In Caenorhabditis elegans, motility depends on the mechanical connections between muscles, epidermis (hypodermis) and cuticle. Within the epidermis, hemidesmosome-intermediate filament complexes known as fibrous organelles play an essential role in transmitting force generated by the skeletal muscles to the cuticle. Mutations in
mua-2 and
ifa-2 (pka
mua-6) weaken the integrity of the fibrous organelles, causing progressive post-embryonic locomotor paralysis due to separation of the skeletal muscle and cuticle. Analysis of tissue disruption in
mua-2 mutants using tissue specific reporter constructs suggests that the epidermis separates from the cuticle. A combination of classical genetic and SNP mapping was used to position
mua-2 to the right of
spe-6 and between pkP3060 and pkP3074 on chromosome III. A
spe-6 containing yeast artificial chromosome, Y66D12, rescues
mua-2(
rh174) in transgenic animals. Three lines of evidence suggest that the gene
y66d12a.11, a gene that encodes a single pass transmembrane receptor, is
mua-2. First, transgenes containing the
y66d12a.11 sequence rescue
mua-2. Secondly, RNAi of
y66d12a.11 results in defects similar to those seen in mutant
mua-2(
rh174) homozygotes, although no muscle detachment in RNAi exposed worms was observed. Finally, the
y66d12a.11 sequence is frame-shifted, resulting in a premature stop codon in the
mua-2(
rh174) allele. Also consistent with
y66d12a.11 being
mua-2 is the observations that a Y66D12A.11::GFP translation fusion protein localizes in a pattern consistent with localization to epidermal hemidesmosomes. It had been previously shown that the cytoplasmic intermediate filament IFA-2 is associated with the fibrous organelles, and mutations or RNAi disruption of
ifa-2 results in epidermal fragility and separation of the apical and basal epidermal surfaces. A weak loss-of function mutation,
rh85, alters the
ifa-2 initiation codon to AUA. We show that this mutated codon is likely still recognized as an initiation codon, resulting in a full length IFA-2. We also show that an IFA-2::GFP protein lacking the IF head domain can completely rescue an
ifa-2 null mutant, thus showing that the head domain is not essential for IFA-2 function.