GPR-1 (G protein regulator 1) is a TPR-GoLoco protein of the AGS3/LGN/Pins family that acts, together with its near-identical paralog GPR-2, in the early C. elegans embryo. Its single C-terminal GoLoco motif binds GDP-bound G-alpha(i/o) subunits GOA-1 and GPA-16 and acts as a guanine nucleotide dissociation inhibitor. At the cell cortex GPR-1/2 forms a ternary complex with G-alpha and the NuMA-related coiled-coil protein LIN-5 that anchors dynein and generates pulling forces on astral microtubules. PAR polarity cues (via LET-99, CSNK-1 and PIP2 synthesis by PPK-1) make GPR-1/2 cortical levels asymmetric, so that greater posterior pulling force drives nuclear centration and rotation, anaphase spindle elongation and posterior spindle displacement, producing the unequal first division. GPR-1/2 also localizes to the spindle and asters, and in later divisions (P1, EMS/P2) its cortical distribution helps orient the spindle.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000022 mitotic spindle elongation | NAS PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | KEEP AS NON CORE | Summary: GPR-1/2 is required for the asymmetric elongation of the anaphase spindle in P-lineage divisions; cortical pulling forces generated by the Galpha-GPR-1/2-LIN-5 complex contribute to spindle elongation. Reason: Supported by Tsou et al. 2003 and Krueger et al. 2010; GPR-1/2 is part of the force generator that pulls on spindle poles, so it does part of the work. Spindle elongation is one readout of the broader spindle-positioning role, which is the core process. Supporting Evidence: PMID:14534135 function together with Galpha (GOA-1 and GPA-16) to generate asymmetric spindle pole elongation during divisions in the P lineage PMID:20421425 resulting in a higher net force toward the posterior that contributes to spindle elongation and displacement |
| GO:0001965 G-protein alpha-subunit binding | IPI PMID:12750478 Translation of polarity cues into asymmetric spindle positio... | ACCEPT | Summary: GPR-1/2 binds GDP-bound GOA-1 through its GoLoco motif, the interaction that underlies its GDI activity. Reason: Direct binding to GDP-GOA-1 shown by Colombo et al. 2003 and in several independent studies; the interaction is abolished by the GoLoco-insensitive GOA-1 mutation (PMID:18984596). Supporting Evidence: PMID:12750478 GPR-1/2 interacted with guanosine diphosphate-bound GOA-1 PMID:18984596 abrogated interaction between the Caenorhabditis elegans Galpha subunit GOA-1 and the GPR-1 GoLoco motif |
| GO:0005092 GDP-dissociation inhibitor activity | IDA PMID:16162648 Cortical localization of the Galpha protein GPA-16 requires ... | ACCEPT | Summary: Nucleotide exchange assays show that GPR-1/2 is a GDI for GPA-16 as well as GOA-1. Reason: Direct biochemical evidence; the GoLoco GDI activity is the core molecular function of GPR-1/2. Supporting Evidence: PMID:16162648 GPR-1/2 acts as a guanine nucleotide dissociation inhibitor (GDI) for GPA-16, as it does for GOA-1 PMID:12814548 the GPR domain of GPR-1 and GPR-2 behaves as a GDP dissociation inhibitor for GOA-1 |
| GO:0005092 GDP-dissociation inhibitor activity | IDA PMID:18984596 A point mutation to Galphai selectively blocks GoLoco motif ... | ACCEPT | Summary: A GPR-1/2 GoLoco peptide (aa 423-461) shows GDI activity on wild-type GOA-1 that is lost on the GoLoco-insensitive GOA-1(N150I) mutant. Reason: Full text confirms the GDI assay on GOA-1 with the GPR-1/2 GoLoco peptide; consistent with the other IDA row. Supporting Evidence: PMID:18984596 we verified that GOA-1(N150I) is indeed resistant to GoLoco motif-mediated GDI activity |
| GO:0005515 protein binding | IPI PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | REMOVE | Summary: Interaction with LIN-5, the NuMA-related coiled-coil partner of GPR-1/2 in the cortical force generator. Reason: Bare protein binding is uninformative under the protein-binding policy. The LIN-5 interaction is real and functionally important; it is captured in core_functions as part of the cortical Galpha-GPR-1/2-LIN-5 complex. Supporting Evidence: PMID:12730122 which associate with LIN-5 in vivo and in vitro and depend on LIN-5 for localization to the spindle and cell cortex |
| GO:0005515 protein binding | IPI PMID:16162648 Cortical localization of the Galpha protein GPA-16 requires ... | REMOVE | Summary: Co-immunoprecipitation and SPR binding of GPR-1/2 to the Galpha GPA-16. Reason: Bare protein binding is uninformative; this interaction is already captured more informatively by G-protein alpha-subunit binding (GO:0001965) and GDI activity (GO:0005092). Supporting Evidence: PMID:16162648 we find that GPA-16 associates with RIC-8 and GPR-1/2 |
| GO:0005515 protein binding | IPI PMID:19123269 Empirically controlled mapping of the Caenorhabditis elegans... | REMOVE | Summary: High-throughput yeast two-hybrid interaction with KXD-1 (WI-2007 interactome). Reason: Bare protein binding from a large-scale Y2H screen; uninformative and with no known functional connection to spindle positioning. |
| GO:0005818 aster | IDA PMID:14534135 LET-99 opposes Galpha/GPR signaling to generate asymmetry fo... | KEEP AS NON CORE | Summary: Immunostaining in Tsou et al. 2003 (abstract only cached) reported GPR-1/2 on asters in addition to the cortex; UniProt also records spindle localization from Srinivasan et al. 2003. Reason: Experimental localization by curators who read the full text; plausible given LIN-5-dependent spindle/aster localization. The functionally relevant pool is cortical, so this is non-core. |
| GO:0005819 spindle | IEA GO_REF:0000044 | MODIFY | Summary: Electronic mapping from the UniProt subcellular location "Cytoskeleton, spindle", which rests on Srinivasan et al. 2003. Reason: Correct but general; the observation is on the mitotic spindle of embryonic divisions, already captured by the IDA row for mitotic spindle (GO:0072686). Proposed replacements: mitotic spindle Supporting Evidence: PMID:12730122 depend on LIN-5 for localization to the spindle and cell cortex |
| GO:0005938 cell cortex | IDA PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | ACCEPT | Summary: GPR-1/2 localizes to the cell cortex in a LIN-5-dependent manner. Reason: The cortex is where GPR-1/2 performs its core function as part of the force generator. Supporting Evidence: PMID:12730122 depend on LIN-5 for localization to the spindle and cell cortex |
| GO:0005938 cell cortex | IDA PMID:14534135 LET-99 opposes Galpha/GPR signaling to generate asymmetry fo... | ACCEPT | Summary: Asymmetric cortical localization of GPR-1/2 in dividing P cells, regulated by PAR-3 and LET-99. Reason: Independent experimental support for cortical localization, the site of the core function. Supporting Evidence: PMID:14534135 the cortical localization of GPR-1/2 is asymmetric in dividing P cells |
| GO:0005938 cell cortex | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic mapping from the UniProt subcellular location "Cytoplasm, cell cortex", which is itself based on the experimental papers above. Reason: Consistent with the IDA rows; the cell cortex is the core location. Supporting Evidence: PMID:12814548 The GPR protein(s) localize around the cortex of one-cell embryos and are enriched at the posterior |
| GO:0007097 nuclear migration | NAS PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | KEEP AS NON CORE | Summary: GPR-1/2 is required for normal rates of pronuclear-centrosome complex centration and rotation, during which it is enriched at the anterior cortex. Reason: Park and Rose 2008 show that GPR-1/2 depletion decreases centration and rotation rates, attributed to cortical force generation; Tsou et al. 2003 show Galpha/GPR are needed for nuclear rotation. The nucleus is moved by the same cortical pulling mechanism, so this is a genuine but secondary readout. Supporting Evidence: PMID:18234174 The depletion of LIN-5 or GPR-1/2 results in decreased centration and rotation rates, indicating a role in force generation at this stage |
| GO:0008277 regulation of G protein-coupled receptor signaling pathway | NAS PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | MARK AS OVER ANNOTATED | Summary: GPR-1/2 regulate Galpha (GOA-1, GPA-16) in a receptor-independent pathway for spindle positioning; no seven-transmembrane receptor is involved. Reason: The GO term describes regulation of signalling initiated by a GPCR. The G protein signalling that GPR-1/2 regulate in the embryo is explicitly receptor-independent, so the term misrepresents the pathway. The molecular regulation of Galpha is captured by GDI activity. Supporting Evidence: PMID:12814548 Here we show that the Galpha subunits are regulated by a receptor-independent mechanism PMID:12730122 Results in C. elegans and other species are consistent with a novel model for receptor-independent activation of Galpha(i/o) signaling |
| GO:0030695 GTPase regulator activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the GoLoco motif (IPR003109). Reason: Correct but general. The GoLoco motif of GPR-1/2 has demonstrated GDI activity toward GOA-1 and GPA-16, so the specific child term GDP-dissociation inhibitor activity (GO:0005092), which the gene already carries by IDA, should replace it. Proposed replacements: GDP-dissociation inhibitor activity Supporting Evidence: PMID:12814548 the GPR domain of GPR-1 and GPR-2 behaves as a GDP dissociation inhibitor for GOA-1 |
| GO:0040001 establishment of mitotic spindle localization | NAS PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | ACCEPT | Summary: GPR-1/2, with Galpha and LIN-5, generate the cortical pulling forces that displace the mitotic spindle posteriorly in the one-cell embryo. Reason: Core biological process. GPR-1/2 is a component of the cortical force generator (Galpha-GPR-1/2-LIN-5 anchoring dynein), so it does part of the work of positioning the spindle; supported by many independent studies beyond the NAS source. Supporting Evidence: PMID:12750478 were essential for generation of proper pulling forces PMID:17922003 the LIN-5, GPR-1/2 and the G alpha proteins promote the presence of the dynein complex at the cell cortex PMID:25548889 a ternary complex comprised of GΞ± (GOA-1/GPA-16), GPR-1/GPR-2, and LIN-5 is essential for anchoring the motor protein dynein to the cell cortex |
| GO:0072686 mitotic spindle | IDA PMID:12730122 A complex of LIN-5 and GPR proteins regulates G protein sign... | KEEP AS NON CORE | Summary: GPR-1/2 is detected on the mitotic spindle, dependent on LIN-5. Reason: Experimental localization; the force-generating function is exerted at the cortex, so the spindle pool is peripheral. Supporting Evidence: PMID:12730122 depend on LIN-5 for localization to the spindle and cell cortex |
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Download this section (compressed HTML)Q: Do GPR-1 and GPR-2 have any non-redundant functions, given that RNAi and antibodies used in all studies to date target both near-identical paralogs?
Q: Is the force-generating species the G-alpha-GDP-GPR-1/2 complex (GDI model) or G-alpha-GTP produced by RIC-8 acting on that complex?
Q: Should GPR-1/2 carry establishment of mitotic spindle orientation (GO:0000132) for the EMS and P2 divisions, where its asymmetric cortical distribution orients the spindle (Werts et al. 2011, PMID:21903670)?
Experiment: Make gpr-1-specific and gpr-2-specific CRISPR null alleles and endogenous tags, and measure spindle pulling forces by spindle severing in each single and the double mutant.
Hypothesis: GPR-1 and GPR-2 are functionally redundant and dose-additive for cortical pulling force.
Experiment: Replace endogenous GPR-1/2 with a GoLoco point mutant that cannot bind G-alpha-GDP (or express GLi GOA-1/GPA-16) and measure cortical LIN-5/dynein recruitment and pulling forces.
Hypothesis: Direct GoLoco-G-alpha binding is required for cortical recruitment of LIN-5 and dynein, not only for G-alpha regulation.
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