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Dev Biol 2011 Apr 15;3522:254-66. doi: 10.1016/j.ydbio.2011.01.021.
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A revised model of Xenopus dorsal midline development: differential and separable requirements for Notch and Shh signaling.

Peyrot SM , Wallingford JB , Harland RM .

The development of the vertebrate dorsal midline (floor plate, notochord, and hypochord) has been an area of classical research and debate. Previous studies in vertebrates have led to contrasting models for the roles of Shh and Notch signaling in specification of the floor plate, by late inductive or early allocation mechanisms, respectively. Here, we show that Notch signaling plays an integral role in cell fate decisions in the dorsal midline of Xenopus laevis, similar to that observed in zebrafish and chick. Notch signaling promotes floor plate and hypochord fates over notochord, but has variable effects on Shh expression in the midline. In contrast to previous reports in frog, we find that Shh signaling is not required for floor plate vs. notochord decisions and plays a minor role in floor plate specification, where it acts in parallel to Notch signaling. As in zebrafish, Shh signaling is required for specification of the lateral floor plate in the frog. We also find that the medial floor plate in Xenopus comprises two distinct populations of cells, each dependent upon different signals for its specification. Using expression analysis of several midline markers, and dissection of functional relationships, we propose a revised allocation mechanism of dorsal midline specification in Xenopus. Our model is distinct from those proposed to date, and may serve as a guide for future studies in frog and other vertebrate organisms.

PubMed ID: 21276789
PMC ID: PMC3282588
Article link: Dev Biol
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: chrd enc1 enc1.2 foxa1 foxa2 foxa4 foxd4l1.1 myc nkx2-2 not notch1 ntn1 pcdh1 ptch1 ptch2 rbpj shh spon1 tbxt vegfa
Antibodies: Notochord Ab1
Morpholinos: shh MO1 shh MO2

Phenotypes: Xla Wt + Cyclopamine (fig.3.b) [+]

Article Images: [+] show captions
References [+] :
Appel, Delta-mediated specification of midline cell fates in zebrafish embryos. 1999, Pubmed