Multiple Wnt Genes Are Required for Segmentation in the Short-Germ Embryo of Tribolium castaneum

Wingless (wg)/Wnt family are essential to development in virtually all metazoans. In short-germ insects, including the red flour beetle (Tribolium castaneum), the segment-polarity function of wg is conserved [1]. Wnt signaling is also implicated in posterior patterning and germband elongation [2-4], but despite its expression in the posterior growth zone, Wnt1/wg alone is not responsible for these functions [1-3]. Tribolium contains additional Wnt family genes that are also expressed in the growth zone [5]. After depleting Tc-WntD/8 we found a small percentage of embryos lacking abdominal segments. Additional removal of Tc-Wnt1 significantly enhanced the penetrance of this phenotype. Seeking alternative methods to deplete Wnt signal, we performed RNAi with other components of the Wnt pathway including wntless (w/s), porcupine (porc), and pangolin (pan). Tc-w/s RNAi caused segmentation defects similar to Tc-Wnt1 RNAi, but not Tc-WntD/8 RNAi, indicating that Tc-WntD/8 function is Tc-w/s independent. Depletion of Tc-porc and Tc-pan produced embryos resembling double Tc-Wnt1,TcWntD/8 RNAi embryos, suggesting that Tc-porc is essential for the function of both ligands, which signal through the canonical pathway. This is the first evidence of functional redundancy between Wnt ligands in posterior patterning in short-germ insects. This Wnt function appears to be conserved in other arthropods [6] and vertebrates [7-9].