The Effect of Pedal Peptide-Type Neuropeptide on Locomotor Behavior and Muscle Physiology in the Sea Cucumber Apostichopus japonicus

Integrated multi-omics analysis and functional validation uncovers RPL26 roles in regulating growth traits of Asian water buffaloes (Bubalus bubalis)

BACKGROUND

Asian water buffaloes (Bubalus bubalis) in the Yangtze River Basin of China are the important meat provider for local residents because of its outstanding body size. Several previous studies have highlighted their genetic basis of growth characteristics, but the crucial genes regulating growth traits via multi-layer omics are still rarely investigated.

RESULTS

We conducted a comprehensive multi-omics analysis integrating blood and muscle transcriptome, plasma metabolome, rumen fluid metagenome, and genome of Haizi water buffaloes. Of note, ribosomal protein L26 (RPL26) located in the evolutionary selection regions associated with body sizes is the top differentially expressed gene (DEG) in both blood and muscle tissues. Further metabolomics and metagenomics identified growth-related molecular biomarkers (myristicin and Bacteroidales) and microbiological composition (Bacteroides and Prevotella). Leveraging cattle quantitative trait loci (QTLs) and genotype-tissue expression (CattleGTEx) databases, we found the significant correlations of QTL_180979 on RPL26 and two identified cis-eQTLs in muscle tissue in the upstream of RPL26 with weight gain. The follow-up cell assay validations confirmed the regulation roles of RPL26 in cell cycle, apoptosis, and differentiation, where the low RPL26 expressions enhanced the antiapoptotic ability and promoted the differentiation of myoblasts into myotubes markedly.

CONCLUSIONS

Our study illustrates RPL26 roles in regulating growth traits via both integrated multi-omics analysis and functional validations that suggests the further applications of RPL26 for growth trait selection of water buffaloes.

Identification and characterization of neuropeptides in sea urchin Strongylocentrotus intermedius

Neuropeptides play essential roles in regulation of feeding, reproduction and behavior in echinoderms. But the neuropeptide function has not been explored extensively in sea urchins. The tube feet contain part of the peripheral nervous system in echinoids, comprising both neurosensory and neuromuscular components. In this study, we sequenced transcriptome of Strongylocentrotus intermedius tube feet and identified 26 neuropeptide precursor transcripts, including ANpeptide, bursicons, calcitonin, corazonin, gonadotropin-releasing hormone (GnRH), glycoprotein-type hormones (GPA & GPB), insulin-related peptides (dilp7 & octinsulin), luqin, NGFFFamide, prolactin-releasing peptide/short neuropeptide F (PrRP/sNPF), orexin, pedal peptides, SALMFamides, somatostatin/allatostatin-C (SS1 & SS2), thyrotropin-releasing hormone (TRH), and vasopressin-oxytocin. In addition, we further compared the expression levels of neuropeptide precursors between red and white tube feet, and found 3 neuropeptides (bursicon β, octinsulin and luqin) had higher expression in red tube feet, potentially related to pigmentation or other pigment-related functions. We also observed ultrastructure of tube feet by transmission electron microscopy (TEM) and found large amount of muscle fibers, nerve plexus and vesicles in tube feet. Neuropeptides might play roles in these structures of tube feet. Our study represents the first identification of neuropeptides in tube feet of S. intermedius, and will contribute to a complete understanding on the roles of various neuropeptides in sea urchin echinoderms.

The neuropeptidomes of the sea cucumbers Stichopus cf. horrens and Holothuria scabra

The Philippines is a renowned marine biodiversity hotspot, home to several sea cucumber species with unusual biological traits. Among these, Stichopus cf. horrens is notable for its ability to undergo rapid body wall liquefaction when stressed, coupled with remarkable regenerative abilities. In contrast, Holothuria scabra has one of the most robust body walls in sea cucumbers and thrives in many regimes in the tropics. Despite their intriguing traits, the neurobiology and chemical diversity of these species remain underexplored. Neuropeptides are important components of an animal's neurobiological toolkit that underlie various physiological and behavioral processes. Thus, the discovery of neuropeptides is a crucial step for understanding the molecular underpinnings of unique traits in sea cucumbers. Leveraging the throughput and sensitivity of tandem mass spectrometry, we obtained an unbiased view of the endogenous peptidomes of radial nerve cord tissues of non-model sea cucumber species, H. scabra and S. cf. horrens. In this work, we sequenced 60 mature peptides from S. cf. horrens that were derived from 22 precursor proteins, and 43 peptides originating from 25 precursor proteins in H. scabra nervous tissues. A total of seven previously unannotated and uncharacterized neuropeptide precursors were identified, thereby expanding the known animal neuropeptide repertoire. Furthermore, we discovered consistent structural features in mature neuropeptides based on the type of post-translational modifications while pushing forward potentially novel proteolytic processing sites during peptide maturation based on the enriched flanking amino acid residues. Collectively, our results provide preliminary data that expand our understanding of echinoderm neurobiology through neuropeptide discovery, potentially paving the way for innovative solutions to address the global demand for echinoderms.

A Putative Role of Vasopressin/Oxytocin-Type Neuropeptide in Osmoregulation and Feeding Inhibition of Apostichopus japonicus

Vasopressin/oxytocin (VP/OT)-type neuropeptide is an ancient neurophysin-associated neuropeptide and has been intensively studied to be involved in multiple physiological processes in protostomian and deuterostome vertebrates. However, little is known about the functions of VP/OT-type neuropeptide in deuterostome invertebrates especially in echinoderms. Here, we firstly report VP/OT-type neuropeptide signaling in an important economic species, Apostichopus japonicus, which is widely cultured in Asia, with high nutritional and medicinal values. Molecular characterization analysis of holotocin and its precursor revealed the highly conserved features of VP/OT family. The candidate receptor for holotocin (AjHOR) was confirmed to be able to activate the signaling via cAMP-PKA and possible Ca2+-PKC pathway, and further activated the downstream ERK1/2 cascade. Holotocin precursor expression profile showed that they were mainly concentrated in circumoral nerve ring. Furthermore, in vitro pharmacological experiments demonstrated that holotocin caused contractile responses in preparations from A. japonicus. And in vivo functional studies indicated that short-term injection of holotocin resulted in body bloat and long-term injection resulted in reduced body mass, suggesting potential roles of holotocin in osmoregulation and feeding co-inhibition with holotocin-CCK. Our findings provided a comprehensive description of AjHOR-holotocin signaling, revealed ancient roles of holotocin in osmoregulation and feeding inhibition by controlling muscle contractions.

Effect of Kisspeptin-Type Neuropeptide on Locomotor Behavior and Muscle Physiology in the Sea Cucumber Apostichopus japonicus

Kisspeptins are neuropeptides encoded by the kiss1 gene, and little is known about them outside the vertebrate lineage. Two kisspeptin-type neuropeptides (KPs) have been discovered in Apostichopus japonicus (AjK1 and AjK2), an edible sea cucumber, and have been linked to reproductive and metabolic regulation. In this study, we evaluated how KPs affected locomotor behavior in one control group and two treatment groups (AjK1 and AjK2). We discovered that AjK1 had a significant dose effect, primarily by shortening the stride length and duration of movement to reduce the sea cucumber movement distance, whereas AjK2 had little inhibitory effect at the same dose. The levels of phosphatidylethanolamine (PE), phosphatidylcholine (PC), uridine, glycine, and L-serine in the longitudinal muscle of A. japonicus treated with AjK1 differed significantly from those of the control, which may explain the observed changes in locomotor behavior. Treatment with AjK2 induced changes in aspartate levels. Our results imply that AjK1 is more likely than AjK2 to have a role in the regulation of A. japonicus locomotion.

Nervous System Development and Neuropeptides Characterization in Embryo and Larva: Insights from a Non-Chordate Deuterostome, the Sea Cucumber Apostichopus japonicus

Here, we described the complex nervous system at five early developmental stages (blastula, gastrula, auricularia, doliolaria and pentactula) of a holothurian species with highly economic value, Apostichopus japonicus. The results revealed that the nervous system of embryos and larvae is mainly distributed in the anterior apical region, ciliary bands or rings, and the feeding and attachment organs, and that serotonergic immunoreactivity was not observed until the embryo developed into the late gastrula; these are evolutionarily conserved features of echinoderm, hemichordate and protostome larvae. Furthermore, based on available transcriptome data, we reported the neuropeptide precursors profile at different embryonic and larval developmental stages. This analysis showed that 40 neuropeptide precursors present in adult sea cucumbers were also identified at different developmental stages of embryos and larvae, and only four neuropeptide precursors (SWYG precursor 2, GYWKDLDNYVKAHKT precursor, Neuropeptide precursor 14-like precursor, GLRFAmprecursor-like precursor) predicted in adults were absent in embryos and larvae. Combining the quantitative expression of ten specific neuropeptide precursor genes (NPs) by qRT-PCR, we revealed the potential important roles of neuropeptides in embryo development, feeding and attachment in A. japonicus larvae. In conclusion, this work provides novel perspectives on the diverse physiological functions of neuropeptides and contributes to understanding the evolution of neuropeptidergic systems in echinoderm embryos and larvae.

Application of MS-Based Metabolomic Approaches in Analysis of Starfish and Sea Cucumber Bioactive Compounds

Today, marine natural products are considered one of the main sources of compounds for drug development. Starfish and sea cucumbers are potential sources of natural products of pharmaceutical interest. Among their metabolites, polar steroids, triterpene glycosides, and polar lipids have attracted a great deal of attention; however, studying these compounds by conventional methods is challenging. The application of modern MS-based approaches can help to obtain valuable information about such compounds. This review provides an up-to-date overview of MS-based applications for starfish and sea cucumber bioactive compounds analysis. While describing most characteristic features of MS-based approaches in the context of starfish and sea cucumber metabolites, including sample preparation and MS analysis steps, the present paper mainly focuses on the application of MS-based metabolic profiling of polar steroid compounds, triterpene glycosides, and lipids. The application of MS in metabolomics studies is also outlined.

Influence of an L-type SALMFamide neuropeptide on locomotory performance and muscle physiology in the sea cucumber Apostichopus japonicus

Neuropeptides in the SALMFamide family serve as muscle relaxants in echinoderms and may affect locomotion, as the motor behavior in sea cucumbers involves alternating contraction and extension of the body wall, which is under the control of longitudinal muscle. We evaluated the effect of an L-type SALMFamide neuropeptide (LSA) on locomotory performance of Apostichopus japonicus. We also investigated the metabolites of longitudinal muscle tissue using ultra performance liquid chromatography and quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) to assess the potential physiological mechanisms underlying the effect of LSA. The hourly distance, cumulative duration and number of steps moved significantly increased in sea cucumbers in the fourth hour after injection with LSA. Also, the treatment enhanced the mean and maximum velocity by 9.8% and 17.8%, respectively, and increased the average stride by 12.4%. Levels of 27 metabolites in longitudinal muscle changed after LSA administration, and the increased concentration of pantothenic acid, arachidonic acid and lysophosphatidylethanolamine, and the altered phosphatidylethanolamine/phosphatidylcholine ratio are potential physiological mechanisms that could explain the observed effect of LSA on locomotor behavior in A. japonicus.