Longer Duct, Better Silk: Unveiling How Anterior Silk Gland Length Boosts Fiber Performance

The mechanical performance of silk is closely tied to the fibrillization process within the anterior segment of silk gland (ASG). While a long and narrow ASG is conserved across silk-spinning species, its biological role remains unclear. Here, we performed a comprehensive structure-function analysis of the silkworm ASG and revealed that its long and narrow morphology plays an essential role in silk fibrillization and fiber performance. A steep reduction in duct diameter at the ASG's onset initiates silk protein transformation, while the extended duct length promotes molecular alignment, crystallization, and orientation. Genetic manipulation to extend ASG length significantly increased the Young's modulus and toughness of silkworm silk fibers. These findings demonstrate the potential of ASG length modulation as an effective strategy to improve silk fiber performance and provide valuable insights into the biological and functional importance of silk gland morphology.