Immunohistochemical localization of GnRH-immunoreactive cell bodies and fibers in the nerve ganglion of Perinereis aibuhitensis (Annelida: Polychaeta)

Sex-specific differential gene expression during stolonization in the branching syllid Ramisyllis kingghidorahi (Annelida, Syllidae)

BACKGROUND

Ramisyllis kingghidorahi (Annelida, Syllidae) is one of few annelid species with a ramified body, one anterior end and hundreds of posterior ends. R. kingghidorahi belongs to the family Syllidae, whose members reproduce by forming stolons, small autonomous reproductive units, at the posterior end. Molecular mechanisms controlling sexual reproduction are still poorly understood, but previous studies support an important role of the anterior end and stolons. The roles of different body regions during sexual reproduction in a complex branched body where there is only one head but multiple posterior ends, which develop hundreds of simultaneous stolons, have never been investigated. Consequently, we aimed to research the transcriptomic basis of sexual maturation and stolonization in R. kingghidorahi by performing differential gene expression analyses.

RESULTS

Transcriptomes were assembled from different body regions (anterior end, midbody, and stolons) of male, female, and non-reproductive individuals. Comparative analyses revealed that body region had a greater impact on gene expression profiles than sex, with the anterior end and stolons showing extensive gene upregulation. Across-sex comparisons revealed sex-specific processes in all body regions, with stolons exhibiting the most differences in differential expression, likely related to gametogenesis and external sexual dimorphism. Fewer genes than expected were differentially expressed in the anterior region, a result for which different possible explanations are discussed. Surprisingly, key genes typically associated with segmentation and metamorphosis, such as Wnt and Hox, showed little differential expression, aligning with recent findings that stolon segments lack a specific segment identity.

CONCLUSIONS

This study presents the first transcriptomic data for a branched annelid species and offers new insights into the complex genetic regulation of reproduction in R. kingghidorahi. Additionally, it provides the first glimpse into the mechanisms of sexual maturation in branched syllids, which must coordinate stolonization across multiple posterior ends. These findings enhance our understanding of annelid reproductive biology and highlight the need for further research to uncover the physiological and molecular pathways regulating sexual maturation and stolonization in syllids and other annelids.

Chromatographic purification of the plasmin-like enzyme from clamworm (Perinereis aibuhitensis Grub) and its fibrinolytic activity by metal ions

In this study, fibrinolytic protease was isolated and purified from Perinereis aibuhitensis Grub, and the extraction process was optimized. The properties of the enzyme, such as the amino acid composition, thermal stability, optimal temperature, and pH, were investigated. After detoxification, proteins collected from fresh Clamworm (Perinereis aibuhitensis Grub) were concentrated via ammonium sulfate precipitation. The crude protease was purified using gel filtration resin (Sephadex G-100), anion exchange resin (DEAE-Sepharose FF), and hydrophobic resin (Phenyl Sepharose 6FF). The molecular weight of the protease was determined by polyacrylamide gel electrophoresis (SDS-PAGE). The optimum temperature and optimum pH of the protease were determined. The activity of crude protease in the 40-60% salt-out section was the highest, reaching 467.53 U/mg. The optimal process for purifying crude protein involved the application of DEAE-Sepharose FF and Phenyl Sepharose 6FF, which resulted in the isolation of a single protease known as Asp60-D1-P1 with the highest fibrinolytic activity; additionally, the enzyme activity was measured at 3367.76 U/mg. Analysis by Native-PAGE and SDS-PAGE revealed that the molecular weight of Asp60-D1-P1 was 44.5 kDa, which consisted of two subunits with molecular weights of 6.5 and 37.8 kDa, respectively. The optimum temperature for Asp60-D1-P1 was 40°C, and the optimal pH was 8.0.

Immunohistochemical Localization of a GnRH-Like Peptide in the Nerve Ganglion of Three Classes of Crustaceans, the Tadpole Shrimp Triops longicaudatus (Branchiopoda), the Barnacle Balanus crenatus (Hexanauplia), and the Hermit Crab Pagurus filholi (Malacostraca)

In vertebrates, gonadotropin-releasing hormone (GnRH) regulates gonadal maturation by stimulating the synthesis and release of pituitary gonadotropins. GnRH has also been identified in invertebrates. Crustacea consists of several classes including Cephalocarida, Remipedia, Branchiopoda (e.g., tadpole shrimp), Hexanauplia (e.g., barnacle) and Malacostraca (e.g., shrimp, crab). In the malacostracan crustaceans, the presence of GnRH has been detected in several species, mainly by immunohistochemistry. In the present study, we examined whether a GnRH-like peptide exists in the brain and/or nerve ganglion of three classes of crustaceans, the tadpole shrimp Triops longicaudatus (Branchiopoda), the barnacle Balanus crenatus (Hexanauplia), and the hermit crab Pagurus filholi (Malacostraca), by immunohistochemistry using a rabbit polyclonal antibody raised against chicken GnRH-II (GnRH2). This antibody was found to recognize the giant freshwater prawn Macrobrachium rosenbergii GnRH (MroGnRH). In the tadpole shrimp, GnRH-like-immunoreactive (ir) cell bodies were located in the circumesophageal connective of the deuterocerebrum, and GnRH-like-ir fibers were detected also in the ventral nerve cord. In the barnacle, GnRH-like-ir cell bodies and fibers were located in the supraesophageal ganglion (brain), the subesophageal ganglion, and the circumesophageal connective. In the hermit crab, GnRH-like-ir cell bodies were detected in the anterior-most part of the supraesophageal ganglion and the subesophageal ganglion. GnRH-like-ir fibers were observed also in the thoracic ganglion and the eyestalk. These results suggest that a GnRH-like peptide exists widely in crustacean species.