Accumulated immature ICM cells in AML1-ETO transgenic zebrafish embryos with Gro3/TLE knockdown are myeloid cells of the granulocytic lineage. Wild-type and AML1-ETO transgenic fish embryos were injected with Gro3 morpholino (MO) and subjected to mild heat shock treatment to induce low levels of AML1-ETO expression. The embryos were fixed at 32 hpf and were subjected to in situ hybridization for (A) the macrophage marker, l-plastin or for (B) myeloperoxidase (mpo), a marker for cells of the granulocytic lineage. The data indicate that knockdown of groucho in the presence of AML1-ETO expression leads to accumulation of mpo⁺ cells in the ventral tail region (arrow).