TCFL5 is expressed in pachytene spermatocytes during male meiosis I. (A,B) A-Myb and Tcfl5 mRNA (A) and protein abundance (B) at distinct developmental stages of mouse spermatogenesis. See Supplemental Figure S1A for uncropped western blot images. (C) Abundance of FLAG-TCFL5 protein in FACS-purified germ cell from Tcfl5+/FLAG mouse. Each lane contained protein from 75,000 germ cells. (D) mRNA abundance of Tcfl5 mRNA measured by single-cell sequencing by Green et al. (2018). (E) Immunohistochemical detection of A-MYB in adult testis section. A-Myb−/− testis sections serve as antibody specificity controls. (F) Immunohistochemical detection of TCFL5 in testis sections from staged mice. Tcfl5em1/em1 testis sections serve as antibody specificity controls. (Spg) Spermatogonia, (SpI) primary spermatocytes, (SpII) secondary spermatocytes, (RS) round spermatids, (ES) elongating spermatids, (SC) Sertoli cells.