pros17 homozygous third instar larval brains exhibit ganglion mother cell dedifferentiation and severe tumor phenotypes, as compared to controls.
pros17/+ mutant larvae do not have significantly different numbers of intermediate neural precursors as compared to wild type.
Entry into quiescence is delayed in cas24 mutant NB3-3T neuroblasts.
Mutant embryos do not show an increased number of "Ap" neurons in the NB5-6T lineage.
When the majority of eye cells are homozygous pros17 mutant using Minute clones, the corneal lenses display slightly irregular shapes and sizes compared with wild-type eyes.
Most homozygous neuroblast clones in the larval brain are significantly larger than control clones. The mutant clones contain an increased number of mitotically active cells compared to controls. Two main types of neuroblast clone are recovered in the central brain. Clones of the first type (3 times more common than the second type) are larger than control clones, but are similar to them in that they contain one or two large cells located on one side of the cluster which seem to correspond to the neuroblast and/or ganglion mother cell. These clones also contain several small BrdU labelled nuclei. Mutant clones of the second type are very large and mostly contain large-to-medium size cells that are scattered throughout the clone. Two comparable types of mutant clone are recovered in the outer proliferation centre, with the first type of clone being 4 times more common than the second type.
Homozygous clones induced by the eyFLP method result in ectopic CO[] neurons on the maxillary palp (MP). The ectopic neurons show dual targeting specificity: in addition to targeting the V-glomerulus they also innervate a set of medial glomeruli normally innervated by two MP olfactory receptor neuron classes. The number of antennal CO[] neurons is reduced to 51.5% of controls. The number of olfactory receptor neurons per maxillary palp is reduced.
pros17 type I neuroblast clones in the larval brain contain ectopic type I neuroblasts. In contrast, pros17 type II neuroblast clones accumulate ectopic Intermediate Neural Progenitors while maintaining single parental neuroblasts.
62% of individual pros17 mutant R7 cells (generated using MARCM) form synaptic boutons in both the R7 and R8 medullar layers.
In third instar larvae, pros17 mutant clones appear to have increased in size and be populating large areas of the central brain compared to wild-type controls. Over 90% of pros17 clones contain 200-1000 cells compared to <100 cells in wild-type clones.
The morphology of the CNS is severely impaired in pros17 stage 15 embryos. The RP2, aCC/pCC and U/CQ neurons are missing but the EL neuron cluster is not affected.
pros17 neuroblast clones overproliferate when generated in the posterior half of the larval brain. Tumours are also formed when clones are induced in the ventral nerve cord. The neuroblasts within the tumours are enlarged.
Whereas wild type neuroblasts generate 2-32 cells (average 16.2 cells) and most exhibit extensive axonal outgrowth, pros17 neuroblasts generate 8-51 cells (average 31.8 cells) and exhibit few if any projections, and the cells are smaller in size.
Whereas wild type ganglion mother cells (GMCs) consistently give rise to just 2 daughter cells, which extend axons, pros17 GMCs give rise to more than 2 daughter cells, which exhibit few if any signs of differentiation, rarely producing projections.
pros17 mutant clones fails to differentiate ganglion mother cells.
The transplantation of pros17 larval neuroblast clones into the abdomen of adult hosts causes tumor growth, with clones growing to 100 times their original size thereby severely damaging and displacing the host's organs. Although genome stability is not grossly affected shortly after transplantation, 40-day-old tumors show karyotype defects such as segmental aneuploidy. Additionally, 15-20% of cells within the tumors have supernumerary centrosomes and these cells tend to be hyperploid.
Only 5% of hemisegments in pros17 mutant embryos have an RP2 neuron/RP2 neuron sib pair. However, there is no imbalance in the RP2/sib ratio in any segments. There is also a reduction in numbers U and CQ lineage neurons per segment (some segments lack neurons all together).
Glial cell fragmentation occurs in sensory organ clusters of the microchaete lineage of the notum in homozygous clones (as occurs in wild type).
When homozygous somatic clones are made in the antenna, various defects are seen. Sensillae are seen with duplicated shafts or sockets. Occasionally three shafts are seen arising from a single socket.
Mutant embryos show a striking loss of NGB 6-4T derived glia. The progeny of the G daughter cell of NGB 6-4T fail to migrate to the midline. These progeny cells fail to express either glial or neuron specific markers suggesting that they are unable to differentiate as glia or neurons. Mutant embryos also show defects in glial cell fate in the NGB 7-4 lineage.
In pros17 mutants the differentiation of the NGB6-4T-derived glial cells is abnormal. the M-CBG and two MM-CBGs are absent.
Mutants show no repo-positive cells of the NB6-4T or NB7-4 lineage. NB6-4T produces the normal number of progeny but none adopt the glial fate, all remaining in the neuronal, lateral position. NB6-4A is not affected by pros mutants.
Mutant embryos show a continuous decrease in myopodia number throughout hours 13-16, with only 2.23 myopodia per muscle remaining at hour 16. Whereas hour 16 wild type muscles show myopodia clustering in 46 of 52 hemisegments examined, pros17 show only 3 of 21 muscle cells with regions of high myopodial density.
Defects in dentritic misrouting are seen in embryos. No obvious cell change is seen in the PNS, but abnormal outgrowth and misrouting of axons from dorsal clusters of sensory neurons is seen. Dorsal branches may cross each other or veer sharply toward the other dorsal branch, unlike wild-type, where dorsal branches stay clear of each other. These sorts of phenotype are seen in about 70% of embryos.
Homozygous clones in the notum contain 86% single bristles (wild type) and 14% double bristles (two bristle shafts emerging from a single or fused double socket) in females. Males also show double bristles but at lower frequency. Homozygous clones in the eye contain 46% single bristles and 54% double bristles. The double bristle sense organs usually contain one morphologically normal bristle and one stunted bristle. The axon of the neuron is stunted in single bristle sense organs and often has a circular trajectory, and the dendrite is extremely stunted and usually fails to connect with the base of the bristle/socket cells.
Most pros17 sensilla on the notum and head have the normal complement of external cells (the tormogen and trichogen). The neuronal cells lying beneath the sensilla are usually missing in these clones, although in a small number of cases the cell body is present but lacks an apical dendrite. Defects in the external sensory organs are seen in clones; sensory organs with twinned shafts and two sockets, two sockets and a single shaft and two shafts and a single socket are seen. Mechanosensory organs in the eye often show twinning of the shafts, and may also lack the underlying neuron.
Peripheral glia are present in embryos, but do not extend cytoplasmic processes. The thoracic intersegmental glia and midline glia are abnormally large.
Haploinsufficiency for Abl, loss of one gene copy of pros exacerbates the Abl- mutant phenotype.
Lack longitudinal tracts and glial differentiation stops at a pre-axonal stage.