Analysis of migratory potential and hemangioblast-like characteristics of primitive myeloid progenitors in spib-depleted embryos. Migration away from the aVBI is the first morphologic sign of primitive myeloid differentiation and is absent in spib-depleted embryos. (A-I) In spib-depleted embryos, we never observed isolated cells far from the aVBI expressing spib, mpo, and cebpa at a time when migration should have already set in. Usual down-regulation of scl and fli (▿, J,M) is eliminated in spib morphants (▼, K,L and N,O). The scl⁺fli⁺ hemangioblast-like characteristics are maintained for longer in a small subset of spib-depleted aVBI tissue.