The miRNA cluster which encodes mir-12, mir-283 and mir-304 has been deleted and replaced by a loxP cassette containing a w^+mW.hs marker. This cluster is present in an intron of Gmap, and the expression of Gmap is reduced compared to wild type in the deletion chromosome.

Df(1)Δ3miR mutants exhibit 88.3% lethality before the L1 stage. Most mutants die well before the end of embryogenesis. In Df(1)Δ3miR mutant dead embryos, nuclei are observed but cell membranes are lacking. Df(1)Δ3miR escaper embryos present wild type organization. No defects in egg chamber organisation are seen in adult escapers. No differences from wild type are observed in the wings, eyes, legs and abdomen. Rescue experiments demonstrate that the lethality is mainly due to the absence of the miRNA cluster, rather than an effect on Gmap.