Fig. 8: Schematics of basement membrane remodeling and AP axis specification.
From: Basement membrane perforations guide anterior–posterior axis formation
Three major cell types, epiblast (EPI), trophectoderm (TE), and primitive Endoderm (PE), constitute the E4.5 pre-implantation blastocyst. At E4.75, biased MMP expression become evident in the Visceral Endoderm (VE) and create uneven basement membrane perforations in between the VE and EPI from E5.0, before DVE migration. At E5.5, basement membrane perforations serve as a guidance cue for unidirectional, collective DVE migration. MMP-dependent basement membrane remodeling remains essential not only before DVE migration to establish directional cues, but also during migration to sustain proper speed and directionality. Right before the primitive streak formation around E6.5, asymmetric basement membrane remodeling facilitates growth of the embryo during gastrulation.
