The brains of l(2)gl1/l(2)gl4 mutant third instar larvae are enlarged.
l(2)gl1 mutants show an overproliferation of central brain neuroblasts in the posterior half of the brain and a concomitant reduction in the amount of neurons. The proliferation begins in the mid-third larval instar and increases dramatically during the late-third instar. Neuroblasts in the anterior half of the brain appear normal in number and spacing.
By the extended germband stages, the epithelia of embryos from l(2)gl1 germ-line clone mothers loose their regular arrangement as epithelial cells round up.
The brain-ventral ganglion complexes of mutant larvae over 5 days old have brain hemispheres which are abnormal in size and morphology. Neuroblastomas of the optic lobes of the brain ganglia and tumourous imaginal discs are present in the mutant larvae.
90% of mutants die as larvae, 2% as pupae. Extreme allele: larval brain and optic lobes become enlarged and disorganised and the imaginal discs are large and clumped. Discs of mutant larvae transplanted into wild-type female abdomens form large contained tumours, whereas transplanted optic primordia from larval brains form invasive neuroblastomas, which grow rapidly, killing the host within 7-14 days. These tumours can be serially cultured in adult abdomens.