The zebrafish dorsal axis is apparent at the four-cell stage.
A central question in the development of multicellular organisms pertains to the timing and mechanisms of specification of the embryonic axes. In many organisms, specification of the dorsoventral axis requires signalling by proteins of the Transforming growth factor-beta and Wnt families. Here we show that maternal transcripts of the zebrafish Nodal-related morphogen, Squint (Sqt), can localize to two blastomeres at the four-cell stage and predict the dorsal axis. Removal of cells containing sqt transcripts from four-to-eight-cell embryos or injection of antisense morpholino oligonucleotides targeting sqt into oocytes can cause a loss of dorsal structures. Localization of sqt transcripts is independent of maternal Wnt pathway function and requires a highly conserved sequence in the 3' untranslated region. Thus, the dorsoventral axis is apparent by early cleavage stages and may require the maternally encoded morphogen Sqt and its associated factors. Because the 3' untranslated region of the human nodal gene can also localize exogenous sequences to dorsal cells, this mechanism may be evolutionarily conserved.
Gore
Aniket V
AV
Vertebrate Development Group, Temasek Life Sciences Laboratory, 1 Research Link, 117604 Singapore.
Maegawa
Shingo
S
Cheong
Albert
A
Gilligan
Patrick C
PC
Weinberg
Eric S
ES
Sampath
Karuna
K
D020413:3' Untranslated Regions / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning; D004625:Embryo, Nonmammalian / Q000166:cytology* / Q000196:embryology* / Q000378:metabolism; D008969:Molecular Sequence Data; D055456:Nodal Signaling Ligands; D009865:Oocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics*; D051176:beta Catenin / Q000378:metabolism
D020413:3' Untranslated Regions; D055456:Nodal Signaling Ligands; D012333:RNA, Messenger; D029961:Zebrafish Proteins; D051176:beta Catenin; C485171:ndr1 protein, zebrafish