(A) BRC-1::HA co-localizes with pro-CO factor COSA-1 in late prophase I. MP/LP = mid-/late pachynema, LP/DP = late pachynema/diplonema. Scale bar, 5 μm. (B) BRC-1::HA co-localizes with ZHP-3 and (C) GFP::MSH-5 in late pachytene nuclei. Scale bar, 5 μm. Bottom: Analysis of embryonic viability and segregation of male progeny shows full functionality of GFP::msh-5 and OLLAS::cosa-1 tagged lines. Embryos scored: WT (1311), GFP::msh-5 (1191), OLLAS::cosa-1 (1098), msh-5 (971), cosa-1 (927). (D) Partial projections of nuclei under super-resolution structured illumination microscopy: different examples show BRC-1::HA localization in the region surrounding the COSA-1-labeled CO site. BRC-1::HA forms a nodule-like structure together with SYP-1. (E) Insets showing magnified details from nuclei in (D).