Pharmacologic doses of RA overcome the maturation block in granulopoietic cells lacking RARα1 and RARγ. Bone marrow cells from RARα1^−/−γ^−/− mice were plated in methycellulose cultures in the presence or in the absence of RA at the indicated concentrations. GM colonies were harvested individually and stained as in Fig 4. Results shown are the average of differential counts of 30 independent colonies in the control group, three colonies for the lower concentration of RA (10⁻⁸ mol/L) and 15 colonies for the higher concentration of RA (10⁻⁷ mol/L) and are expressed as percent total cells within the granulocytic lineage.