The small GTPase Cdc42 regulates shell field morphogenesis in a gastropod mollusk.

In most mollusks (conchiferans), the early tissue responsible for shell development, namely, the shell field, shows a common process of invagination during morphogenesis. Moreover, lines of evidence indicated that shell field invagination is not an independent event, but an integrated output reflecting the overall state of shell field morphogenesis. Nevertheless, the underlying mechanisms of this conserved process remain largely unknown.

The combination of high temperature and Vibrio infection worsens summer mortality in the clam Meretrix petechialis by increasing apoptosis and oxidative stress.

The interaction between environmental factors and Vibrio in bivalves is not well understood, despite the widely held belief that pathogen infection and seawater temperature significantly impact summer mortality. In the present study, we conducted simulated experiments to explore the effects of high temperature and Vibrio infection on the clam Meretrix petechialis. The survival curve analysis revealed that the combined challenge of high temperature and Vibrio infection (31°C-vibrio) led to significantly higher clam mortality compared to the groups exposed solely to Vibrio (27°C-vibrio), high temperature (31°C-control), and the control condition (27°C-control).

Comprehensive Multi-omics Approaches Provide Insights to Summer Mortality in the Clam Meretrix petechialis.

Bivalve mass mortalities have been reported worldwide, which not only can be explained as a result of pathogen infection, but may reflect changes in environments. Although these episodes were often reported, there was limited information concerning the molecular responses to various stressors leading to summer mortality. In the present work, RNA sequencing (RNA-seq), tandem mass tagging (TMT)-based quantitative proteomics, and 16S rRNA sequencing were used to explore the natural outbreak of summer mortality in the clam Meretrix petechialis.

Functional evidence that FGFR regulates MAPK signaling in organizer specification in the gastropod mollusk .

Unlabelled: The D-quadrant organizer sets up the dorsal-ventral (DV) axis and regulates mesodermal development of spiralians. Studies have revealed an important role of mitogen-activated protein kinase (MAPK) signaling in organizer function, but the related molecules have not been fully revealed. The association between fibroblast growth factor receptor (FGFR) and MAPK signaling in regulating organizer specification has been established in the annelid .

The gastropod Lottia peitaihoensis as a model to study the body patterning of trochophore larvae.

The body patterning of trochophore larvae is important for understanding spiralian evolution and the origin of the bilateral body plan. However, considerable variations are observed among spiralian lineages, which have adopted varied strategies to develop trochophore larvae or even omit a trochophore stage. Some spiralians, such as patellogastropod mollusks, are suggested to exhibit ancestral traits by producing equal-cleaving fertilized eggs and possessing "typical" trochophore larvae.

Shell field morphogenesis in the polyplacophoran mollusk Acanthochitona rubrolineata.

Background: The polyplacophoran mollusks (chitons) possess serially arranged shell plates. This feature is unique among mollusks and believed to be essential to explore the evolution of mollusks as well as their shells. Previous studies revealed several cell populations in the dorsal epithelium (shell field) of polyplacophoran larvae and their roles in the formation of shell plates.

Early mesodermal development in the patellogastropod .

Mesodermal development is essential to explore the interlineage variations in the development of spiralians. Compared with model mollusks such as and , knowledge about the mesodermal development of other molluscan lineages is limited. Here, we investigated early mesodermal development in the patellogastropod , which shows equal cleavage and has a trochophore larva.

Nonmuscle Myosin II is Required for Larval Shell Formation in a Patellogastropod.

The molecular mechanisms underlying larval shell development in mollusks remain largely elusive. We previously found evident filamentous actin (F-actin) aggregations in the developing shell field of the patellogastropod , indicating roles of actomyosin networks in the process. In the present study, we functionally characterized nonmuscle myosin II (NM II), the key molecule in actomyosin networks, in the larval shell development of .

Molluskan Dorsal-Ventral Patterning Relying on BMP2/4 and Chordin Provides Insights into Spiralian Development and Evolution.

Although a conserved mechanism relying on BMP2/4 and Chordin is suggested for animal dorsal-ventral (DV) patterning, this mechanism has not been reported in spiralians, one of the three major clades of bilaterians. Studies on limited spiralian representatives have suggested markedly diverse DV patterning mechanisms, a considerable number of which no longer deploy BMP signaling. Here, we showed that BMP2/4 and Chordin regulate DV patterning in the mollusk Lottia goshimai, which was predicted in spiralians but not previously reported.

CRISPR/Cas9-mediated mutagenesis reveals the roles of calaxin in gastropod larval cilia.

Obtaining detectable knockout phenotypes in the G0 generation is essential for gene function studies. Although CRISPR/Cas9-mediated gene editing has been employed to knock out molluscan genes, detectable phenotypes in the G0 generation have not been reported in these animals. In this study, we determined the knockout phenotype of a cilium-related gene, calaxin, using CRISPR/Cas9 technology in the gastropod mollusk Lottia goshimai.

Early shell field morphogenesis of a patellogastropod mollusk predominantly relies on cell movement and F-actin dynamics.

Background: The morphogenesis of the shell field is an essential step of molluscan shell formation, which exhibits both conserved features and interlineage variations. As one major gastropod lineage, the patellogastropods show different characters in its shell field morphogenesis compared to other gastropods (e.g.

Identification of three cell populations from the shell gland of a bivalve mollusc.

The molluscan larval shell formation is a complicated process. There is evidence that the mantle of the primary larva (trochophore) contains functionally different cell populations with distinct gene expression profiles. However, it remains unclear how these cells are specified.

Dorsoventral decoupling of Hox gene expression underpins the diversification of molluscs.

In contrast to the Hox genes in arthropods and vertebrates, those in molluscs show diverse expression patterns with differences reported among lineages. Here, we investigate 2 phylogenetically distant molluscs, a gastropod and a polyplacophoran, and show that the Hox expression in both species can be divided into 2 categories. The Hox expression in the ventral ectoderm generally shows a canonical staggered pattern comparable to the patterns of other bilaterians and likely contributes to ventral patterning, such as neurogenesis.

An investigation of oyster TGF-β receptor genes and their potential roles in early molluscan development.

Though the roles of BMP signaling in development is studied extensively in insects and vertebrates, our knowledge of BMP signaling in molluscan development is limited. In the present study, we performed a genome-based analysis of TGF-β receptors in the Pacific oyster Crassostrea gigas and revealed that C. gigas possessed all five canonical members of the gene family, including three type I and two type II receptors.

Integrated transcriptomic and proteomic analyses reveal potential mechanisms linking thermal stress and depressed disease resistance in the turbot Scophthalmus maximus.

A worldwide increase in the reports of diseases affecting marine organisms has paralleled the climate warming over the past few decades. In this study, we applied omics to explore the mechanisms underlying thermo-linked epizootics, by comparing both the transcriptome- and proteome-wide response of turbots to a mimic pathogen (poly I:C) between high temperature and low temperature using a time-course approach. Our results showed that myeloperoxidase (MPO) and insulin were differentially expressed transcripts shared by all five time-points post poly I:C-injection between high and low temperature and also had a consistent expression trend as differentially expressed proteins at 24 h post injection.

The sea cucumber genome provides insights into morphological evolution and visceral regeneration.

Apart from sharing common ancestry with chordates, sea cucumbers exhibit a unique morphology and exceptional regenerative capacity. Here we present the complete genome sequence of an economically important sea cucumber, A. japonicus, generated using Illumina and PacBio platforms, to achieve an assembly of approximately 805 Mb (contig N50 of 190 Kb and scaffold N50 of 486 Kb), with 30,350 protein-coding genes and high continuity.

Scallop genome provides insights into evolution of bilaterian karyotype and development.

Reconstructing the genomes of bilaterian ancestors is central to our understanding of animal evolution, where knowledge from ancient and/or slow-evolving bilaterian lineages is critical. Here we report a high-quality, chromosome-anchored reference genome for the scallop Patinopecten yessoensis, a bivalve mollusc that has a slow-evolving genome with many ancestral features. Chromosome-based macrosynteny analysis reveals a striking correspondence between the 19 scallop chromosomes and the 17 presumed ancestral bilaterian linkage groups at a level of conservation previously unseen, suggesting that the scallop may have a karyotype close to that of the bilaterian ancestor.

A SoxC gene related to larval shell development and co-expression analysis of different shell formation genes in early larvae of oyster.

Among the potential larval shell formation genes in mollusks, most are expressed in cells surrounding the shell field during the early phase of shell formation. The only exception (cgi-tyr1) is expressed in the whole larval mantle and thus represents a novel type of expression pattern. This study reports another gene with such an expression pattern.

Expression patterns indicate that BMP2/4 and Chordin, not BMP5-8 and Gremlin, mediate dorsal-ventral patterning in the mollusk Crassostrea gigas.

Though several bilaterian animals use a conserved BMP2/4-Chordin antagonism to pattern the dorsal-ventral (DV) axis, the only lophotrochozoan species in which early DV patterning has been studied to date, the leech Helobdella robusta, appears to employ BMP5-8 and Gremlin. These findings call into question the conservation of a common DV patterning mechanism among bilaterian animals. To explore whether the unusual DV patterning mechanism in H.

A comparative proteomic analysis reveals important proteins for the fertilization and early embryonic development of the oyster Crassostrea gigas.

Molluscan development involves important features that are important to understanding not only molluscan ontogeny but also animal evolution. To gain insight into the gamete proteome and protein function in fertilization and early development, we analyzed the proteomes of unfertilized oocytes and early embryos (2/4-cell stage) of the Pacific oyster, Crassostrea gigas. An oocyte reference map containing 116 protein spots, of which 69 were identified, revealed a high abundance of vitellogenin-derived protein spots.

Assessment of housekeeping genes as internal references in quantitative expression analysis during early development of oyster.

The early development of mollusks exhibits important characteristics from the developmental and evolutionary perspective. With the increasing number of genome-wide studies, accurate analyses of quantitative gene expression during development are impeded by the lack of validated reference genes. To improve the situation, in this study, we analyzed the expression stability of seven candidate housekeeping genes during early development of the Pacific oyster Crassostrea gigas: actin, glyceraldehyde-3-phosphate dehydrogenase (gapdh), α subunit of elongation factor 1 (elf1α), adp-ribosylation factor 1 (arf1), heterogeneous nuclear ribonucleoprotein q, ubiquitin-conjugating enzyme e2d2 and ribosomal protein s18.

Characterization and expression of a novel caspase gene: Evidence of the expansion of caspases in Crassostrea gigas.

Caspases are a group of cysteine-aspartate proteases involved in apoptosis and a variety of non-apoptotic processes. In this study, a novel caspase gene was cloned and its potential role in apoptosis was investigated. The caspase gene (CgCasp 3/7) has an open reading frame of 1626bp encoding 541 amino acids containing the conserved functional domains and motifs of effector caspases.

A Calaxin Gene in the Pacific Oyster Crassostrea gigasand Its Potential Roles in Cilia.

calaxin is a newly identified calcium sensor gene that modulates the movement of flagella (and possibly cilia). It was first identified from the ascidian Ciona intestinalis, and its orthologs have been observed in a wide range of animals and choanoflagellates. However, no calaxin-ortholog in a Lophotrochozoa species has been reported so far.

A Label-Free Proteomic Analysis on Competent Larvae and Juveniles of the Pacific Oyster Crassostrea gigas.

Current understandings on the molecular mechanisms underlying bivalve metamorphosis are still fragmentary, and a comprehensive description is required. In this study, using a large-scale label-free proteomic approach, we described and compared the proteomes of competent larvae (CL) and juveniles (JU) of the Pacific oyster, Crassostrea gigas. A total of 788 proteins were identified: 392 in the CL proteome and 636 in the JU proteome.

A GATA2/3 gene potentially involved in larval shell formation of the Pacific oyster Crassostrea gigas.

Shells are one of the most notable features of the majority of mollusks. In addition, the shell is also considered a key characteristic during molluscan evolution and development. However, although the morphological changes during larval shell formation have been well described, the underlying molecular mechanisms remain poorly understood.