A nuclear lamin is required for cytoplasmic organization and egg polarity in Drosophila

Abstract

Nuclear lamins are intermediate filaments that compose the nuclear lamina — the filamentous meshwork underlying the inner nuclear membrane — and are required for nuclear assembly, organization and maintenance. Here we present evidence that a nuclear lamin is also required for cytoplasmic organization in two highly polarized cell types. Zygotic loss-of-function mutations in the Drosophila gene encoding the principal lamin (Dm₀) disrupt the directed outgrowth of cytoplasmic extensions from terminal cells of the tracheal system. Germline mutant clones disrupt dorsal–ventral polarity of the oocyte. In mutant oocytes, transcripts of the dorsal determinant Gurken, a transforming growth factor-α homologue, fail to localize properly around the anterodorsal surface of the oocyte nucleus; their ventral spread results in dorsalized eggs that resemble those of the classical dorsalizing mutations squid and fs(1)K10. The requirement of a nuclear lamin for cytoplasmic as well as nuclear organization has important implications for both the cellular functions of lamins and the pathogenesis of human diseases caused by lamin mutations.