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A revised model of Xenopus dorsal midline development: differential and separable requirements for Notch and Shh signaling.

ABSTRACT: 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.

SUBMITTER: Peyrot SM

PROVIDER: S-EPMC3282588 | biostudies-literature | 2011 Apr

REPOSITORIES: biostudies-literature

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A revised model of Xenopus dorsal midline development: differential and separable requirements for Notch and Shh signaling.

Peyrot Sara M SM Wallingford John B JB Harland Richard M RM

Developmental biology 20110127 2

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 zebra ...[more]

PMID: 21276789

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Project description:Analysis of epithelial explants injected with the intracellular domain of Notch (ICD) to block the formation of multi-ciliate and proton secreting cells or with dominant negative human Mastermind (HMM) to induce the formation of ectopic multi-ciliate and proton secreting cells. Results show which genes are up or down-regulated when HMM is compared to ICD. Specialized epithelial cells in the amphibian skin play important roles in ion transport, but how they arise developmentally is largely unknown. Here we show that proton-secreting cells (PSCs) differentiate in the X. laevis larval skin soon after gastrulation, based on the expression of “kidney” specific form of the H+v-ATPase that localizes to the plasma membrane, orthologs of the Cl-/HCO3- antiporters ae1 and pendrin, and two isoforms of carbonic anhydrase. Like PSCs in other species, we show that the expression of these genes is likely to be driven by an ortholog of foxi1, which is also sufficient to promote the formation of PSC precursors. Strikingly, the PSCs form in the skin as two distinct subtypes that resemble the alpha- and beta-intercalated cells of the kidney. The alpha-subtype expresses ae1 and localizes H+v-ATPases to the apical plasma membrane, whereas the beta-subtype expresses pendrin and localizes the H+v-ATPase cytosolically or basolaterally. These two subtypes are specified during early differentiation, and can be distinguished based on the expression of ubp1, a transcription factor in the grainyhead family. Finally, we show that ectopic expression ubp1 is sufficient to promote the differentiation of beta-subtypes while repressing alpha-subtypes. These results have implications for how PSCs are specified in vertebrates and become functionally heterogeneous. 2-cell stage Xenopus embryos were injected with synthetic mRNA encoding ICD or HMM. At stage 9/10 the presumptive ectoderm was cut off the embryo and cultured on a fibronectin coated coverslip. At stage 22 RNA was harvested from explants and used as the starting material for arrays.

Dataset Information

A revised model of Xenopus dorsal midline development: differential and separable requirements for Notch and Shh signaling.

Publications

A revised model of Xenopus dorsal midline development: differential and separable requirements for Notch and Shh signaling.

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