Fig. 6. The zygotic function of nok/mpp5 is required for myocardial cell remodeling. (A,C,E,F) 36 hpf wild type and (B,D,G) nok^s305 in the Tg(cmlc2:GFP) transgenic background. (H-K) nok^s305 in the Tg(cmlc2:GFP) transgenic background at 32 hpf. Images are reconstructions of confocal Z-stack sections. (A,B) Arrows indicate atrial myocardial cells and arrowheads ventricular myocardial cells. Shape and density of nok^s305 mutant atrial and ventricular cells are similar. (A',A'') Merged confocal serial sections of actin (red) and nuclear stain (SYTOX green nuclear acid stain). (A') Single sections and fusions of up to three sections of confocal serial stacks show that wild-type ventricular myocardial cells have cuboidal cell shapes. (A'') wild-type atrial myocardial cells have squamous cell shapes. (C,D) Comparison of atrial myocardial cells in wild-type and nok^s305 mutant hearts, indicating that nok^s305 mutant atrial myocardial cells fail to expand in size and resemble ventricular myocardial cells. (E-G) Mosaic expression of mRFP within single Tg(cmlc2:GFP) transgenic myocardial cells. (E) Wild-type atrial myocardial cell. (F) Wild-type ventricular myocardial cell. (G) nok^s305 mutant myocardial cell. (H,I) BrdU analysis of nok^s305 mutant myocardial cells. White dotted lines indicate BrdU-positive cells. (J,K) TUNEL analysis of nok^s305 mutant myocardial cells. The white dotted line indicates a TUNEL-positive cell. (L) Quantification of BrdU- and TUNEL-positive cells. (M) nok/mpp5 functions tissue-autonomously within the myocardium during heart tube elongation. A nok^s305 mutant in the Tg(cmlc2:GFP) transgenic background that also carries the Tg(cmlc2:nok) rescue transgene displays an elongated heart tube similar to wild type. Orientation: dorsal view and anterior to the top. A, atrium; V, ventricle.