Abstract
There are different models that explain growth during development. One model is based on insect and amphibian regeneration studies. This model proposes that growth is directed by pattern, and growth takes place by intercalation at a growth discontinuity; therefore, proliferation should surround the discontinuity. Currently, this model, apart from regenerative studies on mostly adult patterning, has not found supporting evidence in Drosophila that shows proliferation surrounding a discontinuity. Despite this lack of evidence, the importance of discontinuities has been shown in different experiments, even under wt conditions, more specifically in the formation of the leg joints because of the occurrence of cell death at their boundaries. Here, we show the existence of a sharp discontinuity in Decapentaplegic (Dpp) in the genital discs at the third larvae stage (L3), which determines the upregulation in the Jun-NH2-Terminal-Kinase (JNK) pathway, reaper (rpr), head involution defective (hid) and active caspases from its boundaries. The proliferation and cell death surrounding the discontinuity suggest that growth can proceed by intercalation and competitive death takes place in this area. Finally, we show that the Rpr, Grim and Hid (RGH) products are a few of the factors that define the growth discontinuity because they are negative regulators of growth, a new function that is unique from their known functions in apoptosis.
Highlights
French et al and Hayne and Bryant (1976) [1, 2] proposed that pattern directs growth and that growth is derived from the confrontation of different growth positional values through proliferation
As observed in the wing disc [7], the discontinuities generated from this overexpression were accompanied by an upregulation in JNK at the boundary of ectopic Dpp expression (Fig. 1C), confirming that Dpp is a repressor of JNK [26], and JNK appeared as a target of Dpp pathway
Our results showed that in the genital discs, a discontinuity in growth conditions exists that coincides with the border of Dpp expression
Summary
French et al and Hayne and Bryant (1976) [1, 2] proposed that pattern directs growth and that growth is derived from the confrontation of different growth positional values through proliferation. Aside from the relationship between pattern and growth, in this model, proliferation is induced at a discontinuity in growth conditions. Their proposal was based on their studies on insect and amphibian regeneration. When a cockroach leg is cut proximally and grafted with a distal portion of the leg, the entire leg is regenerated by intercalary growth. Since growth and pattern for those days (and [3]) in Drosophila was seen to be due to a gradient, Hayne and Bryant said they could
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