Zili Inhibits Transforming Growth Factor-β Signaling by Interacting with Smad4

Mei Zeng,Wenqian Deng,Huaqin Sun,Yongxin Ma,Na Li,Xiaolin Liao,Shu Chen,Dachang Tao,Dan Li,Yanyan Liu

doi:10.1074/jbc.m109.079533

Mei Zeng, Wenqian Deng + Show 8 more

Open Access

https://doi.org/10.1074/jbc.m109.079533

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Abstract

Piwi proteins are required for germ cell proliferation, differentiation, and germ line stem cell maintenance. In normal tissues, human and mouse Piwil2 are primarily expressed in testis but widely expressed in tumors. However, the underlying mechanism remains largely unknown. In vertebrates, transforming growth factor (TGF)-β signaling plays an important role in patterning embryo and control of cell growth and differentiation. A previous study has shown a role for Zili, a Piwil2 gene in zebrafish, in germ cells in zebrafish. Here we report that zili functions in patterning the early embryo and inhibits TGF-β signaling. Whole mount expression analysis shows that zili expresses not only in PGCs but also in axis. Ectopic expression of zili causes fusion of the eyes and reduction of mesodermal marker genes expression, suggesting that zili functions to inhibit Nodal signaling and mesoderm formation. Genetic interaction shows that zili inhibits Nodal and bone morphogenetic protein signaling. The results of protein interaction assays identify that Zili binds to Smad4 via its N-terminal domain and prevents the formation of Smad2/3/4 and Smad1/5/9/4 complexes to antagonize TGF-β signaling. This work shows that zili plays a role in early embryogenesis beyond germ line as a novel negative regulator of TGF-β signaling, extending the function of Piwi proteins in vertebrates.

Highlights

The Piwi clade of Argonaute proteins is found in all animals examined so far, and genomes of multicellular animals encode multiple Piwi proteins [1]
Zili Expresses Not Only in primordial germ cells (PGCs) but in Axis during Early Embryogenesis—The 3656-bp nucleotide sequence of zili mRNA has been deposited in the GenBankTM data base under accession number EF186090
Later, Houwing et al [11] submitted another 3389-bp sequence related to zili gene under accession number FJ168029. They analyzed Zili protein expression in primordial germ cells (PGCs) by an antibody raised against the N terminus of Zili, and found that Zili protein can be detected in PGCs from 3 days post-fertilization onwards

Summary

Introduction

The Piwi clade of Argonaute proteins is found in all animals examined so far, and genomes of multicellular animals encode multiple Piwi proteins [1]. The results of in situ hybridization show that spatiotemporal expression pattern of zili transcript is similar to Zili protein (supplemental Fig. S2).

Results

Conclusion