No myoblast fusion defects are observed in Rho172O
Expression of Rho1N19.Scer\UAS
in founder cells under the control of Scer\GAL4kirre-rP298
disrupts myoblast fusion in wild type embryos. A more severe phenotype is seen in Rho172O
In contrast to the round and dense morphology seen in wild type, the F-actin enriched-structures between unfused fusion-competent myoblasts and miniature myotubes in Rho172O
mutant embryos expressing Rho1N19.Scer\UAS
under the control of Scer\GAL4kirre-rP298
are irregularly shaped and exhibit abnormally long invasive protrusions. Ribosomes and intracellular organelles are frequently observed within the abnormal protrusions. Fusion pores fail to form.
Zygotic mutant embryos show head defects and excess naked cuticle replacing the ventral denticles.
Mutant embryos have holes in the head cuticle.
stage 16 embryos have longer dorsal trunks than normal.
F-actin localisation at the level of the adherens junctions is disrupted in Rho172O
Homozygotes are embryonic lethal, and often have a hole in the head cuticle.
The shape of the invaginated mesoderm is abnormal in embryos with a reduced maternal dose of Rho1+
Homozygous embryos show defects in head involution and organisation of the leading edge at stage 14. At stage 15, puckering of the leading edge is seen.
embryos exhibit dramatic defects in head involution. None of these mutant embryos have a clear dorsal hole, although they frequently show puckering or segment misalignments along the closed midline seam. During dorsal closure lamellipodial and filopodial protrusions are more abundant at the leading edge than in wild-type, significantly increaing the total protrusive area of the leading edge. The cytoskeletal architecture typical of the leading edge is lost.
Laser wounded Rho172R
embryos fail to assemble a continuous actin cable in wound-edge cells and there is little or no initial contraction of the leading edge of these cells. The leading-edge extends filopodia that are longer (extending up to 12 μm) and approximately three times more common than in wild-type embryos. In many instances, several filopodia coalesce to form a lamellipodium. Lamellipodia from adjacent leading-edge cells apparently tug on one another, resulting in the formation of several local zipping fronts around the wound margin, a behaviour only observed in wild-type in the last moments of wound closure, when opposing epithelial fronts are driven close enough together. Despite these differences with the wild-type, Rho172R
embryos are able to close their wounds, but these take on average almost twice as long to repair as in their wild-type counterparts. There is a lag phase of nearly 2 hours (the time in which an equivalent wild-type wound can close fully) before the disorganized leading edge begins to move forward significantly. During this initial period, no obvious changes in cell shape occur in the leading-edge epithelial cells. However, once forward movement begins, the wound closes at a rate that is not significantly different to that of a wild-type wound (7.0+/-1.9 μm2
/min; n = 6 in the mutant compared with 9.0+/-2.6 μm2
/min; n = 5 in the wild type).
Homozygous clones in the mushroom body result in a reduction in the number of neurons produced by the clone and the presence of multinucleated cells.
embryos have dorsal anterior holes in their cuticle. The embryos have compacted posterior spiracles.
Homozygous mushroom body neuroblast clones in larvae cease division within 24 hours after clone induction, in contrast to wild-type clones. 63%, 57% or 29% of larvae contain one homozygous Rho172O
mushroom body neuroblast clone when examined at 36, 18 or 16 hours after heat shock induction of mitotic recombination (which produces the homozygous clone), respectively. This indicates that in the majority of the clones, the last mitosis, which gives rise to two large nuclei (which are characteristic of these clones), has occurred by 18 hours after heat shock. However, BrdU incorporation is still occurring at 18-24 hours after heat shock in all cases, indicating that there is at lease one additional round of DNA replication after the last mitosis in the majority of homozygous clones. The two large nuclei are always present in the same cell body and in addition, one or two cell bodies are found to contain two small nuclei in each homozygous clone. This suggests a cytokinesis defect. Each large nucleus in the clone contains on average 3.30 +/- 0.38-fold more DNA compared with a diploid nucleus. The multinuclear cells containing the large nuclei appear to acquire a differentiated neuronal fate. Neuronal processes are occasionally seen projecting from these cells. Neurons of two cell or single cell mushroom body neuroblast clones homozygous for Rho172O
and generated in newly hatched larvae have axon projections that are indistinguishable from wild type. The number of major and minor branches within the adult γ lobe is not significantly different from wild type. Homozygous Rho172O
mushroom body neuroblast clones show a striking overextension of their dendrites. The length, frequency and number of overextended dendrites is drastically increased compared to wild-type clones.
Homozygotes show a defect in dorsal closure.
In homozygous mutant embryos, cytokinesis is blocked in affected cells. Many cells in the head region of the embryo become polyploid and contain two nuclei per cell. In addition polyploid cells are occasionally found in thoracic or abdominal segments of mutant embryos. Homozygous mutants have an "anterior open" phenotype.
embryos have an "anterior open" phenotype; the epidermis fails to close in the dorsal/anterior region. Rarely, the dorsal epidermis also fails to close. Some head structures are missing.