|
Figure 4
Model for distal outgrowth. (I, ii) Limb is cut at position A, proximal
to positions B-E. This exposes circumferential positions at A. (iii) Healing
leads to the apposing of normally noncontiguous cells (such as 10A and 1A)
near the blastema tip. Cells between the newly apposed tissues proliferate
and acquire positional specification between the two sites. However, these
cells are adjacent to preexisiting cells sharing the same circumferential
values. By the “distalization rule,” such cells acquire more distal positional
value. (iv, v) Intercalation then occurs between these newly specified cells,
creating a new surface that contains all the circumferential values. This
scheme is repeated until the limb is complete. (After Bryant et al., 1981.) |
