Tip-1 induces filopodia growth and is important for gastrulation movements during zebrafish development

Wnt signaling is essential during animal development and also plays important roles in pathological conditions. Two mayor pathways have been described: the beta-catenin-dependent canonical (or classical) pathway and the beta-catenin-independent non-canonical Wnt pathway. Recent binding studies suggest links between the small PDZ protein TIP-1 (Tax-1 interacting protein) to components of both Wnt pathways. We have cloned and characterized the zebrafish tip-1 gene. Whole mount in situ hybridization and semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) indicated that zebrafish tip-1 is present as a maternal RNA and is ubiquitously expressed during early development. After 24 h of development, tip-1 expression was high in the central nervous system (CNS) whereas only weak expression was detected in the caudal regions of the zebrafish embryo. Tip-1 knockdown using antisense morpholino oligonucleotides, as well as ectopic tip-1 expression, led to elongation defects in zebrafish embryos and larvae. Both knockdown and overexpression of tip-1 resulted in a widened goosecoid (gsc) expression domain in shield stage embryos, led to an abbreviated prechordal plate, and to reduced convergent extension movements during gastrulation. We constructed a green fluorescence protein (GFP)/TIP-1 fusion protein which, when expressed in cultured fibroblasts (ZF4-cells), induced filopodia growth. Our observations indicate a role for TIP-1 in gastrulation movements and in filopodia growth induction.