egfr expression and function in embryonic leg development. (A)
egfr mRNA is expressed in early embryos along the germband in both head and thoracic regions. (B) As the limb buds appear, egfr mRNA can be detected in the proximal regions of the limbs, and starts to resolve into rings along the proximal-distal axis (arrowhead). (C) As the legs extend, the number of rings increases, until the formation of five prominent rings that prefigure the junctions between leg segments (D). (E) Mildly affected egfr RNAi embryos show little segmentation defects and only leg length appears to be affected. (F) Moderately and (G) severely affected egfr embryos show segmentation defects in addition to a femur specific constriction (arrow). (H) The legs of mild egfr RNAi embryos are dramatically shorter than WT. Leg measurements for T1 legs, T2 legs, and T3 legs are represented in the different bars; the three measured leg segments - the femur, the tibia, and the tarsus - are represented in the segments of each bar. N = 10; error bars represent ±1 standard error. An asterisk indicates that the test was significant at (P ≤ 0.01). egfr: epidermal growth factor receptor; RNAi: gene knockdown using ribonucleic acid interference; T1, 2, 3: thoracic segments 1, 2, 3; WT: wild type.