DNA-binding protein that seems to act as a transcription factor (By similarity). Mediates with FIBPB FGF-signaling in Kupffer's vesicle ciliogenesis and in the establishment of laterality in the embryo (PubMed:19164561). Interacts with FIBPB. Expressed after the mid-blastula transition (PubMed:19164561). Expressed in Kupffer's vesicle (PubMed:19164561). Morpholino knockdown of the protein causes severe deficits in laterality (PubMed:19164561). Partial loss of Kupffer's vesicle cilia with the length of the remaining cilia reduced (PubMed:19164561). Double morpholino knockdown of IER2 and FIBPB causes an almost complete loss of Kupffer's vesicle cilia (PubMed:19164561). Belongs to the IER family.