Effect of spib knockdown in primitive myeloid progenitors. (A-I) Primitive macrophages defined by the expression of spi1 and mmp7 are absent from spib-depleted embryos. (J-L,O-Q,T-V) WMISH analysis of aVBI in spib morphants; at the earliest point we can identify a pool of primitive myeloid progenitors by the coexpression of spib, mpo, and cebpa. (M,R,W) Quantification of the number of embryos that express spib, mpo, and cebpa and (N,S,X) size of primitive myeloid progenitor pool, by the area of tissue-expressing progenitor markers. Error bars represent the SD of the number of embryos analyzed (n). (O) Amount of tissue was calculated using area ratios of a and a′. Similar results were obtained in either ATG or e1i1 morphants and are in contrast with the uninjected and ATG mismatch control group (CTL). Student t test P values lower than .001 are marked as * and considered statistically significant; P values higher than .05 are not statistically significant and marked as ***.