Fig. 3.

Morphological effects of inducing duplications within the regulatory archipelago. (A) The various duplications were produced by using the same LoxP sites as for Fig. 2 (red arrowheads), and they are depicted by double thick black lines. Below the set of duplications, the position of the del(SB-Atf2) is indicated by a dashed gray line. (B–G) Schematics of the locus after the various duplications (or deletions) were produced are shown in Left, with a hand skeleton at birth shown in Right. In vivo, each configuration was balanced by a chromosome carrying a deletion of Hoxd13 to Hoxd8 [the Del(8–13) allele, indicated as ∆]. For the sake of simplicity, the three segments of the regulatory archipelago, as defined by the positions of LoxP sites, are highlighted using different colors (control in B). In B–G, these colors are used to identify the parts of the archipelago that are duplicated (C–F) or deleted (G). In all cases, LacZ reporter genes were associated with the various configurations. They are indicated on the schemes by a blue rectangle along with the presence of the associated LoxP site (red arrowheads). In E, two such LacZ reporters are present (in the text). (B) WT configuration. (C) Duplication of the full archipelago from Evx2 to Atf2. (D) Duplication of islands I–V. (E) A duplication extending from Evx2 until the proximal half of the gene desert is associated with a shortening of digit II at birth (arrowhead). (F) Duplication of the Prox-GCR segment. (G) Deletion of the distal half of the gene desert complementary to the duplication in E. Note the similar shortening of digit II (arrowhead).