"A gradient of positional information in an insect, Rhodnius"

Date:
1971-1972
Reference:
PP/CRI/H/5/3
Catalogue details

Licence: In copyright

Credit: "A gradient of positional information in an insect, <i>Rhodnius</i>". Source: Wellcome Collection.

    2/128
    SUMMARY Locke (1959) discovered a segmental gradient in Rhodnius which controls the polarity of the epidermal cell and gives positional information. The pol arity is expressed by the orientation of folds in the adult epicuticle, which are aligned parallel to the contours in the gradient. It was later suggested that this gradient could be of a concentration of a diffusible substance (Lawrence, 1966; Stumpf, 1966 ). Because concentration gradients could be maintained in various ways we have simulated several models in the computer, and examined the results of rotating square pieces of model landscape through 90° and allow ing diffusion. The gradient landscapes after different times and at equilibrium are plotted as contour maps and are compared with cuticle patterns from adult insects after rotation of square pieces of epidermis in larvae. One simple model, where the gradient depends only on the activities of a line of source cells at one end of the segment and a line of sink cells at the other, is eliminated by two observations:- (1) the theoretical and experimental patterns are consistently different (2) when adults developing from operated larvae are made to form a supernumerary cuticle the first and second cuticles have almost identical patterns. This suggests that the gradient landscape has reached a steady-state. In another model the cells are considered to act as homeostatic units in the gradient, and when moved to a new position they each attempt to maintain their original or 'set* concentration. Simulation of this model gives equilibrium patt erns which are similar to the experimental results. It is suggested that the cells
    digitised image 1
    digitised image 2
    digitised image 3