Zebrafish eaf1 and eaf2/u19 Mediate Effective Convergence and Extension Movements through the Maintenance of wnt11 and wnt5 Expression

Abstract

Studies have attributed several functions to the Eaf family, including tumor suppression and eye development. Given the potential association between cancer and development, we set forth to explore Eaf1 and Eaf2/U19 activity in vertebrate embryogenesis, using zebrafish. In situ hybridization revealed similar eaf1 and eaf2/u19 expression patterns. Morpholino-mediated knockdown of either eaf1 or eaf2/u19 expression produced similar morphological changes that could be reversed by ectopic expression of target or reciprocal-target mRNA. However, combination of Eaf1 and Eaf2/U19 (Eafs)-morpholinos increased the severity of defects, suggesting that Eaf1 and Eaf2/U19 only share some functional redundancy. The Eafs knockdown phenotype resembled that of embryos with defects in convergence and extension movements. Indeed, knockdown caused expression pattern changes for convergence and extension movement markers, whereas cell tracing experiments using kaeda mRNA showed a correlation between Eafs knockdown and cell migration defects. Cardiac and pancreatic differentiation markers revealed that Eafs knockdown also disrupted midline convergence of heart and pancreatic organ precursors. Noncanonical Wnt signaling plays a key role in both convergence and extension movements and midline convergence of organ precursors. We found that Eaf1 and Eaf2/U19 maintained expression levels of wnt11 and wnt5. Moreover, wnt11 or wnt5 mRNA partially rescued the convergence and extension movement defects occurring in eafs morphants. Wnt11 and Wnt5 converge on rhoA, so not surprisingly, rhoA mRNA more effectively rescued defects than either wnt11 or wnt5 mRNA alone. However, the ectopic expression of wnt11 and wnt5 did not affect eaf1 and eaf2/u19 expression. These data indicate that eaf1 and eaf2/u19 act upstream of noncanonical Wnt signaling to mediate convergence and extension movements. EAF1 (ELL-associated factor 1) was first discovered through its ability to associate with the protein ELL (eleven-nineteen lysine-rich leukemia), a fusion partner of MLL in the t(11; 19)(q23;p13.1) chromosomal translocation associated with acute myeloid leukemia (1, 2). Subsequent studies found a second binding partner for ELL, EAF2, which was independently identified as an androgen up-regulated gene in the rat prostate and named human up-regulated 19 (U19) (3, 4). ELL binds to RNA polymerase II and acts as a transcriptional elongation factor whose targeted deletion leads to embryonic lethality in mice (5, 6). Both EAF1 and EAF2, which share significant sequence homology, stimulate ELL elongation activity (7). Studies by Luo et al. (8) argued that EAF proteins are important in MLL-ELL leukemogenesis, whereas our previous studies showed that EAF2/U19 inhibits xenograft prostate tumor growth and undergoes down-regulation in prostate cancer cell lines (9). These findings link the EAF2/U19 gene with two major human cancers: prostate cancer and acute myeloid leukemia. To investigate the function EAF2/U19 in vivo, we constructed a murine knock-out model. The EAF2...

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