Susceptibility of off-spring of sexually infected mothers to LP-BM5 is APOBEC3-dependent. Age and weight-matched WT, mA3+/-, and mA3-/- male (♂) mice on C57BL/6 background (n = 5) were inoculated with LP-BM5 virus via the IP route. Four weeks after infection, mice were mated (Table 1) for 6 days with age and weight-matched WT, mA3+/-, and mA3-/- female (♀) mice on C57BL/6 background (n = 3). Female mice were removed from their male partners, housed separately throughout the gestation period. Upon parturition, mice were allowed to nurse the off-spring for 3 days and female mice and her off-springs were euthanized. The spleens of all mice (male, female, and off-spring) were collected. Mammary gland tissues from all female mice were also collected, and milk from individual off-spring was obtained as previously described . DNA was extracted from spleen and used to determine level of off-spring infection (A, D, G, J) and genotype of all mice (B, E, H, K). Total RNA was extracted from milk samples and mammary gland tissues and used to determine milk viral load (C, F, I, L) and mammary gland viral load (M). Error bars are standard error; * is significance with p value equal or less than 0.05; and ** is significance with p value equal or less than 0.01. Experiments were performed three different times with similar results. ♂ = male, ♀ = female.