Long-term repopulation assay with α4 integrin^–/– and wild-type embryonic tissues. (A) A representative plot demonstrates repopulation with embryonic E12.5 yolk sac (α4 integrin^–/–) plus 20 000 competitor carrier (wild-type) bone marrow cells using the Ly-5.1/Ly-5.2 system. α4 integrin^–/– repopulating yolk sac–derived cells show an absence of α4 integrin expression (right plot). The intermediate plot demonstrates that recipients of wild-type embryonic transplants express α4 integrin. (B) Transplantations with E12.5 tissues are plotted as the percentage of donor contribution in the peripheral blood of each mouse. (C) Transplantations with 4-day cultured α4 integrin^–/– (•) and wild-type (▴) E11.5 AGM region. Plotted horizontal lines represent the mean percentage level of reconstitution in the peripheral blood for each set of recipient mice. (*P < .05, comparison between wild-type and α4 integrin^–/– reconstitution levels.) Note that by using another method for assessment of reconstitution, which compares the number of reconstituted mice out of the total that received transplants of wild-type and α4 integrin^–/– cells, there is no significant difference between these 2 groups for all tissues transplanted. (For statistics, see Table S2.)