pes-1 is expressed in several lineages during early embryogenesis and encodes a fork head transcription factor. This suggests that
pes-1 has an important role in the regulation of gene expression during early embryonic development. Inactivation of
pes-1 however, either by RNAi or by a Tc1-mediated deletion, does not give rise to any obvious phenotype. We now know this is because of genetic redundancy and
pes-1 functions redundantly with another C. elegans fork head gene,
fkh-2 (T14G12.4).
fkh-2 and
pes-1 have strikingly similar expression patterns.
fkh-2 : :gfp expression appears to start one round of cell divisions later than
pes-1 :: gfp . The D lineage component for both of these expression patterns completely overlaps whereas partial overlap is seen in the AB lineage component of both of these expression patterns. Interestingly, double antibody staining suggests a reciprocal level of expression between
fkh-2 and
pes-1 within the AB lineage . This similar expression pattern suggested to us that
fkh-2 function could overlap with that of
pes-1 even though these fork head genes do not share particular sequence similarity. Inactivation of
fkh-2 alone by RNAi, results in a subtle phenotype of restricted L1 movement. Disruption of both
fkh-2 and
pes-1 function, however, results in a penetrant lethal phenotype. 12% of progeny arrest during variable late stages of embryogenesis and a further 80% of progeny arrest at the first larval stage. Preliminary examination of the arrested larvae reveals anterior pharyngeal defects. A screen is being undertaken for a Tc3-mediated deletion mutant of
fkh-2 . The double mutant phenotype for
pes-1 and
fkh-2 will then be studied in more detail.