PES-1 is expressed during early embryogenesis in Caenorhabditis elegans and has homology to the fork head family of transcription factors.

Promoter trapping has identified a gene, pes-1, which is expressed during C. elegans embryogenesis. The beta-galactosidase expression pattern, directed by the pes-1/lacZ fusion through which this gene was cloned, has been determined precisely in terms of the embryonic cell lineage and has three components. One component is in a subset of cells of the AB founder cell lineage during early embryogenesis, suggesting pes-1 may be regulated both by cell autonomous determinants and by intercellular signals. Analysis of cDNA suggests pes-1 has two sites for initiation of transcription and the two transcripts would encode related but distinct proteins. The predicted PES-1 proteins have homology to the fork head family of transcription factors and therefore may have important regulatory roles in early embryogenesis.