Calcium carbonate in avian eggshell is used as a calcium source for bone formation during embryonic development. We studied ostrich eggshells as a representative avian egg and found that the calcium reserve assembly (CRA) region, eventually dissolving for bone formation, consists of nano-granules comprising amorphous calcium carbonate (ACC) by careful microscopic observation. ACC is unstable phase of calcium carbonate with high solubility and is stabilized by additives. As such a stabilizer, we found small molecules from eggshell internal region. Particularly, the ACC was recreated by the formation of calcium carbonate in the presence of D-myo-inositol 4,5-bisphosphate (Ins(4,5)P₂), isolated from ostrich eggshell for the first time in this study. Further mass spectrometric imaging technique revealed that Ins(4,5)P₂ is localized at the CRA region, suggesting that this compound could play a major role that makes it easier to dissolve and internalize eggshell calcium during embryogenesis.

禽蛋壳中的碳酸钙用作胚胎发育过程中骨骼形成的钙源。我们研究了以鸵鸟蛋壳为代表的禽蛋，并通过仔细的显微镜观察发现，钙储备组合物（CRA）区最终溶解了骨形成，其由包含无定形碳酸钙（ACC）的纳米颗粒组成。ACC是具有高溶解度的碳酸钙不稳定相，并通过添加剂使其稳定。作为这种稳定剂，我们从蛋壳内部区域发现了小分子。特别地，ACC由碳酸钙的形成中的D-存在重建肌肉肌醇4,5-二磷酸（宏（4,5）P2 ₂），这是本研究首次从鸵鸟蛋壳中分离出来的。进一步的质谱成像技术表明，Ins（4,5）P ₂位于CRA区，表明该化合物可能起主要作用，使其在胚发生过程中更容易溶解和内化蛋壳钙。