One of the first jobs an embryo must complete is to orient the body’s head/tail axis. It seems simple enough, but for an early embryo with not many cells, it is an amazing task. A recent paper describes the use of amazing microscopy to visualize this process in a mouse embryo.
The anterior visceral endoderm (AVE) is a subset of cells from the visceral endoderm that sets up the anterior-posterior (head-tail) body axis by migrating to the future anterior region. A recent paper precisely describes AVE migration and the relationship between the AVE and its neighbors. In this paper, Trichas and colleagues show that the AVE cell move by exchanging neighbors, or intercalate, within an unbroken epithelial sheet. In addition, AVE migration is regulated by different localization patterns of actin and certain signaling pathways. Images above are 3D reconstructions of mouse embryo images, with AVE cells labeled green and two different epithelial junction proteins are labeled in magenta (ZO-1 is top, E-cadherin is bottom). Before (left), during (middle), and after (right) migration, the epithelial sheet remains intact due to the cell intercalation of the AVE.
BONUS!! Below is a movie of how 3D renderings compare with the raw images that are acquired on the microscope. For many more awesome movies, check out the link here.
Trichas, G., Joyce, B., Crompton, L., Wilkins, V., Clements, M., Tada, M., Rodriguez, T., & Srinivas, S. (2011). Nodal Dependent Differential Localisation of Dishevelled-2 Demarcates Regions of Differing Cell Behaviour in the Visceral Endoderm PLoS Biology, 9 (2) DOI: 10.1371/journal.pbio.1001019