Transcriptome changes in Eriocheir sinensis megalopae after desalination provide insights into osmoregulation and stress adaption in larvae

Comparative study of lysine acetylation in Vesicomyidae clam Archivesica marissinica and the manila clam Ruditapes philippinarum: adaptation mechanisms in cold seep environments

BACKGROUND

The deep-sea cold seep zone is characterized by high pressure, low temperature, darkness, and oligotrophy. Vesicomyidae clams are the dominant species within this environment, often forming symbiotic relationships with chemosynthetic microbes. Understanding the mechanisms by which Vesicomyidae clams adapt to the cold seep environment is significant. Acetylation modification of lysine is known to play a crucial role in various metabolic processes. Consequently, investigating the role of lysine acetylation in the adaptation of Vesicomyidae clams to deep-sea environments is worthwhile. So, a comparative study of lysine acetylation in cold seep clam Archivesica marissinica and shallow water shellfish Ruditapes philippinarum was conducted.

RESULTS

A total of 539 acetylated proteins were identified with 1634 acetylation sites. Conservative motif enrichment analysis revealed that the motifs -KacR-, -KacT-, and -KacF- were the most conserved. Subsequent gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichment analyses were conducted on significantly differentially expressed acetylated proteins. The GO enrichment analysis indicated that acetylated proteins are crucial in various biological processes, including cellular response to stimulation, and other cellular processes ( p < 0.05 and false discovery rate (FDR) < 0.25). The results of KEGG enrichment analysis indicated that acetylated proteins are involved in various cellular processes, including tight junction, motor proteins, gap junction, phagosome, cGMP-PKG signaling pathways, endocytosis, glycolysis/gluconeogenesis, among others (p < 0.05 and FDR < 0.25). Notably, a high abundance of lysine acetylation was observed in the glycolysis/glycogenesis pathways, and the acetylation of glyceraldehyde 3-phosphate dehydrogenase might facilitate ATP production. Subsequent investigation into acetylation modifications associated with deep-sea adaptation revealed the specific identification of key acetylated proteins. Among these, the adaptation of cold seep clam hemoglobin and heat shock protein to high hydrostatic pressure and low temperature might involve an increase in acetylation levels. Acetylation of arginine kinase might be related to ATP production and interaction with symbiotic bacteria. Myosin heavy chain (Ama01085) has the most acetylation sites and might improve the actomyosin system stability through acetylation. Further validation is required for the acetylation modification from Vesicomyidae clams.

CONCLUSION

A novel comparative analysis was undertaken to investigate the acetylation of lysine in Vesicomyidae clams, yielding novel insights into the regulatory role of lysine acetylation in deep-sea organisms. The findings present many potential proteins for further exploration of acetylation functions in cold seep clams and other deep-sea mollusks.

Unraveling the molecular mechanisms of fish physiological response to freshwater salinization: A comparative multi-tissue transcriptomic study in a river polluted by potash mining

Freshwater salinization is an escalating global environmental issue that threatens freshwater biodiversity, including fish populations. This study aims to uncover the molecular basis of salinity physiological responses in a non-native minnow species (Phoxinus septimaniae x P. dragarum) exposed to saline effluents from potash mines in the Llobregat River, Barcelona, Spain. Employing high-throughput mRNA sequencing and differential gene expression analyses, brain, gills, and liver tissues collected from fish at two stations (upstream and downstream of saline effluent discharge) were examined. Salinization markedly influenced global gene expression profiles, with the brain exhibiting the most differentially expressed genes, emphasizing its unique sensitivity to salinity fluctuations. Pathway analyses revealed the expected enrichment of ion transport and osmoregulation pathways across all tissues. Furthermore, tissue-specific pathways associated with stress, reproduction, growth, immune responses, methylation, and neurological development were identified in the context of salinization. Rigorous validation of RNA-seq data through quantitative PCR (qPCR) underscored the robustness and consistency of our findings across platforms. This investigation unveils intricate molecular mechanisms steering salinity physiological response in non-native minnows confronting diverse environmental stressors. This comprehensive analysis sheds light on the underlying genetic and physiological mechanisms governing fish physiological response in salinity-stressed environments, offering essential knowledge for the conservation and management of freshwater ecosystems facing salinization.

Dynamic Alternative Polyadenylation during Litopenaeus Vannamei Metamorphosis Development

As an important mechanism in the post-transcriptional regulation of eukaryotic gene expression, alternative polyadenylation (APA) plays a key role in biological processes such as cell proliferation and differentiation. However, the role and dynamic pattern of APA during Litopenaeus vannamei metamorphosis are poorly understood. Here, RNA-seq data covering from the embryo to the maturation (16 time points) of L. vannamei were utilized. We identified 247 differentially expressed APA events between early and adult stages, and through fuzzy mean clustering analysis, we discovered five dynamic APA patterns. Among them, the gradual elongation of the 3'UTR is the major APA pattern that changes over time, and its genes are enriched in the pathways of protein and energy metabolism. Finally, we constructed mRNA-miRNA and PPI networks and detected several central miRNAs that may regulate L. vannamei development. Our results revealed the complex APA mechanisms in L. vannamei metamorphosis, shedding new light on post-transcriptional regulation of crustacean metamorphosis.

Identifying low salinity adaptation gene expression in the anterior and posterior gills of the mud crab (Scylla paramamosain) by transcriptomic analysis

In the present study, BGISEQ-500 RNA-Seq technology was adopted to investigate how Scylla paramamosain adapts to salinity tolerance at the molecular level and explores changes in gene expression linked to salinity adaptation following exposure to both low salinity (5 ‰) and standard salinity (23 ‰) conditions. A total of 1100 and 520 differentially expressed genes (DEGs) were identified in the anterior and posterior gills, respectively, and their corresponding expression patterns were visualized in volcano plots and a heatmap. Further analysis highlighted significant enrichment of well-established gene functional categories and signaling pathways, including those what associated with cellular stress response, ion transport, energy metabolism, amino acid metabolism, H2O transport, and physiological stress compensation. We also selected key DEGs within the anterior and posterior gills that encode pivotal stress adaptation and tolerance modulators, including AQP, ABCA1, HSP 10, A35, CAg, NKA, VPA, CAc, and SPS. Interestingly, A35 in the gills might regulate osmolality by binding CHH in response to low salinity stress or serve as a mechanism for energy compensation. Taken together, our findings elucidated the intricate molecular mechanism employed by S. paramamosain for salinity adaptation, which involved distinct gene expression patterns in the anterior and posterior gills. These findings provide the foothold for subsequent investigations into salinity-responsive candidate genes and contribute to a deeper understanding of S. paramamosain's adaptation mechanisms in low-salinity surroundings, which is crucial for the development of low-salinity species cultivation and the establishment of a robust culture model.

Analysis of adaptive molecular mechanisms in response to low salinity in antennal gland of mud crab, Scylla paramamosain

As an important marine aquaculture species, the mud crab (Scylla paramamosain) is a good candidate for studying the osmoregulatory mechanism of crustaceans. While previous studies have focused on the osmoregulatory function of the gills, this study aims to explore the osmoregulatory function of the antennal glands. By the comparative transcriptomic analysis, we found the pathways of ion regulation including "proximal tubule bicarbonate reclamation" and "mineral absorption" were activated in the antennal glands of the crabs long-term dwelling in low salinity. The enhanced ionic reabsorption was associated with up-regulated ion transport genes such as NKA, CA-c, VPA, and NHE, and with energy metabolism genes such as MDH, SLC25, and PEPCK. The upregulation of NKA and CA-c was also verified by the increased enzyme activity. The lowered osmolality and ion concentration of the hemolymph and the enlarged labyrinth lumen and hemolymph capillary inside the antennal glands indicated the infiltration of external water and the responsively increase of urine excretion, which explained the requirement of enhanced ionic reabsorption. To further confirm these findings, we examined the change of gene expression, enzyme activity, internal ion concentration, and external ion concentration during a 96 h low salinity challenge with seven intervals. The results were basically consistent with the results as shown in the long-term low salinity adaptation. The present study provides valuable information on the osmoregulatory function of the antennal glands of S. paramamosain. The implication of this study in marine aquaculture is that it provides valuable information on the osmoregulatory mechanism of mud crabs, which can be used to improve their culture conditions and enhance their tolerance to salinity stress. The identified genes and pathways involved in osmoregulation can also be potential targets for genetic selection and breeding programs to develop more resilient mud crab strains for aquaculture.

Adaptive divergence and underlying mechanisms in response to salinity gradients between two Crassostrea oysters revealed by phenotypic and transcriptomic analyses

Comparing the responses of closely related species to environmental changes is an efficient method to explore adaptive divergence, for a better understanding of the adaptive evolution of marine species under rapidly changing climates. Oysters are keystone species thrive in intertidal and estuarine areas where frequent environmental disturbance occurs including fluctuant salinity. The evolutionary divergence of two sister species of sympatric estuarine oysters, Crassostrea hongkongensis and Crassostrea ariakensis, in response to euryhaline habitats on phenotypes and gene expression, and the relative contribution of species effect, environment effect, and their interaction to the divergence were explored. After a 2-month outplanting at high- and low-salinity locations in the same estuary, the high growth rate, percent survival, and high tolerance indicated by physiological parameters suggested that the fitness of C. ariakensis was higher under high-salinity conditions and that of C. hongkongensis was higher under low-salinity conditions. Moreover, a transcriptomic analysis showed the two species exhibited differentiated transcriptional expression in high- and low-salinity habitats, largely caused by the species effect. Several of the important pathways enriched in divergent genes between species were also salinity-responsive pathways. Specifically, the pyruvate and taurine metabolism pathway and several solute carriers may contribute to the hyperosmotic adaptation of C. ariakensis, and some solute carriers may contribute to the hypoosmotic adaptation of C. hongkongensis. Our findings provide insights into the phenotypic and molecular mechanisms underlying salinity adaptation in marine mollusks, which will facilitate the assessment of the adaptive capacity of marine species in the context of climate change and will also provide practical information for marine resource conservation and aquaculture.

Comparative transcriptome, digital gene expression and proteome profiling analyses provide insights into the brachyurization from the megalopa to the first juvenile in Eriocheir sinensis

Eriocheir sinensis larva normally experiences 11 stages. The reduced abdomen folded beneath the thorax is the most prominent characteristic of morphological alteration from megalopa to juvenile crab. Up to date, the molecular mechanisms of brachyurization remain a mystery. Here, transcriptome library, digital gene expression (DGE) libraries and proteome libraries at two developmental stages [the megalopa stage of E. sinensis (stage M) and the first stage of juvenile crab (stage J1)] of the Chinese mitten crab larva were constructed for RNA sequencing and iTRAQ approaches followed by bioinformatics analysis, respectively. In total, 1106 genes and 871 proteins were differentially expressed between the stage M and stage J1. Moreover, several important pathways were identified, including biosynthesis of secondary metabolites, metabolic pathways, focal adhesion, and some disease pathways. Besides, muscle contraction, oxidative phosphorylation, calcium signaling, PI3K-Akt, DNA replication pathway, and integrin signaling pathway also had important functions in brachyurization process. Furthermore, the components, actin, actin-related protein, collagens, filamin-A/B, laminin, integrins, paxillin, and fibronectin had up-regulated expression levels in M stage compared to J1 stage.

Comparative Transcriptome Analysis of Eriocheir sinensis from Wild Habitats in Han River, Korea

Eriocheir sinensis is an euryhaline crab found from East Asia to Europe and North America. This species can live in freshwater and seawater due to the unique physiological characteristics of their life cycle, which allows them to adapt and inhabit different habitats in a wide range of environments. Despite the wealth of studies focusing on adaptation mechanism of E. sinensis to specific environmental factors, the adaptation mechanisms to wild habitats with coexisting environmental factors are not well understood. In this study, we conducted a transcriptome analysis to investigate gene expression differences related to habitat adaptation of E. sinensis from two wild habitats with different environmental factors in the Han River, Korea. A total of 138,261 unigenes were analyzed, of which 228 were analyzed as differentially expressed genes (DEGs) between the two wild habitats. Among 228 DEGs, 110 DEGs were annotated against databases; most DEGs were involved in energy metabolism, immunity, and osmoregulation. Moreover, DEG enrichment analysis showed that upregulated genes were related to biosynthesis, metabolism, and immunity in an habitat representing relatively high salinity whereas downregulated genes were related to ion transport and hypoxia response in habitats with relatively low salinity and dissolved oxygen. The present findings can serve as foundation for future E. sinensis culture or conservation approaches in natural conditions.

Transcriptome analysis of the mantle tissue of Pinctada fucata with red and black shells under salinity stress

To understand the molecular responses of Pinctada fucata with different shell colors to salinity stress, we used transcriptome sequencing on the mantle of P. fucata with a black shell and red shell color under the salinity of 20, 35, and 50. The 414 and 2371 differentially expressed genes (DEGs) in P. fucata with a black shell under low- or high-salt stress, while there were 588 and 3009 DEGs in P. fucata with a red shell. KEGG pathway enrichment analysis showed that, under low salt stress, the DEGs of P. fucata with the black shell were significantly enriched in pathways MAPK signaling pathway, protein processing in endoplasmic reticulum, vitamin B6 metabolism, longevity regulating pathway-multiple species, estrogen signaling pathway and antigen processing and presentation, the DEGs of P. fucata with a red shell were significantly enriched in pathways vitamin B6 metabolism. Under high salt stress, the DEGs of P. fucata with a red shell were significantly enriched in pathways arginine biosynthesis. 11 DEGs were randomly selected for quantitative real-time PCR, and the results were consistent with the RNA-seq. In addition, under high salt stress, DEGs were enriched into some pathways related to osmotic regulation and immune defense of P. fucata with black shell and red shell, such as Glycolysis / Gluconeogenesis, AMPK signaling pathway, Beta-Alanine metabolism, Glycine, serine and threonine metabolism, MAPK signaling pathway and Phagosome. The study showed that high salt stress had a greater influence on P. fucata with two shell colors, and P. fucata with a black shell made a positive immune defense response. Our results will improve to further understand the salt tolerance mechanism of P. fucata with different shell colors.

Single-Cell Ribonucleic Acid Sequencing Clarifies Cold Tolerance Mechanisms in the Pacific White Shrimp (Litopenaeus Vannamei)

To characterize the cold tolerance mechanism of the Pacific white shrimp (Litopenaeus vannamei), we performed single-cell RNA sequencing (scRNA-seq) of ∼5185 hepatopancreas cells from cold-tolerant (Lv-T) and common (Lv-C) L. vannamei at preferred and low temperatures (28°C and 10°C, respectively). The cells fell into 10 clusters and 4 cell types: embryonic, resorptive, blister-like, and fibrillar. We identified differentially expressed genes between Lv-T and Lv-C, which were mainly associated with the terms “immune system,” “cytoskeleton,” “antioxidant system,” “digestive enzyme,” and “detoxification,” as well as the pathways “metabolic pathways of oxidative phosphorylation,” “metabolism of xenobiotics by cytochrome P450,” “chemical carcinogenesis,” “drug metabolism-cytochrome P450,” and “fatty acid metabolism.” Reconstruction of fibrillar cell trajectories showed that, under low temperature stress, hepatopancreas cells had two distinct fates, cell fate 1 and cell fate 2. Cell fate 1 was mainly involved in signal transduction and sensory organ development. Cell fate 2 was mainly involved in metabolic processes. This study preliminarily clarifies the molecular mechanisms underlying cold tolerance in L. vannamei, which will be useful for the breeding of shrimp with greater cold tolerance.

Toxic effects of metal copper stress on immunity, metabolism and pathologic changes in Chinese mitten crab (Eriocheir japonica sinensis)

Copper (Cu²⁺), which represents a major physiological challenge for crab culture, is ubiquitous in the aquatic culture environment, and gills are the first organs that come into direct contact with the environment. However, the molecular basis of the response of crabs to Cu²⁺ stress remains unclear. Here, we conducted a transcriptome and differential expression analysis on the gills from Chinese mitten crab unexposed and exposed to Cu²⁺ for 24 h. The comparative transcriptome analysis identified 2486 differentially expressed genes (DEGs). GO functional analysis and KEGG pathway analysis revealed some DEGs, which were mostly related to immunity, metabolism, osmotic regulation, Cu²⁺ homeostasis regulation, antioxidant activity, and detoxification process. Some pathways related to humoral and cellular immunity, such as phagosome, peroxisome, lysosome, mTOR signaling pathway, PI3K-Akt signaling pathway, Toll-like receptor signaling pathway, and T cell receptor signaling pathway were enhanced under Cu²⁺ stress. In addition, Cu²⁺ stress altered the expression patterns of key phagocytosis and apoptosis genes (lectin, cathepsin L, Rab7, and HSP70), confirming that Cu²⁺ can induce oxidative stress and eventually even apoptosis. Histological analysis revealed that the copper can induce damage at the cellular level. This comparative transcriptome analysis provides valuable molecular information to aid future study of the immune mechanism of Chinese mitten crab in response to Cu²⁺ stress and provides a foundation for further understanding of the effects of metal toxicity.

The Chinese mitten crab genome provides insights into adaptive plasticity and developmental regulation

The infraorder Brachyura (true or short-tailed crabs) represents a successful group of marine invertebrates yet with limited genomic resources. Here we report a chromosome-anchored reference genome and transcriptomes of the Chinese mitten crab Eriocheir sinensis, a catadromous crab and invasive species with wide environmental tolerance, strong osmoregulatory capacity and high fertility. We show the expansion of specific gene families in the crab, including F-ATPase, which enhances our knowledge on the adaptive plasticity of this successful invasive species. Our analysis of spatio-temporal transcriptomes and the genome of E. sinensis and other decapods shows that brachyurization development is associated with down-regulation of Hox genes at the megalopa stage when tail shortening occurs. A better understanding of the molecular mechanism regulating sexual development is achieved by integrated analysis of multiple omics. These genomic resources significantly expand the gene repertoire of Brachyura, and provide insights into the biology of this group, and Crustacea in general.

A comprehensive examination of the lysine acetylation targets in paper mulberry based on proteomics analyses

Rocky desertification is a bottleneck that reduces ecological and environmental security in karst areas. Paper mulberry, a unique deciduous tree, shows good performance in rocky desertification areas. Its resistance mechanisms are therefore of high interest. In this study, a lysine acetylation proteomics analysis of paper mulberry seedling leaves was conducted in combination with the purification of acetylated protein by high-precision nano LC-MS/MS. We identified a total of 7130 acetylation sites in 3179 proteins. Analysis of the modified sites showed a predominance of nine motifs. Six positively charged residues: lysine (K), arginine (R), and histidine (H), serine (S), threonine (T), and tyrosine (Y) occurred most frequently at the +1 position, phenylalanine (F) was both detected both upstream and downstream of the acetylated lysines; and the sequence logos showed a strong preference for lysine and arginine around acetylated lysines. Functional annotation revealed that the identified enzymes were mainly involved in translation, transcription, ribosomal structure and biological processes, showing that lysine acetylation can regulate various aspects of primary carbon and nitrogen metabolism and secondary metabolism. Acetylated proteins were enriched in the chloroplast, cytoplasm, and nucleus, and many stress response-related proteins were also discovered to be acetylated, including PAL, HSP70, and ERF. HSP70, an important protein involved in plant abiotic and disease stress responses, was identified in paper mulberry, although it is rarely found in woody plants. This may be further examined in research in other plants and could explain the good adaptation of paper mulberry to the karst environment. However, these hypotheses require further verification. Our data can provide a new starting point for the further analysis of the acetylation function in paper mulberry and other plants.

Multi-omic approach provides insights into osmoregulation and osmoconformation of the crab Scylla paramamosain

Osmoregulation and osmoconformation are two mechanisms through which aquatic animals adapt to salinity fluctuations. The euryhaline crab Scylla paramamosain, being both an osmoconformer and osmoregulator, is an excellent model organism to investigate salinity adaptation mechanisms in brachyurans. In the present study, we used transcriptomic and proteomic approaches to investigate the response of S. paramamosain to salinity stress. Crabs were transferred from a salinity of 25 ppt to salinities of 5 ppt or 33 ppt for 6 h and 10 days. Data from both approaches revealed that exposure to 5 ppt resulted in upregulation of ion transport and energy metabolism associated genes. Notably, acclimation to low salinity was associated with early changes in gene expression for signal transduction and stress response. In contrast, exposure to 33 ppt resulted in upregulation of genes related to amino acid metabolism, and amino acid transport genes were upregulated only at the early stage of acclimation to this salinity. Our study reveals contrasting mechanisms underlying osmoregulation and osmoconformation within the salinity range of 5–33 ppt in the mud crab, and provides novel candidate genes for osmotic signal transduction, thereby providing insights on understanding the salinity adaptation mechanisms of brachyuran crabs.

Effects of dietary icariin supplementation on the ovary development-related transcriptome of Chinese mitten crab (Eriocheir sinensis)

The Chinese mitten crab (Eriocheir sinensis) is an economically important aquaculture species in China, with distinct differences in ovarian maturation status between crabs fed with natural diets and artificial diets during the listing period, thus, leading to selling price differentiation. Our previous study showed that dietary supplementation with 100 mg/kg icariin can effectively promote ovarian development of E. sinensis. However, the internal molecular mechanism has not yet been elucidated because of a lack of comprehensive genome sequence information. We compared the ovary transcriptomes of E. sinensis fed with two diets containing 0 and 100 mg/kg ICA using the BGISEQ-500 platform. This yielded 12.54 Gb clean bases and 54,794 unigenes, 13,832 of which were found to be differentially expressed after icariin exposure. Twenty pathways closely related to gonadal development were selected through KEGG analysis. Seven differentially expressed genes relevant to vitellogenesis and oocyte maturation (serine/threonine-protein kinase mos-like, Eg2, cytoplasmic polyadenylation element-binding protein, cyclin B, vitellogenin 1, cathepsin D, and juvenile hormone esterase-like carboxylesterase 1) were validated by qRT-PCR, and four proteins (MEK1/2, ERK1/2, Cyclin B and Cdc2) associated with the progesterone mediated oocyte maturation pathway (i.e., MAPK/MPF pathway) were analyzed by western-blot. The results showed that icariin could promote the synthesis, processing and deposition of vitellogenin in oocytes, and that it also has the potential to promote oocyte maturation (resumption of Meiosis I) by altering the expression of the relevant genes and proteins.

mRNA profile provides novel insights into stress adaptation in mud crab megalopa, Scylla paramamosain after salinity stress

Background

Mud crab, Scylla paramamosain, a euryhaline crustacean species, mainly inhabits the Indo-Western Pacific region. Wild mud crab spawn in high-salt condition and the salinity reduced with the growth of the hatching larvae. When the larvae grow up to megalopa, they migrate back to estuaries and coasts in virtue of the flood tide, settle and recruit adult habitats and metamorphose into the crablet stage. Adult crab can even survive in a wide salinity of 0–35 ppt. To investigate the mRNA profile after salinity stress, S. paramamosain megalopa were exposed to different salinity seawater (low, 14 ppt; control, 25 ppt; high, 39 ppt).

Results

Firstly, from the expression profiles of Na+/K+/2Cl- cotransporter, chloride channel protein 2, and ABC transporter, it turned out that the 24 h might be the most influenced duration in the short-term stress. We collected megalopa under different salinity for 24 h and then submitted to mRNA profiling. Totally, 57.87 Gb Clean Data were obtained. The comparative genomic analysis detected 342 differentially expressed genes (DEGs). The most significantly DEGs include gamma-butyrobetaine dioxygenase-like, facilitated trehalose transporter Tret1, sodium/potassium-transporting ATPase subunit alpha, rhodanese 1-like protein, etc. And the significantly enriched pathways were lysine degradation, choline metabolism in cancer, phospholipase D signaling pathway, Fc gamma R-mediated phagocytosis, and sphingolipid signaling pathway. The results indicate that in the short-term salinity stress, the megalopa might regulate some mechanism such as metabolism, immunity responses, osmoregulation to adapt to the alteration of the environment.

Conclusions

This study represents the first genome-wide transcriptome analysis of S. paramamosain megalopa for studying its stress adaption mechanisms under different salinity. The results reveal numbers of genes modified by salinity stress and some important pathways, which will provide valuable resources for discovering the molecular basis of salinity stress adaptation of S. paramamosain larvae and further boost the understanding of the potential molecular mechanisms of salinity stress adaptation for crustacean species.

Transcriptome Analysis Reveals the Tolerance Mechanism of Mantis Shrimp (Oratosquilla oratoria) under a Lipopolysaccharide Challenge

Lipopolysaccharide (LPS), a major cell wall component of Gram-negative bacteria, is considered to lead to some disease development in commercial crustaceans. However, mantis shrimps Oratosquilla oratoria (Crustacea: Stomatopoda) have a strong vitality and ability to resist disease. To study the tolerance mechanism of mantis shrimp, transcriptome analyses were conducted in hepatopancreas of O. oratoria under LPS challenge investigation. Totally, 84 547 044 clean reads were obtained from transcriptomes (43 159 230 in OP (control), 41 387 814 in OL (treatment), respectively). Unigenes, the longest transcript of each gene, with a total length of 68 318 880 bp and the total number of 100 978 were obtained. 8369 (8.28%) of unigenes were successfully annotated in all databases and 54 888 (54.35%) were annotated in at least one database. Finally, 1012 differentially expressed genes (DEGs) including 439 and 573 showed significantly upregulated and downregulated were determined between OL and OP, respectively. Moreover, those DEGs only expressed in OL or OP accounted for 8.99%. The functional classification based on GO and KEGG indicated that the common enrichment categories for the DEGs are "amino sugar metabolic" and "cellular homeostasis" and that the progress of nutrient metabolic and homeostasis in cells is important in facing variable environmental conditions. Protein-protein interaction analysis elucidated proteins, β-actin (ACTB_G1), T-complex protein subunits (TCPs), heat shock proteins (HSPs), hydroxysteroid dehydrogenase-like protein 2 (HSDL2), kinesin family member 5 (KIF5), methylglutaconyl-CoA hydratase (AUH), and myosin heavy chain (MYH) may play key roles in response to an LPS challenge. This study laid a foundation to further investigate the possible adaptation way that O. oratoria survives in a bacterial challenge.

Gene Expression in the Salivary Gland of Rhipicephalus (Boophilus) microplus Fed on Tick-Susceptible and Tick-Resistant Hosts

The success of cattle tick fixation largely depends on the secretion of substances that alter the immune response of the host. The majority of these substances are expressed by the parasite salivary gland and secreted in tick saliva. It is known that hosts can mount immune responses against ticks and bovine European breeds, and bovine industrial crossbreeds are more susceptible to infestations than are Bos indicus cattle. To identify candidates for the development of novel control strategies for the cattle tick Rhipicephalus (Boophilus) microplus, a salivary gland transcriptome analysis of engorged females fed on susceptible or resistant hosts was performed. Using RNA-Seq, transcriptomes were de novo assembled and produced a total of 235,451 contigs with 93.3% transcriptome completeness. Differential expression analysis identified 137 sequences as differentially expressed genes (DEGs) between ticks raised on tick-susceptible or tick-resistant cattle. DEGs predicted to be secreted proteins include innexins, which are transmembrane proteins that form gap junction channels; the transporters Na⁺/dicarboxylate, Na⁺/tricarboxylate, and phosphate transporter and a putative monocarboxylate transporter; a phosphoinositol 4-phosphate adaptor protein; a cysteine-rich protein containing a trypsin inhibitor-like (TIL) domain; a putative defense protein 3 containing a reeler domain; and an F-actin-uncapping protein LRRC16A with a CARMIL_C domain; these genes were upregulated in ticks fed on tick-susceptible cattle. DEGs predicted to be non-secreted proteins included a small heat shock protein and the negative elongation factor B-like, both acting in a coordinated manner to increase HSP transcript levels in the salivary glands of the ticks fed on tick-susceptible cattle; the 26S protease regulatory subunit 6B and another chaperone with similarity to calnexin, also upregulated in ticks fed on tick-susceptible cattle; an EF-hand calcium binding protein and a serine carboxypeptidase (SCP), both involved in the blood coagulation cascade and upregulated in ticks fed on tick-susceptible cattle; and two ribosomal proteins, the 60S acidic ribosomal protein P2 and the 60S ribosomal protein L19. These results help to characterize cattle tick salivary gland gene expression in tick-susceptible and tick-resistant hosts and suggest new putative targets for the control of tick infestations, as those genes involved in the mechanism of stress response during blood feeding.

Transcriptional responses to starvation stress in the hepatopancreas of oriental river prawn Macrobrachium nipponense

Various crustaceans are farmed using aquaculture, and food deprivation or fasting can occur due to changing of environmental or management strategies. However, the molecular mechanisms underlying responses to starvation in crustaceans remain unclear. To address this, 12 hepatopancreas transcriptomes were compared for oriental river prawn (Macrobrachium nipponense) from four fasting stages (0, 7, 14 and 21 d). Gene Ontology functional annotation and Kyoto Encyclopaedia of Genes and Genomes pathway enrichment analysis of differentially expressed genes were subsequently performed. During the early stages of starvation (0-7 d), drug metabolism via the cytochrome P450 pathway and metabolism of xenobiotics by the cytochrome P450 pathway were enriched, suggesting that they metabolised compounds generated under starvation stress. As starvation proceeded (7-14 d), the retinol (vitamin A) metabolism pathway was activated, based on three up-regulated genes (CYP3, ADH and UGT), along with the two p450 pathways. Meanwhile, vitamin A was gradually consumed. As acute starvation was reached (14-21 d), vitamin A deficiency decreased the mRNA expression levels of IGF-I that is involved in the mTOR signalling pathway, which ultimately affected the growth and development of M. nipponense. Our results implicate drug/xenobiotic metabolism by cytochrome P450s in adaptation to starvation stress. Furthermore, metabolic cascades (CYP and retinol pathways) and growth (mTOR signalling) pathways are clearly triggered in crustaceans during starvation. The findings expand our understanding of the genes associated with hepatopancreas functioning in M. nipponense, and the underlying molecular mechanisms that govern the responses of crustaceans to starvation stress.

The Single-molecule long-read sequencing of Scylla paramamosain

Scylla paramamosain is an important aquaculture crab, which has great economical and nutritional value. To the best of our knowledge, few full-length crab transcriptomes are available. In this study, a library composed of 12 different tissues including gill, hepatopancreas, muscle, cerebral ganglion, eyestalk, thoracic ganglia, intestine, heart, testis, ovary, sperm reservoir, and hemocyte was constructed and sequenced using Pacific Biosciences single-molecule real-time (SMRT) long-read sequencing technology. A total of 284803 full-length non-chimeric reads were obtained, from which 79005 high-quality unique transcripts were obtained after error correction and sequence clustering and redundant. Additionally, a total of 52544 transcripts were annotated against protein database (NCBI nonredundant, Swiss-Prot, KOG, and KEGG database). A total of 23644 long non-coding RNAs (lncRNAs) and 131561 simple sequence repeats (SSRs) were identified. Meanwhile, the isoforms of many genes were also identified in this study. Our study provides a rich set of full-length cDNA sequences for S. paramamosain, which will greatly facilitate S. paramamosain research.

Salinity stress-induced differentially expressed miRNAs and target genes in sea cucumbers Apostichopus japonicus

Environmental salinity is an important abiotic factor influencing normal physiological functions and productive performance in the sea cucumber Apostichopus japonicus. It is therefore important to understand how changes in salinity affect sea cucumbers in the face of global climate change. In this study, we investigated the responses to salinity stress in sea cucumbers using mRNA and miRNA sequencing. The regulatory network of mRNAs and miRNAs involved in salinity stress was examined, and the metabolic pathways enriched for differentially expressed miRNAs and target mRNAs were identified. The top 20 pathways were involved in carbohydrate metabolism, fatty acid metabolism, degradation, and elongation, amino acid metabolism, genetic information processing, metabolism of cofactors and vitamins, transport and catabolism, and environmental information processing. A total of 22 miRNAs showed differential expression during salinity acclimation. The predicted 134 target genes were enriched in functions consistent with the results of gene enrichment based on transcriptome analysis. These results suggested that sea cucumbers deal with salinity stress via changes in amino acid metabolism, ion channels, transporters, and aquaporins, under stimulation by environmental signals, and that this process requires energy from carbohydrate and fatty acid metabolism. Salinity challenge also induced miRNA expression. These results provide a valuable genomic resource that extends our understanding of the unique biological characteristics of this economically important species under conditions of salinity stress.

Comparative transcriptional analysis and RNA interference reveal immunoregulatory pathways involved in growth of the oriental river prawn Macrobrachium nipponense

A source of premium animal protein, crustaceans are widely distributed and cultivated around the world. Short-term or long-term starvation events occur frequently owing to natural environment changes or manual management strategies in the life cycle of crustaceans. The result induced by starvation is that somatic growth of crustaceans will be retarded, while the immune mechanism is activated in this process. The aim of this study was to investigate whether the immune regulatory pathways are involved in the growth of crustaceans. Twelve muscle tissue transcriptomes of the oriental river prawn Macrobrachium nipponense were sequenced across four fasting stages lasting 0, 7, 14 and 21 d. The results showed that three immune-related pathways were involved in the growth of M. nipponense by regulating actin expression inducing the chemokine signaling pathway, the leukocyte transendothelial migration pathway and the FcR-mediated phagocytosis pathway. Furthermore, we employed RNA interference (RNAi) to further verify the effects that genes involved in the pathways had on regulating growth of M. nipponense. Comparative transcriptional analysis and RNA interference reveal that VASP and WAVE positively regulated the expression of actin; however, WASP negatively regulated the expression of actin. This is the first report that the immune regulatory pathways play key roles in the growth of crustaceans. Our results will not only provide an entirely new understanding of the immune mechanism of crustaceans from a unique angle but also further enrich and develop the theory of growth and developmental biology in crustaceans.

Comparative transcriptome analysis of Eriocheir japonica sinensis response to environmental salinity

Chinese mitten crabs (Eriocheir japonica sinensis) are catadromous, spending most of their lives in fresh water, but moving to a mixed salt-fresh water environment for reproduction. The characteristics of this life history might imply a rapidly evolutionary transition model for adaptation to marine from freshwater habitats. In this study, transcriptome-wide identification and differential expression on Chinese mitten crab groups were analysed. Results showed: clean reads that were obtained totalled 93,833,096 (47,440,998 in Group EF, the reference, and 46,392,098 in Group ES, the experimental) and 14.08G (7.12G in Group EF 6.96G in Group ES); there were 11,667 unigenes (15.29%) annotated, and they were located to 230 known KEGG pathways in five major categories; in differential expression analysis, most of the top 20 up-regulated pathways were connected to the immune system, disease, and signal transduction, while most of the top 20 down-regulated pathways were related to the metabolism system; meanwhile, 8 representative osmoregulation-related genes (14-3-3 epsilon, Cu2+ transport ATPase, Na+/K+ ATPase, Ca2+ transporting ATPase, V-ATPase subunit A, Putative arsenite-translocating ATPase, and Cation transport ATPase, Na+/K+ symporter) showed up-regulation, and 1 osmoregulation-related gene (V-ATPase subunit H) showed down-regulation. V-ATPase subunit H was very sensitive to the transition of habitats. These results were consistent with the tests of qRT-PCR. The present study has provided a foundation to further understand the molecular mechanism in response to salinity changing in water.

Adaptively differential expression analysis in gill of Chinese mitten crabs (Eriocheir japonica sinensis) associated with salinity changes

Desalination of marine species has become an important development direction for aquaculture in China and other countries. However, that how to regulate the salt balance to adapt to new freshwater habitats is a serious challenge for marine species in desalination of aquaculture. In the study, Chinese mitten crabs (Eriocheir japonica sinensis) was selected to analyse the adaptively differential expression in salinity changes for their novel characteristics of life history. The results showed that gill was the most relevant tissue in osmoregulation that was validated by biomarkers (Na⁺/K⁺-ATP, V-type H⁺-ATPase) with qPCR. Na⁺/K⁺-ATPase is a primary transporter and maintains the body fluid osmolality by actively pumping Na⁺ to the hemolymph, and V-type H⁺-ATPase is responsible for acid-base balance and nitrogen excretion. So both transcriptome data and qPCR results showed the significantly differential expression of Na⁺/K⁺-ATPase and V-type H⁺-ATPase in gills. Moreover, NAK-α had the most significantly differential expression level in salinity change, and other genes such as GST, HSP90, S27, UBE, VATB also revealed significantly up-regulation. They are considered the key enzymes during the transition from a marine environment to land. Present results have provided a foundation to further understand the molecular adaptive mechanism in desalination of marine species.

First comprehensive analysis of lysine acetylation in Alvinocaris longirostris from the deep-sea hydrothermal vents

Background

Deep-sea hydrothermal vents are unique chemoautotrophic ecosystems with harsh conditions. Alvinocaris longirostris is one of the dominant crustacean species inhabiting in these extreme environments. It is significant to clarify mechanisms in their adaptation to the vents. Lysine acetylation has been known to play critical roles in the regulation of many cellular processes. However, its function in A. longirostris and even marine invertebrates remains elusive. Our study is the first, to our knowledge, to comprehensively investigate lysine acetylome in A. longirostris.

Results

In total, 501 unique acetylation sites from 206 proteins were identified by combination of affinity enrichment and high-sensitive-massspectrometer. It was revealed that Arg, His and Lys occurred most frequently at the + 1 position downstream of the acetylation sites, which were all alkaline amino acids and positively charged. Functional analysis revealed that the protein acetylation was involved in diverse cellular processes, such as biosynthesis of amino acids, citrate cycle, fatty acid degradation and oxidative phosphorylation. Acetylated proteins were found enriched in mitochondrion and peroxisome, and many stress response related proteins were also discovered to be acetylated, like arginine kinases, heat shock protein 70, and hemocyanins. In the two hemocyanins, nine acetylation sites were identified, among which one acetylation site was unique in A. longirostris when compared with other shallow water shrimps. Further studies are warranted to verify its function.

Conclusion

The lysine acetylome of A. longirostris is investigated for the first time and brings new insights into the regulation function of the lysine acetylation. The results supply abundant resources for exploring the functions of acetylation in A. longirostris and other shrimps.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4745-3) contains supplementary material, which is available to authorized users.

Phenotypic and transcriptomic responses to salinity stress across genetically and geographically divergent Tigriopus californicus populations

Species inhabiting the North American west coast intertidal must tolerate an extremely variable environment, with large fluctuations in both temperature and salinity. Uncovering the mechanisms for this tolerance is key to understanding species' persistence. We tested for differences in salinity tolerance between populations of Tigriopus californicus copepods from locations in northern (Bodega Reserve) and southern (San Diego) California known to differ in temperature, precipitation and humidity. We also tested for differences between populations in their transcriptomic responses to salinity. Although these two populations have ~20% mtDNA sequence divergence and differ strongly in other phenotypic traits, we observed similarities in their phenotypic and transcriptomic responses to low and high salinity stress. Salinity significantly affected respiration rate (increased under low salinity and reduced under high salinity), but we found no significant effect of population on respiration or a population by salinity interaction. Under high salinity, there was no population difference in knock-down response, but northern copepods had a smaller knock-down under low salinity stress, corroborating previous results for T. californicus. Northern and southern populations had a similar transcriptomic response to salinity based on a principle components analysis, although differential gene expression under high salinity stress was three times lower in the northern population compared to the southern population. Transcripts differentially regulated under salinity stress were enriched for "amino acid transport" and "ion transport" annotation categories, supporting previous work demonstrating that the accumulation of free amino acids is important for osmotic regulation in T. californicus.

Effects of dietary lipids on the hepatopancreas transcriptome of Chinese mitten crab (Eriocheir sinensis)

Fish oil supplies worldwide have declined sharply over the years. To reduce the use of fish oil in aquaculture, many studies have explored the effects of fish oil substitutions on aquatic animals. To illustrate the effects of dietary lipids on Chinese mitten crab and to improve the use of vegetable oils in the diet of the crabs, 60 male juvenile Chinese mitten crabs were fed one of five diets for 116 days: fish oil (FO), soybean oil (SO), linseed oil (LO), FO + SO (1:1, FSO), and FO + LO (1:1, FLO). Changes in the crab hepatopancreas transcriptome were analyzed using RNA sequencing. There were a total 55,167 unigenes obtained from the transcriptome, of which the expression of 3030 was significantly altered in the FLO vs. FO groups, but the expression of only 412 unigenes was altered in the FSO vs. FO groups. The diets significantly altered the expression of many enzymes involved in lipid metabolism, such as pancreatic lipase, long-chain acyl-CoA synthetases, carnitine palmitoyltransferase I, acetyl-CoA carboxylase, fatty acid synthase, and fatty acyl Δ9-desaturase. The dietary lipids also affected the Toll-like receptor and Janus activated kinase-signal transducers and activators of transcription signaling pathways. Our results indicate that substituting fish oil with vegetable oils in the diet of Chinese mitten crabs might decrease the digestion and absorption of dietary lipids, fatty acids biosynthesis, and immunologic viral defense, and increase β-oxidation by altering the expression of the relevant genes. Our results lay the foundation for further understanding of lipid nutrition in Chinese mitten crab.

High throughput sequencing of RNA transcriptomes in Ruditapes philippinarum identifies genes involved in osmotic stress response

Ruditapes philippinarum, is an economically important marine bivalve species. The ability to cope with low salinity stress is quite important for the survival of aquatic species under natural conditions. In this study, the transcriptional response of the Manila clam to low salinity stress was characterized using RNA sequencing. The transcriptomes of a low salinity-treatment group (FRp1, FRp2), which survived under low salinity stress, and control group (SRp1, SRp2), which was not subjected to low salinity stress, were sequenced with the Illumina HiSeq platform. A total of 196,578 unigenes were generated. GO and KEGG analyses revealed that signal transduction, immune response, cellular component organization or biogenesis, and energy production processes were the most highly enriched pathways among the genes that were differentially expressed under low salinity stress. All these pathways could be assigned to the following biological functions in the low salinity tolerant Manila clam: signal response to low salinity stress, antioxidant response, intracellular free amino acid transport and metabolism, energy production and conversion, cell signaling pathways, and regulation of ionic content and cell volume. In summary, this is the first study using high-throughput sequencing to identify gene targets that could explain osmotic regulation mechanisms under salinity stress in R. philippinarum.

Exploring the molecular basis of adaptive evolution in hydrothermal vent crab Austinograea alayseae by transcriptome analysis

Elucidating the genetic mechanisms of adaptation to the hydrothermal vent in organisms at genomic level is significant for understanding the adaptive evolution process in the extreme environment. We performed RNA-seq on four different tissues of a vent crab species, Austinograea alayseae, producing 725,461 unigenes and 134,489 annotated genes. Genes related to sensory, circadian rhythm, hormone, hypoxia stress, metal detoxification and immunity were identified. It was noted that in the degenerated eyestalk, transcription of phototransduction related genes which are important for retinal function was greatly reduced; three crucial neuropeptide hormones, one molt-inhibiting and two crustacean hyperglycemic hormone precursors were characterized with conserved domains; hypoxia-inducible factor 1 and two novel isoforms of metallothioneins in the vent crabs were discovered. An analysis of 6,932 orthologs among three crabs A. alayseae, Portunus trituberculutus and Eriocheir sinensis revealed 19 positive selected genes (PSGs). Most of the PSGs were involved in immune responses, such as crustins and anti-lipopolysaccharide factor, suggesting their function in the adaptation to environment. The characterization of the first vent crab transcriptome provides abundant resources for genetic and evolutionary studies of this species, and paves the way for further investigation of vent adaptation process in crabs.

Similarities between decapod and insect neuropeptidomes

Background. Neuropeptides are important regulators of physiological processes and behavior. Although they tend to be generally well conserved, recent results using trancriptome sequencing on decapod crustaceans give the impression of significant differences between species, raising the question whether such differences are real or artefacts. Methods. The BLAST+ program was used to find short reads coding neuropeptides and neurohormons in publicly available short read archives. Such reads were then used to find similar reads in the same archives, and the DNA assembly program Trinity was employed to construct contigs encoding the neuropeptide precursors as completely as possible. Results. The seven decapod species analyzed in this fashion, the crabs Eriocheir sinensis, Carcinus maenas and Scylla paramamosain, the shrimp Litopenaeus vannamei, the lobster Homarus americanus, the fresh water prawn Macrobrachium rosenbergii and the crayfish Procambarus clarkii had remarkably similar neuropeptidomes. Although some neuropeptide precursors could not be assembled, in many cases individual reads pertaining to the missing precursors show unambiguously that these neuropeptides are present in these species. In other cases, the tissues that express those neuropeptides were not used in the construction of the cDNA libraries. One novel neuropeptide was identified: elongated PDH (pigment dispersing hormone), a variation on PDH that has a two-amino-acid insertion in its core sequence. Hyrg is another peptide that is ubiquitously present in decapods and is likely a novel neuropeptide precursor. Discussion. Many insect species have lost one or more neuropeptide genes, but apart from elongated PDH and hyrg all other decapod neuropeptides are present in at least some insect species, and allatotropin is the only insect neuropeptide missing from decapods. This strong similarity between insect and decapod neuropeptidomes makes it possible to predict the receptors for decapod neuropeptides that have been deorphanized in insects. This includes the androgenic insulin-like peptide that seems to be homologous to drosophila insulin-like peptide 8.

The identification and characteristics of salinity-related microRNAs in gills of Portunus trituberculatus

MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate gene expression in organisms. To understand the underlying mechanisms behind the molecular response of the crab to low salt-stress, high-throughput Illumina/Solexa deep sequencing technology was used to investigate the expression profiles of miRNAs under low salinity challenged. Two mixed RNA pool libraries of gill tissues from low salinity challenged (LC) and the control groups (NC) were sequenced on the Illumina platform. A total of 6,166,057 and 7,032,973 high-quality reads were obtained from the NC and LC libraries, respectively. Sixty-seven miRNAs consisting of 16 known and 51 novel ones were identified, among which, 12 miRNAs were differentially expressed in LC compared to NC. Thirty-four of the target genes predicted were differentially expressed in the opposite direction to the miRNAs, which were involved in crucial processes related to osmoregulation by gene ontology (GO) functional enrichment analysis, such as anion transport processes (GO:0006820) and chitin metabolic process (GO:0006030). These results provide a basis for further investigation of the miRNA-modulating networks in osmoregulation of Portunus trituberculatus.

Identification and characterization of nascent polypeptide-associated complex alpha from Chinese mitten crab (Eriocheir sinensis): A novel stress and immune response gene in crustaceans

Disease in aquatic animals is tightly linked to environmental challenges and their immune responses are greatly modified by their external environment. The chaperone protein nascent polypeptide-associated complex alpha (NACA) has been suggested to play important roles in the cellular response to stress and immune challenges, while the related biological functions remain largely unknown in invertebrates. In the present study we identified a NACA gene (termed EsNACA) from Chinese mitten crab Eriocheir sinensis and analyzed its expression changes in response to ambient (salinity and pH) stresses and immune challenges. The EsNACA protein is comprised of 209 amino acid residues with a conserved DNA binding domain, a C-Jun binding domain, a NAC domain and an ubiquitin-associated domain and shows the highest sequence identity (87%) with its counterpart in shrimp Penaeus monodon. EsNACA mRNA transcripts are presented in all tested normal tissues with predominant expression in hepatopancreas and lower expression in hemocytes. In addition, EsNACA expression was significantly altered in response to the ambient salinity (15‰ and 30‰ salinities) and pH (pH 6 and 8.5) stresses in gill, hepatopancreas, muscle, hemocytes and intestine tissues. Furthermore, EsNACA gene expression was substantially induced upon LPS and Poly(I:C) immune stimulations in E. sinensis hemocytes in vitro. Finally, EsNACA expression was up-regulated in E. sinensis hemocytes, gill, hepatopancreas, intestine and muscle tissues in response to Vibrio anguillarum challenges in vivo. Taken together, our findings for the first time show that EsNACA is an inducible gene involved in stress and immune response in crustaceans.

Redefining metamorphosis in spiny lobsters: molecular analysis of the phyllosoma to puerulus transition in Sagmariasus verreauxi

The molecular understanding of crustacean metamorphosis is hindered by small sized individuals and inability to accurately define molt stages. We used the spiny lobster Sagmariasus verreauxi where the large, transparent larvae enable accurate tracing of the transition from a leaf-shaped phyllosoma to an intermediate larval-juvenile phase (puerulus). Transcriptomic analysis of larvae at well-defined stages prior to, during, and following this transition show that the phyllosoma-puerulus metamorphic transition is accompanied by vast transcriptomic changes exceeding 25% of the transcriptome. Notably, genes previously identified as regulating metamorphosis in other crustaceans do not fluctuate during this transition but in the later, morphologically-subtle puerulus-juvenile transition, indicating that the dramatic phyllosoma-puerulus morphological shift relies on a different, yet to be identified metamorphic mechanism. We examined the change in expression of domains and gene families, with focus on several key genes. Our research implies that the separation in molecular triggering systems between the phyllosoma-puerulus and puerulus-juvenile transitions might have enabled the extension of the oceanic phase in spiny lobsters. Study of similar transitions, where metamorphosis is uncoupled from the transition into the benthic juvenile form, in other commercially important crustacean groups might show common features to point on the evolutionary advantage of this two staged regulation.

Comparative Transcriptome Analysis Reveals Sex-Biased Gene Expression in Juvenile Chinese Mitten Crab Eriocheir sinensis

Sex-biased genes are considered to account for most of phenotypic differences between males and females. In order to explore the sex-biased gene expression in crab, we performed the whole-body transcriptome analysis in male and female juveniles of the Chinese mitten crab Eriocheir sinensis using next-generation sequencing technology. Of the 23,349 annotated unigenes, 148 were identified as sex-related genes. A total of 29 candidate genes involved in primary sex determination pathways were detected, indicating the sex determination cascade of the mitten crab might be more complex than previously supposed. Differential expression analysis showed 448 differentially expressed genes (DEGs) between the two transcriptomes. Most of DEGs were involved in processes such as metabolism and immunity, and not associated with obvious sexual function. The pathway predominantly enriched for DEGs were related to lysosome, which might reflect the differences in metabolism between males and females. Of the immune DGEs, 18 up-regulated genes in females were humoral immune factors, and eight up-regulated genes in males were pattern recognition receptors, suggesting sex differences of immune defense might exist in the mitten crab. In addition, two reproduction-related genes, vitellogenin and insulin-like androgenic gland factor, were identified to express in both sexes but with significantly higher level in males. Our research provides the first whole-body RNA sequencing of sex-specific transcriptomes for juvenile E. sinensis and will facilitate further studies on molecular mechanisms of crab sexual dimorphism.

Molecular characterization and expression profile of three Fem-1 genes in Eriocheir sinensis provide a new insight into crab sex-determining mechanism

The FEM-1 protein of Caenorhabditis elegans plays a crucial role in the nematode sex-determination pathway. Here, we reported the characterization of three members of Fem-1 gene family in Eriocheir sinensis (designated EsFem-1a, EsFem-1b, and EsFem-1c), which were homologs of the nematode FEM-1 protein. The amino acid sequences of EsFem-1a, EsFem-1b, and EsFem-1c contained eight, nine, and eight ankyrin repeats, respectively. None of the ankyrin repeats had its own specific signature, and the evolution of ankyrin repeat was not completely independent. The predicted three-dimensional structure of EsFem-1 proteins exhibited highly similar superhelical conformation, especially the N-terminal six contiguous ankyrin repeats, which provided a binding surface for the protein-protein interaction. Phylogenetic tree based on the amino acid sequences revealed that EsFem-1a, EsFem-1b, and EsFem-1c were divided into three obvious separated clades. EsFem-1 genes were highly expressed in fertilized egg, 2-4 cell and blastula stage comparing with larval stage (P<0.01), which suggested they might be maternal genes. They also showed a certain degree of sexually dimorphic expression in some tissues. Notably, the highest expression of EsFem-1a was in the hepatopancreas, with EsFem-1b in testes and EsFem-1c in muscle (P<0.05), which indicated their potential role in a broad array of tissues. In addition, the genes initially involved in sex differentiation were not limited to those specifically expressed in the developing gonad. Taken together, these results suggested that EsFem-1 might function in crab early sex determination and late gonad development. The identification of Fem-1 gene family in E. sinensis provides a new insight into crab sex-determination mechanism.