Hawkins, T.A., Cavodeassi, F., Erdelyi, F., Szabo, G., and Lele, Z. (2008) The small molecule Mek1/2 inhibitor U0126 disrupts the chordamesoderm to notochord transition in zebrafish. BMC Developmental Biology. 8(1):42.
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 NC 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 mid-gastrula until the 18-somite stage produces a specific and consistent phenotype with lack of dark pigmentation, shorter tail and an abnormal, undulated NC. Using morphological analysis, in situ hybridization, immunhistochemistry, TUNEL staining and electron microscopy, we demonstrate that in treated embryos the chordamesoderm to NC transition is disrupted and identify a disorganization in the medial layer of the perinotochordal basement mebrane (PNBM) as the probable cause of the undulations and bulges developing in the NC. We also examined and excluded FGF as the upstream signal during NC differentiation. 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 NC differentiation.