A two-step model for the fate determination of presumptive endodermal blastomeres in Xenopus embryos.
Curr Biol
; 9(16): 869-79, 1999 Aug 26.
Article
em En
| MEDLINE
| ID: mdl-10469589
ABSTRACT
BACKGROUND:
In Xenopus, the endoderm germ layer is derived from the vegetal blastomeres of cleavage-stage embryos. Cell transplantation experiments have revealed that the endodermal fate becomes gradually fixed during the late blastula stages. Sox17alpha, Mix.1, Mixer and GATA-4 encode vegetal zygotic transcription factors with endoderm-inducing activity. The accumulation of their transcripts during the late blastula stages may cause determination of the endodermal fate. VegT, a T-box transcription factor, the maternal transcripts of which are vegetally localised, is also required for endoderm formation.RESULTS:
We analysed the events leading to the progressive accumulation of the transcripts for Sox17alpha, Mix.1, Mixer and GATA-4. Two phases could be distinguished in the endodermal programme. In phase 1, Sox17alpha, Mix.1, and the genes encoding transforming growth factor beta-related signalling molecules Xnr1, Xnr2 and Derrière were activated cell-autonomously at around the mid-blastula transition (MBT) by maternal determinants. In phase 2, TGFbeta signalling, possibly involving Xnr1, Xnr2 and Derrière, led to the activation of Mixer and GATA-4 in late blastula stages and to the reinforcement of the expression of Sox17alpha and Mix.1. Overexpression of VegT in animal caps triggered a developmental programme qualitatively similar to that observed in vegetal blastomeres, except that Xnr1 and GATA-4 were not activated by the early gastrula stage.CONCLUSIONS:
Our results support a two-step model for endoderm determination between fertilisation and the onset of gastrulation. The initial cell-autonomous activation of early endodermal genes by maternal determinants including, but not limited to, VegT is relayed by the action of zygotic TGFbetas such as Xnr1, Xnr2 and Derrière.
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Base de dados:
MEDLINE
Assunto principal:
Xenopus
/
Blastômeros
/
Proteínas de Grupo de Alta Mobilidade
/
Proteínas de Xenopus
/
Peptídeos e Proteínas de Sinalização Intercelular
/
Endoderma
Tipo de estudo:
Prognostic_studies
Limite:
Animals
Idioma:
En
Ano de publicação:
1999
Tipo de documento:
Article