Fig. 1. Expression of Notch genes and their ligands. (A) In the upper panel, RT-PCR shows that Notch1 and Notch2 RNA is expressed in liver throughout its development and that Jagged1 RNA is expressed in fetal liver. One-fifteenths of cDNA synthesized from 1 µg of total RNA of developing liver was used for PCR. In the lower panel, a Northern blot shows the expression of Notch1 and Notch2 RNA in the primary culture of E14.5 Dlk⁺ cells at 4 and 24 hours after plating; 10 µg of total RNA was used for the analysis. GAPDH expression was also examined as an internal control in both experiments. (B, C) Frozen sections of E14.5 liver were stained with rat IgG (B) and anti-Notch2 rat monoclonal Ab (C). The sections were counter-stained with hematoxyline. Notch2 is synthesized broadly in E14.5 liver (C). (D-F) Series of frozen E17.5 liver sections, incubated with rat IgG (D), anti-Notch2 Ab (E) and anti-cytokeratin 19 (CK19) Ab (F). Notch2 is abundantly synthesized in E17.5 liver (E) including ductal plates stained by anti-CK19 Ab (F). (G-I) Series of frozen P7 liver sections, incubated with (G) anti-Jagged1-, (H) anti-CK19- and (I) anti- smooth muscle actin (SMA) Abs. Jagged1 is sparsely synthesized around portal veins and the hepatic arteries (G), which are both delineated by SMA⁺ cells (I); CK19⁺ bile ducts are not in contact with Jagged1⁺ cells (H). (J-L) A frozen E15.5 liver section stained with anti-Jagged1 and anti-keratin Abs. Jagged1 is synthesized abundantly around portal veins (red) (J). At this stage, developing cholangiocytes consisting of keratin⁺ ductal plates (green) (K) are in contact with Jagged1⁺ cells (L). bd, bile duct; cv, central vein; dp, ductal plate; ha, hepatic artery; pv, portal vein. Bars, 50 µm.