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Dev Biol 2011 Sep 15;3572:478-91. doi: 10.1016/j.ydbio.2011.06.010.
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An essential role for transcription before the MBT in Xenopus laevis.

Skirkanich J , Luxardi G , Yang J , Kodjabachian L , Klein PS .

Most zygotic genes remain transcriptionally silent in Drosophila, Xenopus, and zebrafish embryos through multiple mitotic divisions until the midblastula transition (MBT). Several genes have been identified in each of these organisms that are transcribed before the MBT, but whether precocious expression of specific mRNAs is important for later development has not been examined in detail. Here, we identify a class of protein coding transcripts activated before the MBT by the maternal T-box factor VegT that are components of an established transcriptional regulatory network required for mesendoderm induction in Xenopus laevis, including the Nodal related ligands xnr5, xnr6, and derrière and the transcription factors bix4, and sox17α. Accumulation of phospho-Smad2, a hallmark of active Nodal signaling, at the onset of the MBT requires preMBT transcription and activity of xnr5 and xnr6. Furthermore, preMBT activation of the Nodal pathway is essential for mesendodermal gene expression and patterning of the embryo. Finally, xnr5 and xnr6 can also activate their own expression during cleavage stages, indicating that preMBT transcription contributes to a feed-forward system that allows robust activation of Nodal signaling at the MBT.

PubMed ID: 21741375
PMC ID: PMC3164747
Article link: Dev Biol
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: bix1.3 chrd foxi1 gsc mixer nodal nodal1 nodal5.2 nodal5.4 nodal6 smad2 sox17a tbxt vegt
Morpholinos: ctnnb1 MO1 nodal5.2 MO1 nodal5.2 MO2 nodal6 MO1 nodal6 MO2

Article Images: [+] show captions
References [+] :
Agius, Endodermal Nodal-related signals and mesoderm induction in Xenopus. 2000, Pubmed, Xenbase