library_construction_protocol: embryonic skin from Sas-4 mutant and control mice was dissected at E13.5 and incubated with trypsin/pancreatin soultion for 5 min at RT and then for 30 min on ice to separate epidermal sheets from the underlying dermal tissue. Epidermal samples were frozen until further RNA isolation. RNA isolation was performed by following the manufacturer's instructions of the Quiagen RNeasy Mini Kit. Total RNA samples were used for RNA-Seq analysis. RNA libraries were prepared for sequencing using standard Illumina protocols