The Pax protein Noi is required for commissural axon pathway formation in the rostral forebrain.
No-isthmus (Noi) is a member of the zebrafish Pax family of transcriptional regulators that is expressed in restricted domains of the developing CNS. In the developing eye and optic nerve, the Noi+ cells are primitive glial cells that line the choroid fissure and optic stalk/nerve to its junction with the optic tract. This pattern of Noi expression is retained in the adult, defining the optic nerve astroglia, which wrap the left and right nerves separately at the midline, thus forming the bodily crossed optic chiasm found in fish. In embryos carrying mutations in the noi gene, the choroid fissure fails to close, glial cells of the optic nerve fail to differentiate and optic axons exhibit abnormal trajectories exiting the eye and at the midline of the diencephalon. Optic axons select inappropriate pathways into the contralateral optic nerve, rostrally towards the anterior commissure and along the ipsilateral optic tract. Noi+ cells also border the pathway of axons in the postoptic commissure, which is located adjacent to the optic chiasm. These postoptic commissural axons are defasciculated and also exhibit pathfinding defects in noi- embryos. These results indicate that Noi is required in cells that line the pathways taken by optic and non-optic commissural axons for guidance across the midline of the diencephalon. We find that expression of two members of the Netrin family of axon guidance molecules and the signalling protein Sonic hedgehog is disturbed in noi- embryos, whereas several members of the Eph family of receptors and ligands show no obvious alterations in expression at the diencephalic midline.
Macdonald
R
R
Developmental Biology Research Centre, Randall Institute, Kings College London, UK.
Scholes
J
J
Strähle
U
U
Brennan
C
C
Holder
N
N
Brand
M
M
Wilson
S W
SW
D000818:Animals; D001253:Astrocytes / Q000502:physiology; D001369:Axons / Q000473:pathology / Q000502:physiology; D002454:Cell Differentiation; D002829:Choroid / Q000196:embryology / Q000502:physiology; D003103:Coloboma; D004268:DNA-Binding Proteins / Q000502:physiology*; D004027:Diencephalon / Q000502:physiology; D004625:Embryo, Nonmammalian / Q000502:physiology; D004627:Embryonic Induction; D005123:Eye / Q000196:embryology / Q000254:growth & development; D005724:Ganglia / Q000473:pathology; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins; D006720:Homozygote; D009154:Mutation; D009414:Nerve Growth Factors / Q000235:genetics; D000075388:Netrin-1; D009457:Neuroglia / Q000502:physiology; D009897:Optic Chiasm / Q000502:physiology; D009900:Optic Nerve / Q000196:embryology / Q000502:physiology; D051762:PAX2 Transcription Factor; D016548:Prosencephalon / Q000196:embryology* / Q000502:physiology; D011506:Proteins / Q000235:genetics; D012160:Retina / Q000196:embryology / Q000254:growth & development / Q000473:pathology / Q000502:physiology; D015534:Trans-Activators; D014157:Transcription Factors / Q000502:physiology*; D025521:Tumor Suppressor Proteins; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics; D029961:Zebrafish Proteins
D004268:DNA-Binding Proteins; D053823:Hedgehog Proteins; D009414:Nerve Growth Factors; D051762:PAX2 Transcription Factor; D011506:Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D029961:Zebrafish Proteins; C497320:pax2a protein, zebrafish; D000075388:Netrin-1