Abnormalities in cell proliferation and apico-basal cell polarity are separable in Drosophila lgl mutant clones in the developing eye

In homozygous mutants of Drosophila lethal-2-giant larvae (lgl), tissues lose apico-basal cell polarity and exhibit ectopic proliferation. Here, we use clonal analysis in the developing eye to investigate the effect of lgl null mutations in the context of surrounding wild-type tissue. lg Gamma,clones in the larval eye disc exhibit ectopic expression of the Gl-S regulator, Cyclin E, and ectopic proliferation, but do not lose apico-basal cell polarity. Decreasing the perdurance of Lgl protein in larval eye disc clones, by forcing extra proliferation of lg Gamma tissue (using a Minute background), leads to a loss in cell polarity and to more extreme ectopic cell proliferation. Later in development at the pupal stage, lgl mutant photoreceptor cells show aberrant apico-basal cell polarity, but this is not associated with ectopic proliferation, presumably because cells are differentiated. Thus in a clonal context, the ectopic proliferation and cell polarity defects of lg Gamma mutants are separable. Furthermore, lg Gamma mosaic eye discs have alterations in the normal patterns of apoptosis: in larval discs some lg Gamma and wild-type cells at the clonal boundary undergo apoptosis and are excluded from the epithelia, but apoptosis is decreased elsewhere in the disc, and in pupal retinas lg Gamma tissue shows less apoptosis. (C) 2007 Elsevier Inc. All rights reserved.