Distribution of CFU-S₁₁ in the aorta and UGRs.

(A, B) The aorta with surrounding mesenchyme and the UGRs were dissected from E10 to E12 embryos, and cell suspensions of these tissues were directly injected into irradiated adult mice to assay for CFU-S₁₁. (C) Organ explant cultures (3 days) of the subdissected tissues were performed prior to transplantation. The total number of CFU-S₁₁ per tissue is given in panel A, the frequency in panel B, and the total number after organ explant culture in panel C (fold increase compared with uncultured tissues are shown in parentheses). The data are the mean of results obtained from individually transplanted mice in a total of 14 independent experiments. CFU-S₁₁ values (given as times 10⁴cells) for the aorta and UGRs ranged from (A) E10: aorta, 0-0.3, and UGRs, 0-0.2; E11: aorta, 0-0.7, and UGRs, 0-0.35; E12: aorta, 0.42-1.0, and UGRs, 0.42-0.75; (B) E10: aorta, 0-4.2, and UGRs, 0-3.17; E11: aorta, 0-5.1, and UGRs, 0-3.2; E12: aorta, 2.8-6.6, and UGRs, 3.2-7.2; and (C) E10: aorta, 0.2-0.71, and UGRs, 0-0.27; E11: aorta, 0.22-3.14, and UGRs, 1.5-3.33; and E12, aorta 0.67-1.1, and UGRs, 0.6-0.9. In panels A and C, the number of CFU-S₁₁ per UGRs at E12 was calculated from the number of CFU-S₁₁ obtained from whole UGRs and partly from the number obtained from isolated gonads and pro/mesonephroi. The number of CFU-S₁₁ obtained per embryo equivalent (ee) of whole E12 UGRs was 0.6 in panel A and 0.75 in panel C; the number obtained from gonads and pro/mesonephroi was 0.1 and 0.4, respectively, in panel A and 0 and 0.7, respectively, in panel C. The frequency of CFU-S₁₁ (panel B) was calculated from the number of colonies per ee and the cell counts per tissue. For direct transplantations (panels A and B) the following total numbers of tissues were injected: E10: both aorta and UGRs, 40 ee; E11: aorta, 53 ee, and UGRs, 47.5 ee; and E12: aorta, 22 ee; UGRs, 8 ee; gonads, 14 ee; and mesonephroi, 14 ee. For the cultured data (panel C): E10, aorta, 26 ee, and UGRs, 27 ee; E11: both aorta and UGRs, 22 ee; and E12: aorta, 26 ee; UGRs, 20 ee; gonad and mesonephri, 6 ee. (D) A summary of the distribution of HSCs in the E10 to E12 aorta and UGRs is given (from de Bruijn et al9). ND indicates not determined.