Worm Breeder's Gazette 6(1): 43

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More on Heterochronic Mutants of C. elegans

M. Kusch, B. Edgar

The previous report by Ambros et.  al.  suggests that mutants 
altered in the genes lin-4 and lin-14 may have major alterations in 
changes that occur at post-embryonic molts.  We report here a few 
preliminary observations concerning e912 and some speculations.
Cox and Staprans (Newsletter vol 5, no.  2, p.  15) have found a 
number of major differences in the gel patterns of proteins extracted 
from L1, L4, adult and dauer cuticles.  We have now examined 
extractable cuticle proteins from L2 and L3 juveniles and find they 
yield a pattern on SDS-PAGE indistinguishable from the L4.  We have 
examined the extractable proteins from sexually mature e912 and find 
they give the L2-L3-L4 gel pattern.  This result is consistent with 
the notion that e912 is arrested at the L1 stage since it is in the L1 
stage that the L2 cuticle materials are synthesized.
We have constructed double mutants containing e912 and several 
cuticle defective mutations that are phenotypically expressed only at 
the adult stage, a roller, rol-1 (e 91) and two blisters, bli-1(SC73) 
and bli-2 (e768)
In none of these doubles is the cuticle defective phenotype 
expressed, e912 behaves as suppressor of these mutations, consistent 
with its neotenic phenotype.
It seems to us conceivable that lin-4 and lin-14 are not, strictly 
speaking lineage genes but rather are genes that control switching 
from one post embryonic stage to another.  It may be useful to think 
of postembryonic development as metamorpic rather than continuous,with 
molting being more concerned with metamorphic change than with growth. 
It is interesting (and fortunate) that while some major aspects of 
postembryonic development are modified (regulated?) by mutations in 
these two genes, others (sexual maturation, the molting cycle) appear 
little affected.
We believe it is worth pointing out that in parasitic nematodes 
shift in habitat (eg. lung to gut) is coincident with molting and with 
major changes in behavior, nutrition, cuticle anatomy etc.  While C.  
elegans may not be parasitic, many of its relatives are.  It may have 
retained residual aspects (cuticle changes?) of a parasitic ancestor.
We are now about to renew attempts to identify more Heterochronic 
mutations using stage specific cuticle mutants to aid in their