Required for normal development of the eye (By similarity). May promote dorsalization of the developing embryo by antagonizing the ventralizing factor bmp4. Functional antagonism of bmp4 may require interaction with smad1. Required for gastrulation and subsequent neural development. May function as a transcriptional repressor. Predominantly localizes to the nucleus, with some cytoplasmic localization. Expressed both maternally and zygotically, during and after gastrulation. Expressed in neurulating embryos at the neural tube, the optic tissue, the developing midbrain and the pharyngeal pouches. Expressed at the tailbud stage in the primitive eye field, the optic recess, the optic cup, the retina, the tectum, the dorsal neural tube and the branchial arches. Belongs to the mab-21 family.