Lefty antagonism of Squint is essential for normal gastrulation.
Activities of a variety of signaling proteins that regulate embryogenesis are limited by endogenous antagonists. The zebrafish Nodal-related ligands, Squint and Cyclops, and their antagonists, Lefty1 and Lefty2, belong to the TGFbeta-related protein superfamily, whose members have widespread biological activities. Among other activities, Nodals direct the formation of most mesendoderm. By inducing their own transcription and that of the Lefties, Nodal signals establish positive and negative autoregulatory loops. To investigate how these autoregulatory pathways regulate development, we depleted zebrafish embryos of Lefty1 and/or Lefty2 by using antisense morpholino oligonucleotides. Loss of Lefty1 causes aberrations during somitogenesis stages, including left-right patterning defects, whereas Lefty2 depletion has no obvious consequences. Depletion of both Lefty1 and Lefty2, by contrast, causes unchecked Nodal signaling, expansion of mesendoderm, and loss of ectoderm. The expansion of mesendoderm correlates with an extended period of rapid cellular internalization and a failure of deep-cell epiboly. The gastrulation defects of embryos depleted of Lefty1 and Lefty2 result from the deregulation of Squint signaling. In contrast, deregulation of Cyclops does not affect morphology or the transcription of Nodal target genes during gastrulation. Furthermore, we find that Cyclops is specifically required for the maintenance of lefty1 and lefty2 transcription.
Feldman
Benjamin
B
Division of Developmental Biology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
Concha
Miguel L
ML
Saúde
Leonor
L
Parsons
Michael J
MJ
Adams
Richard J
RJ
Wilson
Stephen W
SW
Stemple
Derek L
DL
D000818:Animals; D016375:Antisense Elements (Genetics) / Q000494:pharmacology; D015415:Biomarkers; D019521:Body Patterning / Q000235:genetics; D004475:Ectoderm / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000187:drug effects; D004707:Endoderm / Q000378:metabolism; D005775:Gastrula / Q000378:metabolism*; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental; D047908:Intracellular Signaling Peptides and Proteins; D055458:Left-Right Determination Factors; D009154:Mutation; D055456:Nodal Signaling Ligands; D015398:Signal Transduction; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
D016375:Antisense Elements (Genetics); D015415:Biomarkers; D047908:Intracellular Signaling Peptides and Proteins; D055458:Left-Right Determination Factors; D055456:Nodal Signaling Ligands; D016212:Transforming Growth Factor beta; D029961:Zebrafish Proteins; C485171:ndr1 protein, zebrafish; C512832:ndr2 protein, zebrafish