Worm Breeder's Gazette 15(4): 32 (October 1, 1998)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

A neuronal JNK signal transduction pathway regulates coordinated movement in C. elegans

Masato Kawasaki, Naoki Hisamoto, Kunihiro Matsumoto

Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, JAPAN

        The c-Jun NH2-terminal kinase (JNK) belongs to a subgroup of the
mitogen-activated protein kinase (MAPK) superfamily and is activated in
response to a variety of stresses and cytokines in mammalian cells.  To
gain insight into the JNK cascade, we have undertaken a genetic analysis
of the JNK signaling pathway in C. elegans.  The genes for the C.
elegans homolog of JNK, jnk-1 (formerly named sak-1), and its direct
activator, jkk-1 (formerly named sek-2), were isolated based on their
abilities to function in the yeast Hog1 MAP kinase pathway.  JKK-1 is a
novel member of the MAP kinase kinase (MAPKK) superfamily.  Both jnk-1
and jkk-1 are expressed in most neurons.
        To understand the role of JKK-1, we isolated a jkk-1 deletion
allele that lacks most of the kinase domains.  If JKK-1 functions as
MAPKK of JNK-1 in C. elegans, the latter should not be activated in
jkk-1 mutant animals.  To test this possibility, we examined the kinase
activity of JNK-1 immunoprecipitated from wild-type and mutant animals. 
After immunoprecipitating JNK-1 from extracts of wild-type adults with
an anti-JNK-1 antibody, we performed in vitro kinase assays using c-Jun
as a substrate.  JNK-1 prepared from wild-type animals phosphorylated
c-Jun.  However, JNK-1 immunoprecipitated from jkk-1 mutant adults
exhibited little kinase activity.  These results indicate that JNK-1
activity is positively regulated by JKK-1, supporting the idea that they
constitute part of a functional JNK cascade.
        jkk-1 mutants were viable, but exhibited defects in body
movement.  Wild-type C. elegans moves by propagating waves of
alternating dorsal and ventral flexions along its body length, which
produces regular sinusoidal tracks on a bacterial lawn.  In contrast,
the mutant animals left tracks with increased amplitude relative to
those left by the wild type.  Paths also meandered more, seldom running
in a straight trajectory for a long distance, and resulting in a much
shorter migration distance during a given period of time.  Other
behaviors, including pharyngeal pumping, egg laying, and defecation,
were normal in jkk-1 mutants.  Thus, JKK-1 is specifically involved in
the modulation of coordinated locomotion.
        To determine whether the locomotion defects are due to abnormal
development or abnormal cell function, we generated a plasmid which
places the jkk-1 gene under the control of heat-shock promoter and
integrated it to the jkk-1 strain.  These transgenic mutants were
defective in movement without heat treatment.  When heat-treated as
adults, the movement defects were rescued.  These results suggest that
the movement defects are not due to a developmental abnormality, but
rather to a defect in neuronal cell function.  Thus, the JNK  pathway
modulates coordinated movement in C. elegans as a result of its role in
neuronal function.