Enables guanyl-nucleotide exchange factor activity. Acts upstream of or within establishment of epithelial cell polarity. Located in bicellular tight junction; cytosol; and plasma membrane. Is extrinsic component of cytoplasmic side of plasma membrane. Is expressed in brain; sciatic nerve; and spinal cord. Orthologous to human CYTH1 (cytohesin 1). [provided by Alliance of Genome Resources, Apr 2022]