Mi{128xMS2} represents a transgenic construct generated in vivo by using phiC31:int-mediated recombination to replace the attP cassette of a Mi{MIC} element insertion with a '128xMS2' stem-loop cassette that contains 128 copies of Tag:MS2 (the cassette contains 4 tandem repeats of a sequence encoding 32 unique Tag:MS2 stem loops). Insertion of the Mi{128xMS2} cassette in the correct orientation into an intron of a gene of interest allows visualization of nascent transcription of that gene; the Tag:MS2 sequences in the nascent transcript form stem loops that can be detected by a reporter protein that includes Tag:MCP (which binds Tag:MS2).