Fig. 5. SPON-1 maintains muscle-epidermal attachment and muscle
organization. (A-D) Muscle quadrants in 2-fold (A,B) and 3-fold
(C,D) embryos; anti-MHC-A staining is counterstained with anti-AJM-1 in A and
B. 3-fold stage spon-1(ju402) mutants display gaps in MHC staining
due to muscle detachment (arrowhead, D). (E,F)
Anti-PAT-3/β-integrin (MH25) staining in wild type and in arrested
spon-1(ju402) embryos. (G,H) Perlecan (MH3) in
wild-type and spon-1(ju402) embryos. Epidermal cell outlines are
shown by anti-AJM-1 staining. Similar to MHC-A, both β-integrin and
perlecan staining were discontinuous because of muscle detachment (arrowhead
in F,H), but were normal in other regions; the gaps were variable in size and
position from embryo to embryo. (I,J) Epidermal circumferential
F-actin bundles (CFBs), detected by phalloidin labeling in wild-type and
arrested spon-1(ju402) embryos. In the wild type, CFBs in lateral
epidermal cells were circumferentially oriented (I, arrowhead). In arrested
spon-1(ju402) embryos, CFBs in lateral epidermal cells were
misoriented (J, arrow), becoming perpendicular to the circumference.
(K,L) Myotactin patterns (MH46 antibody staining) in the wild
type (K) and in arrested spon-1(ju402) embryos (L). Myotactin
patterns are discontinuous along the body; however, normal circumferential
double band patterns were observed in the remaining Myotactin. Scale bar in
A-L: 10 µm. (M,N) Post-embryonic muscle surfaces visualized
using trIs10; note muscle detachment in ju430 (arrowhead,
N). (O) Percentage of animals displaying muscle-muscle detachment
(n>40 for each condition; Fisher exact test,
*P<0.05, ***P<0.001).
(P-R) Ultrastructure of larval body wall muscle and BM. (P) Wild-type
body muscle, showing dense bodies (db) and regular myofilament lattice;
cuticle is at top. (Q) Muscle in spon-1(ju430) larvae grown at
22.5°C; note absence of dense bodies (db), disorganized myofilament
lattice and invagination of basal lamina (arrowhead). (R) Higher magnification
of basal lamina invagination into muscle (arrowhead). Scale bars in P-R: 500
nm.