Enables heparin binding activity and signaling receptor binding activity. Involved in positive regulation of canonical Wnt signaling pathway. Acts upstream of or within several processes, including male meiotic nuclear division; positive regulation of non-canonical Wnt signaling pathway; and regulation of male germ cell proliferation. Located in extracellular space and nucleus. Is expressed in several structures, including alimentary system; central nervous system; embryo mesenchyme; genitourinary system; and skeleton. Orthologous to human RSPO1 (R-spondin 1). [provided by Alliance of Genome Resources, Apr 2022]