The effect of cell killing by X-irradiation on pattern formation in the chick limb

Abstract

It has been suggested that positional information along the proximo-distal axis of the limb-bud is specified by time spent in the progress zone. Mesenchyme cells have been killed by X-irradiation, reducing the rate cells leave the zone. The time spent there by some cells is thus increased. When limbs, stage 18/19, stage 21, or tips of stage 24, are treated with increasing doses of X-irradiation, from 1000 rads to 2500 rads proximal structures are progressively lost, whereas distal ones— the digits—are relatively unaffected. There was no evidence for intercalation of missing parts. These effects are due to killing or damage of mesenchyme cells: the ectoderm is not affected at these doses. The results are consistent with a quantitative analysis based on the progress zone model, in which viable cells repopulate the progress zone and gradually restore it to normal as non-dividing cells are diluted out. It is suggested that any treatment causing damage to the mesenchyme at early stages will give similar results. The mesenchyme cells appear to be surprisingly resistant to radiation damage. The form of the limb-bud is not altered by damaging the mesenchyme. Differences in the development of structures at similar proximo-distal levels, following irradiation, is considered in terms of the requirement of a threshold number of cells.

The Flash Mode of Proton Irradiation in the Bragg Peak Partly Spares the Embryogenesis of the Quail

“…An analysis of defects in the formation of limbs after the X-irradiation of their buds in hen embryos showed that, 3.5 and 5.5 days after the start of incubation of eggs, predominantly the proximal and distal wing buds, respectively, are damaged [28]. The authors associate this with the death of chondrocyte precursors, a definite amount of which is necessary for the condensation of skeletal elements [29]. At earlier stages, the condensation of more proximal limb parts occurs, and at later stages the condensation of more distal limb parts takes place, which just explains different sensitivity to irradiation.…”

Gastrulation: The mechanism of the spiritual living body

“…This process is called primary neurulation, and it begins with an open neural plate, which creases inward until the edges fuse. In secondary neurulation, the tube forms by hollowing out of the solid precursor, then ends with the neural plate bending in distinct steps [36]. The embryonic disc begins flat and round, then elongates to form a wider cephalic part and narrow-shaped caudal end [37].…”

Julian Hart Lewis. 12 August 1946 — 30 April 2014

“…In Wolpert's group, Cheryll Tickle (FRS 1998) and Muriel Sampford X-irradiated chick embryos to kill large numbers of cells in the developing limb and deplete cells in the progress zone. Grafting these irradiated limbs to host embryos led to outgrowths that lacked proximal limb elements (humerus, radius and ulna) while developing fairly normal size distal elements (digits) (Wolpert et al 1979). Julian devised an astute mathematical model that appeared as the appendix to this paper, and supported the concept that time spent within the progress zone progressively specified increasingly distal positional values.…”