YTHDF2 is required for male fertility and spermatogenesis   (A) The infertility of germ cell-specific Ythdf2 mutants was shown through a mating assay. At 2 months of age, control (n=2) and Ythdf2-vKO mutant (n=4) mice cohabited with two female C57BL/6 mice. Vaginal plugs were checked, and pups were counted. ***P<0.001. (B) Gross morphology of representative testes from 2-month-old control and age-matched Ythdf2-vKO mice. (C,D) Comparison of testis weight (C) and body weight (D) from 2-month-old controls and age-matched Ythdf2-vKO mice. Data are presented as the mean±SEM (n=3 for each genotype). (E) H&E staining of the testes and epididymis from 2-month-old control and age-matched Ythdf2-vKO mice. Spg: spermatogonia; Spc: spermatocytes; Rs: round spermatids; Es: elongating spermatids; S: sperm. Scale bar=40 μm. (F) The sperm counts and the percentages of motile and progressively motile spermatozoa in the cauda epididymides of 2-month-old control and age-matched Ythdf2-vKO mice. Data are presented as the mean±SEM (n=5 for each genotype). ***P<0.001. (G) The morphology of representative sperm from 2-month-old control and age-matched Ythdf2-vKO mice. The red arrow indicates an abnormal head sperm. Scale bar=40 μm. (H) Statistical analysis of normal sperm from 2-month-old control and age-matched Ythdf2-vKO mice. Data are presented as the mean±SEM (n=3 for each genotype, at least 100 sperm were counted for each genotype). ***P<0.001.