Are pioneer axons guided by regulatory gene expression domains in the zebrafish forebrain? High-resolution analysis of the patterning of the zebrafish brain during axon tract formation

Dev Biol. 2001 Jan 15;229(2):271-86. doi: 10.1006/dbio.2000.9980.


Although the principles of axon growth are well understood in vitro the mechanisms guiding axons in vivo are less clear. It has been postulated that growing axons in the vertebrate brain follow borders of neuroepithelial cells expressing specific regulatory genes. In the present study we reexamined this hypothesis by analysing the earliest growing axons in the forebrain of embryonic zebrafish. Confocal laser scanning microscopy was used to determine the spatiotemporal relationship between growing axons and the expression pattern of eight regulatory genes in zebrafish brain. Pioneer axons project either longitudinally or dorsoventrally to establish a scaffold of axon tracts during this developmental period. Each of the regulatory genes was expressed in stereotypical domains and the borders of some were oriented along dorsoventral and longitudinal planes. However, none of these borders clearly defined the trajectories of pioneer axons. In two cases axons coursed in proximity to the borders of shh and pax6, but only for a relatively short portion of their pathway. Only later growing axons were closely apposed to the borders of some gene expression domains. These results suggest that pioneer axons in the embryonic forebrain do not follow continuous pathways defined by the borders of regulatory gene expression domains.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Axons / physiology*
  • Body Patterning*
  • Brain / embryology*
  • Embryo, Nonmammalian / physiology
  • Embryonic Induction
  • Eye Proteins
  • Gene Expression Regulation, Developmental*
  • Genes, Regulator*
  • Hedgehog Proteins
  • Homeodomain Proteins / genetics
  • In Situ Hybridization, Fluorescence
  • Microscopy, Confocal
  • Nerve Tissue Proteins / genetics
  • Neurons / physiology*
  • PAX6 Transcription Factor
  • Paired Box Transcription Factors
  • Prosencephalon / embryology*
  • Proteins / genetics
  • Repressor Proteins
  • Trans-Activators*
  • Zebrafish / embryology


  • Eye Proteins
  • Hedgehog Proteins
  • Homeodomain Proteins
  • Nerve Tissue Proteins
  • PAX6 Transcription Factor
  • Paired Box Transcription Factors
  • Proteins
  • Repressor Proteins
  • Trans-Activators