Worm Breeder's Gazette 13(4): 71 (October 1, 1994)
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.
Department of Biochemistry, University of Texas Southwestern Medical
Center, Dallas, TX 75235-9038.
We study mutants affecting pharyngeal pumping in order to
learn how pharyngeal muscle electrical activity is regulated. As we
reported previously (WBG 13(1): 45), eat-12 plays an important role in
pharyngeal muscle excitation and repolarization. Semi-dominant,
apparent gain-of-function (gf) mutants in eat-12 (e.g., n2368) cause
muscle hypercontraction and delay pharyngeal muscle repolarization,
while recessive, loss-of-function (lf) mutants (e.g., egl-19(n582))
show feeble muscle contractions. n582/nDf41 is viable and has a more
severe phenotype than n582. This result suggested that n582 is not a
null but that null alleles could be obtained by non-complementation
screens.
What might the null phenotype of eat-12 be? If eat-12 affects
muscle directly, one might expect to see a Pat (paralyzed, arrested
elongation at two-fold) phenotype since that's true for many other
genes involved in muscle function or organization (Williams and
Waterston 1994, JCB 124: 475-490). On the other hand, if eat-12
affects muscle contraction by modulating the function of the nervous
system, one might expect a phenotype similar to that of cha-1/unc-17
or unc-104, which is larval arrest.
eat-12 null is Pat. We have collected 20 more EMS-induced lf
alleles by either reverting the gf mutants or by non-complementation
screens against n582. 11 of these have a Pat phenotype. Some viable
alleles show a Vab (variable abnormal morphology) phenotype which
appears to be caused by reduced embryonic rolling and consequent
partial failure of elongation.
Ben Williams has an impressive collection of Pat mutants
(Williams and Waterston 1994). pat-5 maps near eat-12 and turns out to
be allelic to eat-12. pat-5(st556) failed to complement
eat-12(ad1008), eat-12(ad1019) (two Pat alleles) and
egl-19(n582). pat-5 mutants have a phenotype similar to the Pat
alleles of genes that may encode tropomyosin and troponin C,
respectively. This similarity suggests that pat-5 may also play a role
in embryonic muscle excitation or excitation-contraction coupling.
Leslie Lobel has reported the partial cloning of a worm
homolog of a mammalian voltage-gated calcium channel alpha1 subunit and
the rescue of n582 with a pool of three cosmids (Lobel et. al., WBG 13(2):
71). We have narrowed the rescuing activity down to a single cosmid,
C48A7. This cosmid rescues not only egl-19(n582) but also
pat-5(st556).
Considering the phenotypes of eat-12/egl-19/pat-5 and the fact
that mutants can be rescued by a single cosmid containing a sequence
which closely resembles a calcium channel subunit, we are driven to
the idea that eat-12 encodes a calcium channel subunit that functions
in muscles. We are pursuing more direct evidence.
We thank Ben Williams for discussion, for doing the st556/ad1019
complementation test, and for sharing pat-5 mutants. We also thank
Leslie Lobel for YAC grids and a plasmid clone containing his PCR
fragment.