Piwi (P-element-induced wimpy testis) proteins have been shown to play important roles in maintenance of germ line stem cells, germ cell proliferation and differentiation, and control of Piwi-interacting RNAs (PiRNAs). PiRNAs comprise a broad class of small noncoding RNAs that function as an endogenous defense system against transposable elements. Fibroblast growth factor (Fgf) signals, mediated partly by no tail gene (
ntl), are responsible for patterning embryo and mesoderm formation. To understand the function of Piwi proteins, we used zebrafish as a model system. In zebrafish, piwi-like 2 gene (
piwil2) is also required for germ cell differentiation and meiosis. Here we report that
piwil2 knockdown is able to inhibit the expression of
fibroblast growth factor 8a (
fgf8a). In contrast, injection with
piwil2 mRNA enhances
fgf8a expression. Knockdown of
piwil2 reduces the inductive effect of
fgf8a on dorsalized phenotype, in which embryos extend to an oval shape at the end of epiboly stage. Coinjection with
fgf8a and
piwil2 mRNAs led to more seriously dorsalized phenotype than coinjection with
fgf8a mRNA and
piwil2-cMO. In addition, knockdown of
piwil2 inhibits the inductive effect of
fgf8a on
ntl, whereas overexpression of
piwil2 enhances the inductive effect of
fgf8a on
ntl. We also demonstrate that
piwil2 positively regulates
ntl expression at bud stage, while
piwil2 negatively regulates
ntl expression at 24 hours post-fertilization. Thus, the functional consequences of
piwil2 expression vary during early development of zebrafish embryo. Taken together, we suggest that zebrafish
piwil2 is a mediator of Fgf signals in gastrula period.
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