Timed interactions between the Hox expressing non-organiser mesoderm and the Spemann organiser generate positional information during vertebrate gastrulation.
We report a novel developmental mechanism. Anterior-posterior positional information for the vertebrate trunk is generated by sequential interactions between a timer in the early non-organiser mesoderm and the organiser. The timer is characterised by temporally colinear activation of a series of Hox genes in the early ventral and lateral mesoderm (i.e., the non-organiser mesoderm) of the Xenopus gastrula. This early Hox gene expression is transient, unless it is stabilised by signals from the Spemann organiser. The non-organiser mesoderm and the Spemann organiser undergo timed interactions during gastrulation which lead to the formation of an anterior-posterior axis and stable Hox gene expression. When separated from each other, neither non-organiser mesoderm nor the Spemann organiser is able to induce anterior-posterior pattern formation of the trunk. We present a model describing that convergence and extension continually bring new cells from the non-organiser mesoderm within the range of organiser signals and thereby create patterned axial structures. In doing so, the age of the non-organiser mesoderm, but not the age of the organiser, defines positional values along the anterior-posterior axis. We postulate that the temporal information from the non-organiser mesoderm is linked to mesodermal Hox expression.
Wacker
Stephan A
SA
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Uppsalalaan 8, 3584CT, Utrecht, Netherlands.
Jansen
Hans J
HJ
McNulty
Claire L
CL
Houtzager
Erwin
E
Durston
Antony J
AJ
D000818:Animals; D019521:Body Patterning; D005801:Genes, Homeobox; D008648:Mesoderm; D014714:Vertebrates / Q000196:embryology*; D014981:Xenopus