Enables guanyl-nucleotide exchange factor activity. Involved in negative regulation of synapse maturation. Acts upstream of or within retina vasculature morphogenesis in camera-type eye. Located in dendrite. Is expressed in several structures, including adipose tissue; alimentary system; genitourinary system; hemolymphoid system gland; and respiratory system. Orthologous to human ARHGEF15 (Rho guanine nucleotide exchange factor 15). [provided by Alliance of Genome Resources, Apr 2022]