Vitellogenin C-terminal fragments participate in fertilization as egg-coat binding partners of sperm trypsin-like proteases in the ascidian Halocynthia roretzi

Adverse effects of Microcystis aeruginosa exudates on the filtration, digestion, and reproduction organs of benthic bivalve Corbicula fluminea

Cyanobacteria bloom and the secondary metabolites released by the microorganism are extremely harmful to aquatic animals, yet study on their adverse effects in zoobenthos is rare. Corbicula fluminea widely distributed in freshwater environment with algal blooms. It is a typical filter feeding zoobenthos that may be affected by the secondary metabolites of cyanobacteria due to its high filtering rate. In this study, C. fluminea was exposed to Microcystis aeruginosa exudates (MaE) for 96 h, which was obtained from 5 × 105 cells/mL and 2.5 × 106 cells/mL exponential stage M. aeruginosa culture solution that represented cyanobacteria cell density needs environmental risk precaution control and emergent control, respectively. The responses of C. fluminea critical organs to MaE were analyzed and evaluated based on histopathological sections, antitoxicity biomarkers, and organ function biomarkers. The results showed that all the organs underwent structural disorders, cell vacuolization, apoptosis, and necrosis, and the damage levels increased as MaE concentration increased. The detoxification and antioxidant defense systems biomarkers in each organ response to MaE exposure differently and the level of reaction improved when MaE concentration increased. The siphon rate and acetylcholinesterase activity showed that the filtration function decreased significantly as the MaE concentration increased. Increased activity of glutathione S-transferase and amylase in the digestive gland indicate that it is the major detoxification organ of C. fluminea. Increased vitellogenin concentration and enlarged oocytes in the gonad indicate that MaE may have an estrogenic effect on C. fluminea. This study demonstrates that cyanobacteria threat benthic bivalves by inducing oxidative stress, inhibiting filtering feeding system, and disturbing digestion system and reproduction potential of C. fluminea.

Vitellogenin and its upstream gene TOR play essential roles in the reproduction of Dermanyssus gallinae

In Dermanyssus gallinae, a hematophagous mite, the initiation of vitellogenesis induced by blood feeding is essential for its reproduction. However, the precise gene structures and physiological functions of Vg in D. gallinae and its upstream gene, Target of Rapamycin (TOR), have not been fully understood. This study revealed the presence of four homologous genes within D. gallinae, named Dg-Vg1, Dg-Vg1-like, Dg-Vg2, and Dg-Vg2-like, especially, Dg-Vg2-like was firstly identified in the mites. The expression levels of all these Vg genes were significantly higher in adult females than other stages. Following blood feeding, the expression levels of these genes increased significantly, followed by a subsequent decrease, aligning with egg production. Silencing Dg-Vgs by RNA interference (RNAi) led to decreased fecundity and egg hatching rates, as well as abnormal embryonic development, suggesting a vital role for Dg-Vgs in both egg formation and embryonic development. Furthermore, the knockdown of Dg-TOR significantly reduced the expression of Dg-Vgs and negatively impacted the reproductive capabilities of PRMs, indicating that TOR influences PRM reproduction by regulating the expression of Dg-Vgs. In summary, these findings demonstrated the crucial roles of Dg-Vgs and Dg-TOR in PRM reproduction, highlighting their potential as targets for pest control.

Comparative Analyses of Reproductive Caste Types Reveal Vitellogenin Genes Involved in Queen Fertility in Solenopsis invicta

The red imported fire ant (Solenopsis invicta Buren) is a social pest species with a robust reproductive ability that causes extensive damage. Identification of the genes involved in queen fertility is critical in order to better understand the reproductive biology and screening for the potential molecular targets in S. invicta. Here, we used the mRNA deep sequencing (RNA-seq) approach to identify differentially expressed genes (DEGs) in the transcriptomes of three reproductive caste types of S. invicta, including queen (QA) and winged female (FA) and male (MA) ants. The genes that were specific to and highly expressed in the queens were then screened, and the Vg2 and Vg3 genes were chosen as targets to explore their functions in oogenesis and fertility. A minimum of 6.08 giga bases (Gb) of clean reads was obtained from all samples, with a mapping rate > 89.78%. There were 7524, 7133, and 977 DEGs identified in the MA vs. QA, MA vs. FA, and FA vs. QA comparisons, respectively. qRT-PCR was used to validate 10 randomly selected DEGs, including vitellogenin 2 (Vg2) and 3 (Vg3), and their expression patterns were mostly consistent with the RNA-seq data. The S. invicta Vgs included conserved domains and motifs that are commonly found in most insect Vgs. SiVg2 and SiVg3 were highly expressed in queens and winged females and were most highly expressed in the thorax, followed by the fat body, head, and epidermis. Evaluation based on a loss-of-function-based knockdown analysis showed that the downregulation of either or both of these genes resulted in smaller ovaries, less oogenesis, and less egg production. The results of transcriptional sequencing provide a foundation for clarifying the regulators of queen fertility in S. invicta. The functions of SiVg2 and SiVg3 as regulators of oogenesis highlight their importance in queen fecundity and their potential as targets of reproductive disruption in S. invicta control.

Comparative transcriptome sequencing analysis of female and male Decapterus macrosoma

Sexual growth dimorphism is a common phenomenon in teleost fish and has led to many reproductive strategies. Growth- and sex-related gene research in teleost fish would broaden our understanding of the process. In this study, transcriptome sequencing of shortfin scad Decapterus macrosoma was performed for the first time, and a high-quality reference transcriptome was constructed. After identification and assembly, a total of 58,475 nonredundant unigenes were obtained with an N50 length of 2,266 bp, and 28,174 unigenes were successfully annotated with multiple public databases. BUSCO analysis determined a level of 92.9% completeness for the assembled transcriptome. Gene expression analysis revealed 2,345 differentially expressed genes (DEGs) in the female and male D. macrosoma, 1,150 of which were female-biased DEGs, and 1,195 unigenes were male-biased DEGs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the DEGs were mainly involved in biological processes including protein synthesis, growth, rhythmic processes, immune defense, and vitellogenesis. Then, we identified many growth- and sex-related genes, including Igf, Fabps, EF-hand family genes, Zp3, Zp4 and Vg. In addition, a total of 19,573 simple sequence repeats (SSRs) were screened and identified from the transcriptome sequences. The results of this study can provide valuable information on growth- and sex-related genes and facilitate further exploration of the molecular mechanism of sexual growth dimorphism.

Mechanisms of Sperm–Egg Interactions: What Ascidian Fertilization Research Has Taught Us

Fertilization is an essential process in terrestrial organisms for creating a new organism with genetic diversity. Before gamete fusion, several steps are required to achieve successful fertilization. Animal spermatozoa are first activated and attracted to the eggs by egg-derived chemoattractants. During the sperm passage of the egg’s extracellular matrix or upon the sperm binding to the proteinaceous egg coat, the sperm undergoes an acrosome reaction, an exocytosis of acrosome. In hermaphrodites such as ascidians, the self/nonself recognition process occurs when the sperm binds to the egg coat. The activated or acrosome-reacted spermatozoa penetrate through the proteinaceous egg coat. The extracellular ubiquitin–proteasome system, the astacin-like metalloproteases, and the trypsin-like proteases play key roles in this process in ascidians. In the present review, we summarize our current understanding and perspectives on gamete recognition and egg coat lysins in ascidians and consider the general mechanisms of fertilization in animals and plants.

Proteome and Transcriptome Analysis of Gonads Reveals Intersex in Gigantidas haimaensis

Sex has proven to be one of the most intriguing areas of research across evolution, development, and ecology. Intersex or sex change occurs frequently in molluscs. The deep-sea mussel Gigantidas haimaensis often dominates within Haima cold seep ecosystems, but details of their reproduction remain unknown. Herein, we conducted a combined proteomic and transcriptomic analysis of G. haimaensis gonads to provide a systematic understanding of sexual development in deep-sea bivalves. A total of 2,452 out of 42,238 genes (5.81%) and 288 out of 7,089 proteins (4.06%) were significantly differentially expressed between ovaries and testes with a false discovery rate (FDR) <0.05. Candidate genes involved in sexual development were identified; among 12 differentially expressed genes between sexes, four ovary-biased genes (β-catenin, fem-1, forkhead box L2 and membrane progestin receptor α) were expressed significantly higher in males than females. Combining histological characteristics, we speculate that the males maybe intersex undergoing sex change, and implied that these genes may be involved in the process of male testis converting into female gonads in G. haimaensis. The results suggest that this adaptation may be based on local environmental factors, sedentary lifestyles, and patchy distribution, and sex change may facilitate adaptation to a changing environment and expansion of the population. The findings provide a valuable genetic resource to better understand the mechanisms of sex change and survival strategies in deep-sea bivalves.

Silencing of vitellogenin gene contributes to the promise of controlling red palm weevil, Rhynchophorus ferrugineus (Olivier)

Red palm weevil [Rhynchophorus ferrugineus (Olivier)], is native to South Asia and expanding its distribution range globally. Recent invasions of red palm weevil around the world, including Saudi Arabia, has become a global constraint for the production of palm species. Although, several control measures have been tested, none of them seemed successful against this invasive species. Therefore, we focused on silencing the reproduction control gene vitellogenin (Vg) based on RNA interference (RNAi) strategy for its possible application in the management of R. ferrugineus. The Vg is a major yolk protein precursor critical for oogenesis. To do this, fat body transcriptome of R. ferrugineus female adults was sequenced, which provided partial Vg gene transcript (FPKM 5731.60). A complete RfVg gene transcript of 5504 bp encoding 1787 amino acids was then sequenced using RCAE-PCR strategy and characterized. Phylogenetic analysis suggested that RfVg has closer ancestry to the coleopteran insects. The RfVg-based RNAi significantly suppressed the expressions of Vg gene. The 15, 20 and 25 days post-injection periods suppressed Vg expressions by 95, 96.6 and 99%, respectively. The suppressed Vg expressions resulted in the dramatic failure of Vg protein expression, which caused atrophied ovaries or no oogenesis and ultimately eggs were not hatched. These results suggest that knockdown of Vg gene involved in R. ferrugineus reproduction is a promising target for RNAi-based management of R. ferrugineus.

RNAi-mediated silencing of vitellogenin gene curtails oogenesis in the almond moth Cadra cautella

Vitellogenins, major yolk protein precursors, play an essential role in the reproduction and spread of all oviparous species, including insects. To investigate reproductive strategies of the warehouse moth Cadra cautella at the molecular level, a partial transcript of the C. cautella vitellogenin (CcVg) gene was extended through the rapid amplification of cDNA ends PCR and sequenced. The complete CcVg mRNA transcript was 5,334 bp long, which encoded a protein of 1,778 amino acids, including the first 14 amino acids of the signal peptide. The deduced CcVg protein contained a putative cleavage site (RTRR) at the amino-terminal side, similar to several other insect species. DGQR and GI/LCG motifs were present at the CcVg gene C-terminus, followed by nine cysteine residues. CcVg harbored 131 putative phosphorylation sites, numbering 84, 19, and 28 sites for serine, threonine, and tyrosine, respectively. The transcript showed a great resemblance with other lepidopteran Vgs. CcVg protein analysis revealed three conserved regions: 1) vitellogenin-N domain, 2) DUF 1943 (domain of unknown function), and 3) a von Willebrand factor type D domain. Additionally, sex, stage-specific, and developmental expression profiles of the CcVg gene were determined through RT-PCR. The Vg was first expressed in 22-day-old female larvae, and its expression increased with growth. The phylogenetic analysis based on different insect Vgs revealed that the CcVg exhibited close ancestry with lepidopterans. The CcVg-based RNAi experiments were performed, and the effects were critically evaluated. The qRT-PCR results showed that CcVg-based dsRNA suppressed the Vg gene expression up to 90% at 48 h post-injection. Moreover, CcVg-based RNAi effects resulted in low fecundity and egg hatchability in the CcVg-based dsRNA-treated females. The females laid eggs, but because of insufficient yolk protein availability the eggs could not succeed to hatch. The significant difference in the fecundity and hatchability unveils the importance of CcVg gene silencing and confirmed that the Vg gene plays a key role in C. cautella reproduction and it has the potential to be used as a target for RNAi-mediated control of this warehouse pest.

Peptidome analysis of umbilical cord mesenchymal stem cell (hUC-MSC) conditioned medium from preterm and term infants

Background

The therapeutic role of mesenchymal stem cells (MSCs) has been widely confirmed in several animal models of premature infant diseases. Micromolecule peptides have shown promise for the treatment of premature infant diseases. However, the potential role of peptides secreted from MSCs has not been studied. The purpose of this study is to help to broaden the knowledge of the hUC-MSC secretome at the peptide level through peptidomic profile analysis.

Methods

We used tandem mass tag (TMT) labeling technology followed by tandem mass spectrometry to compare the peptidomic profile of preterm and term umbilical cord MSC (hUC-MSC) conditioned medium (CM). Gene Ontology (GO) enrichment analysis and ingenuity pathway analysis (IPA) were conducted to explore the differentially expressed peptides by predicting the functions of their precursor proteins. To evaluate the effect of candidate peptides on human lung epithelial cells stimulated by hydrogen peroxide (H₂O₂), quantitative real-time PCR (qRT-PCR), western blot analysis, and enzyme-linked immunosorbent assay (ELISA) were, respectively, adopted to detect inflammatory cytokines (TNF-α, IL-1β, and IL-6) expression levels at the mRNA and protein levels.

Results

A total of 131 peptides derived from 106 precursor proteins were differentially expressed in the preterm hUC-MSC CM compared with the term group, comprising 37 upregulated peptides and 94 downregulated peptides. Bioinformatics analysis showed that these differentially expressed peptides may be associated with developmental disorders, inflammatory response, and organismal injury. We also found that peptides ⁷¹¹⁸TGAKIKLVGT⁷¹²⁷ derived from MUC19 and ⁵⁰⁸AAAAGPANVH⁵¹⁷ derived from SIX5 reduced the expression levels of TNF-α, IL-1β, and IL-6 in H₂O₂-treated human lung epithelial cells.

Conclusions

In summary, this study provides further secretomics information on hUC-MSCs and provides a series of peptides that might have antiinflammatory effects on pulmonary epithelial cells and contribute to the prevention and treatment of respiratory diseases in premature infants.

CRISPR/Cas9-induced vitellogenin knockout lead to incomplete embryonic development in Plutella xylostella

Vitellogenin (Vg) is important for insect egg maturation and embryo development. In the present study, we characterized the molecular structure and expression profile of Vg gene, and analyzed its reproductive functions in diamondback moth, Plutella xylostella (L.), a destructive pest of cruciferous crops, using CRISPR/Cas9 system. The P. xylostella Vg (PxVg) included all conserved domains and motifs that were commonly found in most insect Vgs except for the polyserine tract. PxVg gene was highly expressed in female pupae and adults. PxVg protein was detected in eggs and female adults. PxVg was mainly expressed in the fat body and its protein was detected in most tissues, except in the midgut. CRISPR/Cas9-induced PxVg knockout successfully constructed a homozygous mutant strain with a 5-base pair nucleotide deletion. No PxVg protein was found in the mutant individuals and in their ovaries. There were no significant differences between wild (WT) and mutant (Mut-5) types of P. xylostella in terms of ovariole length and the number of fully developed oocytes in newly emerged females. No significant difference was observed in the number of eggs laid within two days, but there was a lower egg hatchability (84% for WT vs. 47% for Mut-5). This is the first study presenting the functions of Vg in ovary development, egg maturation, oviposition and embryonic development of P. xylostella. Our results suggest that the reproductive functions of Vg may be species-specific in insects. It is possible that Vg may not be the major egg yolk protein precursor in P. xylostella. Other "functional Vgs" closely involved in the yolk formation and oogenesis would need to be further explored in P. xylostella.

Proteome and Transcriptome Analysis of Ovary, Intersex Gonads, and Testis Reveals Potential Key Sex Reversal/Differentiation Genes and Mechanism in Scallop Chlamys nobilis

Bivalve mollusks exhibit hermaphroditism and sex reversal/differentiation. Studies generally focus on transcriptional profiling and specific genes related to sex determination and differentiation. Few studies on sex reversal/differentiation have been reported. A combination analysis of gonad proteomics and transcriptomics was conducted on Chlamys nobilis to provide a systematic understanding of sex reversal/differentiation in bivalves. We obtained 4258 unique peptides and 93,731 unigenes with good correlation between messenger RNA and protein levels. Candidate genes in sex reversal/differentiation were found: 15 genes differentially expressed between sexes were identified and 12 had obvious sexual functions. Three novel genes (foxl2, β-catenin, and sry) were expressed highly in intersex individuals and were likely involved in the control of gonadal sex in C. nobilis. High expression of foxl2 or β-catenin may inhibit sry and activate 5-HT receptor and vitellogenin to maintain female development. High expression of sry may inhibit foxl2 and β-catenin and activate dmrt2, fem-1, sfp2, sa6, Amy-1, APCP4, and PLK to maintain male function. High expression of sry, foxl2, and β-catenin in C. nobilis may be involved in promoting and maintaining sex reversal/differentiation. The downstream regulator may not be dimorphic expressed genes, but genes expressed in intersex individuals, males and females. Different expression patterns of sex-related genes and gonadal histological characteristics suggested that C. nobilis may change its sex from male to female. These findings suggest highly conserved sex reversal/differentiation with diverged regulatory pathways during C. nobilis evolution. This study provides valuable genetic resources for understanding sex reversal/differentiation (intersex) mechanisms and pathways underlying bivalve reproductive regulation.

Molecular Cloning of the Vitellogenin Gene and the Effects of Vitellogenin Protein Expression on the Physiology of Harmonia axyridis (Coleoptera: Coccinellidae)

Vitellogenin (Vg), the main egg storage protein precursor, plays an integral role in many oviparous animals, including Harmonia axyridis, an important agent for the biological control of many insect pests. In this study, the full-length Vg gene of was cloned. The open reading frame (ORF) of H. axyridis Vg cDNA is 5,403 bp in length and encodes 1,800 amino acids, with a predicted molecular mass of 211.88 KDa (accession number in NCBI: KX442718). Recombinant protein (18 kDa) expressed by the cloned Vg gene was characterized, and the effects of the expression of this protein on the physiology of H. axyridis were investigated. We found that Vg fragment significantly increased the egg production of H. axyridis. Furthermore, we also found that the activities of trypsin and lipase in H. axyridis were significantly higher in the groups treated with Vg fragment compared with those of the controls. The data from this study also reveals that Vg expression has significant effects on the physiology of H. axyridis and leads to increased egg production in these insects. These results may have future implications for increasing the reproduction rates of beneficial insects.

Follicle cell trypsin-like protease HrOvochymase: Its cDNA cloning, localization, and involvement in the late stage of oogenesis in the ascidian Halocynthia roretzi

We previously reported that the sperm trypsin-like protease HrAcrosin and its precursor HrProacrosin participate in fertilization of the ascidian Halocynthia roretzi. The HrProacrosin gene is annotated in the H. roretzi genome database as Harore.CG.MTP2014.S89.g15383; our previously reported sequence of HrProacrosin gene appeared to include four nucleotides inserted near the 3'-end of HrProacrosin, resulting in a frame-shift mutation and a premature termination codon. The gene architecture of HrProacrosin and Harore.CG.MTP2014.S89.g15383 resembles that of Xenopus laevis ovochymase-1/OVCH1 and ovochymase-2/OVCH2, which encode egg extracellular polyproteases. Considering these new observations, we evaluated the cDNA cloning, expression, localization, and function of Harore.CG.MTP2014.S89.g15383, herein designated as HrOvochymase/HrOVCH. We found that HrOVCH cDNA consists of a single open reading frame of 1,575 amino acids, containing a signal peptide, three trypsin-like protease domains, and six CUB domains. HrOVCH was transcribed by the testis and ovary, but the majority of protein exists in ovarian follicle cells surrounding eggs. An anti-HrOVCH antibody inhibited elevation of the vitelline coat at a late stage of oogenesis, during the period when self-sterility is acquired. As trypsin inhibitors are reported to block the acquisition of self-sterility during oogenesis, whereas trypsin induces the acquisition of self-sterility and elevation of the vitelline coat in defolliculated ovarian eggs, we propose that HrOVCH may play a role in the acquisition of self-sterility by late-stage H. roretzi oocytes.

Analysis of the Vitellogenin gene of rice moth, Corcyra cephalonica Stainton

Vitellogenin (Vg) is a precursor of the major yolk protein, an essential nutrient for the embryonic development of oviparous animals including insects. Here, the gene(CceVg [Corcyra cephalonica Vg] ) encoding the Vg (CceVg of moth, C. cephalonica, was cloned and sequenced. The gene sequence was 6,721-bp long and contained 5five introns and six exons that together formed a 5,382-bp open reading frame. The deduced protein (CceVg) consisted of 1,793 amino acid residues, including a 16-amino-acid signal peptide. The putative molecular weight of the primary Vg protein was 202.46 kDa. The CceVg contained all conserved domains and motifs that were commonly found in most insect Vgs except the presence of a polyserine tract at the C-terminal region, which had not been reported in other lepidopteran Vgs. The expression pattern showed that CceVg was first transcribed at a very low level in the early larval stage but disappeared in later stage larva. In female, the CceVg mRNA was detected in early pupal stage and throughout adult stage. Interestingly, the CceVg mRNA was detected only in mated males at low levels, not in the virgin ones. Injection of CceVg double-stranded RNA into early-emergent females caused severely abnormal ovaries.

Tradeoff between reproduction and resistance evolution to Bt-toxin in Helicoverpa armigera: regulated by vitellogenin gene expression

Evolution of resistance to insecticides usually has fitness tradeoffs associated with adaptation to the stress. The basic regulation mechanism of tradeoff between reproduction and resistance evolution to Bacillus thuringiensis (Bt) toxin in the cotton bollworm, Helicoverpa armigera (Ha), based on the vitellogenin (Vg) gene expression was analyzed here. The full-length cDNA of the Vg gene HaVg (JX504706) was cloned and identified. HaVg has 5704 base pairs (bp) with an open reading frame (ORF) of 5265 bp, which encoded 1756 amino acid protein with a predicted molecular mass of 197.28 kDa and a proposed isoelectric point of 8.74. Sequence alignment analysis indicated that the amino acid sequence of HaVg contained all of the conserved domains detected in the Vgs of the other insects and had a high similarity with the Vgs of the Lepidoptera insects, especially Noctuidae. The resistance level to Cry1Ac Bt toxin and relative HaVg mRNA expression levels among the following four groups: Cry1Ac-susceptible strain (96S), Cry1Ac-resistant strain fed on artificial diet with Bt toxin for 135 generations (BtR stands for the Cry1Ac Bt resistance), progeny of the Cry1Ac-resistant strain with a non-Bt-toxin artificial diet for 38 generations (CK1) and the direct descendants of the 135th-generation resistant larvae which were fed on an artificial diet without the Cry1Ac protein (CK2) were analyzed. Compared with the 96S strain, the resistance ratios of the BtR strain, the CK1 strain and the CK2 strain were 2917.15-, 2.15- and 2037.67-fold, respectively. The maximum relative HaVg mRNA expression levels of the BtR strain were approximately 50% less than that of the 96S strain, and the coming of maximum expression was delayed for approximately 4 days. The overall trend of the HaVg mRNA expression levels in the CK1 strain was similar to that in the 96S strain, and the overall trend of the HaVg mRNA expression levels in the CK2 strain was similar to that in the BtR strain. Our results suggest that the changes in reproduction due to the Bt-toxin resistance evolution in the BtR strain may be regulated by the Vg gene expression. The down-regulation of HaVg at the early stages resulted in a period of delayed reproduction and decreased fecundity in the BtR strain. This performance disappeared when the Bt-toxin selection pressure was lost.

Sperm proteases and extracellular ubiquitin-proteasome system involved in fertilization of ascidians and sea urchins

Ascidians (primitive chordates) are hermaphroditic animals that release spermatozoa and eggs almost simultaneously, but some species, including Halocynthia roretzi, show strict self-sterility. In H. roretzi, a 70-kDa vitelline coat (VC) protein consisting of 12 EGF-like repeats, named HrVC70, appears to be a promising candidate for the self/nonself-recognition (or allorecognition) system during gamete interaction. After spermatozoon recognizes the VC as nonself, sperm 700-kDa extracellular ubiquitin-conjugating enzyme complex appears to ubiquitinate Lys234 of HrVC70, and the ubiquitinated HrVC70 is degraded by the sperm 26S proteasome that is located on the sperm head surface. This novel ubiquitin-proteasome system enables spermatozoa to penetrate through the VC. Sperm trypsin-like proteases, acrosin and spermosin, also participate in fertilization, probably as sperm-side 'movable' binding proteins to the VC.

Proteomic characterization and evolutionary analyses of zona pellucida domain-containing proteins in the egg coat of the cephalochordate, Branchiostoma belcheri

Background

Zona pellucida domain-containing proteins (ZP proteins) have been identified as the principle constituents of the egg coat (EC) of diverse metazoan taxa, including jawed vertebrates, urochordates and molluscs that span hundreds of millions of years of evolutionary divergence. Although ZP proteins generally contain the zona pellucida (ZP) structural modules to fulfill sperm recognition and EC polymerization functions during fertilization, the primary sequences of the ZP proteins from the above-mentioned animal classes are drastically different, which makes it difficult to assess the evolutionary relationships of ZP proteins. To understand the origin of vertebrate ZP proteins, we characterized the egg coat components of Branchiostoma belcheri, an invertebrate species that belongs to the chordate subphylum Cephalochordata.

Results

Five ZP proteins (BbZP1-5) were identified by mass spectrometry analyses using the egg coat extracts from both unfertilized and fertilized eggs. In addition to the C-terminal ZP module in each of the BbZPs, the majority contain a low-density lipoprotein receptor domain and a von Willebrand factor type A (vWFA) domain, but none possess an EGF-like domain that is frequently observed in the ZP proteins of urochordates. Fluorescence in situ hybridization and immuno-histochemical analyses of B. belcheri ovaries showed that the five BbZPs are synthesized predominantly in developing eggs and deposited around the extracellular space of the egg, which indicates that they are bona fide egg coat ZP proteins. BbZP1, BbZP3 and BbZP4 are significantly more abundant than BbZP2 and BbZP5 in terms of gene expression levels and the amount of mature proteins present on the egg coats. The major ZP proteins showed high polymorphism because multiple variants are present with different molecular weights. Sequence comparison and phylogenetic analysis between the ZP proteins from cephalochordates, urochordates and vertebrates showed that BbZP1-5 form a monophyletic group and share no significant sequence similarities with the ZP proteins of urochordates and the ZP3 subtype of jawed vertebrates. By contrast, small regions of homology were identifiable between the BbZP and ZP proteins of the non-jawed vertebrate, the sea lamprey Petromyzon marinus. The lamprey ZP proteins were highly similar to the ZP1 and ZP2 subtypes of the jawed vertebrates, which suggests that the ZP proteins of basal chordates most likely shared a recent common ancestor with vertebrate ZP1/2 subtypes and lamprey ZP proteins.

Conclusions

The results document the spectra of zona pellucida domain-containing proteins of the egg coat of basal chordates. Particularly, the study provides solid evidence for an invertebrate origin of vertebrate ZP proteins and indicates that there are diverse domain architectures in ZP proteins of various metazoan groups.

Localization and enzymatic activity profiles of the proteases responsible for tachykinin-directed oocyte growth in the protochordate, Ciona intestinalis

We previously substantiated that Ci-TK, a tachykinin of the protochordate, Ciona intestinalis (Ci), triggered oocyte growth from the vitellogenic stage (stage II) to the post-vitellogenic stage (stage III) via up-regulation of the gene expression and enzymatic activity of the proteases: cathepsin D, carboxypeptidase B1, and chymotrypsin. In the present study, we have elucidated the localization, gene expression and activation profile of these proteases. In situ hybridization showed that the Ci-cathepsin D mRNA was present exclusively in test cells of the stage II oocytes, whereas the Ci-carboxypeptidase B1 and Ci-chymotrypsin mRNAs were detected in follicular cells of the stage II and stage III oocytes. Double-immunostaining demonstrated that the immunoreactivity of Ci-cathepsin D was largely colocalized with that of the receptor of Ci-TK, Ci-TK-R, in test cells of the stage II oocytes. Ci-cathepsin D gene expression was detected at 2h after treatment with Ci-TK, and elevated for up to 5h, and then slightly decreased. Gene expression of Ci-carboxypeptidase B1 and Ci-chymotrypsin was observed at 5h after treatment with Ci-TK, and then decreased. The enzymatic activities of Ci-cathepsin D, Ci-carboxypeptidase B1, and Ci-chymotrypsin showed similar alterations with 1-h lags. These gene expression and protease activity profiles verified that Ci-cathepsin D is initially activated, which is followed by the activation of Ci-carboxypeptidase B1 and Ci-chymotrypsin. Collectively, the present data suggest that Ci-TK directly induces Ci-cahtepsin D in test cells expressing Ci-TK receptor, leading to the secondary activation of Ci-chymotrypsin and Ci-carboxypeptidase B1 in the follicle in the tachykininergic oocyte growth pathway.

Molecular cloning, transcriptional regulation, and differential expression profiling of vitellogenin in two wing-morphs of the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper, Nilaparvata lugens, is a serious pest of rice crops throughout Asia and exhibits wing dimorphism, with brachypterous adults having reduced wings and macropterous adults possessing fully developed wings. To understand the reproductive strategies in two wing-morphs of this insect, the transcript encoding the major yolk protein precursor, vitellogenin (Vg), was cloned. The complete mRNA transcript was 6314 bp, which encodes a protein of 2063 residues including an 18-residue putative signal peptide. Analysis of the mature protein revealed two vitellogenin-N (or lipoprotein amino-terminal) domains near the N-terminus and a von Willebrand factor type D domain near the C-terminus. In addition, a highly conserved motif GL/ICG, and a number of cysteine residues were identified near the C-terminus. Northern blot analysis identified a ∼6.8 kb Vg gene transcript that was expressed exclusively in the adult female fat body cells. The expression profile revealed that the Vg gene starts to be expressed earlier (on day 3) in brachypters as compared to macropters where the mRNA transcript was observed on day 4. However, in both morphs, the amount of Vg mRNA increased to reach high levels during vitellogenic periods [from day 4 (in brachypters) and day 5 (in macropters) and onwards]. Reflecting the RNA transcription pattern, the Vg signal was detected by immunoblotting on day 3 and day 4 in haemolymph of brachypterous and macropterous females, respectively, and that was increased every day and remained high during the vitellogenic periods. Furthermore, the topical application of juvenile hormone (JH) III had up-regulated the Vg gene expression suggesting that the Vg gene is regulated by JH in N. lugens. In addition, it was demonstrated by Southern blot analysis that there exists a single copy of the gene in the N. lugens genome. A delayed trend in expression (of both the transcript and the protein) demonstrated by macropterous females in the present studies supports the hypothesis of prereproductive long distance migration in this wing-dimorphic species.