Tpo differentiates thrombocytes and enhances the proliferation of erythro-myeloid progenitors. Methylcellulose assays using progenitor cells isolated from fractionated WKM of adult transgenic fish (as indicated) grown for 4 days in the presence of recombinant Epo, Tpo, and/or Gcsf. Brightfield (top row), cd41:GFP (middle row), and gata1:dsRed or lyz:dsRed (bottom row) images are shown to illustrate representatives colonies. (A) Epo stimulates growth and differentiation of small CFU-E (*) and large BFU-E (**) colonies that are hemoglobinized and express gata1:dsRed (top). Tpo stimulates growth and differentiation of relatively small CFU-T colonies that express high levels of cd41:GFP and low levels of gata1:dsRed (middle). Combinatorial addition of Epo and Tpo also stimulates mixed CFU-TE colonies, consisting of clusters of erythrocytes and thrombocytes that express high levels of both cd41:GFP and gata1:dsRed (bottom). (B) Epo and Gcsf encourage differentiation of hemoglobinized lyz:dsRed+ colonies (top). Tpo and Gcsf induce differentiation of nonhemoglobinized colonies that express cd41:GFP and lyz:dsRed (middle). Combinatorial addition of Epo, Tpo, and Gcsf expand hemoglobinized colonies that express both cd41:GFP and lyz:dsRed (bottom). All photomicrographs were taken at original magnification ×200. Scale bar (top left) represents 100 µm.