Extended Data Fig. 1. Identification of hemoglobin in chondrocytes.

a, Images for cartilages of P6 (6 days postnatal) mice before (insert) and post laser-based microdissection. Black arrows indicated eosin-positive structures. Scale bar: 10 μm. b, List of top proteins in the eosin-positive structures identified by mass spectrometry analysis. For whole data, see Supplementary Table 1. c, Mass spectrometry analysis of samples from laser capture microdissection. The samples dissected from about 200 chondrocytes were pooled into the cap of a 0.5-mL microcentrifuge tube and dissolved in tissue extraction buffer for mass spectrometry. d, SDS-PAGE of protein extracts from chondrocytes and blood. Black arrow and rectangles indicated the position of hemoglobin. e, f, Mass spectrometry analysis of proteins from red blood cells (e) and cartilages (f) on SDS-PAGE gel. g, h, Mass spectrometry (g) and Western blot (h) confirmed the presence of hemoglobin beta subunit (Hbb), and alpha subunit (Hba) in cartilages. For whole data, see Supplementary Table 2. For gel source data, see Supplementary Fig. 1a. i-k, RNA-seq (i) and quantitative proteomic analysis (j, k) to quantify the expression of Hba and Hbb in cartilaginous tissues. Data are presented as mean ± SEM, Error bars represent SEM. (n = 3 biologically independent samples).