Changes in morphology and cell counts of the E10, E11, and E12 AGM region.

(A) Scanning electron micrographs of the E10 (left), E11 (middle), and E12 (right) AGM region in which the excretory and reproductive systems are undergoing rapid growth and morphogenic changes. A indicates aorta; G, genital ridge/gonad; M, pro/mesonephros; Mn, metanephros; Me, mesenchyme; and Mt, mesentery (original magnification × 40). (B) The ongoing organogenesis results in an increase in the cell number within the AGM from E10 to E12. Viable cell numbers for the subdissected aorta, UGRs, and entire AGM after collagenase treatment are given for each embryonic day (the mean ± SD). UGRs comprised pro/mesonephroi and genital ridges/gonads. Cell counts of E12 UGRs were obtained from counts of whole UGRs (n = 2) and in part from counts of UGRs further subdissected into pro/mesonephroi and gonads (n = 3). At E12 the emerging metanephroi were not included in the cell counts of the total AGM region or UGRs. After 3 days of organ explant culture, the cell counts (given as × 10⁴ cells) for the different tissues were (1) E10: aorta, 5.6; UGRs, 7.1; and AGM, 13.0; (2) E11: aorta, 5.4 ± 2.5; UGRs, 8.2 ± 1.9; and AGM, 22.0 ± 2.7; and (3) E12: aorta, 6.0; UGRs, 18.0; and AGM, 30.8.