The C. elegans gonad looks like two U-shaped tubes connected at the middle of the body. This shape reflects the migration paths of the two gonadal distal tip cells (DTCs). To investigate the mechanism of DTC migration, we are analyzing mutants that are defective in DTC migration. In wild type animals, the DTCs migrate vertically from ventral to dorsal in the late L3 stage and migrate along the AP axis over the dorsal muscle in the L4 stage. The DTCs of
mig-22 mutants often fail to migrate vertically and cannot reach the dorsal muscle. The
mig-22 mutation was mapped between
sma-2 and
unc-32 on LG III by 3-factor mapping and between C06G4 and the left end of K02D10 by SNP mapping. Combining these data,
mig-22 was placed between
sma-2 and the left end of K02D10. PAR2.4 is one of the five predicted genes within this interval and a PCR amplified fragment of PAR2.4 rescued the Mig phenotype of
mig-22 mutants. Both of the two
mig-22 alleles,
k141 and
tk24 , had a mutation in PAR2.4.
k141 is a missense mutation that changes the 227th amino acid from Gly to Glu.
tk24 is a point mutation in the 5' splice consensus sequence of the 5th intron. We therefore conclude that
mig-22 corresponds to PAR2.4. The MIG-22 protein is novel, but it is highly homologous to human KIAA1402 and Drosophila CG9220 which are predicted from the genome projects. MIG-22 has hydrophobic residues near the amino-terminus which could be a secretion signal or a type II transmembrane domain. To identify the cells expressing
mig-22 , a GFP fusion gene was introduced into
mig-22 mutant animals. The fluorescence of GFP was seen in the pharyngeal muscles and DTCs, suggesting that MIG-22 may be required in DTCs for their correct migration.