Worm Breeder's Gazette 14(2): 84 (February 1, 1996)
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.
CNRS-CRBM, Montpellier, France
Kinesin is a microtubule-based molecular motor, driven by ATP and
involved in the anterograde transport of vesicles or material. Little is
know on its actual in vivo role and cargos. We have been pursuing the full
genetic characterization of the four alleles of unc-116, three of which
have, in addition to hypomorphic characters, specific neomorphic features,
such as :
- maternal effect lethality in rh24, due to lack of migration of the
female pronucleus in the one cell embryo (like zyg-9) ;
- zygotic L1 lethality in f122 ;
- and zygotic and maternal lethality in f130, linked to the generation of
aneuploids with very high chromosome numbers. We are truly interested in
understanding in every detail the meaning of these observations on how
kinesin operates in its wild type and mutant forms, so we are identifying
the molecular lesions in the mutants.
Only one allele, e2310, (Patel et al, PNAS 90, 9181-85,1993) behaves
as a simple and very partial loss of function. The cellular defects shared
by this allele and others reflect the wild type function of kinesin, which
seems ubiquitous : all cell types are affected. The shape of cells,
especially elongated ones (neurons, excretory canal, tail spike or male
tail), is deformed, mimicking a guidance defect. The position of vesicles
in the cells is often abnormal (nuclei in hyp7, or vesicles in muscle
cells or oocytes), and there are severe defects in the excretory pathway
leading to the accumulation of droplets between cells and basement
membranes or in the pseudocoelom.
The molecular defect in e2310 is an insertion of TC5 right at the
boundary between rod II and tail, which should, by mental translation,
lead to a kinesin devoid of its cargo holding piece. So the weakness of
the allele was very puzzling. We thus performed a Northern analysis which
showed the presence of two very strong bands in e2310 : a transcript of
about 7 kb probably corresponding to the kinesin-TC5 fusion and encoding
a truncated kinesin, and another band at about the wild type size (~ 3.5
kb). Two size variants were indeed identified in the RT-PCR products
corresponding to the approximately wild type band ; the longer was
apparently a mixture while the shorter differs from the wild type kinesin
transcript by the addition of exactly 24 bp from TC5 : translation of this
spliced transcript should yield a complete kinesin molecule with an
added 8 aa at the rod II-tail junction, which would be consistent with the
hypomorphic phenotype. Antibodies raised against peptides should allow us
to verify our hypothesis. We hope to say more soon on the other alleles.