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

Dev Biol. 2011 Apr 15;352(2):254-66. doi: 10.1016/j.ydbio.2011.01.021. Epub 2011 Jan 27.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Base Sequence
  • Body Patterning / genetics
  • Body Patterning / physiology*
  • DNA Primers / genetics
  • Gastrula / embryology
  • Gene Expression Regulation, Developmental
  • Hedgehog Proteins / genetics
  • Hedgehog Proteins / physiology*
  • Models, Biological*
  • Models, Neurological
  • Neural Plate / embryology
  • Notochord / embryology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Receptors, Notch / genetics
  • Receptors, Notch / physiology*
  • Signal Transduction
  • Xenopus Proteins / genetics
  • Xenopus Proteins / physiology*
  • Xenopus laevis / embryology*
  • Xenopus laevis / genetics
  • Xenopus laevis / physiology*

Substances

  • DNA Primers
  • Hedgehog Proteins
  • NOTCH1 protein, Xenopus
  • RNA, Messenger
  • Receptors, Notch
  • Xenopus Proteins