The maternally expressed zebrafish T-box gene eomesodermin regulates organizer formation.
Early embryonic development in many organisms relies upon maternal molecules deposited into the egg prior to fertilization. We have cloned and characterized a maternal T-box gene in the zebrafish, eomesodermin (eomes). During oogenesis, the eomes transcript becomes localized to the cortex of the oocyte. After fertilization during early cleavage stages, eomes is expressed in a vegetal to animal gradient in the embryo, whereas Eomesodermin protein (Eom) is distributed cytoplasmically throughout the blastoderm. Strikingly, following midblastula transition, nuclear-localized Eomesodermin is detected on the dorsal side of the embryo only. Overexpression of eomes results in Nodal-dependent and nieuwkoid/dharma (nwk/dhm) independent ectopic expression of the organizer markers goosecoid (gsc), chordin (chd) and floating head (flh) and in the formation of secondary axes. The same phenotypes are observed when a VP16-activator construct is injected into early embryos, indicating that eomes acts as a transcriptional activator. In addition, a dominant-negative construct and antisense morpholino oligonucleotides led to a reduction in gsc and flh expression. Together these data indicate that eomes plays a role in specifying the organizer.
Bruce
Ashley E E
AE
Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA. abruce@uchicago.edu
Howley
Cristin
C
Zhou
Yi
Y
Vickers
Sarah L
SL
Silver
Lee M
LM
King
Mary Lou
ML
Ho
Robert K
RK
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D055457:Nodal Protein; D055456:Nodal Signaling Ligands; D020897:Organizers, Embryonic / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020825:T-Box Domain Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins
C103223:EOMES protein, Xenopus; D055457:Nodal Protein; D055456:Nodal Signaling Ligands; D012333:RNA, Messenger; D020825:T-Box Domain Proteins; D016212:Transforming Growth Factor beta; C103966:VegT protein, Xenopus; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; C491197:eomesa protein, zebrafish; C485171:ndr1 protein, zebrafish