Expression of ACE, AGT, renin, and cAT mRNAs during blood island differentiation (stage HH8). Transverse sections in the posterior half of the blastodisc at 29 hours of development (stage HH8) for in situ hybridization. (A-B) ACE expression in the extraembryonic endoderm. (C) Blood islands differentiating in the mesoderm (me), between the ectoderm (ec), and ACE-producing cells in the endoderm (en). Asterisks indicate blood islands (higher magnification of the view from panel A). For comparison, panels D and E show the expression of AGT, panels F and G, the expression of rennin; and panels H and I, the expression of cAT. (A,C,D,F,H) Bright-field illumination. (B,E,G,I) Dark-field illumination. (A-B) Original magnification, × 9; type of the objective lenses, EF × 4; numerical aperture 0.12. (C) Original magnification, × 60; type of the objective lenses, PL APO × 25; numerical aperture 0.70. (D-I) Original magnification, × 22; type of the objective lenses, EF × 10; numerical aperture 0.26. Scale bar: 500 μm (A-B), 100 μm (C), 200 μm (D-I).