocytosis. The second part of the review covers the past two decades of work which focused on the genes that encode the lipoproteins and determination of their amino acid sequences. Most crustacean and chelicerate lipoproteins are in the apolipoprotein B-like (apoB-like) or the vitellogenin-like (Vg-like) families of the superfamily of large lipid transfer proteins involved in the assembly, secretion and metabolism of lipoproteins. Decapod female-specific lipoproteins, vitellogenin/apocrustacein (Vg/apoCr), are in the apoB-like family while the female-specific lipoproteins in other crustacean groups and chelicerates are in the Vg-like family. Each family is characterized by certain major structural domains which are responsible for lipid binding, carbohydrate attachment and receptor binding.