Worm Breeder's Gazette 14(5): 76 (February 1, 1997)

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.

mig-15 encodes a novel ser/thr protein kinase of the Ste-20/p65PAK family

Xiaoping Zhu, Edward Hedgecock

Biology Department, Johns Hopkins University, Baltimore, MD 21218

        mig-15 is important in several developmental processes including
epidermal development, Q neuroblast migrations, and muscle arm
targeting. mig-15(rh148) mutants have an obvious body shape defect that
is easily recognizable under the dissecting microscope. Adult worms are
smaller in size than wild type. Most animals have protruding vulvae and
give small brood sizes of about 40. The QL neuroblast migrations are
reversed in mig-15(rh148) mutants, similar to that in mig-5 and mab-5
animals. Besides the above more commonly described phenotypes,
mig-15(rh148) also show muscle arm targeting defects. Muscle arms are
cytoplasmic extensions of muscle cells that make neuro-muscular
junctions with motor neuron axons. In wild type, muscle cells in the
dorsal quadrant extend arms toward the dorsal nerve cord and ventral
arms extend toward the ventral nerve cord. In mig-15(rh148) mutants,
however, muscle arms are occasionally seen extending from dorsal to
ventral or from ventral to dorsal directions.
        We have cloned the mig-15 gene using the transgenic rescue
method. First we mapped mig-15 between unc-115 and vab-3 on the X
chromosome by three-factor crosses. A single cosmid ZC504 within the
corresponding region on the physical map rescued mig-15(rh148) mutant
phenotypes. Sequence data from the genome consortium predicted four
genes on the cosmid. We constructed subclones that contained only one
gene at a time, and tested each subclone for rescuing activity. A
subclone that contains only ZC504.4 rescued mig-15(rh148) phenotypes
while others failed. When coding sequence of ZC504.4 was disrupted by
site directed mutagenesis, it failed to rescue. Based on the above
evidence, we concluded that ZC504.4 is the mig-15 gene.
        ZC504.4 encodes a novel Ser/Thr protein kinase in the
Ste20/p65PAK family (See Figure). The kinase domain is most homologous
to GC kinases which activate SAPK pathways in response to TNF-a and IL1
(Pombo et al., Nature 377, 750, 1994); These kinases may be regulated
directly by Rab8 or other G-proteins (Ren et al., PNAS 93, 5151, 1996).
Near the C-terminus, there is a 40 residue motif which is shared with
one other protein called citron, a presumptive Rho/Rac effector without
a kinase domain (Madaule et al., FEBS Letters 377, 243, 1995).
        We are currently working on the Mig-15 expression pattern using
the GFP tagging method. Future experiments include isolation and
characterization of additional allele; sequencing mutation and epistatic
analysis between mig-15(rh148) and other genes in the same pathway.