Neutrophil differentiation of EPRO-Gr cells. The effects of G-CSF (100 ng/mL) and/or ATRA (10 μM) on differentiation of EPRO-Gr was monitored by Wright-Giemsa stained cytospins and northern analysis. EPRO-Gr cells (u) were induced by the addition of ATRA (a), G-CSF-alone (g), or the combination of G-CSF plus ATRA (g/a). Cells were harvested daily. (A) Wright-Giemsa–stained cytospins were subjected to morphologic assessment by light microscopy. Shown are representative cells induced for 3 days as described above (original magnification, × 100). (B) Total RNA was isolated from EPRO-Gr cells induced as described above and subjected to Northern analysis. RNA was isolated from uninduced EPRO-Gr and cells induced for 24 hours (D1) and 48 hours (D2). Ten micrograms total RNA from each sample was analyzed by Northern blotting. Blots were sequentially probed with ³²P-labeled cDNA probes for mouse lactoferrin and human C/EBPϵ. To monitor loading of RNA, the blot was probed with mouse β-actin.