Gene structure and expression of cg-ALR1, a type I activin-like receptor from the bivalve mollusc Crassostrea gigas

Cloning and Expression Analysis of TGF-β Type I Receptor Gene in Hyriopsis cumingii

The TGF-β signaling pathway plays an important role in wound healing and immune response. In this study, a TGF-β type I receptor (TGF-βRI) homolog was cloned and characterized from freshwater mussel Hyriopsis cumingii. The full-length cDNA of the TGF-β RI gene was 2017 bp, with a 1554 bp open reading frame (ORF), and encoded 517 amino acids. The predictive analysis further identified distinct regions within the TGF-βRI protein: a signal peptide, a membrane outer region, a transmembrane region, and an intracellular region. Real-time quantitative PCR results showed that the TGF-β RI gene was expressed in all tissues of healthy mussels. The transcripts of TGF-β RI in hemocytes and hepatopancreas were significantly up-regulated at different periods after stimulation with Aeromonas hydrophila and peptidoglycan (PGN) (P < 0.05). The mRNA expression of TGF-β RI progressively increased from day 1 to day 10 after trauma (P < 0.05), and it returned to the initial level by day 15. The expression levels of TGF-β , Smad5, MMP1/19, and TIMP1/2, but not Smad3/4, were significantly up-regulated at different time points after trauma. However, the expression levels of TGF-β , MMP1/19, and TIMP2 were decreased after treatment with the inhibitor SB431542. Furthermore, the recombinant TGF-βRI proteins were expressed in vitro and existed in the form of inclusion bodies. Western blotting results showed that TGF-βRI proteins were expressed constitutively in various tissues of mussels, and their expression was up-regulated after trauma, which was consistent with the mRNA expression trend. These results indicate that TGF-β RI is involved in the process of wound repair and immune response.

Molecular cloning and characteristics analysis of Pmtgfbr1 from Pinctada fucata martensii

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This study obtains the full length of Pmtgfbr1 of the pearl oyster P. fucata martensii.

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Pmtgfbr1 possesses the conserved domain of Tgfbr1.

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Pmtgfbr1 holds negatively effect on the growth of P. fucata martensii.

Pinctada fucata martensii is cultured for pearl production. Growth improvement has received considerable research interest. Transforming growth factor β type Ⅰ receptor (TβR-I), which is involved in signals transmission of transforming growth factor beta (TGF-β), participates in cell proliferation and growth. In this study, we characterized a Tgfbr1 gene which encoded TβR-I from P. fucata martensii (Pmtgfbr1). Pmtgfbr1 cDNA contains an open reading frame of 1569 bp and encodes a polypeptide of 522 amino acids (aa). Pmtgfbr1 possesses a typical TβR-I structure (extracellular receptor ligand domain, transmembrane domain, and cytoplasmic tyrosine kinase catalytic domain). Pmtgfbr1 is expressed in all the studied tissues and exhibited the highest expression level in the adductor muscle. Moreover, Pmtgfbr1 exhibited the lower expression level in the larger group (L) than that in the smaller group (S) and is negatively correlated with growth traits (P < 0.01). Our results indicated that Pmtgfbr1 is a candidate functional gene associated with growth traits.

The receptor genes PfBMPR1B and PfBAMBI are involved in regulating shell biomineralization in the pearl oyster Pinctada fucata

Mounting evidence suggests that TGFβ/BMP signaling pathway is most likely involved in shell biomineralization in molluscs, but the function of pathway receptors is poorly studied. Here, we cloned and identified two homologous BMP receptor genes, PfBMPR1B and PfBAMBI, from the pearl oyster Pinctada fucata. Real-time quantitative PCR and in situ hybridization revealed that these genes were expressed in mantle edge and pallial, specifically located at the outer epithelia. Knockdown of PfBMPR1B by RNA interference (RNAi) significantly decreased the expression levels of matrix protein (MP) genes and induced the abnormal ultrastructure of prismatic and nacreous layers. Conversely, knockdown of PfBAMBI significantly increased the expression levels of a portion of MP genes and induced the overgrowth of nacreous layer crystals. In the RNAi and shell notching experiments, MP gene expressions were competitively regulated by PfBMPR1B and PfBAMBI. In addition, the receptor inhibitor LDN193189 reduced the expression levels of MP genes in mantle primary cells and larvae, and induced abnormal D-shaped shell formation during larval development. Collectively, these results clearly show that PfBMPR1B and PfBAMBI are involved in regulating shell biomineralization in P. fucata. Our study therefore provides the direct evidence that BMP receptors participate in mollusc biomineralization.

Molecular characterization of two distinct Smads gene and their roles in the response to bacteria change and wound healing from Hyriopsis cumingii

The proteins of Smad family are critical components of the TGF-β superfamily signal pathway. In this paper, we cloned two intracellular mediators of TGF-β signaling, Smad3 and Smad5, from the pearl mussel Hyriopsis cumingii. The full length cDNA of HcSmad3 and HcSmad5 were 2052 bp and 1908 bp and encoded two polypeptides of 418 and 461amino acid residues, respectively. The deduced amino acid of HcSmad3 and HcSmad5 possessed two putative conserved domains, MH1 and MH2, a conserved phosphorylation motif SSXS at the carboxyl-terminal. The two Smad genes were detected muscle, mantle, hepatopancreas and gill, but with a very low level in heamocytes. The transcripts of Smad3 and Smad5 were up-regulated in hemocytes and hepatopancreas after A. hydrophila and PGN stimulation. However, the expression of Smad3 and Smad5 were only up-regulated in hepatopancreas after A. hydrophila stimulation. The transcripts of Smad3 and Smad5 had a slight change in hepatopancreas after PGN stimulation. The transcripts of HcSmad3 showed very little increase and HcSmad5 mRNA significantly up-regulated after wounding.

The Kinome of Pacific Oyster Crassostrea gigas, Its Expression during Development and in Response to Environmental Factors

Oysters play an important role in estuarine and coastal marine habitats, where the majority of humans live. In these ecosystems, environmental degradation is substantial, and oysters must cope with highly dynamic and stressful environmental constraints during their lives in the intertidal zone. The availability of the genome sequence of the Pacific oyster Crassostrea gigas represents a unique opportunity for a comprehensive assessment of the signal transduction pathways that the species has developed to deal with this unique habitat. We performed an in silico analysis to identify, annotate and classify protein kinases in C. gigas, according to their kinase domain taxonomy classification, and compared with kinome already described in other animal species. The C. gigas kinome consists of 371 protein kinases, making it closely related to the sea urchin kinome, which has 353 protein kinases. The absence of gene redundancy in some groups of the C. gigas kinome may simplify functional studies of protein kinases. Through data mining of transcriptomes in C. gigas, we identified part of the kinome which may be central during development and may play a role in response to various environmental factors. Overall, this work contributes to a better understanding of key sensing pathways that may be central for adaptation to a highly dynamic marine environment.

Maternal immune transfer in mollusc

Maternal immunity refers to the immunity transferred from mother to offspring via egg, playing an important role in protecting the offspring at early life stages and contributing a trans-generational effect on offspring's phenotype. Because fertilization is external in most of the molluscs, oocytes and early embryos are directly exposed to pathogens in the seawater, and thus maternal immunity could provide a better protection before full maturation of their immunological systems. Several innate immune factors including pattern recognition receptors (PRRs) like lectins, and immune effectors like lysozyme, lipopolysaccharide binding protein/bacterial permeability-increasing proteins (LBP/BPI) and antioxidant enzymes have been identified as maternally derived immune factors in mollusc eggs. Among these immune factors, some maternally derived lectins and antibacterial factors have been proved to endue mollusc eggs with effective defense ability against pathogen infection, while the roles of other factors still remain untested. The physiological condition of mollusc broodstock has a profound effect on their offspring fitness. Many other factors such as nutrients, pathogens, environment conditions and pollutants could exert considerable influence on the maternal transfer of immunity. The parent molluscs which have encountered an immune stimulation endow their offspring with a trans-generational immune capability to protect them against infections effectively. The knowledge on maternal transfer of immunity and the trans-generational immune effect could provide us with an ideal management strategy of mollusc broodstock to improve the immunity of offspring and to establish a disease-resistant family for a long-term improvement of cultured stocks.

Molecular characterization of TGF-β type I receptor gene (Tgfbr1) in Chlamys farreri, and the association of allelic variants with growth traits

BACKGROUND

Scallops are an economically important aquaculture species in Asian countries, and growth-rate improvement is one of the main focuses of scallop breeding. Investigating the genetic regulation of scallop growth could benefit scallop breeding, as such research is currently limited. The transforming growth factor beta (TGF-β) signaling through type I and type II receptors, plays critical roles in regulating cell proliferation and growth, and is thus a plausible candidate growth regulator in scallops.

RESULTS

We cloned and characterized the TGF-β type I receptor (Tgfbr1) gene from Zhikong scallops (Chlamys farreri). The deduced amino acid sequence contains characteristic residues and exhibits the conserved structure of Tgfbr1 proteins. A high expression level of scallop Tgfbr1 was detected during early embryonic stages, whereas Tgfbr1 expression was enriched in the gonad and striated muscle in adults. A single nucleotide polymorphism (SNP, c. 1815C>T) in the 3' UTR was identified. Scallops with genotype TT had higher growth traits values than those with genotype CC or CT in a full-sib family, and significant differences were found between genotypes CC and TT for shell length, shell height, and striated muscle weight. An expression analysis detected significantly more Tgfbr1 transcripts in the striated muscle of scallops with genotype CC compared to those with genotype TT or CT. Further evaluation in a population also revealed higher striated muscle weight in scallops with genotype TT than those with the other two genotypes. The inverse correlation between striated muscle mass and Tgfbr1 expression is consistent with TGF-β signaling having a negative effect on cell growth.

CONCLUSION

The scallop Tgfbr1 gene was cloned and characterized, and an SNP potentially associated with both scallop growth and Tgfbr1 expression was identified. Our results suggest the negative regulation of Tgfbr1 in scallop growth and provide a candidate marker for Zhikong scallop breeding.

Cloning and characterization of the activin like receptor 1 homolog (Pf-ALR1) in the pearl oyster, Pinctada fucata

The signal transduction mechanisms in mollusks are still elusive since the genome information is incomplete and cell lines are not available. In previous study, we cloned a highly conserved Smad3 homolog (designated as Pf-Smad3) from the pearl oyster, Pinctada fucata. It seems that transforming growth factor beta (TGFbeta) signaling may play similar roles in the oyster as in vertebrate. Here we report a cDNA encoding an activin like receptor 1 homolog (designated as Pf-ALR1) of the oyster, another kind of TGFbeta superfamily member. Compared to the activin receptor-like kinases (ALK) in human, the amino acid sequence of Pf-ALR1 is more similar to that of ALK1, especially the L45 loop. Reverse transcription-polymerase chain reaction results indicate that Pf-ALR1 mRNA is expressed ubiquitously in the adult oyster. Thus, Pf-ALR1 may be important for many physiological processes in the oyster. To lay a basis for further investigation of the TGFbeta signal pathway functions in the oyster shell formation, in this report, the Pf-ALR1 mRNA expression in the oyster mantle was detected by in situ hybridization. The results show that Pf-ALR1 in the oyster mantle is mainly expressed at the inner epithelial cells of the outer fold and the outer epithelial cells of the middle fold, similarly as Pf-Smad3. The mRNA levels of Pf-ALR1 and Pf-Smad3 are all changed after shell notching. These results indicate that both Pf-ALR1 and Pf-Smad3 may take part in shell formation and repair. The results of drug treatment experiments with in-vitro cultured oyster mantle tissue cells demonstrate that the mRNA expression levels of Pf-Smad3, Pf-ALR1 and two oyster nuclear factor-kappaB (NF-kB) members can be adjusted and correlated. All our observations suggest that there should be similar TGFbeta signal pathways in the oyster and vertebrate. However, the potential functions of Pf-ALR1 and the relations of TGFbeta and NF-kB members in the oyster all need to be thoroughly investigated.

Structural and functional characterizations of an Activin type II receptor orthologue from the pacific oyster Crassostrea gigas

Members of the Transforming Growth factor beta (TGF-beta) superfamily of cell signalling polypeptides are known to play important roles in cell proliferation and differentiation during development and in various physiological processes of most animal clades. Recent findings in the mollusc Crassostrea gigas demonstrate the occurrence of a diversity of TGF-beta signalling components including various ligands, three type I receptors but only a single type II receptor. This report describes the characterization of Cg-ActRII, a new type II receptor displaying homology with vertebrate and Drosophila Activin type II receptors. The use of zebrafish embryo as a reporter organism revealed that, in a way similar to its zebrafish counterpart, overexpression of Cg-ActRII or its dominant negative acting truncated form resulted in a dose dependent range of dorsoventral defects coupled with anterior disorders. Expression pattern of Cg-ActRII transcripts examined by real time PCR and in situ PCR in C. gigas showed high levels of Cg-ActRII transcripts in early embryonic stages and in the developing larval central nervous system. Except for a high expression in the visceral ganglia, most oyster adult tissues displayed rather low levels of transcripts. Altogether, the data suggest a high degree of conservation at both the structural and functional levels during evolution for this class of receptors.

Characterization of a gonad-specific transforming growth factor-beta superfamily member differentially expressed during the reproductive cycle of the oyster Crassostrea gigas

Through differential screening between oyster families selected for high and low summer survival, we have characterized a new transforming growth factor-beta (TGF-beta) superfamily member. This novel factor, named oyster-gonadal-TGFbeta-like (og-TGFbeta-like), is synthesized as a 307 amino acid precursor and displays 6 of the 7 characteristic cysteine residues of the C-terminal, mature peptide. Sequence comparison revealed that og-TGFbeta-like has a low percentage of identity with other known TGF-beta superfamily members, suggesting that og-TGFbeta-like is a derived member of this large superfamily. Real-time PCR (RT-PCR) analysis in different oyster tissues showed that og-TGFbeta-like is specifically expressed in both male and female gonads, at distinct levels according to the reproductive stage. Og-TGFbeta-like relative expression was the lowest at the initiation of the reproductive cycle and increased as maturation proceeded to achieve a maximal level in fully mature female and male oysters. In situ hybridisation demonstrated that expression was exclusively detected in the somatic cells surrounding oocytes and spermatocytes. The role of this newly-characterized TGFbeta member in the reproduction of cupped oyster is discussed in regard to the specificity and the localization of its expression, which singularly contrasts with the pleiotropic roles in a variety of physiological processes commonly ascribed to most TGF-beta family members identified so far.

Cg-TGF-beta, a TGF-beta/activin homologue in the Pacific Oyster Crassostrea gigas, is involved in immunity against Gram-negative microbial infection

Transforming growth factor-beta (TGF-beta) members represent a widespread protein superfamily in the animal kingdom, but few members have been characterised in lophotrochozoans, a major clade of invertebrates. Here, we report the identification of Crassostrea gigas-TGF-beta (Cg-TGF-beta), a homologue of vertebrate TGF-beta and activin, from the bivalve mollusc C. gigas. Phylogenetic analysis suggests an early ancestral origin of this subgroup of TGF-beta superfamily member. Investigation of the spatio-temporal expression of Cg-TGF-beta gene by real-time quantitative RT-PCR showed a ubiquitous pattern in all adult tissues. These findings imply that Cg-TGF-beta has multiple functions as described for its vertebrate counterparts. Moreover, Cg-TGF-beta was upregulated in haemocytes during infection by a Gram-negative bacterium, suggesting that it could act as a cytokine involved in immunity in molluscs.

New resources for marine genomics: bacterial artificial chromosome libraries for the Eastern and Pacific oysters (Crassostrea virginica and C. gigas)

Large-insert genomic bacterial artificial chromosome (BAC) libraries of two culturally and economically important oyster species, Crassostrea virginica and C. gigas, have been developed as part of an international effort to develop tools and reagents that will advance our ability to conduct genetic and genomic research. A total of 73,728 C. gigas clones with an average insert size of 152 kb were picked and arrayed representing an 11.8-fold genome coverage. A total of 55,296 clones with an average insert size of 150 kb were picked and arrayed for C. virginica, also representing an 11.8-fold genome coverage. The C. gigas and C. virginica libraries were screened with probes derived from selected oyster genes using high-density BAC colony filter arrays. The probes identified 4 to 25 clones per gene for C. virginica and 5 to 50 clones per gene for C. gigas. We conducted a preliminary analysis of genetic polymorphism represented in the C. gigas library. The results suggest that the degree of divergence among similar sequences is highly variable and concentrated in intronic regions. Evidence supporting allelic polymorphism is reported for two genes and allelic and/or locus specific polymorphism for several others. Classical inheritance studies are needed to confirm the nature of these polymorphisms. The oyster BAC libraries are publicly available to the research community on a cost-recovery basis at (www.genome.clemson.edu).

The phylogenetically conserved molluscan chitinase-like protein 1 (Cg-Clp1), homologue of human HC-gp39, stimulates proliferation and regulates synthesis of extracellular matrix components of mammalian chondrocytes

Members of chitinase-like proteins (CLPs) have attracted much attention because of their ability to promote cell proliferation in insects (imaginal disc growth factors) and mammals (YKL-40). To gain insights into the molecular processes underlying the physiological control of growth and development in Lophotrochozoa, we report here the cloning and biochemical characterization of the first Lophotrochozoan CLP from the oyster Crassostrea gigas (Cg-Clp1). Gene expression profiles monitored by real time quantitative reverse transcription-PCR in different adult tissues and during development support the involvement of this protein in the control of growth and development in C. gigas. Recombinant Cg-Clp1 demonstrates a strong affinity for chitin but no chitinolytic activity, as was described for the HC-gp39 mammalian homolog. Furthermore, transient expression of Cg-Clp1 in primary cultures of rabbit articular chondrocytes as well as the use of both purified recombinant protein and conditioned medium from Cg-Clp1-expressing rabbit articular chondrocytes established that Cg-Clp1 stimulates cell proliferation and regulates extracellular matrix component synthesis, showing for the first time a possible involvement of a CLP on type II collagen synthesis regulation. These observations together with the fact that Cg-Clp1 gene organization strongly resembles that of its mammalian homologues argue for an early evolutionary origin and a high conservation of this class of proteins at both the structural and functional levels.

Structural and functional evidence for a singular repertoire of BMP receptor signal transducing proteins in the lophotrochozoan Crassostrea gigas suggests a shared ancestral BMP/activin pathway

The transforming growth factor beta (TGF-beta) superfamily includes bone morphogenetic proteins, activins and TGF-betasensu stricto (s.s). These ligands, which transduce their signal through a heteromeric complex of type I and type II receptors, have been shown to play a key role in numerous biological processes including early embryonic development in both deuterostomes and ecdyzozoans. Lophochotrozoans, the third major group of bilaterian animals, have remained in the background of the molecular survey of metazoan development. We report the cloning and functional study of the central part of the BMP pathway machinery in the bivalve mollusc Crassostrea gigas (Cg-BMPR1 type I receptor and Cg-TGFbetasfR2 type II receptor), showing an unusual functional mode of signal transduction for this superfamily. The use of the zebrafish embryo as a reporter organism revealed that Cg-BMPR1, Cg-TGFbetasfR2, Cg-ALR I, an activin Type I receptor or their dominant negative acting truncated forms, when overexpressed during gastrulation, resulted in a range of phenotypes displaying severe disturbance of anterioposterior patterning, due to strong modulations of ventrolateral mesoderm patterning. The results suggest that Cg-BMPR1, and to a certain degree Cg-TGFbetasfR2 proteins, function in C. gigas in a similar way to their zebrafish orthologues. Finally, based on phylogenetic analyses, we propose an evolutionary model within the complete TGF-beta superfamily. Thus, evidence provided by this study argues for a possible conserved endomesoderm/ectomesoderm inductive mechanism in spiralians through an ancestral BMP/activin pathway in which the singular, promiscuous and probably unique Cg-TGFbetasfR2 would be the shared type II receptor interface for both BMP and activin ligands.

Structural and functional evidences for a type 1 TGF-beta sensu stricto receptor in the lophotrochozoan Crassostrea gigas suggest conserved molecular mechanisms controlling mesodermal patterning across bilateria

The transforming growth factor beta (TGFbeta) superfamily includes bone morphogenetic proteins, activins and TGF-betasensu stricto (s.s.). These ligands have been shown to play a key role in numerous biological processes including early embryonic development and immune regulation. They transduce their signal through a hetromeric complex of type I and type II receptors. Such receptors have been identified in ecdysozoans but none have been found as yet in the other major protostomal clade, the lophotrochozoans. Here, we report the identification of the first lophotrochozoan TGFbetas.s. type I receptor (Cg-TGFbetaRI) from the mollusk Crassostrea gigas. The phylogenetic and structural analyses as well as the expression pattern during early development suggest Cg-TGFbetaRI to belong to the TGFbetas.s./activin type I receptor clade and functional studies corroborate these deductions. The use of the zebrafish embryo as a reporter organism reveals that either Cg-TGFbetaRI or its dominant negative acting truncated form, when overexpressed during gastrulation, resulted in a range of phenotypes displaying severe disturbance of anterioposterior patterning due to a strong modulation of ventrolateral mesoderm patterning. Finally, a Cg-TGFbetaRI cytokine activity during immune regulation in C. gigas has been investigated by real-time PCR in haemocytes and mantle edge during an in vivo bacterial LPS challenge. One piece of evidence from this study suggests that the molecular mechanisms controlling mesodermal patterning and some immune regulations across all bilateria could be conserved through a functional TGF-beta s.s. pathway in lophotrochozoans.

Molecular characterization of a new leucine-rich repeat-containing G protein-coupled receptor from a bivalve mollusc: evolutionary implications

The family of leucine-rich repeat-containing G protein-coupled receptors (LGRs) shows members in both vertebrates and invertebrates including the most ancestral ones. Although this suggests an early evolutionary origin of this family of receptors, little is known about their diversity in molluscs, a major phylum of bilaterian invertebrates. Based on sequences of mammalian and insect LGRs, we have cloned and characterized a new typical LGR in the bivalve mollusc Crassostrea gigas. This receptor named Cg-LGRB exhibits high degree of amino acid sequence identity with both mammalian and Drosophila LGRs. Phylogenetic analysis indicates that Cg-LGRB belongs to the cluster of type B orphan LGRs and suggests that molluscs likely express the three LGR subgroups identified previously in other animals. Quantitative RT-PCR shows that Cg-LGRB is expressed mainly in the digestive gland and only at moderate levels in other organs and developmental stages. A possible involvement in the control of cytological changes occurring in bivalve mollusc digestive gland is discussed.

Molecular and physiological characterization of an invertebrate homologue of a calcitonin-related receptor

Calcitonin is a key hormone involved in the regulation of calcium metabolism in vertebrates. Using oligonucleotide primers derived from consensus sequences of vertebrate calcitonin receptors, we have cloned and characterized the first representative of an invertebrate calcitonin receptor from the bivalve mollusc Crassostrea gigas. This receptor named Cg CT-R exhibits 39% amino acid sequence identity with both human calcitonin and calcitonin gene-related precursor receptors. Cg CT-R is expressed mainly in the gills and the mantle edge as well as at lower levels in muscles, digestive gland, heart, and labial palps. Transfer of animals from seawater to brackish water resulted in a significant decrease of Cg CT-R transcript levels in the gills, thus suggesting a role for ionic balance in molluscs.