A transcriptomic examination of encased rotifer embryos reveals the developmental trajectory leading to long-term dormancy; are they "animal seeds"?

BACKGROUND

Organisms from many distinct evolutionary lineages acquired the capacity to enter a dormant state in response to environmental conditions incompatible with maintaining normal life activities. Most studied organisms exhibit seasonal or annual episodes of dormancy, but numerous less studied organisms enter long-term dormancy, lasting decades or even centuries. Intriguingly, many planktonic animals produce encased embryos known as resting eggs or cysts that, like plant seeds, may remain dormant for decades. Herein, we studied a rotifer Brachionus plicatilis as a model planktonic species that forms encased dormant embryos via sexual reproduction and non-dormant embryos via asexual reproduction and raised the following questions: Which genes are expressed at which time points during embryogenesis? How do temporal transcript abundance profiles differ between the two types of embryos? When does the cell cycle arrest? How do dormant embryos manage energy?

RESULTS

As the molecular developmental kinetics of encased embryos remain unknown, we employed single embryo RNA sequencing (CEL-seq) of samples collected during dormant and non-dormant embryogenesis. We identified comprehensive and temporal transcript abundance patterns of genes and their associated enriched functional pathways. Striking differences were uncovered between dormant and non-dormant embryos. In early development, the cell cycle-associated pathways were enriched in both embryo types but terminated with fewer nuclei in dormant embryos. As development progressed, the gene transcript abundance profiles became increasingly divergent between dormant and non-dormant embryos. Organogenesis was suspended in dormant embryos, concomitant with low transcript abundance of homeobox genes, and was replaced with an ATP-poor preparatory phase characterized by very high transcript abundance of genes encoding for hallmark dormancy proteins (e.g., LEA proteins, sHSP, and anti-ROS proteins, also found in plant seeds) and proteins involved in dormancy exit. Surprisingly, this period appeared analogous to the late maturation phase of plant seeds.

CONCLUSIONS

The study highlights novel divergent temporal transcript abundance patterns between dormant and non-dormant embryos. Remarkably, several convergent functional solutions appear during the development of resting eggs and plant seeds, suggesting a similar preparatory phase for long-term dormancy. This study accentuated the broad novel molecular features of long-term dormancy in encased animal embryos that behave like "animal seeds".

Facing Adversity: Dormant Embryos in Rotifers

An in-depth look at the basic aspects of dormancy in cyclic parthenogenetic organisms is now possible thanks to research efforts conducted over the past two decades with rotifer dormant embryos. In this review, we assemble and compose the current knowledge on four central themes: (1) distribution of dormancy in animals, with an overview on the phylogenetic distribution of embryo dormancy in metazoans, and (2) physiological and cellular processes involved in dormancy, with a strong emphasis on the dormant embryos of cyclically parthenogenetic monogonont rotifers; and discussions of (3) the selective pressures and (4) the evolutionary and population implications of dormancy in these animals. Dormancy in metazoans is a widespread phenomenon with taxon-specific features, and rotifers are among the animals in which dormancy is an intrinsic feature of their life cycle. Our review shows that embryo dormancy in rotifers shares common functional pathways with other taxa at the molecular and cellular level, despite the independent evolution of dormancy across phyla. These pathways include the arrest of similar metabolic routes and the usage of common metabolites for the stabilization of cellular structures and to confer stress resistance. We conclude that specific features of recurrent harsh environmental conditions are a powerful selective pressure for the fine-tuning of dormancy patterns in rotifers. We hypothesize that similar mechanisms at the organism level will lead to similar adaptive consequences at the population level across taxa, among which the formation of egg banks, the coexistence of species, and the possibility of differentiation among populations and local adaptation stand out. Our review shows how studies of rotifers have contributed to improved knowledge of all of these aspects.

Dormancy in Embryos: Insight from Hydrated Encysted Embryos of an Aquatic Invertebrate

Numerous aquatic invertebrates remain dormant for decades in a hydrated state as encysted embryos. In search for functional pathways associated with this form of dormancy, we used label-free quantitative proteomics to compare the proteomes of hydrated encysted dormant embryos (resting eggs; RE) with nondormant embryos (amictic eggs; AM) of the rotifer Brachionus plicatilisA total of 2631 proteins were identified in rotifer eggs. About 62% proteins showed higher abundance in AM relative to RE (Fold Change>3; p = 0.05). Proteins belonging to numerous putative functional pathways showed dramatic changes during dormancy. Most striking were changes in the mitochondria indicating an impeded metabolism. A comparison between the abundance of proteins and their corresponding transcript levels, revealed higher concordance for RE than for AM. Surprisingly, numerous highly abundant dormancy related proteins show corresponding high mRNA levels in metabolically inactive RE. As these mRNAs and proteins degrade at the time of exit from dormancy they may serve as a source of nucleotides and amino acids during the exit from dormancy. Because proteome analyses point to a similarity in functional pathways of hydrated RE and desiccated life forms, REs were dried. Similar hatching and reproductive rates were found for wet and dried REs, suggesting analogous pathways for long-term survival in wet or dry forms. Analysis by KEGG pathways revealed a few general strategies for dormancy, proposing an explanation for the low transcriptional similarity among dormancies across species, despite the resemblance in physiological phenotypes.

Biochemical diversification through foreign gene expression in bdelloid rotifers

Bdelloid rotifers are microinvertebrates with unique characteristics: they have survived tens of millions of years without sexual reproduction; they withstand extreme desiccation by undergoing anhydrobiosis; and they tolerate very high levels of ionizing radiation. Recent evidence suggests that subtelomeric regions of the bdelloid genome contain sequences originating from other organisms by horizontal gene transfer (HGT), of which some are known to be transcribed. However, the extent to which foreign gene expression plays a role in bdelloid physiology is unknown. We address this in the first large scale analysis of the transcriptome of the bdelloid Adineta ricciae: cDNA libraries from hydrated and desiccated bdelloids were subjected to massively parallel sequencing and assembled transcripts compared against the UniProtKB database by blastx to identify their putative products. Of ~29,000 matched transcripts, ~10% were inferred from blastx matches to be horizontally acquired, mainly from eubacteria but also from fungi, protists, and algae. After allowing for possible sources of error, the rate of HGT is at least 8%-9%, a level significantly higher than other invertebrates. We verified their foreign nature by phylogenetic analysis and by demonstrating linkage of foreign genes with metazoan genes in the bdelloid genome. Approximately 80% of horizontally acquired genes expressed in bdelloids code for enzymes, and these represent 39% of enzymes in identified pathways. Many enzymes encoded by foreign genes enhance biochemistry in bdelloids compared to other metazoans, for example, by potentiating toxin degradation or generation of antioxidants and key metabolites. They also supplement, and occasionally potentially replace, existing metazoan functions. Bdelloid rotifers therefore express horizontally acquired genes on a scale unprecedented in animals, and foreign genes make a profound contribution to their metabolism. This represents a potential mechanism for ancient asexuals to adapt rapidly to changing environments and thereby persist over long evolutionary time periods in the absence of sex.

Insight into molecular pathways of retinal metabolism, associated with vitellogenesis in zebrafish

Retinal is the main retinoid stored in oviparous eggs of fish, amphibians, and reptiles, reaching the oocytes in association with vitellogenins, the yolk precursor proteins. During early presegmentation stages of zebrafish embryos, retinal is metabolized to retinoic acid (RA), which regulates genes involved in cell proliferation, differentiation, and tissue function and is therefore essential for normal embryonic development. While synthesis of vitellogenin and its regulation by 17β-estradiol (E(2)) were extensively investigated, pathways for retinal synthesis remain obscure. We determined the expression pattern of 46 candidate genes, aiming at identifying enzymes associated with retinal synthesis, ascertaining whether they were regulated by E(2), and finding pathways that could fulfill the demand for retinoids during vitellogenesis. Genes associated with retinal synthesis were upregulated in liver (rdh10, rdh13, sdr) and surprisingly also in intestine (rdh13) and ovary (rdh1, sdr), concomitantly with higher gene expression and synthesis of vitellogenins in liver but also in extrahepatic tissues, shown here for the first time. Vitellogenin synthesis in the ovary was regulated by E(2). Gene expression studies suggest that elevated retinal synthesis in liver, intestine, and ovary also depends on cleavage of carotenoids (by Bcdo2 or Bmco1), but in the ovary it may also be contingent on higher uptake of retinol from the circulatory system (via Stra6) and retinol synthesis from retinyl esters (by Lpl). Decrease in oxidation (by Raldh2 or Raldh3) of retinal to RA and/or degradation of RA (by Cyp26a1) may also facilitate higher hepatic retinal levels. Together, these processes enable meeting the putative demands of retinal for binding to vitellogenins. Bioinformatic tools reveal multiple hormone response elements in the studied genes, suggesting complex and intricate regulation of these processes.

Long-term survival of hydrated resting eggs from Brachionus plicatilis

Background

Several organisms display dormancy and developmental arrest at embryonic stages. Long-term survival in the dormant form is usually associated with desiccation, orthodox plant seeds and Artemia cysts being well documented examples. Several aquatic invertebrates display dormancy during embryonic development and survive for tens or even hundreds of years in a hydrated form, raising the question of whether survival in the non-desiccated form of embryonic development depends on pathways similar to those occurring in desiccation tolerant forms.

Methodology/Principal Findings

To address this question, Illumina short read sequencing was used to generate transcription profiles from the resting and amictic eggs of an aquatic invertebrate, the rotifer, Brachionus plicatilis. These two types of egg have very different life histories, with the dormant or diapausing resting eggs, the result of the sexual cycle and amictic eggs, the non-dormant products of the asexual cycle. Significant transcriptional differences were found between the two types of egg, with amictic eggs rich in genes involved in the morphological development into a juvenile rotifer. In contrast, representatives of classical “stress” proteins: a small heat shock protein, ferritin and Late Embryogenesis Abundant (LEA) proteins were identified in resting eggs. More importantly however, was the identification of transcripts for messenger ribonucleoprotein particles which stabilise RNA. These inhibit translation and provide a valuable source of useful RNAs which can be rapidly activated on the exit from dormancy. Apoptotic genes were also present. Although apoptosis is inconsistent with maintenance of prolonged dormancy, an altered apoptotic pathway has been proposed for Artemia, and this may be the case with the rotifer.

Conclusions

These data represent the first transcriptional profiling of molecular processes associated with dormancy in a non-desiccated form and indicate important similarities in the molecular pathways activated in resting eggs compared with desiccated dormant forms, specifically plant seeds and Artemia.

Fibrin microbeads loaded with mesenchymal cells support their long-term survival while sealed at room temperature

Efficient transfer of progenitor cells without affecting their survival is a key factor in any practical cell therapy. Fibrin microbeads (FMB) were developed as hard biodegradable cell carriers. The FMB could efficiently isolate mesenchymal stem cells (MSCs) from different sources and support the expansion of matrix-dependent cell types in a three-dimensional culture in slow rotation. The cells on FMB could also undergo induced differentiation for their eventual implantation to enhance tissue regeneration. FMB loaded with isolated human MSC (hMSC) were sealed in tubes topped up with medium. Almost full cell survival was recorded when the sealed cells were maintained in room temperature for up to 10 days, followed by a recovery period of 24 hrs at optimal conditions. Assay of cells recovery after such long room temperature storage showed ∼80%-100% survival of the cells on FMB, with only a marginal survival of cells that were kept in suspension without FMB in the same conditions. The hMSC that survived storage at room temperature preserved their profile of mesenchymal cell surface markers, their rate of proliferation, and their differentiation potential. The cell protective effect was not dependent on the presence of serum in the storage medium. It was clearly shown that over-expression of hypoxia induced factor-1α in hMSC with time, which may have protected the sealed cells on FMB at room temperature storage, was not necessarily related to extreme hypoxic stress. Foreskin normal fibroblasts on FMB sealed at room temperature were similarly protected, but with no elevation of their hypoxia-induced factor-1α expression. The results also show that FMB, unlike other commercially available cell carriers, could be used for delivery and shipping of progenitor cells at room temperature for extended time intervals. This could be highly useful for cell transfer for therapeutic application and for simplified cell transfer between different research centers.

Placental and trophoblastic in vitro models to study preventive and therapeutic agents for preeclampsia

In the field of preeclampsia, enormous efforts are ongoing to identify biomarkers predicting the syndrome already in the first trimester of pregnancy. At the same time, there is the need for in vitro models to test such biomarkers prior to their use in clinical trials. In addition, in vitro models may accelerate the development and evaluation of the benefit of any putative therapeutics. Therefore, in vitro systems have been established to evaluate the release of biomarkers and measure the effect of putative therapeutics using placental villous explants as well as the choriocarcinoma cell line BeWo. For explants, a cryogenic method to freeze, transport and thaw villous explants was developed to use such tissues for a multi-site tissue culture evaluation. Here we focus on three out of many in vitro models that have been established for human placental trophoblast. (1) Choriocarcinoma cell lines such as BeWo, Jeg-3 and Jar cells (2) isolated primary trophoblast cells, and (2) villous explants from normal placentas delivered at term. Cell lines were used to assess the effect of differentiation and fusion on the expression and release of a preeclampsia marker (placental protein 13; PP13) and beta-hCG. Moreover, cell lines were used to study the effect of putative preeclampsia therapeutics such as vitamins C and E, heparin and aspirin on marker release and viability. Cryopreservation of villous explants enabled shipment to a remote laboratory and testing of parameters in different countries using explants from one and the same placenta. Recently published data make it tempting to speculate that the choriocarcinoma cell line BeWo as well as fresh and cryogenically stored placental villous explants may well serve as in vitro models to study preventive and therapeutic agents in the field of preeclampsia.

Design and characterization of genetically engineered zebrafish aquaporin-3 mutants highly permeable to the cryoprotectant ethylene glycol

Background

Increasing cell membrane permeability to water and cryoprotectants is critical for the successful cryopreservation of cells with large volumes. Artificial expression of water-selective aquaporins or aquaglyceroporins (GLPs), such as mammalian aquaporin-3 (AQP3), enhances cell permeability to water and cryoprotectants, but it is known that AQP3-mediated water and solute permeation is limited and pH dependent. To exploit further the possibilities of using aquaporins in cryobiology, we investigated the functional properties of zebrafish (Danio rerio) GLPs.

Results

Water, glycerol, propylene glycol and ethylene glycol permeability of zebrafish Aqp3a, -3b, -7, -9a, -9b, -10a and -10b, and human AQP3, was examined. Expression in Xenopus laevis oocytes indicated that the permeability of DrAqp3a and -3b to ethylene glycol was higher than for glycerol or propylene glycol under isotonic conditions, unlike other zebrafish GLPs and human AQP3, which were more permeable to glycerol. In addition, dose-response experiments and radiolabeled ethylene glycol uptake assays suggested that oocytes expressing DrAqp3b were permeated by this cryoprotectant more efficiently than those expressing AQP3. Water and ethylene glycol transport through DrAqp3a and -3b were, however, highest at pH 8.5 and completely abolished at pH 6.0. Point mutations in the DrAqp3b amino acid sequence rendered two constructs, DrAqp3b-T85A showing higher water and ethylene glycol permeability at neutral and alkaline pH, and DrAqp3b-H53A/G54H/T85A, no longer inhibited at acidic pH but less permeable than the wild type. Finally, calculation of permeability coefficients for ethylene glycol under concentration gradients confirmed that the two DrAqp3b mutants were more permeable than wild-type DrAqp3b and/or AQP3 at neutral pH, resulting in a 2.6- to 4-fold increase in the oocyte intracellular concentration of ethylene glycol.

Conclusion

By single or triple point mutations in the DrAqp3b amino acid sequence, we constructed one mutant with enhanced ethylene glycol permeability and another with reduced pH sensitivity. The DrAqp3b and the two mutant constructs may be useful for application in cryobiology.

Oogenesis in teleosts: how eggs are formed

One of the major objectives of the aquaculture industry is the production of a large number of viable eggs with high survival. Major achievements have been made in recent years in improving protocols for higher efficiency of egg production and viability of progeny. Main gaps remain, however, in understanding the dynamic processes associated with oogenesis, the formation of an egg, from the time that germ cells turn into oogonia, until the release of ova during spawning in teleosts. Recent studies on primordial germ-cells, yolk protein precursors and their processing within the developing oocyte, the deposition of vitamins in eggs, structure and function of egg envelopes and oocyte maturation processes, further reveal the complexity of oogenesis. Moreover, numerous circulating endocrine and locally-acting paracrine and autocrine factors regulate the various stages of oocyte development and maturation. Though it is clear that the major regulators during vitellogenesis and oocyte maturation are the pituitary gonadotropins (LH and FSH) and sex steroids, the picture emerging from recent studies is of complex hormonal cross-talk at all stages between the developing oocyte and its surrounding follicle layers to ensure coordination of the various processes that are involved in the production of a fertilizable egg. In this review we aim at highlighting recent advances on teleost fish oocyte differentiation, maturation and ovulation, including those involved in the degeneration and reabsorption of ovarian follicles (atresia). The role of blood-borne and local ovarian factors in the regulation of the key steps of development reveal new aspects associated with egg formation.

Late embryogenesis abundant (LEA) proteins in nondesiccated, encysted, and diapausing embryos of rotifers

Two genes encoding for late embryogenesis abundant proteins (LEAs) are expressed in encysted diapausing embryos (or resting eggs) of rotifers (Brachionus plicatilis O.F. Müller) and females forming them. The two genes (bpa-leaa and bpa-leab) share approximately 50% of their nucleotides sequence, and bpa-leaa is more than twofold longer than bpa-leab. The deduced amino acid sequences show high abundance of alanine, glycine, lysine, and glutamic acid; a hydropathy index of lower than one; and a relatively high (81-82%) predicted probability of forming alpha-helices in their secondary structure, all of which are characteristic features of LEAs. The predicted molecular masses of bpa-LEAA ( approximately 67 kDa) and bpa-LEAB ( approximately 27 kDa) are similar to the molecular mass determined by Western-blot analyses, suggesting a low probability of posttranslational modifications. In silico analysis reveals that the two LEAs resemble group 3 LEAs based on the repeats for 11mer motifs, although they also display several putative amino acids typical of the 20mer motif of group 1 LEAs. The rotifer LEAs do not contain a predicted target sequence and are more likely localized in the cytosol. LEAs were expressed in resting eggs and females producing them, but not in other female forms or males. LEA transcripts and proteins are degraded during hatching, suggesting that LEAs are developmentally programmed during resting egg formation and hatching. LEAs probably equip the resting eggs to withstand desiccation if that occurs during dormancy. The present study expands our knowledge about the biological pathways associated with formation of rotifer resting eggs and also demonstrates the occurrence of LEAs in dormant, nondesiccated, encysted animal embryos.

Revealing genes associated with vitellogenesis in the liver of the zebrafish (Danio rerio) by transcriptome profiling

Background

In oviparous vertebrates, including fish, vitellogenesis consists of highly regulated pathways involving 17β-estradiol (E2). Previous studies focused on a relatively small number of hepatic expressed genes during vitellogenesis. This study aims to identify hepatic genes involved in vitellogenesis and regulated by E2, by using zebrafish microarray gene expression profiling, and to provide information on functional distinctive genes expressed in the liver of a vitellogenic female, using zebrafish as a model fish.

Results

Genes associated with vitellogenesis were revealed by the following paired t-tests (SAM) comparisons: a) two-month old vitellogenic (Vit2) females were compared with non-vitellogenic (NV) females, showing 825 differentially expressed transcripts during early stages of vitellogenesis, b) four-month old vitellogenic (Vit4) females were compared with NV females, showing 1,046 differentially expressed transcripts during vitellogenesis and c) E2-treated males were compared with control males, showing 1,828 differentially expressed transcripts regulated by E2. A Venn diagram revealed 822 common transcripts in the three groups, indicating that these transcripts were involved in vitellogenesis and putatively regulated by E2. In addition, 431 transcripts were differentially expressed in Vit2 and Vit4 females but not in E2-treated males, indicating that they were putatively not up-regulated by E2. Correspondence analysis showed high similarity in expression profiles of Vit2 with Vit4 and of NV females with control males. The E2-treated males differed from the other groups. The repertoire of genes putatively regulated by E2 in vitellogenic females included genes associated with protein synthesis and reproduction. Genes associated with the immune system processes and biological adhesion, were among the genes that were putatively not regulated by E2. E2-treated males expressed a large array of transcripts that were not associated with vitellogenesis.

The study revealed several genes that were not reported before as being regulated by E2. Also, the hepatic expression of several genes was reported here for the first time.

Conclusion

Gene expression profiling of liver samples revealed 1,046 differentially expressed transcripts during vitellogenesis of which at least ~64% were regulated by E2. The results raise the question on the regulation pattern and temporal pleiotropic expression of hepatic genes in vitellogenic females.

Discovering genes associated with dormancy in the monogonont rotifer Brachionus plicatilis

BACKGROUND

Microscopic monogonont rotifers, including the euryhaline species Brachionus plicatilis, are typically found in water bodies where environmental factors restrict population growth to short periods lasting days or months. The survival of the population is ensured via the production of resting eggs that show a remarkable tolerance to unfavorable conditions and remain viable for decades. The aim of this study was to generate Expressed Sequence Tags (ESTs) for molecular characterisation of processes associated with the formation of resting eggs, their survival during dormancy and hatching.

RESULTS

Four normalized and four subtractive libraries were constructed to provide a resource for rotifer transcriptomics associated with resting-egg formation, storage and hatching. A total of 47,926 sequences were assembled into 18,000 putative transcripts and analyzed using both Blast and GO annotation. About 28-55% (depending on the library) of the clones produced significant matches against the Swissprot and Trembl databases. Genes known to be associated with desiccation tolerance during dormancy in other organisms were identified in the EST libraries. These included genes associated with antioxidant activity, low molecular weight heat shock proteins and Late Embryonic Abundant (LEA) proteins. Real-time PCR confirmed that LEA transcripts, small heat-shock proteins and some antioxidant genes were upregulated in resting eggs, therefore suggesting that desiccation tolerance is a characteristic feature of resting eggs even though they do not necessarily fully desiccate during dormancy. The role of trehalose in resting-egg formation and survival remains unclear since there was no significant difference between resting-egg producing females and amictic females in the expression of the tps-1 gene. In view of the absence of vitellogenin transcripts, matches to lipoprotein lipase proteins suggest that, similar to the situation in dipterans, these proteins may serve as the yolk proteins in rotifers.

CONCLUSION

The 47,926 ESTs expand significantly the current sequence resource of B. plicatilis. It describes, for the first time, genes putatively associated with resting eggs and will serve as a database for future global expression experiments, particularly for the further identification of dormancy related genes.

Alterations in micro-ribonucleic acid expression profiles reveal a novel pathway for estrogen regulation

Estrogens are steroid hormones that have been implicated in a variety of cellular and physiological processes in the development of diseases such as cancer and are also known to be associated with the effects of endocrine disrupting chemicals. Here we show that 17beta-estradiol (E(2)) alters microRNA (miRNA) expression profiles in the adult zebrafish (Danio rerio). An association between E(2) and the expression of 25 miRNAs was found 12 h after treatment. Among the most up-regulated miRNAs were miR-196b and let-7h, and the most down-regulated miRNAs included miR-130c and miR-101a. Tissue-specific changes in the transcripts levels of estrogen receptors (Esr1, Esr2a, and Esr2b) and miRNAs were found after hormone treatment. The most up-regulated miR-196b and its precursors are highly expressed in the skin and showed similar tissue-specific expression patterns after treatment, indicating a common pattern of regulation by E(2). MiR-196b was shown to fine-tune the expression of its target gene Hoxb8a after treatment in whole-body homogenates. Taken together, our results suggest a novel pathway for the multifunctional and pleiotropic effects of estrogens and open new directions for future investigations of their association with miRNAs involved in estrogen-regulated physiological processes and diseases.

Isolation and functional characterization of a new shrimp ovarian peritrophin with antimicrobial activity from Fenneropenaeus merguiensis

Shrimp ovarian peritrophin (SOP), a major protein in jelly layer (JL) and cortical rods (CRs), is proposed to play a role in the protection of spawned eggs. The full sequence of SOP cDNA from Fenneropenaeus merguiensis (Fm-SOP) shares approximately 50% identity with other SOP sequences and contains several putative chitin-binding or peritrophin-A domains. Interestingly, Fm-SOP contains a putative 61-amino acid propeptide located at the N-terminal end, downstream of a 19-amino acid signal peptide, which is unique among penaeid SOP sequences described so far. This 61-amino-acid sequence constitutes a putative chitin-binding domain with six conserved cysteines, and is cleaved at a dibasic recognition site for a furin (subtilisin-like endoprotease). Expression analyses indicated that Fm-SOP mRNA is abundant in early vitellogenic ovaries and scarce in late-vitellogenic ovaries. Conversely, Fm-SOP protein is the most abundant at the end of vitellogenesis. To investigate its biological function, a recombinant Fm-SOP was expressed to generate a glycosylated protein in Spodoptera frugiperda Sf9 cells (rSOP-Sf9) and a nonglycosylated protein (rSOP-Ec) in Escherichia coli. rSOP-Sf9 and rSOP-Ec were found to bind to chitin, similarly to the native protein extracted from F. merguiensis ovaries. Most interestingly, rSOP-Ec displayed a chitinase activity and efficiently inhibited the growth of Vibrio harveyi and Staphylococcus aureus, with minimum inhibitory concentrations of 2.4 and 15.7 microM, respectively. This first report shows that a major component of CR and JL is biologically active against known pathogens and predicts a significant role of JL in the protection of the spawned eggs against pathogens.

Apolipocrustacein, formerly vitellogenin, is the major egg yolk precursor protein in decapod crustaceans and is homologous to insect apolipophorin II/I and vertebrate apolipoprotein B

BACKGROUND

In animals, the biogenesis of some lipoprotein classes requires members of the ancient large lipid transfer protein (LLTP) superfamily, including the cytosolic large subunit of microsomal triglyceride transfer protein (MTP), vertebrate apolipoprotein B (apoB), vitellogenin (Vtg), and insect apolipophorin II/I precursor (apoLp-II/I). In most oviparous species, Vtg, a large glycolipoprotein, is the main egg yolk precursor protein.

RESULTS

This report clarifies the phylogenetic relationships of LLTP superfamily members and classifies them into three families and their related subfamilies. This means that the generic term Vtg is no longer a functional term, but is rather based on phylogenetic/structural criteria. In addition, we determined that the main egg yolk precursor protein of decapod crustaceans show an overall greater sequence similarity with apoLp-II/I than other LLTP, including Vtgs. This close association is supported by the phylogenetic analysis, i.e. neighbor-joining, maximum likelihood and Bayesian inference methods, of conserved sequence motifs and the presence of three common conserved domains: an N-terminal large lipid transfer module marker for LLTP, a DUF1081 domain of unknown function in their central region exclusively shared with apoLp-II/I and apoB, and a von Willebrand-factor type D domain at their C-terminal end. Additionally, they share a conserved functional subtilisin-like endoprotease cleavage site with apoLp-II/I, in a similar location.

CONCLUSION

The structural and phylogenetic data presented indicate that the major egg yolk precursor protein of decapod crustaceans is surprisingly closely related to insect apoLp-II/I and vertebrate apoB and should be known as apolipocrustacein (apoCr) rather than Vtg. These LLTP may arise from an ancient duplication event leading to paralogs of Vtg sequences. The presence of LLTP homologs in one genome may facilitate redundancy, e.g. involvement in lipid metabolism and as egg yolk precursor protein, and neofunctionalization and subfunctionalization, e.g. involvement in clotting cascade and immune response, of extracellular LLTP members. These protein-coding nuclear genes may be used to resolve phylogenetic relationships among the major arthropod groups, especially the Pancrustacea-major splits.

Yolk proteolysis and aquaporin-1o play essential roles to regulate fish oocyte hydration during meiosis resumption

In marine fish, meiosis resumption is associated with a remarkable hydration of the oocyte, which contributes to the survival and dispersal of eggs and early embryos in the ocean. The accumulation of ions and the increase in free amino acids generated from the cleavage of yolk proteins (YPs) provide the osmotic mechanism for water influx into the oocyte, in which is involved the recently identified, fish specific aquaporin-1o (AQP1o). However, the timing when these processes occur during oocyte maturation, and the regulatory pathways involved, remain unknown. Here, we show that gilthead sea bream AQP1o (SaAQP1o) is synthesized at early vitellogenesis and transported towards the oocyte cortex throughout oocyte growth. During oocyte maturation, shortly after germinal vesicle breakdown and before complete hydrolysis of YPs and maximum K(+) accumulation is reached, SaAQP1o is further translocated into the oocyte plasma membrane. Inhibitors of yolk proteolysis and SaAQP1o water permeability reduce sea bream oocyte hydration that normally accompanies meiotic maturation in vitro by 80% and 20%, respectively. Thus, yolk hydrolysis appears to play a major role to create the osmotic driving force, while SaAQP1o possibly facilitates water influx into the oocyte. These results provide further evidence for the role of AQP1o mediating water uptake into fish oocytes, and support a novel model of fish oocyte hydration, whereby the accumulation of osmotic effectors and AQP1o intracellular trafficking are two highly regulated mechanisms.

Role of cathepsins in ovarian follicle growth and maturation

Several complex processes are involved in the production of viable eggs. The aim of this review is to provide an overview on the role played by lysosomal enzymes, especially cathepsins B, D, and L, during ovarian follicle growth and maturation. Specific attention is focused on the relationship between the second proteolytic cleavage of yolk proteins (YP) and the resumption of the meiosis during germinal vesicle break down (GVBD). Maturation represents the final stage of oocytes development prior to ovulation. Oocytes in this phase appear translucent. In many teleosts GVBD is accompanied by water uptake and among marine teleosts with pelagic eggs, most of the final volume is reached by this process. The last phase of maturation in benthonic eggs also occurs concomitant to a second proteolytic cleavage and is related with a slight hydration process. In vitro maturation by 17alpha,20beta-dihydroxy-4-pregnen-3one in class III Danio rerio oocytes, induced 80% of GVBD. The maturation of these oocytes is known to be associated with proteolysis of their major yolk components. In the present study, we show that inhibition of specific enzymes (cathepsins) involved in the second YP processing, did not affect the occurrence of GVBD as the oocytes become translucent and display a slight increase in size. More specifically, in vitro incubation of the maturing oocytes with a cathepsin B inhibitor suppressed both cathepsin B and L activities and the proteolysis of YP. On the contrary, the addition of cathepsin L inhibitor, only affected cathepsin L activity, indicating that cathepsin B is probably involved in Cathepsin L activation, and this enzyme is probably responsible for the second YP processing. These results, together with previous studies, indicate that the GVBD process is independent of the occurrence of the second proteolytic process. It supports the hypothesis that the maturation process is under K+ ion flux control, while yolk proteolysis is related to the temporal and specific activation of cathepsins by acidification of yolk spheres.

Studies on retinol-binding protein during vitellogenesis in the Rainbow Trout (Oncorhynchus mykiss)

Retinoids are important regulatory signaling molecules during embryonic development and therefore, should be present in the eggs of oviparous animals that develop independently of the maternal organism. Studies were initiated in Rainbow Trout to elucidate the role of retinol-binding protein (RBP), the specific retinol carrier protein in vertebrate plasma, during vitellogenesis. Plasma levels of RBP in pre-vitellogenic, vitellogenic, and post-vitellogenic females were compared to plasma of male trout, using a rabbit polyclonal antiserum that was generated to His-tagged RBP recombinant protein. Western-blot analyses showed that there were no differences in the relative plasma levels of RBP between pre-vitellogenic, vitellogenic or post-vitellogenic females and similar levels were also found in males. In contrast, strong elevation of vitellogenin (VTG) was observed in the plasma from vitellogenic females. Northern-blot analysis of hepatic mRNA revealed that there were no dramatic changes in the abundance of RBP transcripts in the liver of females during vitellogenesis, but showed a significant increase in the expression of VTG in the livers of vitellogenic females. These results indicate differences in the regulation of RBP and VTG during vitellogenesis, suggesting that RBP may not be the main transporter protein for retinoids to fish egg. Recent publications on the association of retinal with VTG in fish and the occurrence of RBP transcripts in ovarian tissues raise the need for reevaluation of the role of RBP during vitellogenesis in oviparous non-mammalian vertebrate species.

Carotenoid and retinoid transport to fish oocytes and eggs: what is the role of retinol binding protein?

Fish eggs contain carotenoids, retinals (retinal and dehydroretinal) and retinols (retinol, dehydroretinol and retinyl-esters) that are utilized during embryonic development, after fertilization. The carotenoids (mainly astaxanthins) are transported in the plasma by the low density lipoproteins, high density lipoproteins, and very high density lipoproteins (VHDL) and were found to be associated also with serum albumin. Retinals were found to be associated vitellogenin (VTG), a component of the plasma VHDL fraction that is internalized by oocytes during vitellogenesis. However, the transport of retinols and retinyl-esters that were located in the oil droplet fraction of homogenized eggs, has yet to be elucidated. Retinols are more abundant in freshwater fish eggs than in eggs of marine fish species. Since retinol is transported in the plasma of vertebrates in association with retinol binding protein (RBP), recent studies on the molecular characterization and expression sites of RBP, could contribute to determining the involvement of RBP in transporting retinol to developing oocytes in vertebrates.Recently, results from our laboratory show that RBP mRNA levels in the liver and RBP plasma levels did not significantly change with the onset and during vitellogenesis in the Rainbow trout. These results were in contrast with a dramatic elevation in the mRNA levels of VTG in the liver and an increase in VTG plasma levels that was observed in the same females. Moreover, 17beta-estradiol treatment of immature fish, resulted in relatively lower mRNA levels of RBP in the liver, concomitantly with an increase in the level of VTG transcripts and the appearance of VTG in the plasma of treated fish. In addition, RBP was localized in the cytosol of ovulated oocytes. These results for Rainbow trout are similar to those reported for the chicken but differ from those of Xenopus, where an increase in RBP mRNA was reported in the liver and higher levels of retinal and retinol were found in the plasma of 17beta-estradiol treated animals. The results, reported here for the first time in Rainbow trout, showing RBP transcripts in the ovary, oviduct (the ovarian tissue adjacent to the gonopore) and oocytes, suggest a modulating role for RBP in follicular development, as has been suggested for the bovine ovary.

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.

Response of Penaeus indicus females at two different stages of ovarian development to a lethal infection with Vibrio penaeicida

An association between vitellogenesis and the immune system was suggested in crustaceans from studies on plasma lipoproteins. The present research studies the effect of an experimentally induced bacterial infection on vitellogenesis in females of the shrimp Penaeus indicus, as a model for penaeid species. Pre-vitellogenic and vitellogenic P. indicus females were experimentally infected with an extremely pathogenic bacterium, Vibrio penaeicida. The peak in mortality occurred earlier in pre-vitellogenic animals than in vitellogenic ones, although the final mortality level ( approximately 64-74%) 52h post-infection was nearly the same for the two groups. Twenty hours after infection, the total number of haemocytes was significantly reduced in vitellogenic females while there was no change in the pre-vitellogenic group. Protein synthesis in ovaries was not significantly affected by infection, at the two stages of ovarian development. No differences were found in mRNA levels of shrimp ovarian peritrophin protein (SOP), but preliminary results showed that mRNA expression of vitellin (VT) was reduced in a heavily infected vitellogenic female. The total amount of lipids in the haemolymph of vitellogenic females was almost twice higher than that of pre-vitellogenic ones. However, there was no change in the total content of lipids, lipid classes and fatty acid distribution in haemolymph or hepatopancreas following infection. Although vitellogenic and pre-vitellogenic females probably respond differently to a lethal bacterial infection, physiological differences may be concealed by the rapid onset of mortality.

Inhibition of de novo synthesis of a jelly layer precursor protein by crustacean hyperglycemic hormone family peptides and posttranscriptional regulation by sinus gland extracts in Penaeus semisulcatus ovaries

Mature penaeid oocytes possess extracellular cortical rods (CR) that contain precursor proteins of the jelly layer (JL) that forms a protective layer around eggs immediately after spawning and dissipates following the assembly of the hatching envelope. The temporal pattern of protein synthesis and mRNA expression of a jelly layer precursor protein in Penaeus semisulcatus ovaries was followed during vitellogenesis, and the regulation by sinus gland extracts (SGE) and crustacean hyperglycemic hormone (CHH) family peptides was evaluated. An approximately 33-kDa jelly layer precursor protein was previously identified in ovaries, CR, and JL and was named shrimp ovarian peritrophin-like protein (SOP), because its deduced amino acid sequence shows structural similarities to insect peritrophins. SOP was synthesized in ovarian explant fragments that were removed from vitellogenic ovaries and incubated in vitro, but synthesis was not detected in explants that were collected from previtellogenic ovaries. SOP transcripts were detected in all stages of ovarian development, but were more abundant in previtellogenic ovaries than in other stages. De novo synthesis of SOP was inhibited by P. semisulcatus SGE and by CHH family peptides that were purified from P. japonicus sinus glands. Sinus gland extracts, however, did not affect the steady state levels of SOP transcripts at any stage of ovarian development. These results suggest that SGE regulate SOP synthesis at the posttranscriptional level.

Retinol binding protein in rainbow trout: molecular properties and mRNA expression in tissues

Retinoids are important regulatory signaling molecules during embryonic development. The molecular properties of rainbow trout (Oncorhynchus mykiss) retinol-binding protein (rtRBP), the specific retinol carrier in vertebrate plasma, were studied to elucidate its role in transporting retinols to developing fish oocytes. A 954-nucleotide rtRBP cDNA was cloned from the liver coding for a 176-amino-acid (aa) mature protein, with an estimated molecular mass of 20,267 Da. The nucleotide sequence suggests a putative 16-aa signal peptide and shows all the aa residues that were previously identified as critical for the retinol binding pocket. Five of the eight amino acid residues that are associated with the interaction of RBP and transthyretin in mammalian and non-mammalian species are conserved. The deduced aa sequence of rtRBP shows 60-66% identity with zebrafish, chicken, mouse, rat, horse, bovine, and human RBPs and 56% identity with Xenopus RBP. Northern blot analysis revealed a approximately 1.1-kb hepatic mRNA transcript. RBP is highly expressed in the liver, but low levels were also detected in the spleen, kidney, ovary, and brain. In the rainbow trout, 17beta-estradiol treatment led to a decrease in the RBP mRNA signal relative to that of the controls. The efficacy of the 17beta-estradiol treatment was verified by an induction of vitellogenin (VTG) mRNA expression in the liver and occurrence of VTG in the plasma.

Molecular characterization and high expression during oocyte development of a shrimp ovarian cortical rod protein homologous to insect intestinal peritrophins

Penaeoid shrimp oocytes nearing the completion of oogenesis are enveloped in an acellular vitelline envelope and possess extracellular cortical rods (CRs) that extended into the cortical cytoplasm. These cortical specializations are precursors of the jelly layer (JL) of the egg. In searching for highly expressed mRNAs during oogenesis in the marine shrimp (Penaeus semisulcatus), two related cDNAs have been isolated that encode a mature protein of 250 amino acid residues. The deduced amino acid sequences revealed the presence of repeated cysteine-rich domains that are related to the chitin-binding domains of insect intestinal peritrophins. Similar cysteine-rich domains were reported in insect intestinal mucin, crustacean tachycitin, and invertebrate chitinases. The shrimp ovarian peritrophin (SOP) is glycosylated and can bind chitin when extracted from CRs. Its apparent molecular mass in SDS-PAGE is 29-35 kDa and 33-36 kDa, under nonreducing or reducing conditions, respectively. SOP is a major protein of CRs and the JL, and was immunodetected in ovaries; purified CRs; fertilized eggs that were surrounded by a JL matrix; and in the cloudy, whitish flocculent material appearing in sea water immediately after spawning. Immunolocalization in tissue sections determined that SOP was present in oocyte cytoplasm and in extraoocytic CRs. Shrimp expressed SOP mRNA in ovaries at all oocyte developmental stages, whereas expression in the hepatopancreas was restricted to vitellogenic stages. SOP mRNA was abundant in the shrimp ovary and was detected before the presence of the corresponding protein. This is the first demonstration that a protein with similar features to insect intestinal peritrophins is a component of CRs and is therefore a main precursor of the JL of spawned shrimp eggs.

Characterization of Satellite DNA Sequences from the Commercially Important Marine Rotifers Brachionus rotundiformis and Brachionus plicatilis

This study was initiated to search for species-specific and strain-specific satellite DNA sequences for which oligonucleotide primers could be designed to differentiate between various commercially important strains of the marine monogonont rotifers Brachionus rotundiformis and Brachionus plicatilis. Two unrelated, highly reiterated satellite sequences were cloned and characterized. The eight sequenced monomers from B. rotundiformis and six from B. plicatilis had low intrarepeat variability and were similar in their overall lengths, A + T compositions, and high degrees of repeated motif substructure. However, hybridizations to 19 representative strains, sequence characterizations, and GenBank searches indicated that these two satellites are morphotype-specific and population-specific, respectively, and share little homology to each other or to other characterized sequences in the database. Primer pairs designed for the B. rotundiformis satellite confirmed hybridization specificities on polymerase chain reaction and could serve as a useful molecular diagnostic tool to identify strains belonging to the SS morphotype, which are gaining widespread usage as first feeds for marine fish in commercial production.

Lipid accumulation in the ovaries of a marine shrimp penaeus semisulcatus (de haan)

By the end of oocyte development, the ovaries of Penaeus semisulcatus have accumulated almost equal amounts (approximately 16 mg lipid g-1 protein) of phospholipids and triacylglycerols. The phospholipids consist mainly of phosphatidylcholine (75–80 %) and phosphatidylethanolamine (20–25 %). Approximately 30 % of the total fatty acid content of both phospholipids and triacylglycerols is made up of polyunsaturated fatty acids. In fractions obtained by centrifugation of ovarian homogenates, most of the increase in levels of ovarian lipids during ovarian maturation was associated with an increase in triacylglycerol levels in the floating fat fraction and of phospholipids in the infranatant fraction. The presence of polyunsaturated fatty acids in the ovaries indicates the occurrence of lipid transport to the ovary during oocyte maturation. The gradual decrease in the relative abundance of polyunsaturated fatty acids as the ovaries matured supports previously published results suggesting intra-ovarian synthesis of saturated and mono-unsaturated fatty acids. Most of the lipids found in the female haemolymph (64.8 %) were recovered in the high-density lipoprotein fraction after density ultracentrifugation. The haemocyanin fraction recovered from this stage of fractionation contained substantial amounts of lipid (16.8 %) that could be removed by further sequential centrifugation at a higher NaBr density, leaving less than 0.9 % of the total haemolymph lipids associated with this fraction. While 16.2 % of the lipids were recovered from the very high-density lipoprotein fractions, these lipoproteins carried only 64–89 microg lipid mg-1 protein compared with 538.9 microg lipid mg-1 protein in the high-density lipoprotein fraction, indicating that the high-density lipoproteins are more likely to be the main transporters of lipids to the ovary. However, the contribution of very high-density lipoproteins to lipid transport cannot be ruled out at this stage. In this study, we present two models for lipid transport to the ovary based on the abundance of phospholipids and triacylglycerols in the haemolymph and on the amounts of polyunsaturated fatty acids accumulated within the ovary during vitellogenesis.

Hyperglycaemic hormones inhibit protein and mRNA synthesis in in vitro-incubated ovarian fragments of the marine shrimp Penaeus semisulcatus

The present work shows for the first time that peptides belonging to the Crustacean hyperglycaemic hormone family (CHH-family hormones) from Penaeus japonicus affect protein and mRNA synthesis in in vitro-incubated ovarian explant fragments removed from vitellogenic females of Penaeus semisulcatus. Reduced levels of protein synthesis, determined by TCA-precipitable 35S-labeled proteins, were found in the presence of crude sinus gland extracts from both P. semisulcatus and P. japonicus. A similar inhibitory effect compared to controls was found with each of the seven CHH-family peptides. Non-CHH-family peptides did not reduce protein synthesis. Crude sinus gland extracts prepared from P. semisulcatus were at least 20-fold more effective than sinus gland extracts of P. japonicus. The inhibition level was directly related to the concentration of the peptide in the incubation media, but its degree varied among the different tested peptides. The profile of proteins synthesized during in vitro incubation was analyzed using polyacrylamide gel electrophoresis under denatured and reduced conditions (SDS-PAGE), followed by autoradiography. Synthesis of several proteins was reduced, including proteins with electrophoretic mobility similar to that of vitellin. Immunoprecipitation with antiserum prepared against native ovarian vitellin confirmed the inhibitory effect of CHH-family peptides on vitellin synthesis. The crude sinus gland extract and CHH-family peptides also inhibited RNA synthesis, as determined by [3H]uridine incorporation into mRNA of ovarian fragments. It is concluded that in addition to their role in carbohydrate metabolism, CHH-family peptides may also influence ovarian physiology in crustaceans.

Isolation and characterization of the high-density lipoproteins from the hemolymph and ovary of the penaeid shrimp Penaeus semisulcatus (de Haan): apoproteins and lipids

The high-density lipoproteins (HDLs) found in the male and female hemolymph of Penaeus semisulcatus de Haan were isolated by NaBr (1.22 g/ml) followed by sucrose gradient (5-25%) ultracentrifugation. The male HDL contained one protein, lipoprotein 1 (LP1), composed of one 110-kDa peptide subunit. The female HDL contained two proteins: 1) the LP1 that was immunoidentical to the male LP1 and was similarly composed of one 110-kDa peptide subunit and 2) vitellogenin (Vg), reacting positively with the rabbit antiserum generated against vitellin (Vt) that was isolated from vitellogenic ovaries. Both Vg and Vt consisted mainly of three polypeptide subunits (200, 120, and 80 kDa) as revealed by denatured PAGE and Western blot. The LP1 from males or females did not react with the Vt rabbit antiserum. Similarly, Vg and Vt did not react with the rabbit antiserum prepared against LP1. Phospholipids (PL) constituted 71-76% of the total lipids in the hemolymph and HDLs of both male and female hemolymph. Cholesterol (Ch) amounted to 17-20%, and small amounts (5%) of diacylglycerols (DAG) were also carried by these HDLs. Both the PL and DAG contained highly unsaturated fatty acids (20:5 omega 3 and 22:6 omega 3) that are transported from the food or hepatopancreas to the tissues, including the vitellogenic ovaries in females. In the present study we show for the first time the separate lipid composition of female LP1 and Vg and compare them with the lipids attached to the Vt. Vg had a lower lipid content than LP1 (540 and 1089 mg/g protein, respectively). Differences were also found in the relative abundance of PL, Ch, and DAG classes in the LP1 in comparison with Vg. Furthermore, small amounts (approximately 3.8%) of triacylglycerols (TAG) were found only in the hemolymph of vitellogenic females, and they were associated with the Vg. Although Vg and Vt were composed of similar polypeptides, their lipid composition was different Vt, in contrast to Vg, carried considerable amounts of TAG (approximately 22%) and only trace amounts of DAG. The significance of the TAG in the hemolymph of vitellogenic females is not known, and the functional relationship between Vg and Vt requires future extensive studies. Lipids were not detected in hemocyanin that was purified from clotted hemolymph.

Are vitellin and vitellogenin coded by one gene in the marine shrimp Penaeus semisulcatus?

A cDNA clone encoding a female-specific ovarian protein (presumably vitellin, Vt) has been isolated from a cDNA library prepared from poly (A)+ RNA extracted from vitellogenic ovaries of the shrimp Penaeus semisulcatus. The cDNA library was constructed and screened using a major cDNA band which was observed following analysis of total cDNA products by gel electrophoresis. This band, as well as the cDNA insert purified from the library, was estimated to have 1.1 kb. Both hybridized to mRNA prepared from ovaries or hepatopancreas (HEP) of vitellogenic females and showed a faint signal with ovaries from non-vitellogenic females, but did not hybridize to HEP from non-vitellogenic females or to HEP from males or testes. The size of the transcripts from the ovary and HEP was estimated to be 1.1 kb, similar to that of the cDNA insert, suggesting that a full length cDNA had been synthesized. Furthermore, the identical sizes of the transcripts from ovary and HEP and the ability of the ovarian cDNA to detect a transcript in HEP mRNA suggest that Vt from the ovary and vitellogenin (Vg) from HEP are the gene products of one gene. Alternatively, the homology between Vt and Vg is very high.

Cell-free synthesis of vitellin in the shrimp Penaeus semisulcatus (de Haan)

The vitellogenic ovary of Penaeus semisulcatus contains mRNA specific for vitellin (Vt), low levels of which are found in nonvitellogenic ovaries, and is absent from testes. Immunoisolation from cell-free translation of poly(A)+ RNA using antiserum against purified Vt produced a 35-kDa polypeptide. No differences were found between Vt precipitated from the translation products of the rabbit reticulocyte system and that from the wheat germ extract. The specificity of the immunoprecipitation reaction was demonstrated by the absence of precipitation with nonimmunized rabbit serum and with antibodies prepared against purified hemocyanin or lipoprotein I (LPI), which are crustacean hemolymph proteins. In addition, competition with the radioactively labeled translation product occurred only in the presence of purified Vt, but not BSA or LPI. Vt synthesized in the translation system had a significantly lower molecular weight than that of the purified Vt or that synthesized by ovaries incubated in vitro. The possibility that this difference may be because of the non-glycosylated nature of a cell-free translation product was tested. The removal of oligosaccharides from purified Vt by enzymatic digestion with N-glycosidase F resulted in the appearance of a smaller polypeptide of 36 kDa, which reacted immunologically with Vt antiserum in a Western blot. The size of this fragment is very close to the molecular weight of the translation product.

Protein, Vitellogenin, and Vitellin Levels in the Hemolymph and Ovaries during Ovarian Development in Penaeus semisulcatus (de Haan)

The concentration of vitellogenin (Vg) in the hemolymph of Penaeus semisulcatus was found to increase from an average of 50 μg ml-1 to 439 μg ml-1 in female shrimp during ovarian development. The most significant increase in Vg occurred concomitant with the increase in the vitellin (Vt) content of oocytes with an average diameter (AOD) ranging between 150 and 250 μm. The amount of Vt in the oocytes was found to increase linearly from a mean of 0.0126 mg to 4.55 mg per gm body weight. However, the percentage of Vt in the total protein was found to decrease, from 67% in ovaries with AOD of 150-250 μm, to 39.7% in ovaries with AOD of 350 μm or larger. The volume of the hemolymph was found to be 0.4 ml per gm body weight and did not change significantly during ovarian development. Assuming that Vg in the hemolymph represents either an extraovarian origin of Vt or an active secretion from the ovary, a turnover rate of two to three times per day was calculated over one full cycle of oocyte development. However, during the most significant increase in Vt in the ovary (in ovaries with AOD of 150-250 μm), the turnover rate in the hemolymph could reach seven to eight times per day. The results lead to the conclusion that the contribution of Vg to the formation of Vt in the ovary is quantitatively insignificant.

Is There Extraovarian Synthesis of Vitellogenin in Penaeid Shrimp?

Extraovarian synthesis of vitellogenin (Vg), has been reported for several crustaceans, mainly in the subepidermal adipose tissue (SAT) or the hepatopancreas (HEP). The precise site(s) of Vg synthesis in penaeid shrimp is hitherto unknown and was investigated in a large local species Penaeus semisulcatus de Haan. Protein synthesis was determined in SAT and HEP tissue pieces incubated in vitro. Incubations were at 25{deg}C for eight hours in an oxygen enriched atmosphere, under sterile conditions in a physiological medium, containing 14C-leucine. At the end of the incubation period, tissue homogenates and medium samples were analyzed for de novo protein synthesis. Total protein synthesis was determined by trichloroacetic acid precipitation. Specific vitellin (Vt) synthesis was determined by radioimmunoprecipitation with a polyclonal Vt-specific antiserum. Characterization of other de novo synthesized proteins was carried out by fluorography from polyacrylamide gels. Subepidermal adipose tissues removed from females at all stages of ovarian development did not synthesize Vt-specific proteins, in spite of the fact that total protein synthesis levels were high. The major protein synthesized de novo in the SAT of males and females is a protein with an identical electrophoretic mobility as hemocyanin in polyacrylamide gels. In vitro protein synthesis in HEP tissues was low compared to SAT or ovary systems. Vt-specific de novo synthesized protein was identified in HEP's from early vitellogenic females, but constituted less than 15% of total protein synthesis. We have previously shown that ovarian tissues from vitellogenic females incubated in vitro exhibited high levels of protein synthesis, an average of 38% of which is Vt-specific (Browdy et al., 1990, J. Exp. Zool. 255:205-215). The calculated Vt synthesis rates in ovaries were up to 23 times higher than in HEP. We conclude that the extraovarian contribution to vitellogenesis in P. semisulcatus is low.