Development of floor plate, neurons and axonal outgrowth pattern in the early spinal cord of the notochord-deficient chick embryo

Abstract

The notochord is probably involved in the development of the neural tube. In this study, a fragment of caudal notochord was extirpated in ovo from chick embryos at 1.5 days of incubation. At 4.5 days a distinct notochord-deficient region at thoracolumbar level was found. Profound effects were seen, especially at the cranial site of this region. Somites were smaller than normal, or even not recognizable, and in some cases the myotomes were fused in the midline. The spinal cord appeared reduced in size and lacked a floor plate. The average amount of spinal cord neurons was 23% of the normal value, the cells being located circularly along the outer margin of the spinal cord, except for the roof plate. Axonal roots left the cord in the ventral midline only. Caudal to this site, neurons or floor plate cells were alternately present in the ventral spinal cord, and axonal roots left bilaterally. In a caudal direction, a normal morphology gradually reappeared. The possibility is discussed that reduction in spinal cord size and amount of neurons is a direct or indirect effect of the absence of the notochord, and that the sclerotome may be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiogenic potential of the avian somite

“…Removal of the notochord results in the fusion of the right and left dermomyotomes beneath the neural tube (Christ, 1970;van Straaten and Hekking, 1991), and outgrowth of axonal roots in the ventral midline (van Straaten and Hekking, 1991). Disturbed axonal guidance is also found in the notochord defective mutant of the mouse, Dunforth's short-tail (Bovolenta and Dodd, 1991).…”

The relationships between notochord and floor plate in vertebrate development revisited

“…This idea was initially based on experiments performed in the chick in which the notochord was removed in the posterior region of the embryo. Removal of the notochord results in the absence of floor plate and motoneurons on a short segment located in the caudalmost part of the operated territory (13)(14)(15). The conclusion was drawn that the notochord is inducing a floor plate in the midline of the neural plate.…”

“…The notochord extirpation experiments, which suggested that floor plate differentiation was the result of an induction, were generally performed in chicken embryos at stages ranging from 10-to 20-somite stage (ss) (13)(14)(15)(28)(29)(30). The notochord was removed either mechanically or enzymatically from the level of the last formed somites down to Hensen's node, which was in principle excluded from the operation.…”

Signals from the notochord and floor plate regulate the region-specific expression of two Pax genes in the developing spinal cord

“…The importance of the notochord in dorsoventral patterning of the neural tube has been highlighted in studies utilising surgical manipulation of early embryos (Kitchin, 1949;van Straaten et al, 1985van Straaten et al, , 1988van Straaten and Drukker, 1987;van Straaten and Hekking, 1991;Yamada et al, 1991). Removal of the notochord results in the loss of the floor plate (van Straaten and Hekking, 1991) and the adjacent bilaterally located motor neuron pools (Yamada et al, 1991).…”

“…Removal of the notochord results in the loss of the floor plate (van Straaten and Hekking, 1991) and the adjacent bilaterally located motor neuron pools (Yamada et al, 1991). As a result, cells throughout the neural tube appear to be left with a dorsal phenotype (Yamada et al, 1991).…”