Oogenesis and meiotic prophase proceed normally in Tex19.1^−/− female mice. (A) Hematoxylin-stained paraffin sections from Tex19.1^+/+ and Tex19.1^−/− adult ovaries. No gross abnormalities were evident in Tex19.1^−/− ovaries. Primary, secondary, and antral follicles containing growing oocytes were observed in Tex19.1^+/+ and Tex19.1^−/− ovaries. Scale bar, 1 mm. (B) Example of chromosome counts from parthenogenetically activated anaphase II oocytes. Anaphase II chromosome masses are those shown in Fig. 1 F. Centromeres were visualized by FISH for major satellites (red), and DNA was stained with DAPI (cyan). Scale bar, 20 µm. (C) Immunostained E18.5 chromosome spreads from Tex19.1^+/± and Tex19.1^−/− oocytes showing chromosome synapsis. Axial elements and transverse filaments of the synaptonemal complex were stained with anti-SYCP3 (red) and anti-SYCP1 (green) antibodies, respectively. Scale bar, 10 µm. (D) Quantification of synapsis in E18.5 pachytene chromosome spreads. Asynapsis was present in 24 of 184 pachytene Tex19.1^+/± oocytes and 28 of 204 pachytene Tex19.1^−/− oocytes (ns, Fisher’s exact test, no significant difference). Data are derived from five Tex19.1^+/± and five Tex19.1^−/− fetuses. (E) SYCP3-positive nuclei in E18.5 oocyte chromosome spreads were classified into substages of meiotic prophase based on SYCP3 and SYCP1 immunostaining. The distribution of prophase substages was not significantly different between Tex19.1^+/± and Tex19.1^−/− oocytes (ns, Fisher’s exact test, no significant difference; n = 195, 219). Data are derived from five Tex19.1^+/± and five Tex19.1^−/− fetuses. (F) Chromosome axis lengths in pachytene nuclei from E18.5 fetal oocyte chromosome spreads as determined by anti-SYCP3 and anti-SYCP1 immunostaining. Chromosomes are ordered on the basis of size. 20 nuclei were scored for each fetus, and the mean axis length for each chromosome is plotted. Data for three Tex19.1^+/± and three Tex19.1^−/− fetuses are shown. Tex19.1^+/± and Tex19.1^−/− axis lengths are not significantly different for any chromosome (t test; n = 3). (G) Chromosome spreads from prometaphase I Tex19.1^+/± and Tex19.1^−/− oocytes 3 h after GVBD. DNA is stained with DAPI. Scale bar, 10 µm. (H) Quantification of number of prometaphase I oocytes containing univalents. Tex19.1^+/± and Tex19.1^−/− oocytes had similar frequencies of oocytes containing univalents (1/59 and 1/72 respectively; ns, Fisher’s exact test, no significant difference). All 59 Tex19.1^+/± and 72 Tex19.1^−/− oocytes had 40 chromosomes; therefore Tex19.1^−/− oocytes are not already aneuploid before the first meiotic division. Data are derived from three Tex19.1^+/± and three Tex19.1^−/− female mice.