Transcriptional repressor. Acts in a ventral signaling pathway downstream of bmp4 to antagonize the Spemann organizer and ventrally pattern the embryonic mesoderm. Represses transcription of the dorsal genes gsc and otx2. Widely expressed in the embryo prior to gastrulation. Becomes restricted to the ventral marginal zone by mid/late gastrulation. Ventral localization persists during gastrulation and neurulation in the ventral region of the closed blastopore and in the proctodeum during tail bud stages. Expression begins at a low level shortly after the mid-blastula transition. Expression then increases during early and mid-gastrulation.