Mouse Sptbn1 cDNA was generated from isolated glomeruli of C57BL/6 mice. FL-Sptbn1 cDNA was amplified by using KOD plus Neo DNA polymerases (Toyobo) and subcloned into a pCAT7 neo vector, which provides an N-terminal double T7-tag (49 (link)). Sptbn1 cDNA fragments 1A, 1B, and 1C were amplified using KOD Fx Neo or KOD plus Neo DNA polymerases (Toyobo) and subcloned into a p3XFLAG-CMV-10 (Sigma-Aldrich) vector. A FLAG-tagged human FL-SPTBN1 expression vector was provided by Tomozumi Imamichi (50 (link)). IgJ chain cDNA was generated from the mRNA of isolated GC B cells of C57BL/6 mice using KOD plus Neo DNA polymerases (Toyobo), fused with a His-tag at the C terminus, and subcloned into the pMXs-ires-GFP (green fluorescent protein) vector (49 (link)).