Extended Data Fig. 1: Keratin filaments in the preimplantation mouse embryo.

a, 3D views of mouse embryos at multiple developmental stages, stained for K18. K18 expression and localization resemble that of K8. Note the initial assembly of filaments in a specific subset of cells in the 8-cell embryo. Data are from five independent experiments. b, Double immunofluorescence for K8 and K18 shows their colocalization in filament structures within the same embryo. Data are from three independent experiments. c, Double immunofluorescence using a pan-keratin antibody and K18 shows colocalization in filament structures within the same embryo. Data are from three independent experiments. d, High-magnification views highlight keratin filament organization at multiple developmental stages (top). Surface render of computationally-segmented cells and keratin filaments with top and side views show the changes in cell morphology and keratin filament organization at different developmental stages. The density of the keratin filament network increases over time and the filaments become enriched at cell-cell junctions. Data are from five independent experiments. e, Live imaging of embryos expressing K18-Emerald. A subset of cells begins to assemble keratin filaments at the eight-cell stage, similar to observations from immunofluorescence for endogenous keratins. No keratin filaments are detected in four-cell or early uncompacted eight-cell embryos. Data are from three independent experiments. f, g, Colocalization of K18-Emerald and immunofluorescence against K8 (f) or K18 (g). Bottom panels show zoomed views of single cells expressing keratin filaments, with arrows pointing to an example of signal colocalization. Data are from three independent experiments. Scale bars, 10 μm.