Arginine methyltransferase that can both catalyze the formation of omega-N monomethylarginine (MMA) and symmetrical dimethylarginine (sDMA), with a preference for the formation of MMA. Specifically mediates the symmetrical dimethylation of arginine residues in the small nuclear ribonucleoproteins Sm D1 (SNRPD1) and Sm D3 (SNRPD3); such methylation being required for the assembly and biogenesis of snRNP core particles. Specifically mediates the symmetric dimethylation of histone H4 'Arg-3' to form H4R3me2s. Plays a role in gene imprinting by being recruited by CTCFL at the H19 imprinted control region (ICR) and methylating histone H4 to form H4R3me2s, possibly leading to recruit DNA methyltransferases at these sites. May also play a role in embryonic stem cell (ESC) pluripotency. Also able to mediate the arginine methylation of histone H2A and myelin basic protein (MBP) in vitro; the relevance of such results is however unclear in vivo (By similarity). L-arginyl-[protein] + S-adenosyl-L-methionine = H(+) + N(omega)-methyl-L-arginyl-[protein] + S-adenosyl-L-homocysteine Homodimer and heterodimer. Interacts with PRMT5 and SNRPD3 (By similarity). Interacts with CTCFL. Present in undifferentiated embryonic stem and germ cells; expression is lost when cells differentiate. In the developing testis, it is expressed at all stages. Present in all cells within the developing tubule, including gonocytes and spermatogonia (at protein level). It the developing kidney, it is confined to the nephrogenic zone in the cortical region, where the tips of the ureteric bud induce de novo formation of epithelia in the metanephric mesenchyme and early glomeruli. Expression is around 8-fold lower in adult kidneys. Mutants, shortly after birth, display significant reduced body size, reduced weight and shortened fifth metatarsals. They are subviable with about 45% of the expected number of mutant pups at P14. Surviving adult mice exhibit increased fat mass, reduced length and limb abnormalities. They also have reduced bone mineral content and density. Knockout mice show sexually dimorphic phenotypes, including changes in bone mineral content, bone mineral density and fifth metacarpal length that are only significant in females. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family. PRMT7 subfamily. Truncated N-terminus.