library_construction_protocol: Skin tissues were harvested from Tie1 knockout and control mice (E17.5) and kept frozen in liquid nitrogen. Total RNA was extracted from the tissues using Trizol (Invitrogen) according to the manufacturer's instruction Oligo(dT)-attached magnetic beads were used to purify mRNA. Purified mRNA was fragmented, converted into cDNA and amplified by PCR, and finally made into RNAseq libraries.