A post-mid-blastula transition requirement for TGF beta signaling in earlyendodermal specification

Citation
Cb. Chang et A. Hemmati-brivanlou, A post-mid-blastula transition requirement for TGF beta signaling in earlyendodermal specification, MECH DEVEL, 90(2), 2000, pp. 227-235
Citations number
41
Categorie Soggetti
Cell & Developmental Biology
Journal title
MECHANISMS OF DEVELOPMENT
ISSN journal
09254773 → ACNP
Volume
90
Issue
2
Year of publication
2000
Pages
227 - 235
Database
ISI
SICI code
0925-4773(200002)90:2<227:APTRFT>2.0.ZU;2-#
Abstract
In Xenopus, endodermal cell fate is determined gradually from late blastula to early gastrula stages, cell-cell interaction plays an important role in this process. Here we use a cell dissociation assay to show that extracell ular signaling is required continuously before endoderm determination. Acti vin and Vg1, but not BMP2 or basic FGF, rescue the expression of endodermal markers in dissociated cells when provided at the mid-blastula transition (MBT, the time in which zygotic transcription begins). Removal of exogenous ly added activin or Vg1 before MBT results in reduction of endodermal gene expression in dissociated vegetal cells. In vivo, endogenous endodermal mar kers are reduced in vegetal explants when activin-like signaling is blocked with dominant negative receptors. VegT, a maternal transcription factor sh own to be critical for endoderm specification, relies on an active TGF beta pathway to induce endoderm in animal caps. These results indicate that TGF beta signaling may be activated by the maternally expressed VegT to partic ipate in endoderm determination. In addition, VegT function seems to be req uired in parallel with the TGF beta pathway, as overexpression of activin d oes not relieve endoderm repression by a dominant negative VegT mutant in v egetal cells. Our data suggest that maternal VegT first activates a zygotic TGF beta signal, then cooperates with this signal to determine the endoder mal cell fate. (C) 2000 Elsevier Science ireland Ltd. All rights reserved.