Developmental Compartments

Abstract

Developing tissues are in some cases subdividing into developmental compartments. These are spatially restricted regions between which proliferating and migrating cells cannot mix, even though cells in adjacent compartments can be immediate neighbours in a single epithelium or mesenchyme. Compartments not only serve to subdivide tissues but also, through signalling between compartments, often establish boundary zones that themselves become organising centres for the tissue. First described in the fruit fly Drosophila melanogaster , examples have also been described in vertebrate tissues including the neuroepithelium and limb bud. To establish compartments, cells must retain stable compartmental properties that restrict intermixing of cell lineages at compartmental boundaries. A great deal is now known both about the specification of compartmental cells and their impact on patterning, but much remains to be learned especially about the molecular basis of cell segregation. Key Concepts Developmental compartments require that cells acquire stable regional identities and have mechanisms that prevent intermixing with unlike cells. Sharply defined regions in developing tissues are not necessarily compartments: cells can also maintain regions using regionalised signalling to change their identities. Techniques for tracing cell lineages, each with its own advantages and pitfalls, are required to establish the existence of a compartment. Compartmental cell identities can be specified by the expression of one or two selector transcription factors or by more complex combinations. Cell segregation can require the establishment of compartment boundary cells. Several alternative mechanisms have been proposed to segregate cells between specific developmental compartments. The most well‐defined molecular mechanism for compartmental cell segregation is the Eph–Ephrin signalling of the rhombomeres of the vertebrate hindbrain.

A refutation to 'A new A-P compartment boundary and organizer in holometabolous insect wings.'

“…Also, these two boundaries align with sources that generate gradients of the two organiser molecules, Dpp and Wg [11][12][13][14][15][16] . Our current understanding of the patterning processes in the wing is based on these two boundaries [17][18][19][20][21] .…”