Genome-wide identification and expression analyses of Toll-like receptors provide new insights on adaptation to intertidal benthic environments in Urechis unicinctus (Annelida, Echiura)

Genome-wide identification and expression analysis of neuropeptide G protein-coupled receptors in Urechis unicinctus (Annelida, Echiura)

Neuropeptide G protein-coupled receptors (GPCRs) are membrane protein receptors with 7 transmembrane helices, regulating physiological processes like reproduction, development, and behavior. However, little is known about neuropeptide GPCRs in marine benthic invertebrates. To explore the GPCR composition and potential neuropeptide GPCRs involved in larval development, we performed a genome-wide search of neuropeptide GPCR family genes in the echiuran worm Urechis unicinctus, a marine benthic burrowing Annelida with typical larval settlement and metamorphosis processes during the larval development. A total of 71 putative neuropeptide GPCR genes were identified including 60 family-A GPCRs and 11 family-B GPCRs. Both families contained the conserved 7-transmembrane domain, with family-B GPCRs evolving more conservatively. The clustering of family-A GPCRs formed a large central cluster, where 12 GPCR genes were likely ancestral genes in the evolution of this family. About one-third of neuropeptide GPCR genes were highly expressed in embryos, larvae and adult organs of U. unicinctus. However, the specific GPCRs involved in larval development and adult organ function may differ. In addition, the binding of several neuropeptide GPCRs to larval settlement-related mature peptides was predicted by AlphaFold3 docking. The dual luciferase reporter gene assay showed that the affinity of neuropeptide GPCR Uu-A25 to MIP2 was higher than that to MIP1 in U. unicinctus. Inhibitor (H89 and calmidazolium) and activator (forskolin and Bay K 8644) experiments proved that the cAMP and Ca2+ pathways, mediated commonly by neuropeptide GPCRs, play important roles in the regulation of the larval settlement of U. unicinctus. This study provides a better understanding of neuropeptide GPCR evolution in marine benthic invertebrates and provides fundamental data for future functional exploration of the specific neuropeptide GPCRs in U. unicinctus larval development.

Transcriptional memories mediate the plasticity of sulfide stress responses to enable acclimation in Urechis unicinctus

To cope with environmental stresses, organisms often adopt a memory response upon primary stress exposure to facilitate a quicker and/or stronger reaction to recurring stresses. Somatic stress memory is essential in dealing with contemporary stress. The earliest sign of somatic stress memory is a change in gene transcription levels, which alters physiology and phenotype to better cope with stress. Sulfide is a common environmental pollutant; however, some organisms have successfully colonized sulfur-rich environments. Whether stress memory plays important role in sulfide stress adaptation remains unclear. In this study, to determine whether Urechis unicinctus, a sulfur-tolerant organism, retains the memory of previous sulfide stress, we simulated a repetitive sulfide stress/recovery system. The results showed that the tolerance of U. unicinctus to sulfide stress was significantly increased after priming with 50 µM sulfide. Further, transcriptional memory genes (TMGs) involved in regulating sulfide stress memory were identified, classified according to their expression patterns, and functionally analyzed. TMGs involved in sulfide metabolism, sugar metabolism, and protein homeostasis pathway showed an enhanced response, whereas those related to DNA repair pathway demonstrated a modified response pattern. Our study indicated that U. unicinctus retains memory of sulfide stress priming, which mediates plasticity to accelerate sulfide stress adaptation.

Aquatic Invertebrate Antimicrobial Peptides in the Fight Against Aquaculture Pathogens

The intensification of aquaculture has escalated disease outbreaks and overuse of antibiotics, driving the global antimicrobial resistance (AMR) crisis. Antimicrobial peptides (AMPs) provide a promising alternative due to their rapid, broad-spectrum activity, low AMR risk, and additional bioactivities, including immunomodulatory, anticancer, and antifouling properties. AMPs derived from aquatic invertebrates, particularly marine-derived, are well-suited for aquaculture, offering enhanced stability in high-salinity environments. This study compiles and analyzes data from AMP databases and over 200 scientific sources, identifying approximately 350 AMPs derived from aquatic invertebrates, mostly cationic and α-helical, across 65 protein families. While in vitro assays highlight their potential, limited in vivo studies hinder practical application. These AMPs could serve as feed additives, therapeutic agents, or in genetic engineering approaches like CRISPR/Cas9-mediated transgenesis to enhance resilience of farmed species. Despite challenges such as stability, ecological impacts, and regulatory hurdles, advancements in peptidomimetics and genetic engineering hold significant promise. Future research should emphasize refining AMP enhancement techniques, expanding their diversity and bioactivity profiles, and prioritizing comprehensive in vivo evaluations. Harnessing the potential of AMPs represents a significant step forward on the path to aquaculture sustainability, reducing antibiotic dependency, and combating AMR, ultimately safeguarding public health and ecosystem resilience.

Exploring the innate immune system of Urechis unicinctus: Insights from full-length transcriptome analysis

The Echiura worm Urechis unicinctus refers to a common benthic invertebrate found in the intertidal zone of Huanghai as well as Bohai Bay. U. unicinctus is known to contain various physiologically active substances, making it highly valuable in terms of its edibility, medicinal properties, and economic potential. Nonetheless, the limited study on the immune system of U. unicinctus poses difficulties for its aquaculture and artificial reproduction. Marine invertebrates, including shellfish and U. unicinctus, are thought to primarily depend on their innate immune system for disease protection, owing to the severalinnate immune molecules they possess. Herein, we employed PacBio single-molecule real-time (SMRT) sequencing technology to perform the full-length transcriptome analysis of U. unicinctus individuals under five different conditions (room temperature (RT), low temperature (LT), high temperature (HT), without water (DRY), ultraviolet irradiation (UV)). Concequently, we identified 59,371 unigenes that had a 2,779 bp average length, 2,613 long non-coding RNAs (lncRNAs), 59,190 coding sequences (CDSs), 35,166 simple sequence repeats (SSRs), and 1,733 transcription factors (TFs), successfully annotating 90.58 % (53,778) of the unigenes. Subsequently, key factors associated with immune-related processes, such as non-self-recognition, cellular immune defenses, and humoral immune defenses, were searched. Our study also identified pattern recognition receptors (PRRs) that included 17 peptidoglycan recognition proteins (PGRPs), 13 Gram-negative binding proteins (GNBPs), 18 scavenger receptors (SRs), 74 toll-like receptors (TLRs), and 89 C-type lectins (CLTs). Altogether, the high-quality transcriptome obtained data will offer valuable insights for further investigations into U. unicinctus innate immune response, laying the foundation for subsequent molecular biology studies and aquaculture.

Nonspecific immune, histology and accumulation of marine worm, Urechis unicinctus in response to bisphenol A (BPA)

Bisphenol A (BPA) is one of the environmental endocrine disruptors, due to its chemical stability it exists in abundant concentrations in water and soil consequently accumulating in the food chain and causing many endocrine-related health problems. So far, studies on the effects of BPA on marine invertebrates have focused on acute toxicity, endocrine regulation, reproduction, and development. However, fewer studies have been conducted on marine benthos. The current study aimed to detect the accumulation of BPA and its impact on tissue structure, antioxidant capacity, and immune indexes in marine worm, Urechis unicinctus. U. unicinctus, as a common marine benthic animal, were exposed to different concentrations of BPA. Blood cells and intestinal tract were taken for tissue structure inspection, and supernatant of the coelomic fluid was collected for oxidative and antioxidant biomarkers. Results showed that the accumulation of BPA in muscles of U. unicinctus tended to increase with exposure time. BPA induced a rise in H2O2 and MDA content, and altered the activities of CAT, T-SOD, GST, LSZ and ACP, weaken the immune system functions. Moreover, pathological observation showed that BPA caused severe histopathology in the respiratory intestine, stomach, and midgut. These results will be helpful to understand the response mechanism of U. unicinctus under BPA exposure and provide a reference for controlling the aquaculture conditions and marine water quality of U. unicinctus.