Inscuteable (Insc) is a Drosophila cytoskeletal adaptor/scaffold protein that couples apical-basal cell polarity to mitotic-spindle orientation during asymmetric cell division (ACD) in neural progenitors (neuroblasts) and sensory-organ precursors (pI cells). The protein has an N-terminal disordered region, a central ARM-like repeat region and a conserved Inscuteable C-terminal (Insc_C) domain, but no catalytic domain. Insc localizes to the apical cell cortex from interphase through metaphase, where it acts as a molecular bridge linking the Par complex (Bazooka/Par3-atypical PKC) to the Partner-of-Inscuteable (Pins/raps, the Drosophila LGN ortholog)-Galphai spindle-tethering machinery. Through this bridging activity Insc nucleates an apical protein complex that (i) orients and rotates the mitotic spindle along the apical-basal axis, (ii) directs apical localization of partner proteins, and (iii) is required for basal segregation of cell-fate determinants (Numb, Prospero, Miranda, Staufen) and prospero mRNA into the ganglion mother cell. Insc is thereby required for correct neuroblast sibling-cell fate specification, the glia-neuron cell-fate switch, and normal CNS and peripheral nervous system development; loss of insc (also known as nem) additionally perturbs somatic muscle and other precursor populations that rely on asymmetric division.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0045179 apical cortex | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation placing Insc at the apical cortex, the canonical site of Insc action, corroborated by multiple experimental IDA annotations. Reason: Insc apical-cortex localization is one of the best-established facts about the protein and is supported by several independent experimental papers as well as this phylogenetic inference. It represents a core aspect of Insc function. Supporting Evidence: PMID:11707517 The Inscuteable protein localizes to the apical cell cortex in neuroblasts from interphase to metaphase, but disappears in anaphase. |
| GO:0008093 cytoskeletal adaptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation of the core molecular function - Insc is a cytoskeletal adaptor that bridges the Par complex to the Pins/Galphai spindle machinery. Reason: This is the central molecular function of Insc and is directly supported by structural/biochemical work showing Insc is the adaptor bridging Par3 to the spindle-tethering machinery, consistent with the original genetic characterization of Insc as a candidate cytoskeleton adaptor protein. Supporting Evidence: PMID:22171003 the adaptor Inscuteable (Insc) bridges between Par3 and the spindle tethering machinery assembled on PMID:8626022 shows certain features common to a family of putative cytoskeletal associated proteins |
| GO:0009786 regulation of asymmetric cell division | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation that Insc functions in regulating asymmetric cell division - a core biological process for this gene. Reason: Insc is a canonical regulator of asymmetric cell division; loss of insc disrupts spindle orientation and basal determinant localization. Well supported phylogenetically and experimentally. Supporting Evidence: PMID:8779714 orientation of the mitotic spindle and correct localization of Numb and Prospero in these cells require the inscuteable gene |
| GO:0045176 apical protein localization | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) annotation that Insc functions in apical protein localization, consistent with its role in nucleating the apical complex. Reason: Insc directs apical localization of partner proteins and nucleates the apical complex; supported both phylogenetically and experimentally. Supporting Evidence: PMID:11707517 Inscuteable also directs asymmetric protein localization to the apical cell cortex during later stages of mitosis |
| GO:0008356 asymmetric cell division | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-to-GO (IEA) mapping from the Inscuteable InterPro signature to asymmetric cell division. Reason: The IEA maps the Inscuteable family signature (IPR039921) to asymmetric cell division, which is the defining biological role of this protein family. The term is slightly broader than the experimental annotations (e.g. asymmetric neuroblast division) but is a correct and appropriate parent-level mapping. Supporting Evidence: PMID:12526793 A complex of apically localized molecules mediates basal localization of cell fate determinants and apicobasal orientation of the mitotic spindle |
| GO:1990499 raps-insc complex | IDA PMID:22171003 Inscuteable and NuMA proteins bind competitively to Leu-Gly-... | ACCEPT | Summary: Insc is a subunit of the raps(Pins)-insc complex, demonstrated directly by the crystal structure of the Drosophila Pins TPR domain bound to the Insc peptide. Reason: Direct experimental (IDA) evidence, including a co-crystal structure, establishes Insc as part of the raps(Pins/LGN)-Insc complex (ComplexPortal CPX-3174). raps is the Drosophila LGN/Pins ortholog. This complex membership is a core structural feature underlying Insc adaptor function. Supporting Evidence: PMID:22171003 The crystal structure of the Drosophila ortholog of LGN (known as Pins) in complex with Insc reveals a modular interface contributed by evolutionary conserved residues |
| GO:0050829 defense response to Gram-negative bacterium | IMP PMID:19046341 Genetic analysis of Drosophila melanogaster susceptibility t... | KEEP AS NON CORE | Summary: An insc mutant showed increased susceptibility to intestinal Vibrio cholerae (a Gram-negative bacterium) in a genome-wide susceptibility screen, but the mechanism was explicitly uncharacterized. Reason: This IMP derives from a large forward-genetic V. cholerae susceptibility screen in which insc was one of many hits that increased susceptibility. The authors state the role of these proteins in immunity was not characterized, and any effect is plausibly indirect (e.g. via asymmetric division/renewal of gut epithelial cells). It is a legitimate experimental annotation but clearly peripheral and mechanistically unresolved, not a core Insc function; kept but marked non-core. Supporting Evidence: PMID:19046341 Inscuteable and Cyp6a20, both of which increased susceptibility to V. cholerae infection PMID:19046341 The role of these proteins in immunity to infection has not been characterized |
| GO:0007400 neuroblast fate determination | IDA PMID:19782677 On the roles of Notch, Delta, kuzbanian, and inscuteable dur... | KEEP AS NON CORE | Summary: Insc is required for correct sibling-cell fate specification during neuroblast lineage progression, acting through asymmetric cell division that feeds into differential Notch signalling. Reason: This annotation captures Insc's contribution to neuroblast-lineage fate decisions, which is a downstream consequence of its core asymmetric-division/spindle-orientation role rather than a direct determinant of neuroblast identity per se. The requirement is lineage- and stage-dependent. Kept as a valid but non-core developmental annotation. Supporting Evidence: PMID:19782677 Inscuteable plays a major role in controlling asymmetric cell division, which ultimately leads to differential activation of the Notch signalling pathway and correct specification of the two daughter cells PMID:19782677 three neuroblast lineages (NB1-1, NB4-2, and NB7-1) require insc function for sibling cell fate specification in cells born from early GMCs |
| GO:0061382 Malpighian tubule tip cell differentiation | IMP PMID:10625542 Multiple signalling pathways establish cell fate and cell nu... | KEEP AS NON CORE | Summary: Insc is implicated in the asymmetric division of the Malpighian tubule tip mother cell, consistent with insc expression in the Malpighian tubule primordium. Reason: The cited paper (an IMP by a FlyBase curator with access to the full text) dissects tip-cell fate via wingless/Notch/Numb; the cached abstract does not name insc, but insc is expressed in Malpighian tubules and the tip cell arises by an asymmetric (SOP-like) division that would use the Insc apical machinery. Not removed (experimental annotation, full text not available to verify); kept as a peripheral, tissue-specific developmental annotation. Supporting Evidence: PMID:8626022 whose expression is coincident with sites of cell shape changes or cell and tissue movement in the embryo, e.g., neuroblasts, trachea, Malphigian tubules PMID:10625542 Second, Notch signalling is restricted by the asymmetric segregation of Numb, as the tip mother cell divides |
| GO:0005515 protein binding | IPI PMID:11707517 Inscuteable-dependent apical localization of the microtubule... | MODIFY | Summary: Yeast two-hybrid/IPI evidence that Insc binds the coiled-coil microtubule-binding protein Cornetto (FBgn0259173). protein binding is uninformative and should be replaced by the specific partner-binding molecular function this interaction serves. Reason: Bare GO:0005515 protein binding conveys no functional information. The GOA WITH/FROM partner for this IPI is Cornetto (FBgn0259173), a coiled-coil cytoskeletal (microtubule-associated) protein, so the informative binding term is cytoskeletal protein binding (GO:0008092). This keeps the annotation faithful to the physical-interaction evidence; Insc's downstream cytoskeletal adaptor activity (GO:0008093) is separately captured by its IBA and IMP annotations. Proposed replacements: cytoskeletal protein binding Supporting Evidence: PMID:11707517 In a two-hybrid screen for Inscuteable-binding proteins, we have identified the coiled-coil protein Cornetto |
| GO:0045176 apical protein localization | IMP PMID:11707517 Inscuteable-dependent apical localization of the microtubule... | ACCEPT | Summary: Loss/perturbation of insc abolishes apical localization of the partner protein Cornetto, demonstrating an Insc requirement for apical protein localization. Reason: Direct genetic (IMP) evidence that Insc is required for apical protein localization (Cornetto forms an apical crescent in an inscuteable-dependent manner). This is a core Insc biological process. Supporting Evidence: PMID:11707517 forms an apical crescent during telophase in an inscuteable-dependent manner |
| GO:0045176 apical protein localization | IPI PMID:11707517 Inscuteable-dependent apical localization of the microtubule... | ACCEPT | Summary: Physical-interaction (IPI) support for Insc's role in apical protein localization, via its interaction with Cornetto. Reason: Duplicate GO term with IPI evidence linking the Insc-Cornetto interaction to apical protein localization; consistent with and reinforcing the IMP annotation. Retained as a valid core-process annotation. Supporting Evidence: PMID:11707517 Inscuteable also directs asymmetric protein localization to the apical cell cortex during later stages of mitosis |
| GO:0009786 regulation of asymmetric cell division | IMP PMID:19088087 Ancestry-independent fate specification and plasticity in th... | ACCEPT | Summary: Regulation of asymmetric cell division is a well-established core Insc function, though the cached text of the cited reference focuses on the T-box gene mid rather than insc. Reason: The term correctly captures a core Insc function. The GOA reference (PMID:19088087) is a study of mid/midline in the RP2/sib lineage; its cached abstract and text do not describe insc experiments, so its specific relevance to insc could not be verified here. Because the function itself is strongly supported by canonical primary studies, the term is accepted and supported by those references; the original citation is flagged as unverified in reference_review. Supporting Evidence: PMID:8779714 orientation of the mitotic spindle and correct localization of Numb and Prospero in these cells require the inscuteable gene PMID:12526793 A complex of apically localized molecules mediates basal localization of cell fate determinants and apicobasal orientation of the mitotic spindle |
| GO:0051960 regulation of nervous system development | IMP PMID:19088087 Ancestry-independent fate specification and plasticity in th... | KEEP AS NON CORE | Summary: A broad developmental term; Insc regulates nervous-system development indirectly by controlling asymmetric divisions that generate neuronal diversity. Reason: Regulation of nervous system development is a high-level, pleiotropic term that is a downstream consequence of Insc's core asymmetric-division role. As with the paired annotation, the cited reference (PMID:19088087) concerns mid and does not, in the cached text, document insc experiments. Kept as a valid but non-core developmental annotation; reference flagged as unverified. Supporting Evidence: PMID:19782677 Inscuteable plays a major role in controlling asymmetric cell division, which ultimately leads to differential activation of the Notch signalling pathway and correct specification of the two daughter cells |
| GO:0045179 apical cortex | IDA PMID:9888987 Identification of Miranda protein domains regulating asymmet... | ACCEPT | Summary: Direct localization evidence placing Inscuteable at the apical cortex of interphase neuroblasts, among the asymmetrically localized apical proteins. Reason: IDA localization to the apical cortex, a core and repeatedly confirmed aspect of Insc cell biology. Supporting Evidence: PMID:9888987 All of these factors are apically localized during interphase, and all except Inscuteable move to the basal cortex at mitosis |
| GO:0045179 apical cortex | IDA PMID:17726110 Galphai generates multiple Pins activation states to link co... | ACCEPT | Summary: Insc is recruited to the apical cortex by Pins/Galphai (a Mud-independent Pins function), placing Insc at the apical cortex. Reason: IDA apical-cortex localization; this study shows Galphai-bound Pins recruits Insc to the apical cortex, reinforcing the core localization and the Insc-Pins relationship. Supporting Evidence: PMID:17726110 recruitment of Insc to the apical cortex |
| GO:0045179 apical cortex | IDA PMID:16377571 Microtubule-induced Pins/Galphai cortical polarity in Drosop... | ACCEPT | Summary: Insc/Par apical-cortex localization; the Inscuteable/Par pathway coordinates neuroblast cortical polarity with tissue polarity from prophase. Reason: IDA supporting apical-cortex localization of Insc as part of the Insc/Par pathway. Core localization. Supporting Evidence: PMID:16377571 The Inscuteable/Par pathway initiates at prophase to coordinate neuroblast cortical polarity with CNS tissue polarity |
| GO:0055059 asymmetric neuroblast division | IGI PMID:12526793 Apical complex genes control mitotic spindle geometry and re... | ACCEPT | Summary: Genetic-interaction evidence that insc, as an apical-complex gene, controls mitotic spindle geometry and daughter-cell size during asymmetric neuroblast (and pI) divisions. Reason: Asymmetric neuroblast division is the defining core biological process of Insc. IGI evidence with apical-complex partners (Bazooka/aPKC and Pins/Galphai pathways) supports this directly. Supporting Evidence: PMID:12526793 mitotic spindle geometry and unequal daughter cell size are controlled by two parallel pathways (Bazooka/DaPKC and Pins/G alpha i) within the apical complex |
| GO:0005737 cytoplasm | IDA PMID:9267024 Inscuteable and Staufen mediate asymmetric localization and ... | KEEP AS NON CORE | Summary: Insc detected in the cytoplasm; a broad, non-specific localization relative to its functional apical-cortex site. Reason: Cytoplasm is a correct but uninformative localization. Insc's functionally relevant location is the apical cell cortex; a diffuse cytoplasmic pool (e.g. before cortical recruitment) does not represent a core functional site. Retained but marked non-core. Supporting Evidence: PMID:9267024 Inscuteable and Staufen interact and colocalize with prospero RNA on the apical cortex of interphase neuroblasts |
| GO:0005938 cell cortex | IDA PMID:10903176 Mechanism of glia-neuron cell-fate switch in the Drosophila ... | ACCEPT | Summary: Cell-cortex localization of Insc in the NB6-4T lineage, where insc is required for the correct glia-neuron fate switch. Cell cortex is the parent of the more specific apical cortex. Reason: Cell cortex is a correct (if broader) localization consistent with the canonical apical-cortex annotations. The study also documents insc requirement for the NB6-4T asymmetric division outcome, supporting Insc cortical function in this lineage. Supporting Evidence: PMID:10903176 miranda and inscuteable mutations altered the behavior of Pros, resulting in failure to correctly switch the glial and neuronal fates |
| GO:0006403 RNA localization | IMP PMID:9267024 Inscuteable and Staufen mediate asymmetric localization and ... | KEEP AS NON CORE | Summary: Insc is required for apical localization of prospero mRNA, acting upstream by nucleating the apical complex that (via Staufen) localizes the RNA. Reason: Insc's effect on RNA (prospero mRNA) localization is an indirect, downstream consequence of its scaffold/adaptor role - Insc nucleates the apical complex and Staufen mediates the actual RNA localization. A valid experimental annotation but not a core Insc molecular activity; the general RNA localization term could also be refined toward intracellular mRNA localization. Kept as non-core. Supporting Evidence: PMID:9267024 Inscuteable nucleates an apical complex and is required for protein localization, spindle orientation, and RNA localization |
| GO:0007422 peripheral nervous system development | IMP PMID:7615665 The mutant not enough muscles (nem) reveals reduction of the... | KEEP AS NON CORE | Summary: The insc allele nem shows peripheral nervous system defects (chordotonal organs), indicating a requirement in PNS development. Reason: The nem mutation is an allele of insc (UniProt/FlyBase synonym). Its PNS (chordotonal organ) defects reflect Insc's requirement in the asymmetric divisions that build sensory lineages - a genuine but pleiotropic developmental role, kept non-core relative to the core ACD/spindle-orientation function. Supporting Evidence: PMID:7615665 it may be required for the development of the somatic musculature and the chordotonal organs of the PNS |
| GO:0007423 sensory organ development | TAS PMID:10973066 Genetics of heart development. | KEEP AS NON CORE | Summary: Insc functions in sensory-organ development through asymmetric divisions of sensory-organ precursors (pI cells). NOTE - the GOA reference for this TAS appears to be a mis-citation. Reason: Sensory-organ development is a real Insc-associated process (Insc/apical-complex genes control pI/SOP asymmetric divisions). However, the cited reference PMID:10973066 is a review titled Genetics of heart development whose abstract concerns cardiac development and does not mention insc or sensory organs - it looks like a wrong/mis-applied citation. The term is retained (non-core) and supported by an appropriate primary reference; the original citation is flagged in reference_review. Supporting Evidence: PMID:12526793 In sensory organ precursors, Bazooka/DaPKC and Pins/G alpha i localize to opposite sides of the cortex |
| GO:0007525 somatic muscle development | IMP PMID:7615665 The mutant not enough muscles (nem) reveals reduction of the... | KEEP AS NON CORE | Summary: The insc allele nem shows reduced/disrupted somatic musculature, indicating a requirement (likely indirect) in somatic muscle development. Reason: nem is an allele of insc; nem mutants show partial absence of somatic muscles and unfused myoblasts. This is a genuine experimental phenotype but is peripheral and probably an indirect consequence of defective asymmetric divisions/precursor specification, not a core Insc molecular role. Kept non-core. Supporting Evidence: PMID:7615665 it may be required for the development of the somatic musculature and the chordotonal organs of the PNS |
| GO:0008093 cytoskeletal adaptor activity | IMP PMID:8626022 inscuteable, a neural precursor gene of Drosophila, encodes ... | ACCEPT | Summary: Original genetic/molecular characterization of insc as encoding a candidate cytoskeleton adaptor protein localized to the apical submembranous cortex. Reason: This is the founding experimental support for the core molecular function. The protein was identified as a candidate cytoskeleton adaptor, apically localized, with a mutant phenotype consistent with a role in cytoskeleton organization - later refined to the Par3-Pins bridging adaptor activity. Supporting Evidence: PMID:8626022 The Inscuteable protein is localized to the apical submembranous surface of neuroblasts and other cell types and shows certain features common to a family of putative cytoskeletal associated proteins |
| GO:0008104 intracellular protein localization | IMP PMID:8779714 Role of inscuteable in orienting asymmetric cell divisions i... | KEEP AS NON CORE | Summary: Insc is required for correct intracellular localization of cell-fate determinants (Numb and Prospero) to the basal cortex during asymmetric division. Reason: This broad term captures Insc's requirement for basal segregation of determinants (Numb, Prospero), complementary to the apical-protein-localization annotations. It is correct but general; retained as a non-core annotation because the more specific apical-localization and asymmetric-division terms better represent the core function. Supporting Evidence: PMID:8779714 orientation of the mitotic spindle and correct localization of Numb and Prospero in these cells require the inscuteable gene |
| GO:0040001 establishment of mitotic spindle localization | IMP PMID:10620800 Rotation and asymmetry of the mitotic spindle direct asymmet... | MODIFY | Summary: Insc is required for correct positioning/orientation of the mitotic spindle; the more precise term for the Insc phenotype is establishment of mitotic spindle orientation. Reason: The canonical, repeatedly demonstrated Insc phenotype is misorientation of the mitotic spindle relative to the apical-basal polarity axis (spindle rotation fails / spindle not aligned), which is precisely captured by GO:0000132 establishment of mitotic spindle orientation rather than the more generic GO:0040001 establishment of mitotic spindle localization. This study documents neuroblast spindle rotation that is disrupted when the apical machinery is impaired. Proposed replacements: establishment of mitotic spindle orientation Supporting Evidence: PMID:10620800 neuroblast spindles are initially formed in the same axis as epidermal cells, but rotate before cell division |
| GO:0040001 establishment of mitotic spindle localization | IMP PMID:8779714 Role of inscuteable in orienting asymmetric cell divisions i... | MODIFY | Summary: Insc is genetically required to orient the mitotic spindle; ectopic Insc reorients spindles. Best captured by establishment of mitotic spindle orientation. Reason: Direct genetic evidence that spindle orientation requires insc and that ectopic insc reorients spindles - this is spindle orientation, more accurately GO:0000132 establishment of mitotic spindle orientation than the generic GO:0040001 spindle localization term. Proposed replacements: establishment of mitotic spindle orientation Supporting Evidence: PMID:8779714 ectopic expression of inscuteable in other epithelial cells leads to spindle reorientation |
| GO:0045179 apical cortex | IDA PMID:8779714 Role of inscuteable in orienting asymmetric cell divisions i... | ACCEPT | Summary: Insc localizes to the apical cell cortex before mitosis, establishing polarity for asymmetric division. Reason: IDA apical-cortex localization from the foundational functional study; core localization. Supporting Evidence: PMID:8779714 The Inscuteable protein localizes to the apical cell cortex before mitosis, suggesting that Inscuteable functions in establishing polarity for asymmetric cell division |
| GO:0045179 apical cortex | IDA PMID:9267024 Inscuteable and Staufen mediate asymmetric localization and ... | ACCEPT | Summary: Insc localizes to (and nucleates an apical complex at) the apical cortex of interphase neuroblasts, colocalizing with Staufen and prospero RNA. Reason: IDA apical-cortex localization; Insc colocalizes with Staufen/prospero RNA apically and nucleates the apical complex there. Core localization. Supporting Evidence: PMID:9267024 Inscuteable and Staufen interact and colocalize with prospero RNA on the apical cortex of interphase neuroblasts |
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Download this section (compressed HTML)Q: What is the direct mechanistic basis for the insc mutant susceptibility to intestinal Vibrio cholerae infection (PMID:19046341) - is it an indirect consequence of altered asymmetric division/renewal in the gut epithelium, or a distinct role?
Q: Are the somatic-muscle and Malpighian-tubule phenotypes of insc(nem) direct requirements for Insc in those precursor divisions, or secondary to CNS/PNS defects?
Experiment: Generate structure-guided separation-of-function alleles disrupting the Insc-Par3 versus Insc-Pins interfaces and assay each for apical complex assembly, spindle orientation, and basal determinant segregation in neuroblasts.
Hypothesis: The Insc-Par3 and Insc-Pins interactions are separable arms of a single adaptor bridge, each required for a distinct step of asymmetric division.
Type: structure-function mutagenesis and in vivo imaging
Experiment: Perform tissue-specific insc knockdown in adult intestinal stem cells during V. cholerae challenge and score epithelial integrity, cell death, and survival.
Hypothesis: The infection-susceptibility phenotype reflects an insc requirement in asymmetric division/renewal of the adult gut epithelium rather than a direct immune function.
Type: conditional RNAi and infection assay
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