A Lateral Line Specific Mucin Involved in Cupula Growth and Vibration Detection in Zebrafish.

The lateral line system in fish is crucial for detecting water flow, which facilitates various behaviors such as prey detection, predator avoidance, and rheotaxis. The cupula, a gelatinous structure overlaying the hair cells in neuromasts, plays a key role in transmitting mechanical stimuli to hair cells. However, the molecular composition of the cupula matrix remains poorly understood. In this study, we found that Mucin-5AC, a novel family of mucin proteins, composed of 2-27 cysteine-rich domains, presents in cartilaginous and bony fishes. Using in situ hybridization and transgenic reporter assays, we demonstrated that zebrafish is specifically expressed in the support cells of neuromasts. Knockdown of via antisense morpholino resulted in shorter cupulae in zebrafish lateral line. Additionally, we generated zebrafish mutants using CRISPR/Cas9 and found that cupulae in mutants were significantly shorter than that in wild-types, but the hair cell number in neuromasts was not changed obviously. Furthermore, mutant zebrafish larvae displayed compromised sensitivity to vibration stimuli compared to wild-type larvae. This study provides the first evidence linking the gene to cupula development and vibration detection in zebrafish. Our findings suggest that Mucin-5AC is likely a critical component of the cupula matrix, offering an important clue to the molecular composition of the lateral line cupula in fish.