Functional redundancy of Tcf7 and Lef1, transcription factors mediating the Wnt signaling pathway, during zebrafish fin development

Gembu Abe, Saori Nagayoshi, and Koichi Kawakami
(Mol. Dev. Biol., NIG)

  We have been developing insertional mutagenesis methods using the Tol2 transposable element in zebrafish. Recently, we performed an enhancer trap screen by using a Tol2-based enhancer trap construct containing the GFP gene and the hsp70 promoter, and created 73 fish lines that carried single copy insertions and expressed GFP in specific cells, tissues and organs. This revealed that enhancer trapping using the hsp70 promoter worked effectively.
  Among these fish, we found a line expressing GFP in the edge of the median fin fold and the pectoral fins. In this line, the transposon was integrated in the first exon of the tcf7 gene, which encodes a transcription factor mediating the Wnt signaling pathway, and disrupted its function. Homozygous embryos showed shorter and wavy median and pectoral fins, indicating that Tcf7 plays a role in morphogenesis of these fins. However, the phenotypes seemed weaker than that expected when Wnt signaling was prohibited in the regions. We found another member of the Tcf/Lef family, Lef1, is expressed in the pectoral fin. We knocked down the Lef1 the Lef1 activity by microinjection of lef1 MO into the tcf7 mutant. The lef1 MO injection caused severer defects in the pectoral fin; i.e., only rudimentary fins were formed and the AER makers were not induced. The formation of the median fin fold was also abolished. These indicated that Tcf7 and Lef1 are functionally redundant during development of these fins. This also indicates that there may be a common regulatory pathway that was conserved between evolutionarily distantly related paired and median fins.
Tcf7 fin Tol2