The small molecule Mek1/2 inhibitor U0126 disrupts the chordamesoderm to notochord transition in zebrafish.
BACKGROUND
Key molecules involved in notochord differentiation and function have been identified through genetic analysis in zebrafish and mice, but MEK1 and 2 have so far not been implicated in this process due to early lethality (Mek1-/-) and functional redundancy (Mek2-/-) in the knockout animals.


RESULTS
Here, we reveal a potential role for Mek1/2 during notochord development by using the small molecule Mek1/2 inhibitor U0126 which blocks phosphorylation of the Mek1/2 target gene Erk1/2 in vivo. Applying the inhibitor from early gastrulation until the 18-somite stage produces a specific and consistent phenotype with lack of dark pigmentation, shorter tail and an abnormal, undulated notochord. Using morphological analysis, in situ hybridization, immunhistochemistry, TUNEL staining and electron microscopy, we demonstrate that in treated embryos the chordamesoderm to notochord transition is disrupted and identify disorganization in the medial layer of the perinotochordal basement mebrane as the probable cause of the undulations and bulges in the notochord. We also examined and excluded FGF as the upstream signal during this process.


CONCLUSIONS
Using the small chemical U0126, we have established a novel link between MAPK-signaling and notochord differentiation. Our phenotypic analysis suggests a potential connection between the MAPK-pathway, the COPI-mediated intracellular transport and/or the copper-dependent posttranslational regulatory processes during notochord differentiation.
Hawkins
Thomas A
TA
Department of Anatomy and Developmental Biology, University College London, Gower Street, London, WC1E 6BT, UK. thomas.hawkins@ucl.ac.uk
Cavodeassi
Florencia
F
Erdélyi
Ferenc
F
Szabó
Gábor
G
Lele
Zsolt
Z
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001485:Basement Membrane / Q000187:drug effects; D002070:Butadienes / Q000494:pharmacology*; D003599:Cytoskeleton / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005346:Fibroblast Growth Factors / Q000235:genetics; D054262:Gastrulation / Q000187:drug effects; D018507:Gene Expression Regulation, Developmental; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors*; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors*; D008648:Mesoderm / Q000187:drug effects / Q000196:embryology*; D009570:Nitriles / Q000494:pharmacology*; D009672:Notochord / Q000187:drug effects / Q000196:embryology*; D010641:Phenotype; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics
D002070:Butadienes; D004791:Enzyme Inhibitors; D009570:Nitriles; C113580:U 0126; D005346:Fibroblast Growth Factors; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2