The role of the Spemann organizer in anterior–posterior patterning of the trunk

Abstract

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.

Identification of hoxb1b downstream genes: hoxb1b as a regulatory factor controlling transcriptional networks and cell movement during zebrafish gastrulation

“…Because of the whole-genome duplication event in the Actinopterygii (ray-with the Spemann organiser (the 'time-space translator model', (Jansen et al, 2007;Wacker et al, 2004)). The specific combination of expressed hox genes (the 'hox code', (Kessel and Gruss, 1991)) of the involuted mesoderm is transferred in a temporally and spatially specific manner to the overlying posterior neuroectoderm by which this tissue becomes patterned in the A/P axis of the embryo.…”

A time space translation hypothesis for vertebrate axial patterning

“…This again emphasises the importance of stabilisation of Hox expression in NE Fig. S3B [19].Very posterior primitive streak from a donor chicken embryo (=very venrtral NOM + EE) was transplanted to the edge of the blastodisc of a host embryo and treated with the anti-BMP organiser factor noggin. If taken from an early gastrula (st. 5), this later expressed only Hoxb3 and Hoxb4.…”

“…It was found that axial patterning and Hox spatial collinearity in neurectoderm can be achieved by tBr anti BMP mediated dorsalisation of the ectoderm of a UV ventralised embryo only without any need for an organiser or for dorsalisation of the embryo's mesoderm (Text Box 3, Fig. S3B) [19]. This suggests that an axial pattern can be achieved simply by organiser induction of ectoderm to neurectoderm only without the need for organiser action on mesoderm (Fig.…”

“…We thank Mechanisms of Development and Elsevier for permission to reproduce Fig. 3 from [19]. We thank Developmental Biology and Elsevier for permission to reproduce Fig.…”

Colloidosomes as Single Implantable Beads for the In Vivo Delivery of Hydrophobic Drugs

“…The Denhart's solution was prepared according to the procedure published by Jansen and co-workers. [ 30 ] The samples…”