Fig. 1: Nkapl KO males show infertility and defects during meiotic exit.

a Schematic representation of mouse Nkap and Nkapl genes architecture. Exons were shown in black. b Evolution of the retrogene Nkapl by phylogenetic sequence analysis. c Western blot analysis of NKAPL protein in P21 wild-type and Nkapl KO testes. Experiments were performed in biological triplicates. d Significant size reduction in 8-week-old Nkapl KO males. e–g Testis weights (e), body weights (f) and epididymal sperm counts (g) of wild-type (n = 4) and Nkapl KO (n = 4) at 8-week-old. Data are presented as mean ± SD. ***p < 0.001, ****p < 0.0001, ns: not significant, two-tailed unpaired Student’s t test. h Histological analysis of testes from 8-week-old wild type and Nkapl KO mice. Scale bars, 20 μm. i Enlarged images of the Nkapl KO tubule. Apoptotic late stages of spermatocytes in stage XII tubules of Nkapl KO are marked by arrows, and black lines indicate round spermatids. Scale bar, 20 μm. j Histological analysis of juvenile Nkapl KO testes also revealed defects in meiotic exit in the first wave of spermatogenesis. Mouse testes from Nkapl KO mice at P18, P23 and P35 were collected. Biological duplicates were prepared for each time point during the first wave of spermatogenesis. Scale bars, 20 μm. k A diagram representing arrested stages of germ cell development in Nkapl KO mice. Blue and red crosses on lines indicate the earliest and ultimate time point of spermatogenic arrest, respectively. Lep: Leptotene; Zyg: Zygotene; e-Pac: early-Pachytene; m-Pac: middle-Pachytene; l-Pac: late-Pachytene; Dip: Diplotene; RS: round spermatids; ES: elongating spermatids.