No abstract

Wnt genes encode a family of secretory glycoproteins that are involved in various stages of organ development through regulation of cell proliferation, differentiation, and growth. Recently, Wnt genes have been shown to play an important role in regeneration processes. However, there have been no previous genome-wide analyses of the Wnt gene family members in crab species. In this study, a total of 13 Wnt family genes were identified from the genome of the swimming crab Portunus trituberculatus and classified into three main groups based on the conserved domain, protein sequence, and motifs. Chromosome location analysis showed that tandem duplication may have resulted in the expansion of the PtWnt gene family. RNA-seq results indicated that most PtWnt genes had a higher Fragments Per Kilobase of transcript sequences per Million base pairs (FPKM) value in the regenerating limb bud muscle than in the normal limb muscle, and the genes were enriched in a number of pathways that had biological functions underlying limb regeneration such as the cell surface receptor signaling pathway, the hippo signaling pathway, receptor binding, and basal cell carcinoma. Moreover, quantitative real-time PCR (RT-qPCR) analysis confirmed that the expression levels of nine PtWnts except for PtWnt1, PtWnt2, and PtWnt6 had a consistently increasing trend during limb regeneration. PtWnt1, PtWnt2, and PtWnt6 exhibited significantly up- or down-regulated expression at different limb regeneration stages. These results provide valuable information for further evolutionary and functional characterization of PtWnt genes and indicate the complexity and specialized mechanism of the Wnt signaling pathway regulating regeneration in crustaceans.

Biogenic amines (BAs) play an important role in the aggressive behavior of crustaceans. In mammals and birds, 5-HT and its receptor genes (5-HTRs) are characterized as essential regulators involved in neural signaling pathways during aggressive behavior. However, only one 5-HTR transcript has been reported in crabs. In this study, the full-length cDNA of the 5-HTR1 gene, named Sp5-HTR1, was first isolated from the muscle of the mud crab Scylla paramamosain using the reverse-transcription polymerase chain reaction (RT-PCR) and rapid-amplification of cDNA ends (RACE) methods. The transcript encoded a peptide of 587 amino acid residues with a molecular mass of 63.36 kDa. Western blot results indicate that the 5-HTR1 protein was expressed at the highest level in the thoracic ganglion. Furthermore, the results of quantitative real-time PCR show that the expression levels of Sp5-HTR1 in the ganglion at 0.5, 1, 2, and 4 h after 5-HT injection were significantly upregulated compared with the control group (p < 0.05). Meanwhile, the behavioral changes in 5-HT-injected crabs were analyzed with EthoVision. After 0.5 h of injection, the speed and movement distance of the crab, the duration of aggressive behavior, and the intensity of aggressiveness in the low-5-HT-concentration injection group were significantly higher than those in the saline-injection and control groups (p < 0.05). In this study, we found that the Sp5-HTR1 gene plays a role in the regulation of aggressive behavior by BAs, including 5-HT in the mud crab. The results provide reference data for the analysis of the genetic mechanism of aggressive behaviors in crabs.

Providing shelters is considered an effective method to prevent self-harm and improve the survival rate of Scylla paramamosain. In this study, four shelter groups—the shelters of which included fine sand, arched tiles, PVC pipes, and trapezoidal net cages—and one group without shelters were established to investigate the effects of shelters on S. paramamosain by calculating their feeding rate, molting rate, survival rate, and growth index. The results showed that the feeding rates of the fine sand and PVC pipe groups were greater than 12% and that the feeding rates of the arched tile and trapezoidal net cage groups were greater than 9%, while the feeding rate of the group without shelters was only 6.7%. The food conversion rates of both the fine sand and PVC pipe groups exceeded 21%. In contrast, the food conversion rate of the non-shelter group was the lowest at 14%. The molting rates of the fine sand and PVC pipe groups were the highest, reaching 29% in the later stages of the experiment, while the molting rate of the non-shelter group was only 19%. There was no significant difference in survival rates among the groups during the first 20 days of the experiment. However, on the 60th day, the survival rate of the fine sand group was 92%, while the non-shelter group had a survival rate of 79%. The experimental results showed that the incidence of cheliped injuries in the fine sand group was 16%, while it was 25% in the non-shelter group. During the daytime, the occupancy rate of burrows by the four shelter groups was 60–70%, while during the night, the occupancy rate of each shelter decreased to 40–50%, and there was no significant difference in occupancy rates among the shelter groups during the night. The weight and full carapace width of S. paramamosain in the fine sand and PVC pipe groups were significantly higher than those in the other groups (P&lt; 0.05), and the weight gain rate and specific growth rate of the fine sand and PVC pipe groups were significantly higher than those of the other groups (P&lt; 0.05). Research has shown that fine sand and PVC pipes, as shelters for S. paramamosain, can effectively prevent cannibalism, increase feeding rates and survival rates, and promote growth and molting. This study provides scientific guidance for the proper selection of shelters in the farming process of S. paramamosain.