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Figure 1. Development of the M1 transgenic line of Xenopus laevis. A-D: Endogenous expression of Msx1 in Xenopus hindlimbs from stage 52 to 55. Scale bars = 250 mu m, and limbs are oriented with distal to the left and posterior uppermost. Expression is restricted to the distal mesenchyme and excluded from the apical epidermal ridge (AER; black arrowheads in A). There is also an early proximal-anterior located expression (white arrowhead, A). Later expression is interdigital. E: Schematic representation of the eveMsx1 transgene. At 24 or below, the transgene is silent. At 34, however, heat shock factors (black circles) bind to the hsp70 promoter sequence and activate transcription of eveMsx1. The construct is fused to a second transgene containing the gamma -crystallin promoter driving green fluorescent protein (GFP). F,G: Phenotypes of tadpoles following heat shock at stage 14. WT embryos develop normally and are unaffected by the heat shock (F). Transgenic tadpoles have a flattened anterior head, reduced eye size, reduced number of melanocytes (pigment cells), and a shortened tail (G). H,I: In situ hybridization using an Msx1 probe to show the normal expression of Msx1 (H) is expanded and up-regulated in heat shocked transgenic animals (I). |
