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.