Enables guanyl-nucleotide exchange factor activity. Involved in neural tube formation and small GTPase-mediated signal transduction. Predicted to be located in cell junction. Predicted to be active in centrosome and cytoplasm. Is expressed in anterior neural tube; neural rod; and neural tube. Human ortholog(s) of this gene implicated in hydrocephalus and spinocerebellar ataxia type 40. Orthologous to human CCDC88C (coiled-coil domain containing 88C).