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Fig. 4. Myocardial epithelial organization is disrupted in has/prkci
and nok/mpp5 morphants. All images represent reconstructions of
confocal Z-stack sections imaged on whole mounts. (A-E,G) cmlc2:GFP, green
(nuclear GFP within myocardial cells); PRKC/aPKC, red; ZO-1, blue. PRKC and
ZO-1 were used as a counterstain to visualize the embryonic midline (see also
dotted line in D). (F,H) cmlc2:GFP, green and ZO-1, blue. (Q-S) cmlc2:GFP and
filamentous actin. (A) At the 16-somite stage, wild-type myocardial
cells are organized into two bilateral sheets of cells. (B) Both sheets
converge onto the midline, where they fuse to form the heart cone around the
20-somite stage. (C) Further convergence leads to a narrowing of the
heart cone and expansion along the dorsoventral axis around the 24-somite
stage. The entire heart cone moves out of the midline toward the left and
anterior. (D) Heart cone tilting places the heart into the
anterior-posterior orientation by the 28-somite stage. The atrium (arrowhead)
is located to the left and anterior whereas the ventricle (arrow) is oriented
toward the midline and posterior. (E,G) nok/mpp5 morphants
display a delay in myocardial fusion to form the heart cone. (F,H)
has/prkci morphants undergo heart cone fusion at the midline but
tilting of the heart cone into the anterior-posterior orientation fails. Note
the disrupted appearance of the myocardial layer, with holes and rough edges
(arrows). (I-P) All images are details of confocal reconstructions of
confocal Z-stacks imaged from 16-somite stage whole mounts, separated into the
individual channels. (I-K) At the 16-somite stage, wild-type myocardial cells
have an epithelial organization with junctional distribution of PRKC and ZO-1.
(L-N) At the 16-somite stage, nok/mpp5 morphants display a diffuse
distribution of PRKC along membranes and ZO-1 junctional belts are disrupted
and appear as spots. (O,P) At the 16-somite stage, has/prkci
morphants display a spotted distribution of ZO-1. (Q,R) Dorsal view
onto the heart cone shown in S. (S) During tilting, specialized
elongated myocardial cells containing actin-cables attach the heart cone to
surrounding tissues (see arrow). Orientation: dorsal view and anterior to the
top, except in S, lateral view and anterior to the left.
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