Fig. 2. Localization of EGFP and lacZ-expressing cells in the endoderm following electroporation of expression vectors. Distribution of EGFP-expressing cells at the mid-streak (MS) stage (3 hours), at the early-head-fold-stage (24 hours) and in the early-somite-stage embryo (46-48 hours) after electroporation of the endoderm of mid-streak-stage (E7.0) embryos at seven sites: (A) lateral, (B) anterior-proximal, (C) anterior-distal, (D) posterior-proximal, (E) posterior-middle, (F) posterior-distal and (G) distal. Examples of the pattern of distribution of EGFP-fluorescent cells after electroporation and in vitro culture are shown as a set of three (at 3 hours, 24 hours and 46-48 hours) for each site. All figures are lateral views with anterior to the left, except for anterior views of anterior-proximal (24 hours and 46-48 hours) and anterior-distal (46-48 hours), and posterior views of posterior-proximal (24 hours and 46-48 hours) and posterior-middle (46-48 hours) sites. (H-L) Localization of the electroporated lacZ-expressing cells in (H,J) whole-mount and (I,K,L) histological sections of the embryo. (H,I) Endoderm of an E7.0 MS-stage embryo after 3 hours of in vitro culture. (J-L) endoderm of the dorsal foregut (K) and the middle region (L) of an early-somite-stage embryo (J) after 24 hours of in vitro culture. The faint staining in I at the basal region of the epilast is probably due to the spillage of the product of the X-gal-staining reaction, as opposed to genuine staining, which would be found in the whole cell.