Gene expression analysis in the zebrafish fractured scale

Bone is a connective tissue which undergoes continuous remodeling, including bone resorption and formation by osteoclasts (OCs) and osteoblasts (OBs), respectively. Recently, extracellular vesicles (EVs) are increasingly appreciated as a regulator of intercellular communication between OCs and OBs. The zebrafish scale is a thin membranous bone embedded in the skin and consists of OBs, OCs, and bone matrix, providing an elegant model to visualize OC-OB communication. Here, we developed a double-transgenic zebrafish line, trap:GFP; osterix:mCherry, which expresses GFP and mCherry under the control of the OC-specific trap (tartrate-resistant acid phosphatase) and OB-specific osterix enhancer, respectively. Utilizing this double-transgenic line, in combination with Hoechst 33342 (Hoe) staining, we isolated four distinct fractions from the scale at 1 day post-fracture by flow cytometry, GFP(–) mCh(+) Hoe(high) (OB fraction), GFP(low) mCh(+) Hoe(high) (OC precursor (pOC) fraction), GFP(high) Hoe(high) (mature OC (mOC) fraction), and mCh(+) Hoe(–) (OB-derived extracellular vesicle (EV) fraction). In this study, we have performed RNA-seq analysis using these four fractions to examine the gene expression profile of each fraction. Overall design: mRNA profiles of isolated OBs, pOCs, mOCs, and OB-derived EVs in the zebrafish fractured scales were generated by Quartz-seq using Illumina NextSeq500.