Fig. 6. ET_A-expression retrovirus and in ovo infection. (A) Proviral structures of control viruses, CXL and CXIZ (Mikawa et al., 1992; Mima et al., 1995) and ET_A expression virus, CXIZ-ETA. LTR, long terminal repeat; IRES, internal ribosome entry site; lacZ, ß-galactosidase gene. (B) Northern blot of ET_A expression from CXIZ-ETA. Total RNAs (20 µg) from E10 heart (lane a), cells transduced with CXIZ (lane b), and cells transduced with CXIZ-ETA (lanes c and d) were separated on agarose gel, stained with Ethidium Bromide (right panel), hybridized with probe for ET_A and autoradiographed (left panel). Endogenous ET_A and heterogeneous ET_A fused to IRES and lacZ are indicated. 28S, 28S ribosomal RNA; 18S, 18S ribosomal RNA. (C,G) E4 embryos infected with (C) CXIZ and (G) CXIZ-ETA at E3. (D,H) High power views of the boxed areas in C,G. (E,I) E15 hearts infected with (E) CXIZ and (I) CXIZ-ETA. (F,J) Ventricular segments infected with (F) CXIZ and (J) CXIZ-ETA at E3, isolated at E4, and cultured for 5 days. Blue staining in C-J indicates ß-gal positive cells infected with virus.