Embryonic and post-embryonic development of the spider Polybetes pythagoricus (Sparassidae): A biochemical point of view.

Analysis of energy expense during development has achieved special interest through time on account of the crucial role of the consumption of resources required for offspring survival. Spider eggs have a fixed composition as well as some initial energy that is supplied by mothers. These resources are necessary to support the metabolic expense not only through the embryonic period but also during the post-embryonic period, as well as for post emerging activities before spiderlings become self-sustaining. Depletion of these resources would be critical for spiders since it could give rise to prey competition as well as filial cannibalism. Even though spiders represent a megadiverse order, information regarding the metabolic requirements during spiders development is very scarce. In this study, we analyse the changes in protein, lipid and carbohydrate content as well as the variation in lipovitellin reserves and hemocyanin content during Polybetes pythagoricus development. Our results show that lipovitellins and phospholipids represent the major energy source throughout embryonic and post-embryonic development. Lipovitellin apolipoproteins are gradually consumed but are later depleted after dispersion. Phosphatidylethanolamine is mainly consumed during the post-embryonic period, while triacylglycerides are consumed after juveniles' dispersion. Finally, hemocyanin concentration starts to increase in postembryonic stages.

Arachnid Hemocyanins.

Hemocyanin (Hc), a copper-containing extracellular multimeric protein, is the major protein component of hemolymph in different arachnid groups. Hc possesses 7 or 8 very well-characterized types of monomers with molecular weights ranging from 70 to 85 kDa, organized in hexamers or multiple of hexamers. The present chapter compiles the existing data with relation to the function of this protein in the arachnids. Hc has as main function the reversible transport of O2, but it shows many secondary though not less important functions. With reference to this, it has been described that Hc can transport hydrophobic molecules (lipid-derived hormones and lipids) to the different organs, having a key role in the lipid transport system. In arachnids, like in other arthropods and invertebrates, Hc has phenoloxidase function which is related to different metabolic processes such as melanin formation and defense against pathogens. In addition, Hc has additional defensive functions since it can serve as precursor for the production of antimicrobial peptides. In short, the evolution of this protein has led to the development of multiple functions essential for organisms possessing this protein.

Analysis of lipid and fatty acid composition of three species of scorpions with relation to different organs.

Within arthropods most of the information related to the type of mobilization and storage of lipids is found in insects and crustaceans. Literature is scarce with relation to scorpions. This order is a remarkably important model of the biochemistry, since it is characterized as an animal with very primitive traits which have varied minimally through time. In the present study we characterize and compare lipids and fatty acids present in three species of scorpion: Timogenes elegans, Timogenes dorbignyi, and Brachistosternus ferrugineus, focusing the study on the main organs/tissues involved in the dynamics of lipids. As found in the fat body of insects, hepatopancreas of crustaceans and midgut diverticula of spiders, the hepatopancreas of the three species studied here turned out to be the organ of lipid storage (great quantity of triacylglycerides). With relation to the hemolymph and muscles, a great quantity of phospholipids was observed, which is possibly involved in membrane formation. It is important to highlight that unlike what happens in insects, in scorpions the main circulating energetic lipid is the triacylglyceride. This lipid is found in greater proportion in the hepatopancreas of females, surely for reproduction. The fatty acid of the different organs/tissues analyzed remained constant in the three species studied with certain characteristic patterns, thus observing saturated and unsaturated most abundant fatty acids of C16 and C18. Finally, it could be observed that in T. elegans, T. dorbignyi and B. ferrugineus scorpions, there is a lack of 20:4 that generates a special condition within fatty acids of arthropods.

Characterization of phenoloxidase activity from spider Polybetes pythagoricus hemocyanin.

Hemocyanin of the spider Polybetes pythagoricus, in addition to its typical role as an oxygen transporter, also exhibits a phenoloxidase activity induced by micellar concentrations of SDS. In the present work, we found the kinetic parameters Km and Vmax of Polybetes pythagoricus hemocyanin (PpHc) PO activity to be 0.407 mM and 0.081 µmolmin(-1) mg protein(-1) , respectively. Dopamine was used as the substrate with SDS at a final concentration of 10 mM and a 30-min incubation at 25°C. Conformational changes in Hc associated with the SDS treatment were analyzed using far-UV circular dichroism, intrinsic fluorescence and absorption spectroscopy. The secondary and tertiary structural changes of PpHc induced by SDS led to increases in α-helical content and tryptophan fluorescence intensity. A reduction in the absorption spectrum at 340 nm in the presence of SDS was also observed. These results suggest that the SDS-induced PO activity of PpHc can be ascribed to conformational changes in the local environment of the typer-3 copper active site.

Energy sources from the eggs of the wolf spider Schizocosa malitiosa: isolation and characterization of lipovitellins.

In oviparous species, proteins and lipids found in the vitellus form the lipoproteins called lipovitellins that are the major source of energy for the development, growth, and survival of the embryo. The energy resources provided by the lipovitellins have not yet been investigated in the Order Araneae. Using the wolf spider Schizocosa malitiosa (Lycosidae) as an experimental model, we identified and characterized the lipovitellins present in the cytosol, focusing on the energetic contribution of those lipoprotein particles in the vitellus. Two lipovitellins (LV) named SmLV1 and SmLV2 were isolated. SmLV1 is a high-density lipoprotein with 67% lipid and 3.6% carbohydrate, and SmLV2 is a very high-density lipoprotein with 9% lipid and 8.8% carbohydrate. Through electrophoresis in native conditions we observed that SmLV1 has a molecular mass of 559 kDa composed of three apolipoproteins of 116, 87, and 42 kDa, respectively. SmLV2 comprised several proteins composed of different proportions of the same subunits (135, 126, 109, and 70 kDa). The principal lipids of these lipovitellins are sphingomyelin + lysophosphatidylcholine, esterified sterols, and phosphatidylcholine. Lipovitellin-free cytosol contains abundant phospatidylcholine and triacylglyceride related to the yolk nuclei (the vitellus organizing center). The principal fatty acids of SmLV1 and SmLV2 are 18:2 n-6, 18:1 n-9, and 16:0. Spectrophotometry detected no pigments in either the lipovitellins or the cytosol. The egg caloric content was 92 cal/g, at proportions of 59.8% protein, 20.1% carbohydrate, and 19.9% lipid. SmLV1 and SmLV2 provided 19.5% and 17.1% of the calories, respectively. Both lipovitellins contribute mainly with proteins (15.8-18%), with the input of carbohydrates and lipids being lower than 1.3%.

In vitro lipid transfer between lipoproteins and midgut-diverticula in the spider Polybetes pythagoricus.

It has been already reported that most hemolymphatic lipids in the spider Polybetes pythagoricus are transported by HDL1 and VHDL lipoproteins. We studied in vitro the lipid transfer among midgut-diverticula (M-diverticula), and either hemolymph or purified lipoproteins as well as between hemolymphatic lipoproteins. M-diverticula and hemolymph were labeled by in vivo (14)C-palmitic acid injection. In vitro incubations were performed between M-diverticula and either hemolymph or isolated lipoproteins. Hemolymph lipid uptake was associated to HDL1 (67%) and VHDL (32%). Release from hemolymph towards M-diverticula showed the opposite trend, VHDL 75% and HDL1 45%. Isolated lipoproteins showed a similar behavior to that observed with whole hemolymph. Lipid transfer between lipoproteins showed that HDL1 transfer more (14)C-lipids to VHDL than vice versa. Only 38% FFA and 18% TAG were transferred from M-diverticula to lipoproteins, while on the contrary 75% and 73% of these lipids, respectively, were taken up from hemolymph. A similar trend was observed regarding lipoprotein phospholipids. This study supports the hypothesis that HDL1 and hemocyanin-containing VHDL are involved in the uptake and release of FFA, phospholipids and triacylglycerols in the spider P. pythagoricus. The data support a directional flow of lipids from HDL1 and VHDL suggesting a mode of lipid transport between lipoproteins and M-diverticula.

Isolation and characterization of two vitellins from eggs of the spider Polybetes pythagoricus (Araneae: Sparassidae).

Despite vitellins being essential yolk proteins, their presence in spiders remains almost unknown. Two vitellins from the spider Polybetes pythagoricus, named LV1 and LV2, were isolated and their size, shape, lipids, fatty acids, proteins and carbohydrates moieties were determined. LV1 has a density similar to that of HDL with 49.3% lipids, and LV2 has a density similar to that of VHDL with 9.7% lipids. The major neutral lipid present in both vitellins was found to be esterified cholesterol, 16% for LV1 and 24% for LV2. The major fatty acid was 18:1n-9 in LV1 and LV2. Results from native PAGE showed a lipoprotein of 550 kDa for LV1 and three lipoproteins of 571, 400 and 257 kDa for LV2. SDS-PAGE evidenced two major apolipoproteins of 64 and 25 kDa in LV1. The three lipoproteins of LV2 were electroeluted and analyzed by SDS-PAGE, showing different proportions of the same apolipoproteins (181, 67 and 60 kDa). LVs were analyzed by spectrophotometry, immunochemical and electron microscopy, showing that the respiratory pigment hemocyanin was not present as apolipoprotein. This fact evidenced that these LVs were not related to hemolymphatic lipoproteins.

First insight into the lipid uptake, storage and mobilization in arachnids: role of midgut diverticula and lipoproteins.

The importance of midgut diverticula (M-diverticula) and hemolymph lipoproteins in the lipid homeostasis of Polybetes phythagoricus was studied. Radioactivity distribution in tissues and hemolymph was analyzed either after feeding or injecting [1-(14)C]-palmitate. In both experiments, radioactivity was mostly taken up by M-diverticula that synthesized diacylglycerols, triacylglycerols and phospholipids in a ratio close to its lipid class composition. M-diverticula total lipids represent 8.08% (by wt), mostly triacylglycerols (74%) and phosphatidylcholine (13%). Major fatty acids were (in decreasing order of abundance) 18:1n-9, 18:2n-6, 16:0, 16:1n-7, 18:0, 18:3n-3. Spider hemocyanin-containing lipoprotein (VHDL) transported 83% of the circulating label at short incubation times. After 24h, VHDL and HDL-1 (comparable to insect lipophorin) were found to be involved in the lipid uptake and release from M-diverticula, HDL-2 playing a negligible role. Lipoprotein's labelled lipid changed with time, phospholipids becoming the main circulating lipid after 24h. These results indicate that arachnid M-diverticula play a central role in lipid synthesis, storage and movilization, analogous to insect fat body or crustacean midgut gland. The relative contribution of HDL-1 and VHDL to lipid dynamics indicated that, unlike insects, spider VHDL significantly contributes to the lipid exchange between M-diverticula and hemolymph.

Fenitrothion-induced structural and functional perturbations in the yolk lipoproteins of the shrimp Macrobrachium borellii.

Two lipovitellin (LV) forms containing the same apoproteins but differing in their lipid composition were isolated from Macrobrachium borelii eggs at early (LVe) and late (LVI) embryogenic stages and characterized. These two forms of LV, as well as liposomes prepared with lipids extracted from them, were used as simpler models to study the effect of the pesticide fenitrothion (FS) on their structures and functions. Rotational diffusion and fluorescence lifetime of two fluorescent probes [1,6-diphenyl-1,3,5-hexatriene (DPH) and 3-(p-(6-phenyl)-1,3,5-hexatrienal)phenylpropionic acid (DPH-PA)] were used to obtain information on structural changes induced by FS in the inner and outer regions of the LV, respectively. Comparison of the rotational behavior of these probes in native LV and liposomes (LP) from extracted LV lipids suggests that apoprotein-lipid interactions result in an ordered neutral lipid core. FS increased the lipid phase polarity of both LV and LP forms. The rotation of these probes in LP was not affected, suggesting a dependence of FS action on lipid-protein interactions. DPH-PA steady-state anisotropy showed that, unlike the LVe form, the LVI form was sensitive to extremely low FS concentrations. The ability of both LV to transfer palmitic acid to albumin was increased, but in a dissimilar manner, by the presence of FS. Such differences in the sensitivity of the LV at different steps of embryogenesis to FS influence the toxic action of this insecticide.