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Dev Biol June 15, 2005; 282 (2): 442-54.
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Temporal analysis of the early BMP functions identifies distinct anti-organizer and mesoderm patterning phases.

Marom K , Levy V , Pillemer G , Fainsod A .

BMP signaling performs multiple important roles during early embryogenesis. Signaling through the BMP pathway is mediated by different BMP ligands expressed in partially overlapping temporal and spatial patterns. Assignment of different BMP-dependent activities to the individual ligands has relied on the patterns of expression of the various BMP genes. Temporal analysis of BMP signaling prior to and during gastrulation was performed using glucocorticoid-controlled Smad proteins. Overexpression of the BMP-specific Smad1 and Smad5 revealed that suppression of Spemann''s organizer formation in Xenopus embryos can only take place by activating the BMP pathway prior to the onset of gastrulation. Blocking BMP signaling with the inhibitory Smad, Smad6, results in dorsalized embryos or secondary axis induction, only when activated up to early gastrula stages. BMP2 efficiently represses organizer-specific transcription from the midblastula transition onwards while BMP4 is unable to prevent the early activation of organizer-specific genes. Manipulation of the BMP pathway during mid/late gastrula affects mesodermal patterning with no external phenotypic effects. These observations suggest that the malformations resulting from inhibition or promotion of organizer formation, ventralized or dorsalized, respectively, are the result of a very early BMP function, through its antagonism of organizer formation. This function is apparently fulfilled by BMP2 and only at its latest phase by BMP4. Subsequently, BMP functions in the patterning of the mesoderm with no apparent phenotypic effects.

PubMed ID: 15950609
Article link: Dev Biol

Species referenced: Xenopus
Genes referenced: acta4 actc1 actl6a bmp2 bmp4 gsc h4c4 muc2 myod1 ncam1 not otx2 smad1 smad6 smad6.2 wnt8a

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