Extended Data Fig. 4 |. The A142 splice trap transposon is inserted into CG2556/meduse, the Drosophila homolog of the mammalian actin bundling protein MISP.

a, Genomic location of the splice trap transposon in the A142 line. The insertion was mapped by inverse PCR and genomic PCR to the large first intron of CG2556, approximately 10.6 kb downstream of the splice site in Exon 1. The transposon is inserted in the proper orientation to capture transcripts from CG2556, which would result in an N-terminal GFP tag on the nearly undisrupted protein (Exon 1 encodes only 7 amino acids, including the initiator Met). CG2556 was previously identified as a homolog of the mammalian Mitotic Interactor and Substrate of PLK1 (aka Mitotic Spindle Positioning, MISP)⁹³. MISP is an actin bundling protein that localizes to the rootlets of mouse and human intestinal microvilli⁹⁴. The tentacular appearance of the fusion protein in oocytes prompted us to name the gene meduse (mdu). b, Mdu::GFP (cyan) co-localizes with cortical actin filaments (magenta, Rhodamin-phalloidin) in Stage 10 oocytes. Image is representative of 10 oocytes. c, Latrunculin B (LatB) treatment disrupts cortical actin filaments in the oocyte and leads to abrogation of the oocyte Mdu::GFP signal. Note that LatB does not disrupt actin in ring canals; localization of Mdu::GFP to ring canals is visible in Panels (c) and (c′). Image is representative of 10 oocytes. Full genotype in Supplementary Table 1.