Determining the mechanisms responsible for programmed muscle remodeling provides insights for how remodeling occurs in pathologies such as heart disease and cancer. The male anal depressor (anal dep) muscle undergoes structural and functional reorganization during the L4 larval stage. Two dorsal/ventral sarcomeres that control defecation in hermaphrodites and L1-L3 males are disassembled and reorganized into four anterior/posterior sarcomeres that adjust spicule position to allow sperm transfer during mating. To determine what genes control sarcomere remodeling, we screened developmental mutants and identified a role for WNT ligands
egl-20 and
lin-44, as well as frizzled receptor
lin-17, in regulating anal dep disassembly.
lin-17 is required in both the anal dep as well as the underlying rectal epithelium.
lin-44 interacts with
lin-17 in the rectal epithelium, where downstream signaling involves the planar cell polarity (PCP) pathway. In contrast,
egl-20 interacts with
lin-17 in the anal dep. Secreted, non-cell autonomous
egl-20, as well as both secreted and membrane-tethered cell autonomous
egl-20, regulate anal dep disassembly. We determined that the Ca2+ signaling pathway is downstream of
egl-20/lin-17 in the anal dep. We performed a mutant screen for disassembly defects and discovered
egl-8/PLC-? is required for normal sarcomere disassembly, and also identified WNT/Ca2+ components including
goa-1,
itr-1,
unc-68, and calcineurin further promote anal dep remodeling. Additionally, we showed that calcium levels increase in wild type male anal deps during L4, and that this increase is not present in males lacking the WNT signaling controlled by
egl-20. We determined that
egl-8;
egl-20 double mutants are similar to either single mutant, indicating they are in the same pathway, and that
egl-8 functions in the anal dep to regulated disassembly. To determine that the Ca2+ increase we see in the muscle is downstream of WNT, we artificially increased the Ca2+ levels in
egl-20 males using the C. elegans version of DREADD, a modified muscarinic receptor that responds to Clorozipine N-Oxide. Increasing Ca2+ over the developmental stages of the male results in males with normal anal depressors, indicating that it is the increase in Ca2+ levels promoted by
egl-20 in the anal dep that are important for sarcomere rearrangement.