library_construction_protocol: Skulls were microdissected 7 d after defect creation.  Cranial bone with a defect at the center, with an approximate edge length of 3mm, was minced and subjected to six sequential enzymatic digestions with a mixture containing collagenase type I (1 mg/ml; Worthington Biochemical Corporation, Lakewood, NJ, USA, LS004197) and collagenase type II (1 mg/ml; Worthington Biochemical Corporation, LS004177).  Cell fractions (from sequential digestions 1 to 6) were collected and resuspended in red blood cell lysis buffer (37°C for 5 min). Digestions were subsequently filtered through 40-μm sterile strainers. Cells were then washed in PBS and resuspended in HBSS at a concentration of ~1000 cells/μl. for all samples, 10x Genomics Chromium standard protocol