Extended Data Figure 9. Posterior localisation of basement membrane perforations and MMP14 expression in pre-gastrula and gastrula stages.

A) Representative examples of early gastrula embryos showing posterior expression of MMP14. n=15 embryos B) En-face posterior view of early gastrula embryo. n= 10 embryos For A,B: MMP14 expression follows the pattern of basement membrane perforations. White arrowhead: Posterior and prospective primitive streak. Purple arrowheads: breached basement membrane/primitive streak. C) Representative examples of E6.0-E6.5 embryos showing the pattern of basement membrane perforations in pre-gastrula stages. Basement membrane perforations pre-pattern the primitive streak in pre-gastrula stages. n=30 embryos D) En face posterior and anterior views of pre-gastrula embryos showing that basement membrane perforations are found only at the embryo’s posterior side. n=10 embryos. Scale bars= 20um.