Dorsoventral patterning of the avian mesencephalon/metencephalon: role of the notochord and floor plate in suppressing Engrailed-2.
Transcription factors that are spatially and temporally restricted within the embryo may be used for dorsoventral and rostrocaudal positional information during development. The Engrailed-2 (En-2) gene is expressed across the mesencephalon/metencephalon (mes/met) boundary in the cerebellar primordium with strong dorsolateral expression and limited expression in the floor plate. In a previous experiment we demonstrated that, after removal of Hensen's node, embryos lacked a notochord in the head and the pattern of En-2 expression was normal rostrocaudally, but it was expanded into the ventral midline of the neural tube. This suggested that the notochord suppresses En-2 in the ventral neural tube during normal development. To test further the ability of the notochord (and floor plate) to suppress En-2, we transplanted ventral midline tissues from HH 5-9 quail embryos beneath the rostral neural plate of HH 4-6 chick embryos. After 24 hours in culture, 90% of the embryos with quail notochord or floor plate near the mes/met of the host lacked En-2 expression adjacent to the graft, and suppression was distance dependent. Enzymatically isolated notochords also suppressed En-2 (71%), but the results from isolated floor plates were inconclusive. Other grafts served as controls and included tissues from the trunk ventral midline, mes/met level dorsolateral neural plate, and trunk dorsolateral neural plate/somite. Collectively, the results suggest that during normal development the notochord and possibly the floor plate are important regulators of normal En-2 expression.
Darnell
D K
DK
Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City 84132-0001.
Schoenwolf
G C
GC
D000818:Animals; D016380:Brain Tissue Transplantation / Q000502:physiology; D002642:Chick Embryo; D002678:Chimera; D003370:Coturnix / Q000502:physiology*; D015536:Down-Regulation / Q000502:physiology; D016332:Fetal Tissue Transplantation / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D007150:Immunohistochemistry; D008636:Mesencephalon / Q000196:embryology* / Q000502:physiology*; D009672:Notochord / Q000196:embryology* / Q000502:physiology*; D014183:Transplantation, Heterologous / Q000502:physiology