Schwann cell precursors contribute to skeletal formation during embryonic development in mice and zebrafish

Abstract

Immature multipotent embryonic peripheral glial cells, the Schwann cell precursors (SCPs), differentiate into melanocytes, parasympathetic neurons, chromaffin cells, and dental mesenchymal populations. Here, genetic lineage tracing revealed that, during murine embryonic development, some SCPs detach from nerve fibers to become mesenchymal cells, which differentiate further into chondrocytes and mature osteocytes. This occurred only during embryonic development, producing numerous craniofacial and trunk skeletal elements, without contributing to development of the appendicular skeleton. Formation of chondrocytes from SCPs also occurred in zebrafish, indicating evolutionary conservation. Our findings reveal multipotency of SCPs, providing a developmental link between the nervous system and skeleton.

Keywords: Schwann cell precursors; bone; cartilage; glia; mesenchymal cells.

Fig. 1.

SCPs generate mesenchymal cells during murine embryonic development. (A–C) Genetic tracing of Plp1^CreERT2;R26R^{Confetti/Confetti} embryos revealed SCP contribution to proximal mesenchymal cells. Confetti clones expressing RFP, YFP, and/or CFP proteins are shown in A. The same tissue section was immunostained with PGP9.5 (for neuron) and GFP (for confetti) in B. (C) The traced cells off TUJ1⁺ nerves were positive for mesenchymal marker, PDGFRa. In A–C, arrowheads indicate traced cells on nerves and arrows indicate traced cells that become mesenchymal cells.

Fig. 2.

SCPs generate chondroprogenitors in craniofacial region and trunk during murine embryonic development. Genetic labeling in Plp1^CreERT2;R26R^YFP/+ embryos from E11.5 to E12.5 revealed no overlap between SCPs and SOX9⁺ chondroprogenitors (A and B). Prolonged tracing revealed appearance of SCP progeny in cartilage at E15.5 (C and D) and E17.5 (E and F). Orange arrowheads and white arrows indicate YFP⁺ cells on TUJ1⁺ nerves and close to nerves and cartilage, respectively, and white arrowheads indicate YFP⁺SOX9⁺ chondrocytes in C′ and D′. The orange arrow in E′ indicates an YFP⁺ perichondrial cell. These images represent at least 5 Cre⁺ embryos from independent litters. A total of 5 facial and 2 trunk skeletal elements in each embryo were checked (see SI Appendix, Fig. S4 for details).

Fig. 3.

SCPs generate osteoprogenitor cells and osteocytes in facial region and trunk during murine embryonic development. (A–C) SCPs progeny in Plp1^CreERT2;R26R^YFP/+ embryos traced from E11.5 to E17.5 were positive for osteoprogenitor marker OSX in the ossified parts of mandible (A), rib (B), and scapula (C). The white arrowheads indicate double-positive cells. (D) Quantification of YFP⁺ cells among the OSX⁺ population. Data represent mean ± SEM where at least 3 embryos from independent litters were analyzed. (E and F) The same traced embryos were positive for Dmp1 RNA probe. A′′′′, B′′′′, and C′′′′ depict the same tissue sections as A–C but stained with von Kossa and Alcian blue (vK and Ab). The white dashed lines outline the mineralized portion of the bone.