Mono-ADP-ribosyltransferase that mediates mono-ADP-ribosylation of target proteins (By similarity). Plays a role in nuclear envelope stability and nuclear remodeling during spermiogenesis (PubMed:25673562). L-aspartyl-[protein] + NAD(+) = 4-O-(ADP-D-ribosyl)-L-aspartyl-[protein] + nicotinamide L-cysteinyl-[protein] + NAD(+) = H(+) + nicotinamide + S-(ADP-D-ribosyl)-L-cysteinyl-[protein] L-glutamyl-[protein] + NAD(+) = 5-O-(ADP-D-ribosyl)-L-glutamyl-[protein] + nicotinamide L-lysyl-[protein] + NAD(+) = H(+) + N(6)-(ADP-D-ribosyl)-L-lysyl-[protein] + nicotinamide Colocalizes with NUP153 at nuclear pores. Predominantly expressed in testis, preferentially in postmeiotic germ cells. Also detectable in other tissues, including liver, lung, spleen, thymus and brain. Undetectable in testis until postnatal day 18. Sharply up-regulated from postnatal days 18 to 21. This timeframe corresponds to the appearance of the first spermatids of the first wave of spermatogenesis just before initiation of elongation. Remains elevated in adult animals. Auto-mono-ADP-ribosylated. Knockout mice are viable and are born in normal Mendelian ratios. Knockout males, but not females, exhibit a striking fertility defect, with the majority of males being sterile and a minority producing infrequent and small litters. Sperm from mutant mice exhibits mild to severe teratozoospermia, with structural defects in elongating spermatid nuclear envelope and chromatin detachment associated with abnormal nuclear shaping. Belongs to the ARTD/PARP family.