ALTERING CELL FATES IN SEA-URCHIN EMBRYOS BY OVEREXPRESSING SPOTX, ANORTHODENTICLE-RELATED PROTEIN

While many general features of cell fate specification in the sea urch in embryo are understood, specific factors associated with these event s remain unidentified, SpOtx, an orthodenticle-related protein, has be en implicated as a transcriptional activator of the aboral ectoderm-sp ecific Spec2a gene. Here, we present evidence that SpOtx has the poten tial to alter cell fates, SpOtx was found in the cytoplasm of early cl eavage stage embryos and was translocated into nuclei between the 60- and 120-cell stage, coincident with Spec gene activation. Eggs injecte d with SpOtx mRNA developed into epithelial halls of aboral ectoderm s uggesting that SpOtx redirected nonaboral ectoderm cells to an aboral ectoderm fate, At least three distinct domains on SpOtx, the homeobox and regions in the N-terminal and C-terminal halves of the protein, we re required for the morphological alterations, These same N-terminal a nd C-terminal regions were shown to be transactivation domains in a ye ast transactivation assay, indicating that the biological effects of o verexpressing SpOtx were due to its action as a transcription factor, Our results suggest that SpOtx is involved in aboral ectoderm differen tiation by activating aboral ectoderm-specific genes and that modulati ng its expression can lead to changes in cell fate.