Drivers of mantle-governed shell biogenesis gene transcription in Mediterranean mussels from the Northwestern Adriatic Sea: environmental variables, endogenous factors, and the physiological control

Shell biogenesis is a critical physiological process in bivalves, underpinning protection, growth, and resilience to environmental stressors. This study investigated seasonal and sex-related transcriptional profiles of key shell-formation genes in mantles of Mytilus galloprovincialis sampled from a model farm in the NW Adriatic Sea (Italy), a region characterized by strong environmental gradients and intensive aquaculture. We quantified the expression of extrapallial protein (EP), alpha carbonic anhydrase (CA), and chitin synthase (CS) by quantitative real time PCR, assessed sex and gonad maturation, and related molecular patterns to timeseries of environmental parameters and physiological indices. CA and EP expression were significantly higher in males and declined by 50-60 % from winter to summer, whereas females maintained relatively stable CA/EP expression across seasons. In contrast, CS expression showed winter to summer increases in both sexes, suggesting enhanced organic matrix functions under the (summer) more challenging environmental conditions. Environmental variables, gonad maturation, and shell growth indices contributed to observed transcriptional patterns, particularly in males. Neuroendocrine molecular markers associated with steroid and serotonin signaling were significantly related to shell biogenesis gene transcriptions, indicating potential regulatory roles. These findings demonstrate pronounced physiological plasticity in mussel shell formation and highlight sex-specific regulatory strategies that may impact mussel resilience to environmental change and aquaculture sustainability. Meanwhile, they envisaged a potential use of molecular markers targeting the shell building process in monitoring studies to assess variations of mussel physiological performances with environmental cues.