Nodal Dependent Differential Localisation of Dishevelled-2 Demarcates Regions of Differing Cell Behaviour in the Visceral Endoderm

Abstract

The anterior visceral endoderm (AVE), a signalling centre within the simple epithelium of the visceral endoderm (VE), is required for anterior-posterior axis specification in the mouse embryo. AVE cells migrate directionally within the VE, thereby properly positioning the future anterior of the embryo and orientating the primary body axis. AVE cells consistently come to an abrupt stop at the border between the anterior epiblast and extra-embryonic ectoderm, which represents an end-point to their proximal migration. Little is known about the underlying basis for this barrier and how surrounding cells in the VE respond to or influence AVE migration. We use high-resolution 3D reconstructions of protein localisation patterns and time-lapse microscopy to show that AVE cells move by exchanging neighbours within an intact epithelium. Cell movement and mixing is restricted to the VE overlying the epiblast, characterised by the enrichment of Dishevelled-2 (Dvl2) to the lateral plasma membrane, a hallmark of Planar Cell Polarity (PCP) signalling. AVE cells halt upon reaching the adjoining region of VE overlying the extra-embryonic ectoderm, which displays reduced neighbour exchange and in which Dvl2 is excluded specifically from the plasma membrane. Though a single continuous sheet, these two regions of VE show distinct patterns of F-actin localisation, in cortical rings and an apical shroud, respectively. We genetically perturb PCP signalling and show that this disrupts the localisation pattern of Dvl2 and F-actin and the normal migration of AVE cells. In Nodal null embryos, membrane localisation of Dvl2 is reduced, while in mutants for the Nodal inhibitor Lefty1, Dvl2 is ectopically membrane localised, establishing a role for Nodal in modulating PCP signalling. These results show that the limits of AVE migration are determined by regional differences in cell behaviour and protein localisation within an otherwise apparently uniform VE. In addition to coordinating global cell movements across epithelia (such as during convergence extension), PCP signalling in interplay with TGFβ signalling can demarcate regions of differing behaviour within epithelia, thereby modulating the movement of cells within them.

Cell Chirality Induces Collective Cell Migration in Epithelial Sheets

“…This phenomenon is known as collective cell migration [1][2][3][4]. The unidirectional motion of cohesive cells contributes to the morphogenesis of multicellular organisms, for example in the left-right symmetry breaking of organs [5,6].…”

Cell fate decisions and axis determination in the early mouse embryo

“…6). A recent study (Trichas et al, 2011) has suggested that there are regional differences in F-actin and dishevelled 2 (Dvl2) protein localization between embryonic VE and extra-embryonic VE, and that these differences may explain why DVE cells do not pass the embryonic/extra-embryonic junction.…”

“…6). A recent study (Trichas et al, 2011) has suggested that there are regional differences in F-actin and dishevelled 2 (Dvl2) protein localization between embryonic VE and extra-embryonic VE, and that these differences may explain why DVE cells do not pass the embryonic/extra-embryonic junction.What might be the driving force of DVE cell migration? As the involvement of Rac1 and the WAVE complex suggests, time-lapse observations (Takaoka et al, 2011) have shown that DVE migration is an active and rapid process (it takes 5 hours for a DVE cell to move from the distal tip of the embryo to the embryonic/extra-embryonic junction).…”

A microdevice to locally electroporate embryos with high efficiency and reduced cell damage

“…Hex-GFP (Rodriguez et al, 2001). This approach has demonstrated that DVE cells migrate while keeping epithelial integrity by intercalating between other VE cells (Migeotte et al, 2010;Srinivas et al, 2004;Trichas et al, 2011Trichas et al, , 2012. Moreover, cell tracking has shown that the whole VE layer is involved in a global reorganisation initiated by DVE motion (Rivera-Perez et al, 2003;Takaoka et al, 2011;Trichas et al, 2011).…”

“…This approach has demonstrated that DVE cells migrate while keeping epithelial integrity by intercalating between other VE cells (Migeotte et al, 2010;Srinivas et al, 2004;Trichas et al, 2011Trichas et al, , 2012. Moreover, cell tracking has shown that the whole VE layer is involved in a global reorganisation initiated by DVE motion (Rivera-Perez et al, 2003;Takaoka et al, 2011;Trichas et al, 2011). Detailed observation of DVE cells at the migration front revealed that they send long actin-dependent projections, which possibly sense the environment for orientation cues (Migeotte et al, 2010;Srinivas et al, 2004).…”