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Development September 1, 2002; 129 (17): 4015-25.

Repression of organizer genes in dorsal and ventral Xenopus cells mediated by maternal XTcf3.

Houston DW , Kofron M , Resnik E , Langland R , Destree O , Wylie C , Heasman J .

In the early Xenopus embryo, the dorsal axis is specified by a Wnt signal transduction pathway, involving the movement of beta-catenin into dorsal cell nuclei and its functional association with the LEF-type transcription factor XTcf3. The subsequent function of XTcf3 is uncertain. Overexpression data has suggested that it can be both an activator and repressor of downstream genes. XTcf3 mRNA is synthesized during oogenesis in Xenopus and is stored in the egg. To identify its role in dorsal axis specification, we depleted this maternal store in full-grown oocytes using antisense deoxyoligonucleotides, and fertilized them. The developmental effects of XTcf3 depletion, both on morphogenesis and the expression of marker genes, show that primarily, XTcf3 is an inhibitor, preventing both dorsal and ventral cells of the late blastula from expressing dorsal genes. We also show that simple relief from the repression is not the only factor required for dorsal gene expression. To demonstrate this, we fertilized eggs that had been depleted of both XTcf3 and the maternal transcription factor VegT. Dorsal genes normally repressed by XTcf3 are not activated in these embryos. These data show that normal dorsal gene expression in the embryo requires the transcriptional activator VegT, whilst XTcf3 prevents their inappropriate expression on the ventral side of the embryo.

PubMed ID: 12163405
Article link: Development
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: bmp4 chrd.1 fabp2 gsc hba4 nodal1 nodal3.1 nodal3.2 nodal6 odc1 pdx1 sia1 tbxt.2 tcf3 tcf4 tcf7l1 vegt wnt8a

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