Sequence encoding the N-terminal domain of baz has been replaced with 'FUS[[S]]' (amino acid residues 1-141 of the human Hsap\FUS gene, part of the unstructured low-complexity domain) in the endogenous baz locus and GFP has been knocked-in, such that all splicing isoforms are tagged with GFP (nucleotides corresponding to position 127-270 of the baz PA isoform have been deleted and replaced with an in-frame GFP-linker FUS[[S]] sequence).