Cis-regulatory code for determining the action of Foxd as both an activator and a repressor in ascidian embryos

In early embryos of Ciona, an invertebrate chordate, the animal-vegetal axis is established by combinatorial actions maternal factors. One target these factors, Foxd, specifically expressed in vegetal hemisphere and stabilizes activating hemisphere-specific genes repressing animal genes. This dual functionality essential for embryogenesis ascidian embryos; however, mechanism which Foxd can act as both a repressor activator unknown. Here, we identify binding site upstream Lhx3/4, activated compare it with repressive Dmrt.a. We found that sites bind low affinity while high affinity. Reporter assays confirm this qualitative difference between sufficient to change functionality. therefore conclude outcome transcriptional regulation encoded cis-regulatory elements.