Rac GTPases regulates cellular morphogenesis and axon pathfinding. Three C. elegans RAC proteins (CED-10, MIG-2 and RAC-2/3) are functionally redundant in cell migration and axon pathfinding. Previously, synthetic lethality has been reported in
ced-10;
mig-2 and
ced-10;
unc-34 doubles (1, 2), also unc phenotype was reported when
ced-10 mutation is heterozygous with
mig-2 mutant and vice versa. Still very little is known about how RACs interact with each other and what other molecules play role with RACs in cell migration and axon outgrowth and pathfinding in C. elegans. Interestingly, functional redundancy in single RAC protein(s) but synthetic lethality with double RAC mutation allowed us to screen for more partners for CED-10 RAC, using
ced-10 synthetic lethal phenotype. To date, three new mutations,
lq13,
lq17 and
lq20 have been isolated.
mig-2(
lq13) and
unc-34(
lq17) mutations are hits in the known CED-10 interacting molecules, whereas
ced-10(
lq20) is a new mutation in CED-10 itself. Interestingly all three are the Gain-of-Function mutations.
mig-2(
lq13) mutation (S75F) falls in the switch 2 region of RAC protein whereas
ced-10(
lq20) mutation (P29L) perturb the switch 1 region.
unc-34(
lq17) mutation is in 5' splice site which causes the use of cryptic splice site, hence causing premature stop codon, and resulting in truncated EVH2 domain of UNC-34 Enabled. Due to premature stop codon, degradation of
unc-34(
lq17) transcript by mRNA surveillance process might occurred which results in enhancement of unc and axon guidance phenotype, suggesting that
unc-34(
lq17) is a Gain-of-Function mutation, further
unc-34(
lq17) mutation probably blocking UNC-34 Enabled tetramerization in vivo. Results from studies of cell migration, axonal guidance and axon outgrowth defects caused by
lq13,
lq17 and
lq20 mutations, functional redundancy and Gain-of-Function in transgenic animals will be presented. References: 1. Lundquist E. et al. Development 128, 4475-4488, 2001. 2. Gitai Z. et al. Neuron 37, 53-65, 2003.