Figure 4

Cells derived from transferred yolk sac progenitors express surface CSF1R. Cells were isolated from the blood of EGFP⁺ embryos at 3 days of development (HH16), prior to the onset of definitive hematopoiesis (which occurs around HH17 to HH19 [26]), and injected into the yolk sac circulation of age-matched non-transgenic recipients. Embryos were incubated until stage HH33 (day 8 of development). The identity of the EGFP⁺ cells derived from the donor transfer was confirmed by immunolocation of specific antigens. (A-C) Show different sections of embryonic mesoderm from three separate recipients immunostained for CSF1R. Note that the all EGFP⁺ cells are also positive for surface CSF1R (yellow) and exhibit a diverse range of morphologies. (D-F) Show sections of the limb bud inter-digit region immunostained for CSF1R. Note again that all EGFP⁺ cells are also CSF1R⁺. In each case, the labeled cells contain numerous DAPI-stained fragments (arrow heads) indicative of the uptake of apoptotic cells. Scale bars = 10 μm.