Mussel is an economically and ecologically important species widely distributed throughout the world. The mussel adheres to the attachment substrate by secreting byssus external to the body. Various environmental and biological factors influence the process of byssus secretion, and the present study investigated the effect of starvation on byssal secretion in the hard-shelled mussel Mytilus coruscus. Histological changes in mussel foot secretory glands and gene expression of mussel foot proteins were also determined. The experimental setup consisted of starvation treatments for 7, 14 and 21 days, and the control groups. The results showed that the number of produced byssus was higher in the starvation group compared to the control (CTR) group, and the starvation group had a significantly higher of byssal shedding number from 6 days of starvation treatment onwards (p < 0.05). The byssal thread diameter was significantly reduced in all starvation treatment groups (p < 0.05). However, starvation treatment had no effect on the length of the byssal thread (p > 0.05). After 21 days of starvation treatment, the byssal thread volume was significantly lower than that of the CTR group (p < 0.05). A significant decrease in the breaking force of the byssal thread was observed after 14 and 21 days of starvation treatment (p < 0.05), along with an upward shift in the breakpoints. Starvation treatment significantly reduced the percentage of foot secretory glands area to total tissue (p < 0.05). The expression of the mussel foot protein genes (Mcfp-1P and Mcfp-1T) was significantly up-regulated at 7 days of starvation treatment (p < 0.05). These findings reveal that starvation weakens byssal thread performance by influencing mussel foot secretory glands, which increases the dislodgment risks of suspended-cultured mussels.
Many marine invertebrate larvae undergo complex morphological and physiological changes during the planktonic—benthic transition (a.k.a. metamorphosis). In this study, transcriptome analysis of different developmental stages was used to uncover the molecular mechanisms underpinning larval settlement and metamorphosis of the mussel, Mytilus coruscus. Analysis of highly upregulated differentially expressed genes (DEGs) at the pediveliger stage revealed enrichment of immune-related genes. The results may indicate that larvae co-opt molecules of the immune system to sense and respond to external chemical cues and neuroendocrine signaling pathways forecast and trigger the response. The upregulation of adhesive protein genes linked to byssal thread secretion indicates the anchoring capacity required for larval settlement arises prior to metamorphosis. The results of gene expression support a role for the immune and neuroendocrine systems in mussel metamorphosis and provide the basis for future studies to disentangle gene networks and the biology of this important lifecycle transformation.
The metamorphosis process is a critical life-changing event for marine invertebrate planktonic larvae to transform into benthic adults, which is crucial for the shellfish bed’s ecosystem stability and seed production in aquaculture. The mechanism of neuroendocrine regulation in the larval metamorphosis of bivalves remains ambiguous. In the present study, the expression of two deiodinase genes, McDx and McDy, was analyzed by whole-mount in situ hybridization at four larval stages in the hard-shelled mussel Mytilus coruscus. The McDx and McDy localized in visceral tissues, nervous system, mantle, and velum, indicating that two deiodinase genes are essential for larval development in M. coruscus. Knockdown of the McDx and McDy in the pediveliger larvae of M. coruscus using electroporation of siRNA significantly (p < 0.001) reduced McDx and McDy expression. McDx and McDy knockdown reduced larval metamorphosis in 45% and 49% of the pediveliger larvae induced by epinephrine (EPI). It is hypothesised that the knockdown effects of McDx and McDy repress metamorphic induction rather than larval viability, which does not elicit a lethal effect. The present study corroborates a synergistic action of the adrenergic and thyroid hormones signalling pathway in M. coruscus, and suggests the role of McDx and McDy in larval development and metamorphic transition.
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