Emeline Raguin (1), Richard Weinkamer (1), Clemens Schmitt (1), Luca Curcuraci (1), Peter Fratzl (1)
Advanced Science. (19 May 2023). DOI: https://doi.org/10.1002/advs.202301231

Keywords

Bone development, chick embryo, cryo FIB-SEM, mineral transport, mineralization, vesicles

Abstract

During skeletal development, bone growth and mineralization require transport of substantial amounts of calcium, while maintaining very low concentration. How an organism overcomes this major logistical challenge remains mostly unexplained. To shed some light on the dynamics of this process, cryogenic focused ion beam-scanning electron microscopy (cryo-FIB/SEM) is used to image forming bone tissue at day 13 of a chick embryo femur. Both cells and matrix in 3D are visualized and observed as calcium-rich intracellular vesicular structures. Counting the number of these vesicles per unit volume and measuring their calcium content based on the electron back-scattering signal, the intracellular velocity at which these vesicles need to travel to transport all the calcium required for the mineral deposited in one day within the collagenous tissue can be estimated. This velocity at 0.27 µm s−1 is estimated, which is too large for a diffusion process and rather suggests active transport through the cellular network. It is concluded that calcium logistics is hierarchical and based on several transport mechanisms: first through the vasculature using calcium-binding proteins and the blood flow, then active transport over tens of micrometers through the network of osteoblasts and osteocytes, and finally diffusive transport over the last one or two microns.

How Our Software Was Used

Stacks alignment and image processing were performed using Dragonfly’s post-processing toolkit, and segmentations were generated from a deep model trained with Dragonfly’s Deep Learning Tool.

Author Affiliation

(1) Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam, Germany