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FB2026_01
,
released March 12, 2026
In 60% of SAKUbi.T:Avic\GFP neuroblasts, supernumerary centrosomes are detected.
Flies expressing SAKUbi.T:Avic\GFP appear morphologically normal but exhibit a delay in development compared to wild type flies.
Approximately 60% of third instar larval neuroblasts expressing SAKUbi.T:Avic\GFP contain more than the usual two centrosomes. Usually, three to six centrosomes are present in the cells with extra centrosomes, but cells with higher numbers are occasionally observed. Similar results are seen in larval imaginal disc cells. Half of the spindle poles examined contain multiple centrioles.
The centrosomal asymmetry seen in early mitosis in wild type larval neuroblasts is not observed in SAKUbi.T:Avic\GFP mutant cells with extra centrosomes. Although the centrosomes are often of different sizes, no clear dominant centrosome is seen with respect to recruitment of pericentriolar material or microtubule nucleation.
93% of SAKUbi.T:Avic\GFP cells with extra centrosomes have formed a bipolar spindle by metaphase. Several of the additional centrosomes are clustered at the poles of the spindle, while some are not associated with either pole. The centrosomes not associated with a pole contain less pericentriolar material than the centrosomes located at the poles and are usually not associated with robust asters of microtubules. The frequency of multipolar and abnormal metaphase spindles is slightly increased in SAKUbi.T:Avic\GFP mutant neuroblasts compared to wild type (2% and 5% compared to 0% and 2% respectively), but by anaphase all spindles are bipolar and there is only a slight increase in the frequency of aneuploidy compared to wild type. The mitotic index is higher in SAKUbi.T:Avic\GFP brains in comparison with wild type.
In some neuroblasts expressing SAKUbi.T:Avic\GFP the metaphase plate is not oriented correctly with respect to the polarity axis. The spindle fails to align correctly in 40% of neuroblasts that contain extra centrosomes, with 15% of spindles aligned at right angles to the aPKC crescent, a phenotype not observed in wild type. These spindle alignment defects are not observed in SAKUbi.T:Avic\GFP cells that contain only the normal two centrosomes. 91% of neuroblasts with extra centrosomes go on to divide asymmetrically as expected, but 9% divide symmetrically, a phenotype never observed in wild type. The number of neuroblasts in the brain lobes of animals expressing SAKUbi.T:Avic\GFP is slightly, but significantly, increased compared to wild type. The flies show no obvious evidence of tumour growth.
Transplantation of brains expressing SAKUbi.T:Avic\GFP into the abdomen of wild type hosts results in tumor formation, with several animals going on to develop one or more metastases far from the original site of injection. These flies invariably die within 10 to 15 days. No tumors are seen on transplantation of wild type brains.
SAKUbi.GFP has abnormal developmental rate phenotype, enhanceable by ncd1
SAKUbi.GFP has abnormal mitotic cell cycle phenotype, enhanceable by ncd1
SAKUbi.GFP has abnormal developmental rate phenotype, suppressible by Sas-4s2214
SAKUbi.GFP has abnormal developmental rate phenotype, suppressible by mad2G6595
SAKUbi.GFP has abnormal mitotic cell cycle phenotype, suppressible by mad2G6595
SAKUbi.GFP is a non-enhancer of abnormal developmental rate phenotype of Sas-4s2214
SAKUbi.GFP is a non-suppressor of abnormal developmental rate phenotype of mad2G6595
SAKUbi.GFP, mad2G6595 has lethal | pupal stage phenotype
SAKUbi.GFP has centrosome phenotype, enhanceable by mad2G6595
SAKUbi.GFP has centrosome | increased number phenotype, suppressible by Sas-4s2214
SAKUbi.GFP has neuroblast phenotype, suppressible by Sas-4s2214
SAKUbi.GFP has centrosome | increased number phenotype, non-suppressible by jubE1
SAKUbi.GFP has neuroblast phenotype, non-suppressible by jubE1
SAKUbi.GFP, Sas-4s2214 has centriole phenotype
The generation of supernumerary centrosomes in SAKUbi.T:Avic\GFP mutant neuroblasts is suppressed by a Sas-4s2214 background.
The generation of supernumerary centrosomes in SAKUbi.T:Avic\GFP mutant neuroblasts is not suppressed by a jubE1 background.
Homozygous Sas-4s2214 partially suppresses the developmental delay seen in flies expressing SAKUbi.T:Avic\GFP, producing a slight delay as is seen in Sas-4s2214 mutants alone. Eclosion occurs at a similar rate to wild type. As in Sas-4s2214 mutants, the flies contain no detectable centrioles.
Homozygous mad2G6595 suppresses the developmental rate defects seen in larvae expressing SAKUbi.T:Avic\GFP, producing instead a slight increase in the rate of development as is seen in mad2G6595 mutants alone. The mitotic index in mad2G6595 SAKUbi.T:Avic\GFP brains is lower than in either wild type or SAKUbi.T:Avic\GFP expressing neuroblasts. The number of multipolar and defective spindles is dramatically increased compared to flies expressing SAKUbi.T:Avic\GFP and polyploidy, aneuploidy and lagging chromosomes are all seen during anaphase. The number of centrosomes per cell is increased compared to SAKUbi.T:Avic\GFP.
ncd1 enhances the developmental rate defects seen in flies expressing SAKUbi.T:Avic\GFP, although the flies that hatch are all morphologically normal. A dramatic increase is seen in the rate of spindle multipolarity during prophase and metaphase, but as in SAKUbi.T:Avic\GFP alone, no multipolar spindles are seen during anaphase. Polyploidy, aneuploidy and lagging chromosomes are all seen during anaphase. The mitotic index is higher than in flies expressing SAKUbi.T:Avic\GFP alone.
SAKUbi.GFP rescues SAKAa74
Expression SAKUbi.GFP/+ rescues the uncoordinated and no centriole phenotypes of SAKAa74 homozygous adults.