Fig. 5. Aplnr-expressing mesodermal cells are required to establish a Toddler gradient.

Cell transplantation assays to test for the necessity of Aplnr-expressing mesodermal cells as a Toddler sink. Transplanted LifeAct-GFP–labeled wild-type reporter cells were used as a read-out for the presence of a Toddler gradient. (A) Schematic representation of scenarios tested. From left to right: (i) Transplantation of reporter cells into a wild-type host embryo (n = 21). (ii) Transplantation of reporter cells into an MZoep^−/− host embryo (n = 22). (iii) Transplantation of reporter cells into an MZoep^−/−, toddler^−/− double-mutant host embryo. Additional transplantation of Dextran–Alexa Fluor 568–labeled control source cells to the animal pole (n = 16). (iv) Transplantation of reporter cells into an MZoep^−/−, toddler^−/− double-mutant host embryo. Additional transplantation of Toddler-expressing source cells to the animal pole (n = 15). (v) Transplantation of reporter cells into an aplnr ^MO embryo (n = 20). (vi) Cotransplantation of one to five reporter cells and a large number of Dextran–Alexa Fluor 568–labeled Aplnr-deficient control cells into aplnr^MO host embryo (n = 15). (vii) Cotransplantation of one to five reporter cells and a large number of Aplnr-expressing cells into aplnr^MO host embryos (n = 16). (B) Tracks of transplanted reporter cells [order as described in (A)]. Cells were tracked for 90 min after internalization. x axis = margin; y axis = animal-vegetal axis; coordinate origin = start of track. (C) Rose plots showing relative enrichments of orientations of polarity. 90° = animal pole; 0° = ventral/dorsal; −90° = vegetal pole.