FoxO is a member of the evolutionary conserved family of transcription factors containing a Forkhead box, involved in many signaling pathways of physiological and pathological processes. In mammals, mutations or dysfunctions of the gene have been implicated in diverse diseases. FoxO homologs have been found in some invertebrates, including echinoderms. We have isolated the FoxO cDNA from the sea urchin () and characterized the corresponding gene and mRNA. In silico studies showed that secondary and tertiary structures of protein corresponded to the vertebrate FoxO3 isoform, with highly conserved regions, especially in the DNA-binding domain. A phylogenetic analysis compared the deduced protein with proteins from different animal species and confirmed its evolutionary conservation between vertebrates and invertebrates. The increased expression of mRNA following the inhibition of the PI3K signaling pathway paralleled the upregulation of target genes involved in apoptosis or cell-cycle arrest events (, , ). In silico studies comparing molecular data from sea urchins and other organisms predicted a network of protein-protein interactions, as well as identified potential miRNAs involved in gene regulation. Our data may provide new perspectives on the knowledge of the signaling pathways underlying sea urchin development.