Phosphorylation of SYP-5 S541 during meiotic prophase. (A) Amino acid alignment of SYP-5/6 orthologs from Caenorhabditis species using the T-Coffee algorithm. Amino acids are colored using the Clustal X color scheme: hydrophobic (blue), positive (red), negative (purple), polar (green), cysteine (pink), glycine (orange), proline (yellow), aromatic (cyan), and unconserved (white). The black line above the sequence alignment indicates the phosphopeptide used to generate phospho-specific antibodies and the arrow indicates the PLK phosphorylation sites characterized in this study. (B) Composite projection images of a full-length gonad dissected from a worm strain expressing GFP::COSA-1, 3xFlag::SYP-5, and HA::SYP-6 are shown for DNA (top) and SYP-5 pS541 (bottom). Scale bar, 50 µm. (C) Zoomed-in images of leptotene/zygotene (upper panels) and pachytene nuclei (lower panels) as indicated by white boxes in B. 3xFlag::SYP-5 (magenta) and SYP-5 pS541 (green) staining are shown. Scale bar, 10 µm. (D) Zoomed-in images of late pachytene nuclei as indicated by the white box in B. DNA, 3xFlag::SYP-5 (magenta), SYP-5 pS541 (green), and GFP::COSA-1 (red) staining are shown. Scale bar, 5 µm.