Dynamics of anterior–posterior axis formation in the developing mouse embryo

Abstract

The development of an anterior–posterior (AP) polarity is a crucial process that in the mouse has been very difficult to analyse, because it takes place as the embryo implants within the mother. To overcome this obstacle, we have established an in-vitro culture system that allows us to follow the step-wise development of anterior visceral endoderm (AVE), critical for establishing AP polarity. Here we use this system to show that the AVE originates in the implanting blastocyst, but that additional cells subsequently acquire AVE characteristics. These 'older' and 'younger' AVE domains coalesce as the egg cylinder emerges from the blastocyst structure. Importantly, we show that AVE migration is led by cells expressing the highest levels of AVE marker, highlighting that asymmetry within the AVE domain dictates the direction of its migration. Ablation of such leading cells prevents AVE migration, suggesting that these cells are important for correct establishment of the AP axis.

Embryoids, organoids and gastruloids: new approaches to understanding embryogenesis

“…Self-assembly/ organization has also been observed directly in attached mammalian blastocysts in vitro. These studies established that human (Deglincerti et al, 2016a;Shahbazi et al, 2016) and mouse (Bedzhov et al, 2014b;Morris et al, 2012) embryos can be cultured ex vivo in the absence of maternal tissues, showing important selforganizing events. Although these assays are currently ethically limited to studying human embryos for only up to 14 days of development, they provide a complementary approach to embryoid and gastruloid experiments for quantitatively studying early human development and are likely to become increasingly popular in the coming years.…”

β-Pix directs collective migration of anterior visceral endoderm cells in the early mouse embryo

“…Collective AVE migration is complex and involves highly coordinated protrusive activity, cell translocation, cell division, and intercalation during a period of embryo growth and global cell movements (Srinivas et al 2004;Migeotte et al 2010;Takaoka et al 2011;Trichas et al 2011Trichas et al , 2012Morris et al 2012). To analyze AVE migration in more detail, we used high-resolution confocal video microscopy on live embryos expressing two transgenes: the AVE cell marker Hex-GFP and a ubiquitous membrane marker, GFP-GPI (Srinivas et al 2004;Rhee et al 2006).…”

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

“…Previous studies had reported that DVE cells at the migration front are required to initiate DVE movement, therefore acting as a leading population (Morris et al, 2012;Takaoka et al, 2011). Their displacement involves intercalation and production of long and stable basal projections (Migeotte et al, 2010;Srinivas et al, 2004).…”

“…In addition, upon reaching the proximity of the Emb/Xemb border, non-leading DVE cells extend very long projections that appear to contact the first or second cell rows of the migration front. It is tempting to speculate that distally located Emb VE cells need to make contact with the subpopulation of leading DVE cells, which is characterised by a distinct origin and specific expression of the markers Cer1 and Lefty1 (Morris et al, 2012;Takaoka et al, 2011), in order to receive the signals that regulate their migration and/or arrest.…”

“…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). Ablation experiments during the initial phase of migration indicated that front row cells act as leading cells and are essential for subsequent movements in the VE (Morris et al, 2012;Takaoka et al, 2011). By contrast, it has been difficult to scrutinise the shape and behaviour of DVE cells located in the midst of the migrating fluorescent population or of other non-labelled VE cells.…”