Transcriptome and quantitative proteome analysis reveals molecular processes associated with larval metamorphosis in the polychaete Pseudopolydora vexillosa

Identification of the principal neuropeptide MIP and its action pathway in larval settlement of the echiuran worm Urechis unicinctus

BACKGROUND

Larval settlement and metamorphosis represent critical events in the life history of marine benthic animals. Myoinhibitory peptide (MIP) plays a pivotal role in larval settlement of marine invertebrates. However, the molecular mechanisms of MIP involved in this process are not well understood.

RESULTS

In this study, we evaluated the effects of thirteen MIP mature peptides on triggering the larval settlement of Urechis unicinctus (Xenopneusta, Urechidae), and determined that MIP2 was the principal neuropeptide. Transcriptomic analysis was employed to identify differentially expressed genes (DEGs) between the MIP2-treated larvae and normal early-segmentation larvae. Both cAMP and calcium signaling pathways were enriched in the DEGs of the MIP2-treated larvae, and two neuropeptide receptor genes (Spr, Fmrfar) were up-regulated in the MIP2-treated larvae. The activation of the SPR-cAMP pathway by MIP2 was experimentally validated in HEK293T cells. Furthermore, fourteen cilia-related genes, including Tctex1d2, Cfap45, Ift43, Ift74, Ift22, Cav1 and Mns1, etc. exhibited down-regulated expression in the MIP2-treated larvae. Whole-mount in situ hybridization identified two selected ciliary genes, Tctex1d2 and Cfap45, were specially expressed in circumoral ciliary cells of the early-segmentation larvae. Knocking down Tctex1d2 mRNA levels by in vivo RNA interference significantly increased the larval settlement rate.

CONCLUSION

Our findings suggest that MIP2 inhibits the function of the cilia-related genes, such as Tctex1d2, through the SPR-cAMP-PKA pathway, thereby inducing larval settlement in U. unicinctus. The study contributes important data to the understanding of neuropeptide regulation in larval settlement.

TRPM7-Mediated Ca2+ Regulates Mussel Settlement through the CaMKKβ-AMPK-SGF1 Pathway

Many marine invertebrates have planktonic larval and benthic juvenile/adult stages. When the planktonic larvae are fully developed, they must find a favorable site to settle and metamorphose into benthic juveniles. This transition from a planktonic to a benthic mode of life is a complex behavioral process involving substrate searching and exploration. Although the mechanosensitive receptor in the tactile sensor has been implicated in sensing and responding to surfaces of the substrates, few have been unambiguously identified. Recently, we identified that the mechanosensitive transient receptor potential melastatin-subfamily member 7 (TRPM7) channel, highly expressed in the larval foot of the mussel Mytilospsis sallei, was involved in substrate exploration for settlement. Here, we show that the TRPM7-mediated Ca2+ signal was involved in triggering the larval settlement of M. sallei through the calmodulin-dependent protein kinase kinase β/AMP-activated protein kinase/silk gland factor 1 (CaMKKβ-AMPK-SGF1) pathway. It was found that M. sallei larvae preferred the stiff surfaces for settlement, on which TRPM7, CaMKKβ, AMPK, and SGF1 were highly expressed. These findings will help us to better understand the molecular mechanisms of larval settlement in marine invertebrates, and will provide insights into the potential targets for developing environmentally friendly antifouling coatings for fouling organisms.

Transcriptome Dynamics of an Oyster Larval Response to a Conspecific Cue-Mediated Settlement Induction in the Pacific Oyster Crassostrea gigas

The molecular mechanisms underlying the conspecific cue-mediated larval settlement in Crassostrea gigas is not yet fully understood. In this study, we described and compared the transcriptomes of competent pediveligers (Pedi) and conspecific cue-induced postlarvae (PL). A total of 2383 candidate transcripts were identified: 740 upregulated and 1643 downregulated transcripts, after settlement. Gene Ontology analysis revealed active chitin binding, calcium ion binding, and extracellular region processes in both stages. Results showed that the differential expression trend of six candidate transcripts were consistent between the quantitative real-time PCR and transcriptome data. The differential transcript expression related to shell formation showed closely linked dynamics with a gene regulatory network that may involve the interplay of various hormone receptors, neurotransmitters, and neuropeptide receptors working together in a concerted way in the Pedi and PL stages. Our results highlight the transcriptome dynamics underlying the settlement of oysters on conspecific adult shells and demonstrate the potential use of this cue as an attractant for wild and hatchery-grown oyster larval attachment on artificial substrates. It also suggests the possible involvement of an ecdysone signal pathway that may be linked to a neuroendocrine-biomineralization crosstalk in C. gigas settlement.

RNA-Seq reveals divergent gene expression between larvae with contrasting trophic modes in the poecilogonous polychaete Boccardia wellingtonensis

The polychaete Boccardia wellingtonensis is a poecilogonous species that produces different larval types. Females may lay Type I capsules, in which only planktotrophic larvae are present, or Type III capsules that contain planktotrophic and adelphophagic larvae as well as nurse eggs. While planktotrophic larvae do not feed during encapsulation, adelphophagic larvae develop by feeding on nurse eggs and on other larvae inside the capsules and hatch at the juvenile stage. Previous works have not found differences in the morphology between the two larval types; thus, the factors explaining contrasting feeding abilities in larvae of this species are still unknown. In this paper, we use a transcriptomic approach to study the cellular and genetic mechanisms underlying the different larval trophic modes of B. wellingtonensis. By using approximately 624 million high-quality reads, we assemble the de novo transcriptome with 133,314 contigs, coding 32,390 putative proteins. We identify 5221 genes that are up-regulated in larval stages compared to their expression in adult individuals. The genetic expression profile differed between larval trophic modes, with genes involved in lipid metabolism and chaetogenesis over expressed in planktotrophic larvae. In contrast, up-regulated genes in adelphophagic larvae were associated with DNA replication and mRNA synthesis.

Molecular identification and larval morphology of spionid polychaetes (Annelida, Spionidae) from northeastern Japan

Planktonic larvae of spionid polychaetes are among the most common and abundant group in coastal meroplankton worldwide. The present study reports the morphology of spionid larvae collected mainly from coastal waters of northeastern Japan that were identified by the comparison of adult and larval 18S and 16S rRNA gene sequences. The molecular analysis effectively discriminated the species. Adult sequences of 48 species from 14 genera (Aonides Claparède, 1864; Boccardia Carazzi, 1893; Boccardiella Blake & Kudenov, 1978; Dipolydora Verrill, 1881; Laonice Malmgren, 1867; Malacoceros Quatrefages, 1843; Paraprionospio Caullery, 1914; Polydora Bosc, 1802; Prionospio Malmgren, 1867; Pseudopolydora Czerniavsky, 1881; Rhynchospio Hartman, 1936; Scolelepis Blainville, 1828; Spio Fabricius, 1785; Spiophanes Grube, 1860) and larval sequences of 41 species from 14 genera (Aonides; Boccardia; Boccardiella; Dipolydora; Laonice; Paraprionospio; Poecilochaetus Claparède in Ehlers, 1875; Polydora; Prionospio; Pseudopolydora; Rhynchospio; Scolelepis; Spio; Spiophanes) of spionid polychaetes were obtained; sequences of 27 of these species matched between adults and larvae. Morphology of the larvae was generally species-specific, and larvae from the same genus mostly shared morphological features, with some exceptions. Color and number of eyes, overall body shape, and type and arrangement of pigmentation are the most obvious differences between genera or species. The morphological information on spionid larvae provided in this study contributes to species or genus level larval identification of this taxon in the studied area. Identification keys to genera and species of planktonic spionid larvae in northeastern Japan are provided. The preliminary results of the molecular phylogeny of the family Spionidae using 18S and 16S rRNA gene regions are also provided.

Proteome of larval metamorphosis induced by epinephrine in the Fujian oyster Crassostrea angulata

Background

The Fujian oyster Crassostrea angulata is an economically important species that has typical settlement and metamorphosis stages. The development of the oyster involves complex morphological and physiological changes, the molecular mechanisms of which are as yet unclear.

Results

In this study, changes in proteins were investigated during larval settlement and metamorphosis of Crassostrea angulata using epinephrine induction. Protein abundance and identity were characterized using label-free quantitative proteomics, tandem mass spectrometry (MS/ MS), and Mascot methods. The results showed that more than 50% (764 out of 1471) of the quantified proteins were characterized as differentially expressed. Notably, more than two-thirds of the differentially expressed proteins were down-regulated in epinephrine-induced larvae. The results showed that “metabolic process” was closely related to the development of settlement and metamorphosis; 5 × 10^− 4 M epinephrine induced direct metamorphosis of larvae and was non-toxic. Calmodulin and MAPK pathways were involved in the regulation of settlement of the oyster. Expression levels of immune-related proteins increased during metamorphosis. Hepatic lectin-like proteins, cadherins, calmodulin, calreticulin, and cytoskeletal proteins were involved in metamorphosis. The nervous system may be remodeled in larval metamorphosis induced by epinephrine. Expression levels of proteins that were enriched in the epinephrine signaling pathway may reflect the developmental stage of the larvae, that may reflect whether or not larvae were directly involved in metamorphosis when the larvae were treated with epinephrine.

Conclusion

The study provides insight into proteins that function in energy metabolism, immune responses, settlement and metamorphosis, and shell formation in C. angulata. The results contribute valuable information for further research on larval settlement and metamorphosis.

Graphical abstract

Transcriptome and proteome dynamics in larvae of the barnacle Balanus Amphitrite from the Red Sea

Background

The barnacle Balanus amphitrite is widely distributed in marine shallow and tidal waters, and has significant economic and ecological importance. Nauplii, the first larval stage of most crustaceans, are extremely abundant in the marine zooplankton. However, a lack of genome information has hindered elucidation of the molecular mechanisms of development, settlement and survival strategies in extreme marine environments. We sequenced and constructed the genome dataset for nauplii to obtain comprehensive larval genetic information. We also investigated iTRAQ-based protein expression patterns to reveal the molecular basis of nauplii development, and to gain information on larval survival strategies in the Red Sea marine environment.

Results

A nauplii larval transcript dataset, containing 92,117 predicted open reading frames (ORFs), was constructed and used as a reference for the proteome analysis. Genes related to translation, oxidative phosphorylation and cytoskeletal development were highly abundant. We observed remarkable plasticity in the proteome of Red Sea larvae. The proteins associated with development, stress responses and osmoregulation showed the most significant differences between the two larval populations studied. The synergistic overexpression of heat shock and osmoregulatory proteins may facilitate larval survival in intertidal habitats or in extreme environments.

Conclusions

We presented, for the first time, comprehensive transcriptome and proteome datasets for Red Sea nauplii. The datasets provide a foundation for future investigations focused on the survival mechanisms of other crustaceans in extreme marine environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2262-1) contains supplementary material, which is available to authorized users.

A homologue gene of β-catenin participates in the development of shrimps and immune response to bacteria and viruses

β-Catenin is a multifunctional protein that is involved in many physiological processes, including development, cell proliferation, cell migration, and apoptosis. However, the function of β-Catenin in crustacean is unknown. In this study, the first shrimp homologous gene of β-catenin in Marsupenaeus japonicus (i.e., Mjβ-catenin) was identified and characterized. The full-length of the complementary DNA of Mjβ-catenin is 3130 bp, including a 2463 bp open reading frame that encodes 821 amino acid. Multiple alignment of β-Catenin proteins suggested that the Armadillo/β-Catenin-like repeat domains were conserved. Phylogenetic analysis showed that β-Catenin from shrimp was clustered into one group with invertebrate β-Catenin. The transcription of β-catenin in various development stages of shrimp was detected and persistently increased as the shrimp matured. In adult shrimp, β-catenin was widely distributed in detected tissues and has the relatively high expression level in gills, hemocytes, testes, and ovaries. The transcripts of β-catenin in tissues of adult shrimp were significantly up-regulated at various time points after infecting with Staphylococcus aureus, Vibrio anguillarum, and white-spot syndrome virus. Furthermore, knockdown of β-catenin resulted in impaired bacterial clearance ability and increased virus copy in shrimp in vivo. Therefore, β-Catenin in shrimp participates in the development and immune response of shrimps.

Proteomic profiling during the pre-competent to competent transition of the biofouling polychaete Hydroides elegans

The polychaete, Hydroides elegans, is a tube-building worm that is widely distributed in tropical and subtropical seas. It is a dominant fouling species and thus a major target organism in antifouling research. Here, the first high-throughput proteomic profiling of pre-competent and competent larvae of H. elegans is reported with the identification of 1,519 and 1,322 proteins, respectively. These proteins were associated with a variety of biological processes. However, a large proportion was involved in energy metabolism, redox homeostasis, and microtubule-based processes. A comparative analysis revealed 21 proteins that were differentially regulated in larvae approaching competency.

Quantitative proteomics study of larval settlement in the Barnacle Balanus amphitrite

Barnacles are major sessile components of the intertidal areas worldwide, and also one of the most dominant fouling organisms in fouling communities. Larval settlement has a crucial ecological effect not only on the distribution of the barnacle population but also intertidal community structures. However, the molecular mechanisms involved in the transition process from the larval to the juvenile stage remain largely unclear. In this study, we carried out comparative proteomic profiles of stage II nauplii, stage VI nauplii, cyprids, and juveniles of the barnacle Balanus amphitrite using label-free quantitative proteomics, followed by the measurement of the gene expression levels of candidate proteins. More than 700 proteins were identified at each stage; 80 were significantly up-regulated in cyprids and 95 in juveniles vs other stages. Specifically, proteins involved in energy and metabolism, the nervous system and signal transduction were significantly up-regulated in cyprids, whereas proteins involved in cytoskeletal remodeling, transcription and translation, cell proliferation and differentiation, and biomineralization were up-regulated in juveniles, consistent with changes associated with larval metamorphosis and tissue remodeling in juveniles. These findings provided molecular evidence for the morphological, physiological and biological changes that occur during the transition process from the larval to the juvenile stages in B. amphitrite.

Proteomic changes between male and female worms of the polychaetous annelid Neanthes arenaceodentata before and after spawning

The Neanthesacuminata species complex (Polychaeta) are cosmopolitan in distribution. Neanthesarenaceodentata, Southern California member of the N. acuminata complex, has been widely used as toxicological test animal in the marine environment. Method of reproduction is unique in this polychaete complex. Same sexes fight and opposite sexes lie side by side until egg laying. Females lose about 75% of their weight and die after laying eggs. The male, capable of reproducing up to nine times, fertilizes the eggs and incubates the embryos for 3-4 weeks. The objective of this study was to determine if there is any set of proteins that influences this unique pattern of reproduction. Gel-based two-dimensional electrophoresis (2-DE) and gel-free quantitative proteomics methods were used to identify differential protein expression patterns before and after spawning in both male and female N. arenaceodentata. Males showed a higher degree of similarity in protein expression patterns but females showed large changes in phosphoproteme before and after spawning. There was a decrease (about 70%) in the number of detected phosphoproteins in spent females. The proteins involved in muscular development, cell signaling, structure and integrity, and translation were differentially expressed. This study provides proteomic insights of the male and female worms that may serve as a foundation for better understanding of unusual reproductive patterns in polychaete worms.