|Feature type||allele||Associated gene||Dmel\Sgt1|
|Map ( GBrowse )||
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|Nature of the Allele|
|Mutations Mapped to the Genome|
transposable element insertion site
|Associated Sequence Data|
|Nature of the lesion|
Insertion at nucleotide +55 of the transcription unit, which is upstream of the initiator ATG codon.
|Caused by insertion|
|Phenotype Manifest In|
Third larval instar Sgt1[c01268] neuroblasts have abnormal mitotic phenotypes, including a high proportion of prometaphases with hypercondensed chromosomes and anaphases with lagging chromatids. Sgt1[c01268] has no overall effect upon mitotic index. There is a significant reduction in the frequency of prophases, a severe increase in the frequency of prometaphases and a reduction of cells exiting mitosis compared to control cells. Compared to controls, many fewer mutant neuroblasts incorporate BrdU. Treatment of Sgt1[c01268] neuroblasts with colchicine does not lead to the accumulation of cells in mitosis, in contrast to control cells. 22% of Sgt1[c01268] neuroblasts have monopolar spindles, with either a dispersed or well-focused centrosome at the centre. 30% of cells have just one centrosome and 20% have a diffuse centrosome. When Sgt1[c01268] larval neuroblasts are observed in primary culture, the following mitotic behaviours are observed; 55% enter mitosis with no apparent microtubule-organizing centre (MTOC), but after nuclear envelope breakdown (NEBD) are able to form a microtubule array that grows out from the kinetochores, they are unable to focus at the spindle poles and mitotic progression is delayed in prometaphase for more than 1 hours. 15% of the cells enter mitosis with a single MTOC, form a bipolar spindle and reach metaphase with a short delay but eventually exit mitosis with a significant delay (35 minutes after NEBD). 5% of the cells enter mitosis with more than two MTOCs, fail to organise a proper bipolar spindle and consequently fail to congress the chromosomes and arrest for long periods. 25% of the mutant neuroblasts enter mitosis with two MTOCs (as occurs in wild type). Only 40% of Sgt1[c01268] neuroblasts have a normal set of centriole pairs, approximately 40% have more than two centriole pairs and some cells have less than two centriole pairs. There is a clear correlation between increase in centriole number and increase in ploidy in the mutant cells.
|Phenotype Manifest In|
Sgt1c01268 has centrosome phenotype, suppressible | partially by poloScer\UAS.P\T.cMa/Scer\GAL4da.G32
Sgt1c01268 has neuroblast phenotype, suppressible | partially by poloScer\UAS.P\T.cMa/Scer\GAL4da.G32
Sgt1[c01268] ; Bub3 double mutant larval brain neuroblasts have a very low mitotic index. Compared to Sgt1[c01268] single mutant cells, the Sgt1[c01268] ; Bub3 double mutant cells enter mitosis more readily, do not accumulate in prometaphase and exit mitosis more frequently (as shown by the increase in anaphase and telophase figures). The double mutant cells do not show chromosome hypercondensation. Expression of polo[Scer\UAS.P\T.cMa] under the control of Scer\GAL4[da.G32] significantly rescues the mutant phenotypes of Sgt1[c01268] larval brain neuroblasts; there is an increase in cells with a normal number of centrosomes and a normal bipolar spindle and the cells show mostly normal mitotic progression.
|Complementation & Rescue Data|
|Stocks ( 1 )|
|Notes on Origin|
Precise excision of the insertion results in a full restoration of viability.
|External Crossreferences & Linkouts|
|Synonyms & Secondary IDs ( 3 )|
|Secondary FlyBase IDs|
|References ( 2 )|
|Personal communication to FlyBase|