Molting is required for progression between larval stages
in the life cycle of nematodes. We have identified four
mutant alleles of a <i>Caenorhabditis elegans</i> metalloprotease
gene, <i>nas-37</i>, that cause incomplete ecdysis. At each molt
the cuticle fails to open sufficiently at the anterior end and
the partially shed cuticle is dragged behind the animal. The
gene is expressed in hypodermal cells 4 hours before ecdysis
during all larval stages. The <i>NAS-37</i> protein accumulates
in the anterior cuticle and is shed in the cuticle after
ecdysis. This pattern of protein accumulation places NAS-
37 in the right place and at the right time to degrade the
cuticle to facilitate ecdysis. The nas-37 gene has orthologs
in other nematode species, including parasitic nematodes,
and they undergo a similar shedding process. For example,
<i>Haemonchus contortus</i> molts by digesting a ring of cuticle
at the tip of the nose. Incubating <i>Haemonchus</i> larvae in
extracted exsheathing fluids causes a refractile ring of
digested cuticle to form at the tip of the nose. When
<i>Haemonchus</i> cuticles are incubated with purified NAS-37,
a similar refractile ring forms. NAS-37 degradation of the
<i>Haemonchus</i> cuticle suggests that the metalloproteases and
the cuticle substrates involved in exsheathment of parasitic
nematodes are conserved in free-living nematodes
