Borealin-related (borr) encodes Drosophila Borealin, a subunit of the mitotic chromosomal passenger complex (CPC) with Aurora B, Incenp and Deterin (Survivin). Borr binds Incenp directly, self-associates and binds DNA in vitro, and with Deterin forms the localization module that targets the CPC. It is nuclear in interphase, associates with chromosome arms and centromeres/kinetochores from prophase to metaphase, then transfers to the central spindle and concentrates at the spindle midzone and midbody. Borr is needed to localize Aurora B and Incenp to the mitotic spindle; borr mutant cells lose histone H3 serine-10 phosphorylation, arrest transiently in prometaphase, form multipolar spindles and become polyploid. Borr is present in all mitotic tissues and acts in acentrosomal female meiosis, where it supports chromatin recruitment of the CPC and its transfer to the central spindle, but is absent from male meiotic divisions, where its paralog Australin replaces it. In late cytokinesis Borr binds the ESCRT-III protein Shrub at the midbody.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000070 mitotic sister chromatid segregation | IMP PMID:16224046 Loss of Drosophila borealin causes polyploidy, delayed apopt... | ACCEPT | Summary: borr mutant cells show CPC-type mitotic defects and become polyploid. Reason: Loss-of-function evidence for a core CPC process. Supporting Evidence: PMID:16224046 borr mutant cells show multiple mitotic defects that are consistent with loss of CPC function |
| GO:0000070 mitotic sister chromatid segregation | NAS PMID:25798441 The chromosomal passenger complex (CPC) as a key orchestrato... | ACCEPT | Summary: Author statement (review) that the CPC orchestrates chromosome segregation. Reason: Consistent with direct borr mutant evidence (PMID:16224046). Treated identically across CPC subunits. Supporting Evidence: PMID:25798441 The CPC orchestrates proper chromosome segregation with cytokinesis by targeting to specific locations at different stages of mitosis |
| GO:0000281 mitotic cytokinesis | NAS PMID:25798441 The chromosomal passenger complex (CPC) as a key orchestrato... | ACCEPT | Summary: Author statement (review) on CPC role in cytokinesis. Reason: Consistent with polyploidy of borr mutant cells (PMID:16224046). Supporting Evidence: PMID:25798441 The CPC orchestrates proper chromosome segregation with cytokinesis by targeting to specific locations at different stages of mitosis |
| GO:0000775 chromosome, centromeric region | IBA GO_REF:0000033 | ACCEPT | Summary: Centromeric region (IBA). Reason: Conserved Borealin localization; donors include borr and aust (FB) and human CDCA8 (Q53HL2). |
| GO:0000775 chromosome, centromeric region | IEA GO_REF:0000044 | ACCEPT | Summary: Centromere (UniProt subcellular location, from PMID:16224046). Reason: Consistent with direct localization data. Supporting Evidence: file:DROME/borr/borr-uniprot.txt Chromosome, centromere {ECO:0000269|PubMed:16224046} |
| GO:0000776 kinetochore | IDA PMID:18268101 Australin: a chromosomal passenger protein required specific... | ACCEPT | Summary: Borr at metaphase kinetochores. Reason: Immunofluorescence in embryos and neuroblasts. Supporting Evidence: PMID:18268101 By metaphase, the antibodies recognized specific dots that presumably correspond to the kinetochores |
| GO:0000785 chromatin | IDA PMID:16224046 Loss of Drosophila borealin causes polyploidy, delayed apopt... | KEEP AS NON CORE | Summary: Borr associates with chromatin (chromosome arms) in prophase. Reason: Abstract-only reference; Borr associates with chromosome arms before concentrating at centromeres. Accurate for the prophase pool but peripheral to the defining centromere/midzone locations. Supporting Evidence: file:DROME/borr/borr-uniprot.txt Localizes on chromosome arms and inner centromeres from prophase through metaphase |
| GO:0003677 DNA binding | IDA PMID:18268101 Australin: a chromosomal passenger protein required specific... | ACCEPT | Summary: Borr binds DNA in vitro. Reason: Direct biochemical evidence (MBP-Borr binds DNA-cellulose), conserved with human Borealin and thought to contribute to chromatin targeting of the CPC. Supporting Evidence: PMID:18268101 MBP-Borr and MBP-Aust but not MBP alone were able to interact with DNA |
| GO:0005515 protein binding | IPI PMID:22724069 The chromosomal passenger complex controls the function of e... | REMOVE | Summary: Protein binding (Borr-Shrb interaction). Reason: Uninformative protein binding term; the Borr-Shrb (ESCRT-III) interaction is real (PMID:22724069) but GO has no ESCRT-III complex binding term to replace it with. |
| GO:0005634 nucleus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Borr is nuclear in interphase. Reason: Correct interphase location of a chromosomal passenger; peripheral to its mitotic locations. Supporting Evidence: PMID:18268101 During interphase, Borr was present in the nucleus |
| GO:0005819 spindle | IEA GO_REF:0000044 | MODIFY | Summary: Spindle (UniProt subcellular location mapping). Reason: Correct but general; Borr's spindle localization is the central spindle midzone, so replace with spindle midzone (GO:0051233), which borr already carries. Proposed replacements: spindle midzone Supporting Evidence: PMID:18268101 Borr transferred onto the forming central spindle MTs, concentrating on the central spindle midzone by late anaphase and telophase |
| GO:0005938 cell cortex | IDA PMID:16224046 Loss of Drosophila borealin causes polyploidy, delayed apopt... | KEEP AS NON CORE | Summary: Borr at the cell cortex. Reason: Abstract-only reference. The CPC is known to localize to the equatorial cortex during cytokinesis; plausible and deferred to the curator, but peripheral. Supporting Evidence: PMID:18268101 During cytokinesis, the CPC localizes to both the central spindle midzone and the equatorial plasma membrane |
| GO:0007080 mitotic metaphase chromosome alignment | IBA GO_REF:0000033 | ACCEPT | Summary: Mitotic metaphase chromosome alignment (IBA). Reason: IBA from node PTN001815752 with human CDCA8 (Q53HL2) as donor; Borealin is required for chromosome alignment through CPC function, and borr mutant cells arrest in prometaphase (PMID:16224046). |
| GO:0032133 chromosome passenger complex | IBA GO_REF:0000033 | ACCEPT | Summary: CPC membership (IBA). Reason: Conserved Borealin function; donors include borr itself. |
| GO:0032133 chromosome passenger complex | IDA PMID:18268101 Australin: a chromosomal passenger protein required specific... | ACCEPT | Summary: Borr is a chromosomal passenger in mitosis. Reason: Direct localization and biochemical evidence for CPC membership. Supporting Evidence: PMID:18268101 Thus, Borr is a chromosomal passenger protein during mitosis but does not appear to be present during male meiosis |
| GO:0032133 chromosome passenger complex | IDA PMID:22724069 The chromosomal passenger complex controls the function of e... | ACCEPT | Summary: Borr co-purifies with the CPC and binds Incenp directly. Reason: Affinity purification and direct interaction evidence. Supporting Evidence: PMID:22724069 Because Borr and INCENP interact directly |
| GO:0032133 chromosome passenger complex | NAS PMID:25798441 The chromosomal passenger complex (CPC) as a key orchestrato... | ACCEPT | Summary: Author statement (review) of CPC composition. Reason: Consistent with direct evidence. Supporting Evidence: PMID:25798441 The chromosomal passenger complex (CPC), which is composed of Aurora B, INCENP, Borealin and Survivin, is one of the most widely studied and highly conserved hetero-tetrameric complexes |
| GO:0051233 spindle midzone | IBA GO_REF:0000033 | ACCEPT | Summary: Spindle midzone (IBA). Reason: Conserved Borealin localization (node PTN001815752); in flies Borr concentrates at the spindle midzone in mitosis (PMID:18268101) and at the central spindle of acentrosomal oocyte meiosis, so the general midzone term is appropriate here. |
| GO:0051233 spindle midzone | IDA PMID:16224046 Loss of Drosophila borealin causes polyploidy, delayed apopt... | MODIFY | Summary: Borr concentrates at the spindle midzone in anaphase. Reason: Correct but general; this paper examines mitotic cells (wing disc and other mitotic tissues), so the specific term is mitotic spindle midzone (GO:1990023). Proposed replacements: mitotic spindle midzone Supporting Evidence: PMID:18268101 Borr transferred onto the forming central spindle MTs, concentrating on the central spindle midzone by late anaphase and telophase |
| GO:0051256 mitotic spindle midzone assembly | NAS PMID:25798441 The chromosomal passenger complex (CPC) as a key orchestrato... | ACCEPT | Summary: Author statement that the CPC drives central spindle assembly. Reason: Consistent with Borr being required to localize Aurora B and Incenp to the spindle (PMID:16224046). Supporting Evidence: PMID:16224046 Borr colocalises with the CPC components Aurora B kinase and Incenp in mitotic Drosophila cells, and is required for their localisation to the mitotic spindle |
| GO:1902889 protein localization to spindle microtubule | IMP PMID:16224046 Loss of Drosophila borealin causes polyploidy, delayed apopt... | ACCEPT | Summary: Borr is required to localize Aurora B and Incenp to the mitotic spindle. Reason: Direct loss-of-function evidence; this is the targeting role of the Borealin subunit. Supporting Evidence: PMID:16224046 Borr colocalises with the CPC components Aurora B kinase and Incenp in mitotic Drosophila cells, and is required for their localisation to the mitotic spindle |
| GO:1990385 meiotic spindle midzone | IDA PMID:18268101 Australin: a chromosomal passenger protein required specific... | MODIFY | Summary: Meiotic spindle midzone, attributed to PMID:18268101. Reason: The cited paper (full text cached) states that Borr does not accumulate at the meiotic central spindle midzone in spermatocytes and is replaced by Australin in male meiosis; what it shows for Borr is midzone localization in mitotic cells (embryos, neuroblasts, gonial mitoses). The supported term for this reference is mitotic spindle midzone (GO:1990023). This is a correction of the cited source, not a claim that Borr lacks a meiotic midzone pool: Borr acts on the central spindle in acentrosomal female meiosis (see notes), so meiotic spindle midzone may be true but needs an oocyte reference; the general spindle midzone IBA row is retained to cover it. Proposed replacements: mitotic spindle midzone Supporting Evidence: PMID:18268101 Note that Borr is present in the nuclei of G2 spermatocytes but does not accumulate at the central spindle midzone of meiotic cells PMID:18268101 Borr transferred onto the forming central spindle MTs, concentrating on the central spindle midzone by late anaphase and telophase |
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Download this section (compressed HTML)Q: Does the Borr-Shrub interaction at the midbody inhibit Shrub polymerization in Drosophila cells, and is it required for the Aurora B abscission-delay function in germline stem cells?
Q: Is DNA binding by Borr required for CPC centromere targeting in vivo, or is targeting driven mainly by histone-mark recognition by Deterin?
Experiment: Map and mutate the Shrb-binding region of Borr, rescue borr mutants with the mutant protein, and assay midbody Shrb dynamics and abscission timing in S2 cells and germline stem cells.
Hypothesis: Borr-Shrub binding is required for abscission timing.
Type: structure-function rescue
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Download this section (compressed HTML)borealin-related (borr) encodes one of the three targeting subunits for the product of aurB in the chromosomal passenger complex. It helps to target the complex to the centromere region of chromosomes and the cleavage furrow during cytokinesis. At centromeres the complex is involved both in pausing mitotic progression when there are chromosome mis-attachments and in correcting those mis-attachments. At the cleavage furrow, the complex is involved in regulating the process of abscission (cell separation).
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