Two types of protractor muscle contractile behaviors are evident during male mating: periodic contractions and tonic contraction.
unc-103(
sy557) is a dominant loss of function mutation that causes 60% of the males spicule muscles to undergo tonic contraction in the absence of mating cues. UNC-103 is an ERG-like K+ channel that regulates contraction of the male sex muscles before and during mating.1 We have found that pharyngeal muscles and cholinergic neurons of the nerve ring, ventral cord, and male genitalia express an
unc-103::GFP reporter construct. Interestingly, the only observable phenotype seen is constitutive contraction of the male spicule muscles; hermaphrodites appear normal. To determine other molecules that work with
unc-103 to control spicule protraction, we EMS mutagenized
unc-103 (
sy557) hermaphrodites and screened for suppressors. From this screen, we isolated
lev-11 (
rg1), which reduced
sy557-induced protraction to 15%. The
rg1 mutation in tropomyosin is located near the region of troponin T interaction. Troponin T (TNT) is a component of the tropomyosin/troponin complex that mediates calcium regulation of muscle contraction.2unc-103
(sy557) could cause abnormal calcium influx in the cells that normally express
unc-103. We hypothesized that removing the specific calcium sensor that is inappropriately activated by
unc-103(
sy557) would suppress the spicule muscle defect. Of the four troponin T isoforms, we found reducing TNT-4 via RNAi in males suppresses the
unc-103 (
sy557)-induced spicule contraction. Surprisingly, an
tnt-4::GFP reporter construct shows expression is limited to the pharyngeal muscles. To verify the site of action for
lev-11(
rg1), tissues specific rescue constructs were injected into the
lev-11(
rg1);
unc-103(
sy557) double mutants and each line was assayed for
sy557-induced spicule protraction. As expected, we found that body wall-specific
lev-11 restored the
sy557-induced spicule muscle defect; interestingly, we found that the pharyngeal-specific form also restored the defect. To investigate this further, we ablated the pharyngeal neuron, NSM, in
lev-11(
rg1);
unc-103(
sy557) males and discovered this also restores the
sy557 muscle defect. Combined, these results suggest that pharyngeal muscle activity can regulate spicule muscle contractile behaviors by signaling to the tail through the NSM. 1. Garcia and Sternberg. 2003 Apr 1. J Neurosci. 23(7):2696-705. 2. Potter et al. 1995. J. Biol. Chem. 270:2557-2562.