The role of the Spemann organizer in anterior-posterior patterning of the trunk.
The formation of the vertebrate body axis during gastrulation strongly depends on a dorsal signaling centre, the Spemann organizer as it is called in amphibians. This organizer affects embryonic development by self-differentiation, regulation of morphogenesis and secretion of inducing signals. Whereas many molecular signals and mechanisms of the organizer have been clarified, its function in anterior-posterior pattern formation remains unclear. We dissected the organizer functions by generally blocking organizer formation and then restoring a single function. In experiments using a dominant inhibitory BMP receptor construct (tBr) we find evidence that neural activation by antagonism of the BMP pathway is the organizer function that enables the establishment of a detailed anterior-posterior pattern along the trunk. Conversely, the exclusive inhibition of neural activation by expressing a constitutive active BMP receptor (hAlk-6) in the ectoderm prohibits the establishment of an anterior-posterior pattern, even though the organizer itself is still intact. Thus, apart from the formerly described separation into a head and a trunk/tail organizer, the organizer does not deliver positional information for anterior-posterior patterning. Rather, by inducing neurectoderm, it makes ectodermal cells competent to receive patterning signals from the non-organizer mesoderm and thereby enable the formation of a complete and stable AP pattern along the trunk.
Jansen
Hans J
HJ
Leiden University, Institute of Biology, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
Wacker
Stephan A
SA
Bardine
Nabila
N
Durston
Antony J
AJ
D000005:Abdomen / Q000196:embryology* / Q000528:radiation effects; D000818:Animals; D019521:Body Patterning / Q000502:physiology* / Q000528:radiation effects; D004627:Embryonic Induction / Q000502:physiology / Q000528:radiation effects; D008648:Mesoderm / Q000166:cytology / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000166:cytology / Q000502:physiology / Q000528:radiation effects; D020897:Organizers, Embryonic / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects; D013909:Thorax / Q000196:embryology* / Q000528:radiation effects; D014466:Ultraviolet Rays; D014982:Xenopus laevis