Biosynthesis of lipovitellin by the crustacean ovary

Diacylglycerol acyltransferase (DGAT) in Crangon crangon and Pandalus montagui (Decapoda, Caridea) - Implications for lipid storage capacities and life history traits

Lipids play essential roles in cell-structuring, cell-signaling, and as efficient metabolic energy stores. Lipid storage capacities determine life history traits of organisms and, thus, their ecological function. Among storage lipids, triacylglycerols (TAGs) are widespread in marine invertebrates. However, abilities to accumulate TAGs can vary even between closely related species, such as the caridean shrimps Crangon crangon and Pandalus montagui. The first species shows low TAG levels throughout the year in the main storage organ, the midgut gland, while the latter accumulates high TAG-levels, peaking in summer. TAGs synthesis is facilitated by the terminal step of the Kennedy-pathway, where the enzyme diacylglycerol-acyltransferase (DGAT) catalyzes the esterification of diacylglycerols with activated fatty acids. We investigated DGAT activity in the midgut gland using a fluorescent enzyme assay. Sequence information was extracted from whole transcriptome shotgun assembly data, that is publicly available on NCBI, and catalytic properties were deduced from molecular structure analysis. C. crangon showed significantly lower TAG synthesis rates than P. montagui, which explains the native TAG levels. Transcriptome data yielded several isoforms of DGAT enzymes in both species. C. crangon DGAT showed point mutations, which are capable of obstructing the catalytic capacity. The consequences are limited starvation resistance and, thus, presumably restricting C. crangon to a habitat with year-round sufficient food. In contrast, higher TAG synthesis rates presumably enable P. montagui to extend into northern subarctic habitats with limited food availability in winter. Moreover, the limited TAG synthesis and accumulation in the midgut gland may force C. crangon to direct energy into the ovaries, which results in multiple spawnings.

Two vitellogenins in the loliginid squid Uroteuthis edulis: Identification and specific expression in ovarian follicles

Vitellogenenesis is a physiological process common in oviparous animals. The molecular profile, modifications, and utilization of vitellogenin (VTG), a precursor of yolk protein, have been characterized in various taxa to understand oogenesis within different modes of reproduction. Hormonal regulation of VTGs has been investigated in invertebrates, such as insects and crustaceans; conversely, little is known for cephalopods. In this study, we isolated two VTG genes (ue-VTG1 and ue-VTG2) from the loliginid swordtip squid, Uroteuthis edulis, via a comprehensive survey of a transcriptome database and subsequent cDNA cloning. Structural analysis of the two ue-VTGs revealed their unique features, namely the absence of two domains usually found in VTGs from other organisms: the von Willebrand factor D domain (vWD) and the domain of unknown function 1943 (DUF1943). Levels of ue-VTG1 and ue-VTG2 transcripts in the ovary, specifically in follicular cells, increased during the late-vitellogenic phase, suggesting that yolk accumulation progresses via paracrine interactions involving follicular cells and oocytes. N-terminal amino acid sequencing of biochemically purified yolk protein revealed its origins from these two VTGs, indicating that both are functional precursors of yolk protein. These results provide information that is essential to understanding the physiological pathway of yolk synthesis, accumulation, and storage in loliginid squids.

The ovary structure and oogenesis in the basal crustaceans and hexapods. Possible phylogenetic significance

Recent large-scale phylogenetic analyses of exclusively molecular or combined molecular and morphological characters support a close relationship between Crustacea and Hexapoda. The growing consensus on this phylogenetic link is reflected in uniting both taxa under the name Pancrustacea or Tetraconata. Several recent molecular phylogenies have also indicated that the monophyletic hexapods should be nested within paraphyletic crustaceans. However, it is still contentious exactly which crustacean taxon is the sister group to Hexapoda. Among the favored candidates are Branchiopoda, Malacostraca, Remipedia and Xenocarida (Remipedia + Cephalocarida). In this context, we review morphological and ultrastructural features of the ovary architecture and oogenesis in these crustacean groups in search of traits potentially suitable for phylogenetic considerations. We have identified a suite of morphological characters which may prove useful in further comparative studies.

Effects of estradiol and progesterone on the reproduction of the freshwater crayfish Cherax albidus

In this study we have investigated the role of 17beta-estradiol and progesterone in the reproduction of the crayfish Cherax albidus by using vitellogenin (VTG) as a biomarker. Early-vitellogenic (EV), full-vitellogenic (FV), and non-vitellogenic (NV) females of Cherax albidus were treated with 17beta-estradiol, progesterone, or both for 4 weeks. Levels of VTG mRNA in the hepatopancreas were detected by RT-PCR. The PCR product was sequenced and showed 97% homology with Cherax quadricarinatus VTG. 17beta-estradiol was more effective than progesterone and 17beta-estradiol plus progesterone in increasing the vitellogenin transcript in the hepatopancreas of EV and FV females. On the contrary, progesterone was more effective than 17beta-estradiol and 17beta-estradiol plus progesterone in increasing the vitellogenin concentration in the hemolymph of EV and FV females. Hepatopancreas histology and fatty acid composition of females injected with hormones showed major modifications. No effects were registered in NV females. In conclusion, 17beta-estradiol and progesterone influence VTG synthesis, although our data indicate that they act through different pathways and are not effective until the proper hormonal environment is established, as demonstrated by their inefficacy in NV females.

Vitellogenin and Its Messenger RNA During Ovarian Development in the Female Blue Crab, Callinectes sapidus: Gene Expression, Synthesis, Transport, and Cleavage1

Blue crab vitellogenin (VTG) cDNA encodes a precursor that, together with two other Brachyuran VTGs, forms a distinctive cluster within a phylogenetic tree of crustacean VTGs. Using quantitative RT-PCR, we found that VTG was primarily expressed in the hepatopancreas of a vitellogenic female, with minor expression in the ovary. VTG expression in the hepatopancreas correlated with ovarian growth, with a remarkable 8000-fold increase in expression from stage 3 to 4 of ovarian development. In contrast, the VTG levels in the hepatopancreas and hemolymph decreased in stage 4. Western blot analysis and N-terminal sequencing revealed that vitellin is composed of three subunits of approximately 78.5 kDa, 119.42 kDa, and 87.9 kDa. The processing pathway for VTG includes an initial hepatopancreatic cleavage of the primary precursor into approximately 78.5-kDa and 207.3-kDa subunits, both of which are found in the hemolymph. A second cleavage in the ovary splits the approximately 207.3-kDa subunit into approximately 119.4-kDa and approximately 87.9-kDa subunits. The hemolymph VTG profiles of mated and unmated females during ovarian development indicate that early vitellogenesis and ovarian development do not require mating, which may be essential for later stages, as VTG decreased to the basal level at stage 4 in the unmated group but remained high in the mated females. Our results encompass comprehensive overall temporal and spatial aspects of vitellogenesis, which may reflect the reproductive physiology of the female blue crab, e.g., single mating and anecdysis in adulthood.

Effects of 17 beta-estradiol on the vitellogenin synthesis and oocyte development in the ovary of kuruma prawn (Marsupenaeus japonicus)

The effects of 17 beta-estradiol on induction of vitellogenin synthesis and oocyte development were investigated in previtellogenic ovary of immature kuruma prawn (Marsupenaeus japonicus) incubated with Medium 199. After three days incubation of previtellogenic ovary, Vg concentrations in media containing 3.6 nM, 36.7 nM, 367 nm and 3671 nM 17 beta-estradiol were significantly (p<0.01) greater than that of Ringer solution or the pure ethanol vehicle. Furthermore, a more advanced stage of oocyte development at oil globule stage (primary vitellogenic stage), which is surrounded by round and greatly expanded follicle cells, was observed in previtellogenic ovarian pieces incubated in media containing 3.6, 36.7, 367 and 3671 nM 17 beta-estradiol. The results of these studies show that 17 beta-estradiol induces Vg synthesis and appearance of primary vitellogenic oocyte in the ovary of immature prawns.

Relationship between vitellogenin and vitellin in a marine shrimp (Penaeus semisulcatus) and molecular characterization of vitellogenin complementary DNAs

The source of yolk proteins in crustacean ovaries has been the subject of controversy for several decades, and both extraovarian and intraovarian synthesized proteins have been implicated. To offer a new insight into the relationship of vitellogenin (VTG) and vitellin (VT), a comparison of extraovarian VTG and ovarian VT of the marine shrimp Penaeus semisulcatus was performed at the protein and cDNA levels. Two cDNAs (7920 and 2068 nucleotides [nt]) were sequenced for VTG from the ovary and one cDNA (7920 nt) was sequenced from the hepatopancreas. VTG cDNA from hepatopancreas was similar to VTG cDNA from ovary. Although a VTG gene was also found in the males, approximately 7.8-kilobase transcripts were only detected in the ovary and hepatopancreas of females. The mRNA expression pattern was related to the stage of ovarian development and to the molt cycle, as determined by real-time polymerase chain reaction assay. VTG and VT apoproteins were composed of two and three major subunits, respectively, as shown by SDS-PAGE. N-terminal sequences of these subunits revealed the presence of a cleavage site at a consensus motif for a subtilisin-like endoprotease in VTG and VT and an additional cleavage site in VT revealed by an unidentified endoprotease. These results indicate that penaeid shrimps constitute a unique model for vitellogenesis, showing intraovarian gene expression and synthesis of yolk protein.

Variation in lipid composition of Chinese mitten-handed crab, Eriocheir sinensis during ovarian maturation

This experiment was conducted to investigate the variation in lipid composition during the ovarian maturation of the crab Eriocheir sinensis. The Chinese mitten-handed crab broodstock was divided into six different maturation periods according to the size and color of ovary. Ovary, hepatopancreas, muscle, and hemolymph of broodstock in different maturation periods were analyzed for total lipid and fatty acids using gas chromatography, and lipid classes by thin-layer chromatography. The ovarian lipid concentration (expressed as percent wet ovarian weight) increased steadily from stage II (5.4%) to stage IV (19.1%), and decreased to the lowest levels after spawning (stage V, 6.6%). The hepatopancreatic lipid concentration (expressed as percent wet hepatopancreatic weight) increased with maturity of the ovaries, reached a maximum at stage III(2) (29.9%), and decreased during the subsequent period to spawning (16.7%). The muscular and hemolymph lipid concentration did not change markedly during the ovarian development. These results suggest the possible movement of hepatopancreatic lipids to the ovaries during the ovarian maturation. Both triacylglycerol and phosphatidylcholine were responsible for the increase in ovarian lipid concentration during sexual maturation. The fatty acids of total lipid, triacylglycerol, and phosphatidylcholine of the ovaries did not vary systematically during the ovarian maturation, but the ratio between n-3PUFA (polyunsaturated fatty acid) and n-6PUFA did change regularly with the ovarian lipid. These suggest that enough PUFA, especially n-3PUFA, should be supplied to the crab during ovarian maturation.

Development of an anti-vitellin ELISA for the assessment of reproduction in the ridgeback shrimp, Sicyonia ingentis

To investigate the reproductive regulation of the ridgeback shrimp, Sicyonia ingentis, vitellin (Vn) synthesis was studied. Using gel filtration chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Vn was found to have a molecular mass of 322 kDa and to be composed of three subunits of 182, 91 and 85 kDa. Purified Vn was used to prepare anti-Vn antiserum, which was used to develop an enzyme-linked immunosorbent assay (ELISA) with a dynamic range of 0.3-300 ng. The ELISA was used to measure hemolymph levels of yolk proteins. The mean hemolymph concentrations in fresh caught animals ranged from 256 (+/-36.6 S.E.M.) to 1073 (+/-87.6 S.E.M.) mg/ml in stage 2 and 4 animals, respectively. The ELISA was also used to determine the effects of steroid hormone injections in adult non-reproductive female shrimp. One milligram injections of progesterone, 17alpha-hydroxyprogesterone or 17beta-estradiol were administered for three consecutive days to individual females. There were no changes in hemolymph vitellogenin levels during the successive 7-day period following the first injection of any steroid.

Synthesis and organization of vitellogenin and vitellin molecules from the land crab Potamon potamios

We have previously reported that vitellogenin (Vg) of some female animals contained four polypeptides with molecular mass of 181, 115, 105 and 85 kDa, whereas Vg of most animals contained three polypeptides with molecular mass of 115, 105 and 85 kDa. In the present investigation, we examined whether the 181 kDa polypeptide is the precursor of 115 and 105 kDa Vg and vitellin (Vn) polypeptides. Labeling studies, using [35S]methionine on normal vitellogenic animals, showed that the radioactivity was distributed first among the 181 and 85 kDa polypeptides. SDS-PAGE analysis of purified hemolymph Vg from eyestalk ablated female animals revealed in most animals two polypeptides with an apparent molecular mass of 181 and 85 kDa. These results from in vivo experiments corroborated the view that the 115 and 105 kDa Vg and Vn polypeptides are derived from heaviest 181 kDa polypeptide. In addition it was demonstrated that hepatopancreas and ovary of Potamon potamios incubated in vitro with [35S]methionine synthesized five polypeptides with apparent molecular mass of 224, 181, 115, 105, and 85 kDa while the hepatopancreas appeared to secrete the 181, 115, 105 and 85 kDa polypeptides. The major 115, 105 and 85 kDa polypeptides were found to be components of egg Vn, while the 224 kDa polypeptide was found to be minor component of Vg and Vn from hepatopancreas and ovary extracts, respectively. We conclude that the Vn polypeptides produced by ovary are similar to those produced by hepatopancreas.

Hepatopancreas is the likely organ of vitellogenin synthesis in the freshwater prawn, Macrobrachium rosenbergii

The objective of the present study was to investigate the source of vitellogenin in the freshwater prawn, Macrobrachium rosenbergii. Ovarian development of M. rosenbergii was classified into five stages (stage I-V). Vitellin/vitellogenin was detected in the ovary and the hepatopancreas in different stages by native-PAGE and Western blotting. Two and three subunits of vitellin were observed in the ovary at the early- (I-II), mid- and late- (III-V) stages, respectively. The subunit of vitellogenin was not detected in the hepatopancreas at different stages of prawns. Hepatopancreas had positive immunocytological staining (against vitellin antibody) in different ovarian stages of prawn. Only vitellogenic oocyte but not previtellogenic oocytes and follicle cells had a positive immunocytological staining. Hepatopancreas could synthesize radiolabeled immunoreactive proteins after incubation with radiolabeled glycine on the basis of immunoprecipitation (against vitellin antiserum). Therefore, it is concluded that hepatopancreas is the most likely organ to synthesize vitellogenin in the freshwater prawn, M. rosenbergii.

The concentrations of vitellogenin (vitellin) and protein in hemolymph, ovary and hepatopancreas in different ovarian stages of the freshwater prawn, Macrobrachium rosenbergii

The objectives were to measure the concentrations of vitellogenin (vitellin) and protein in hemolymph, ovary, and hepatopancreas of the freshwater prawn, Macrobrachium rosenbergii, in different stages of ovarian development. The ovarian development of M. rosenbergii was classified into five developmental stages (Stages I-V). Vitellogenin concentrations increased in the hemolymph of prawns in the early stages of ovarian development (Stage I or II) and were maintained at high levels until Stage V. There was no close association between ovarian development and the concentrations of circulating vitellogenin. Concentrations of protein in hemolymph and hepatopancreas remained constant during various stages of ovarian development. The ovarian stages closely correlated with the gonadosomatic index, the concentrations of ovarian vitellin and protein, respectively. Vitellogenin levels in hepatopancreas remained very low in different stages of the prawn although the highest levels were observed in Stage IV. No close association between hemolymph vitellogenin and ovarian vitellin was observed. The increase of vitellogenin concentration in hemolymph occurred earlier than vitellin content in ovary.

Serum high-density lipoproteins in the crab, Cancer antennarius--III. Density-gradient profiles and lipid composition of subclasses

1. Prestaining the serum total lipoprotein (LP) fraction and density-gradient ultracentrifugation revealed up to five LPs, all in the high-density class (HDL; 1.187 greater than d greater than 1.080 g/ml). These are group-designated as HDL1, HDL2 and HDL3, lowest to highest buoyant density, respectively. The number and precise density of the LPs varied with individual crab and were not gender specific. 2. The percentage of total mass due to triacylglycerides was progressively higher from HDL1 and HDL3, whereas that of phospholipids, cholesterol and combined fat was progressively lower. The percentage mass of combined fat was higher in females than males. 3. As in hemolymph, the LP of eggs was entirely HDL; instances of each HDL subclass were seen, but HDL3 was predominant. Compared with serum HDL, egg HDL was strikingly low in triacyglyceride mass and relatively high in protein. 4. Hemolymph HDL titers of individual females varied independently with egg size through most of the year, but was positively correlated with the egg size in October to December when 2-3-fold increases in HDL titer occur in the female population.

Structural modulation of the surface and cytoplasm of oocytes during vitellogenesis in the lobster, Homarus americanus. An electron microscope-protein tracer study

The present investigation describes the ultrastructural changes which occur at the surface and in the cytoplasm of developing oocytes of the lobster, Homarus americanus, during vitellogenesis. The immature oocytes showed no surface specializations of the oolemma and no pinocytotic activity was observed. Horseradish peroxidase (HRP) tracer studies showed penetration of the tracer into the perivitelline space, but no uptake by the oocytes. The surfaces of oocytes examined during vitellogenesis, when yolk protein accumulation was maximal, exhibited numerous microvilli that projected into the perivitelline space, often appearing to be embedded in the follicular cell mass. In addition, the plasma membrane of vitellogenic oocytes contained many pinocytotic pits frequently situated at the bases of microvilli. The perivitelline space was engorged with electrondense material which appeared similar to that contained in pinocytotic structures of the oocytes. Vitellogenic oocytes incubated in HRP showed uptake of tracer reaction product by the coated pits and vesicles of the oolemma. Aggregation and subsequent fusion of these vesicles into large multivesicular bodies of ingested material were also observed in vitellogenic oocytes. Animals artificially induced to undergo vitellogenesis exhibited modulations of oocyte ultrastructure similar to those of normal vitellogenesis, notably, pinocytotic incorporation of extra-oocytic material and hypertrophy of oocyte surface microvilli. This study supports the hypothesis for a dual source of yolk protein in the American lobster.

[Lipovitellins in Palaemon adspersus (Rathke, 1837)]

The study of the ovarian cycle of Palaemon adspersus shows the occurrence of two lipo-glycoproteins accumulated into the ovocytes during vitellogenesis. The molecular weight of the main protein constituent in vitellus is evaluated to about 350 000 daltons. This protein is formed by two subunits having a similar molecular weight. The incorporation in vitro of [14C] leucine shows the participation of the ovary to lipovitellin synthesis.

Biosynthesis of crustacean lipovitellin. III. The incorporation of labeled amino acids into the purified lipovitellin of the crab Pachygrapsus crassipes

Electrophoretically pure subunits were obtained from the lipovitellin (LV) of the intertidal crab, Pachygrapsus crassipes. The molecular weights of these subunits were determined. In addition, it was demonstrated that the ovaries of Pachygrapsus, incubated in vitro, incorporated 3H-leucine into the two principal subunits of lipovitellin. At the end of a 30 hour incubation the specific activity of each of the principal subunits was approximately 30,000 dpm/mg protein. It is concluded that the ovaries of Pachygrapsus crassipes are capable of synthesizing the proteinaceous yolk found in the mature egg.

Biosynthesis of lipovitellin by the crustacean ovary. II. Characterization of and in vitro incorporation of amino acids into the purified subunits

The amino acid composition has been determined for two of the five subunits of the crayfish lipovitellin. In addition the molecular weight of each subunit has also been ascertained. Most importantly, it is demonstrated that following in vitro incubation radioactive amino acids are incorporated into each of three purified subunits. These data strongly support the suggestion that the vitellogenic ovary of the crayfish is capable of in situ synthesis of lipovitellin.