Distal phalanges in bat wings have been hypothesized to be cartilaginous to allow for flight. We provide new evidence on how bat wing development might facilitate flight though protein-based regulation of bone mineralization and lead to more deflection at phalanx than humerus. Between Pteropus poliocephalus and Pteropus hypomelanus, two large bat species, we detected 112 proteins including 11 associated with mineralization and analyzed their distribution between the wing bones. Here, in contrast to previous reports, we found no cartilage-specific proteins and demonstrate that distal phalanges in bat wings are in fact low density bone that contain collagen I (the main constituent of bone's organic matrix) and proteins associated with mineralization in bone such as osteomodulin, bone-specific protein osteocalcin. The functional relevance of these changes was explored by measuring changes in mineral (crystal sizes, packing and density), material (Young's modulus and hardness) and structural characteristics. Consistent with changes in proteins associated with mineralization, mineral crystal thickness and alignment decreased from humerus to phalanges, and the mineral platelets were less densely packed along the wing length. Crystal thickness was negatively correlated with proteins associated with inhibition of mineralization as well as with two types of small leucine-rich proteoglycans, indicating the mineral growth and maturity is down regulated by these proteins independent of mineral quantity. The Young's modulus decreased across the wing and was significantly correlated with bone mineral density. Thus, the results from two bat species, studied here, demonstrate progressive alterations in bone mineralization occur in concert with the changes in secretion of bone regulatory proteins along the wing length. This altered mineralization together with structural changes serve to lighten the limb bone and optimize biomechanical properties conducive to flight.

蝙蝠翅膀的远端指骨被假设为软骨性以允许飞行。我们提供了关于蝙蝠翅膀发育如何通过基于蛋白质的骨矿化调节促进飞行并导致指骨比肱骨更多偏转的新证据。在Pteropus poliocephalus和Pteropus hypomelanus 之间，两种大型蝙蝠物种，我们检测到 112 种蛋白质，其中 11 种与矿化有关，并分析了它们在翼骨之间的分布。在这里，与之前的报告相反，我们没有发现软骨特异性蛋白质，并证明蝙蝠翅膀的远端指骨实际上是低密度骨，含有胶原蛋白 I（骨骼有机基质的主要成分）和与骨骼矿化相关的蛋白质，例如如骨调节素，骨特异性蛋白骨钙素。通过测量矿物（晶体尺寸、堆积和密度）、材料（杨氏模量和硬度）和结构特征的变化来探索这些变化的功能相关性。与矿化相关的蛋白质变化一致，矿物晶体厚度和排列从肱骨到指骨减少，矿物薄片沿机翼长度排列的密度较小。晶体厚度与抑制矿化相关的蛋白质以及两种类型的富含亮氨酸的小蛋白多糖呈负相关，表明这些蛋白质对矿物质生长和成熟度的下调与矿物质数量无关。整个机翼的杨氏模量降低，并且与骨矿物质密度显着相关。因此，这里研究的两种蝙蝠物种的结果表明，骨矿化的逐渐改变与沿翅膀长度的骨调节蛋白分泌的变化相一致。这种改变的矿化以及结构变化有助于减轻肢体骨骼的重量并优化有利于飞行的生物力学特性。