2000A: RIC-8 and GOA-1 (Go) Regulate Centrosome Movements in Young Embryos
While making goa-1; ric-8 double mutants for analysis of RIC-8's function in the nervous system, we found that the progeny of goa-1/+; ric-8/ ric-8 mutants exhibited close to 100% embryonic lethality. We then found partial embryonic lethality in ric-8 single mutants (29%) and goa-1 single mutants (11%). A study from Ron Plasterk's lab had previously found high rates of embryonic lethality in gpb-1 (G beta) single mutants, and they subsequently observed defects in mitotic spindle alignment during early embryogenesis. However, although G beta proteins usually function in conjunction with a G alpha subunit, no G alpha protein had yet been identified that regulated mitotic spindle alignments.
We decided to determine if GOA-1 (Go) was the missing piece of this puzzle. To do this, we sliced open gravid adults with a razor blade, squeezed out the recently fertilized embryos/ eggs, quickly mounted them on slides and watched as they developed from just after fertilization to about the 8-cell stage (about 30 min) using high resolution Nomarski Microscopy. The C. elegans embryo is a beautiful system for watching cell biology in action because, without any staining, you can see the dynamic movements of nuclei, centrosomes, and mitotic spindles in real time as the embryo develops. I didn't have a digital camera at that point, so I used Kodak Tmax 400 ASA film along with a timer so I could record the precise times after the first cleavage that each event took place.
We decided to determine if GOA-1 (Go) was the missing piece of this puzzle. To do this, we sliced open gravid adults with a razor blade, squeezed out the recently fertilized embryos/ eggs, quickly mounted them on slides and watched as they developed from just after fertilization to about the 8-cell stage (about 30 min) using high resolution Nomarski Microscopy. The C. elegans embryo is a beautiful system for watching cell biology in action because, without any staining, you can see the dynamic movements of nuclei, centrosomes, and mitotic spindles in real time as the embryo develops. I didn't have a digital camera at that point, so I used Kodak Tmax 400 ASA film along with a timer so I could record the precise times after the first cleavage that each event took place.
Each cell in young zygote has a name and a position. The first cell, P0, divides along its anterior-posterior axis to form AB and P1. AB then divides along its dorsal-ventral axis to form ABa and ABp, and P1 divides along its anterior-posterior axis to form EMS and P2.
Before each cell divides, tiny organelles known as centrosomes divide and migrate to opposite sides of the nuclear membrane. The 2 points at which they come to rest determines the cleavage plane for that cell's division because the "microtubules" that pull the replicated chromosomes to each side of the cell grow out from each centrosome, and then cleavage of the cell occurs perpendicular through the mitotic spindle. In general, ric-8 and goa-1 mutants were defective in a subset of centrosome movements and shape changes, with some cells and centrosome movements being more affected than others. The most obvious centrosome movement defect resulted from the centrosomes not migrating to their proper position before the mitotic spindle began to form. This resulted in spindle misalignments, These were the likely cause of the embryonic lethality because, in the more extreme cases, they result in a completely disorganized mass of cells. We found that the spindles of AB, P1, ABa, and ABp were misaligned in 30 - 50% of ric-8 single mutant embryos and 66 - 100% of goa-1/+; ric-8/ric-8 embryos. A more subtle centrosome movement defect we observed was defective P1 centrosome flattening. In wild type, the centrosome inherited by the P1 cell forms as flat disk, as opposed to spherical shape of centrosome in its sister AB cell. Embryos derived from ric-8 and goa-1 mutants had spherical P1 centrosomes. We also noticed that each cell's nucleus seemed to undergo a stereotyped series of movements that positioned it optimally for the next cell division. This is likely to be important due to the large size of the early embryonic cells, but may be less important as cell sizes become smaller in more mature embryos. The nuclear movements also appear linked to centrosome movements. Each nucleus is born with a single centrosome, inherited from its parent cell, which is attached to its membrane at a location perpendicular to the cleavage plane. The centrosome appears to "drag" the new nucleus to a specific location. Upon coming to rest, the centrosome replicates and the daughter centrosomes migrate to opposite sides of the nuclear membrane to set up the next cleavage plane. We documented an intricate and invariant series of nuclear movements in 2-cell and 4-cell wild type embryos. However, in ric-8 and goa-1 mutant embryos, the nuclei remain near their points of origin for abnormally long times before slowly migrating outward, and often do not reach the same locations as wild type nuclei. Using immunostaining, we found that GOA-1 (Go) localized to the cell membranes, with fainter clouds of staining at the centrosomes, consistent with G protein signaling occurring at centrosomes. |
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Miller KG and Rand JB (2000). A role for RIC-8 (Synembryn) and GOA-1 (Gao) in regulating a subset of centrosome movements during early embryogenesis in Caenorhabditis elegans. Genetics 156(4), 1649-1660. PMCID: PMC1461398.
cited by 88 papers as of April, 2018
cited by 88 papers as of April, 2018
Related Studies
In the same year, we showed that RIC-8 is required for the (GOA-1) Go signaling in the nervous system. In the nervous system ric-8 and goa-1 mutants have opposite phenotypes, whereas in the young embryo, ric-8 and goa-1 mutants have the same phenotypes. One possible explanation is the RIC-8 positively regulates both GOA-1 and EGL-30 signaling in the nervous system; however, because EGL-30 acts downstream of GOA-1 in the nervous system, reducing RIC-8's function results in an egl-30 - like phenotype rather than a goa-1 - like phenotype. In the embryo, where EGL-30 (Gq) does not play a role, reducing RIC-8's function results in a goa-1 - like phenotype.
Miller KG, Emerson MD, McManus JB, and Rand JR (2000). RIC-8 (Synembryn): A novel conserved protein that is required for Gqa signaling in the C. elegans nervous system. Neuron 27(2), 289-299. PMID: 10985349. See Adventures > 1996-2000.
Prior to our study, a pioneering Cell paper from Ron Plasterk's lab provided the first evidence that G proteins were involved in mitotic spindle alignments during early embryogenesis by showing that GPB-1 (G beta) mutants had embryonic lethality and mitotic spindle misalignments. However, the G alpha subunit is thought to be the main signaling switch of G protein pathways, and no study prior to ours had identified a G alpha protein involved in mitotic spindle alignment. In addition to being the first study to show that the newly discovered RIC-8 protein was also required for the function of this pathway, our study was also the first to generalize the G protein pathway function in the early embryo by noting that all G alpha pathway functions could be described in terms of regulation of centrosome movements. We did this by showing that the G alpha signaling pathway regulates one-cell posterior centrosome rocking, P1 centrosome flattening, and nuclear migration in addition to the centrosome movements that determine mitotic spindle alignments.
Zwaal, R. R., J. Ahringer, H. G. A. M. van Luenen, A. Rushforth, P. Anderson et al., 1996 G proteins are required for spatial orientation of early cell cleavages in C. elegans embryos. Cell 86: 619-629.
While our Genetics paper was out for review, two papers were published in Cell and Current Biology showing that a protein called Pins (Partner of Inscuteable) was required for mitotic spindle alignment in Drosophila neuroblasts and that a protein identified as either Go or Gi physically interacts with Pins. However, a requirement for the unidentified G alpha protein, or any G alpha protein, in mitotic spindle alignment was not demonstrated until our study.
Schaefer, M., Shevchenko, A., Shevchenko, A., and Knoblich, J.A. (2000). A protein complex containing Inscuteable and the Galpha-binding protein Pins orients asymmetric cell divisions in Drosophila. Curr Biol 10, 353-362.
Yu, F., Morin, X., Cai, Y., Yang, X., and Chia, W. (2000). Analysis of partner of inscuteable, a novel player of Drosophila asymmetric divisions, reveals two distinct steps in inscuteable apical localization. Cell 100, 399-409.
Three months after our Genetics paper was published, Julie Ahringer's lab at Cambridge published a Nature Cell Biology paper that also identified GOA-1 (Go) as the relevant G alpha subunit for centrosome movements during early embryogenesis. Although they did not investigate the role of the newly discovered RIC-8 protein like we did, their paper broke new ground by showing that another closely related G alpha protein, GPA-16, acts redundantly with GOA-1. This nicely explained our finding that embryonic lethality was only 11% in goa-1 null mutants, but 100% in goa-1+; ric-8/ric-8 mutants. Their paper also confirmed our immunolocalization of GOA-1 (Go), our finding that PAR polarity is not disrupted in G protein signaling mutants, and our findings that one-cell posterior centrosome rocking, P1, centrosome flattening, and nuclear migration are also disrupted in the G protein signaling mutants. Interestingly, and perhaps mistakenly, I had tipped off their lead author, Monica Gotta, about all of these phenotypes months before our paper was published, and our paper was not cited by them. Their paper also claimed evidence that the G alpha phenotypes were caused by excess G beta gamma activity, and this conclusion contributed to the paper's title. However, they did not provide a strong genetic test of that hypothesis and, in a 2005 review by the lead author, that early hypothesis was not even mentioned as a possibility.
Gotta, M., and Ahringer, J. (2001). Distinct roles for G alpa and G beta gamma in regulating spindle position and orientation in Caenorhabditis elegans. Nature Cell Biology 3, 297-300.
Bellaiche, Y., and Gotta, M. (2005). Heterotrimeric G proteins and regulation of size asymmetry during cell division. Curr Opin Cell Biol 17, 658-663. [Review]
A year after our paper was published, Juergen Knoblich's group published a Cell paper identifying the relevant Drosophila G protein as Gi (a protein closely related to Go) and confirmed that reducing its function caused defects in mitotic spindle alignments in neuroblasts and sensory organ precursor cells. This paper was also the first to propose that Pins could be a receptor-independent activator of Go.
Schaefer, M., Petronczki, M., Dorner, D., Forte, M., and Knoblich, J.A. (2001). Heterotrimeric G proteins direct two modes of asymmetric cell division in the Drosophila nervous system. Cell 107, 183-194.
Over the next 4 years, this little field treally exploded, with many papers confirming our foundational work and identifying other components in the embryonic G protein pathway.
In 2003, 3 studies from the labs of Pierre Gonczy, Sander van den Heuvel, and Julie Ahringer's lab showed that GPR-1 and GPR-2, which are the C. elegans homologs of Pins, function in the same pathway as GOA-1 (Go) and are enriched at the posterior membrane of the one-cell embryo, suggesting that they could be involved in the positional activation of the GOA-1 (Go) pathway.
Colombo, K., Grill, S.W., Kimple, R.J., Willard, F.S., Siderovski, D.P., and Gonczy, P. (2003). Translation of polarity cues into asymmetric spindle positioning in Caenorhabditis elegans embryos. Science 300, 1957-1961.
Gotta, M., Dong, Y., Peterson, Y.K., Lanier, S.M., and Ahringer, J. (2003). Asymmetrically distributed C. elegans homologs of AGS3/PINS control spindle position in the early embryo. Curr Biol 13, 1029-1037.
Srinivasan, D.G., Fisk, R.M., Xu, H., and van den Heuvel, S. (2003). A complex of LIN-5 and GPR proteins regulates G protein signaling and spindle function in C elegans. Genes Dev 17, 1225-1239.
In 2003, Greg Tall in Al Gilman's lab published his paper showing that mouse RIC-8 could act as a GDP-GTP exchange factor (a "GEF") for G alpha proteins and proposed that it could contribute to "receptor-independent" activation of G alpha proteins. However, Greg and others later showed that RIC-8 can also function as a molecular chaperone for G protein alpha subunits that is necessary for G alpha stability. It is still not clear whether RIC-8 functions mainly as a chaperone, or whether it can also function as a receptor-independent GEF in some contexts.
Tall, G. G.. Ric-8 Regulation of Heterotrimeric G Proteins. 2013. J Recept Signal Transduct Res. 33(3): 139-143 [Excellent review of Ric-8]
In 2004, 3 groups published papers in Cell and Current Biology that basically confirmed our results published in our 2000 Genetics paper that ric-8 mutants have defects in centrosome movements during early embryogenesis and that further confirmed Greg Tall's results that RIC-8 directly interacts with G alpha proteins and stimulates GDP-GTP exchange. The paper from Michael Koelle's group further identified RGS-7 as the relevant RGS protein (GTPase activating protein) for Go during early embryogenesis.
Afshar, K., Willard, F.S., Colombo, K., Johnston, C.A., McCudden, C.R., Siderovski, D.P., and Gonczy, P. (2004). RIC-8 is required for GPR-1/2-dependent Ga function during asymmetric division of C. elegans embryos. Cell 119, 219-230.
Couwenbergs, C., Spilker, A.C., and Gotta, M. (2004). Control of embryonic spindle positioning and Ga activity by C. elegans RIC-8. Curr Biol 14, 1871-1876.
Hess, H.A., Roper, J.C., Grill, S.W., and Koelle, M.R. (2004). RGS-7 completes a receptor-independent heterotrimeric G protein cycle to asymmetrically regulate mitotic spindle positioning in C. elegans. Cell 119, 209-218.
In 2005, three Drosophila groups caught up with C. elegans researchers and published 3 papers in Nature Cell Biology confirming that RIC-8 and Gi/o are also required for the orientation and positioning of mitotic spindles (and the centrosomes from which they grow) during asymmetric cell divisions of neural progenitors (neuroblasts) and sensory precursor cells in Drosophila embryos. Further emphasizing the fundamental roles of RIC-8 and Gi/o in guiding centrosome movements throughout the animal kingdom, Greg Tall in Al Gilman's lab also demonstrated similar biochemical interactions using the mammalian orthologs of the fly and worm embryonic G protein pathway, and a 2010 study from John Kehl's lab at NIH demonstrated that the mammalian orthologs of RIC-8 and Gi/o help orient the mitotic spindle in adherent mammalian cells and in polarized MDCK cells.
David, N.B., Martin, C.A., Segalen, M., Rosenfeld, F., Schweisguth, F., and Bellaiche, Y. (2005). Drosophila Ric-8 regulates Galphai cortical localization to promote Galphai-dependent planar orientation of the mitotic spindle during asymmetric cell division. Nat Cell Biol 7, 1083-1090.
Hampoelz, B., Hoeller, O., Bowman, S.K., Dunican, D., and Knoblich, J.A. (2005). Drosophila Ric-8 is essential for plasma-membrane localization of heterotrimeric G proteins. Nat Cell Biol 7, 1099-1105.
Matsuzaki, F. (2005). Drosophila G-protein signalling: intricate roles for Ric-8? Nat Cell Biol 7, 1047-1049. [News and Views]
Tall, G.G., and Gilman, A.G. (2005). Resistance to inhibitors of cholinesterase 8A catalyzes release of Galphai-GTP and nuclear mitotic apparatus protein (NuMA) from NuMA/LGN/Galphai-GDP complexes. Proc Natl Acad Sci U S A 102, 16584-16589.
Wang, H., Ng, K.H., Qian, H., Siderovski, D.P., Chia, W., and Yu, F. (2005). Ric-8 controls Drosophila neural progenitor asymmetric division by regulating heterotrimeric G proteins. Nat Cell Biol 7, 1091-1098.
Woodard, G.E., Huang, N.N., Cho, H., Miki, T., Tall, G.G., and Kehrl, J.H. (2010). Ric-8A and Gi alpha recruit LGN, NuMA, and dynein to the cell cortex to help orient the mitotic spindle. Mol Cell Biol 30, 3519-3530.
Miller KG, Emerson MD, McManus JB, and Rand JR (2000). RIC-8 (Synembryn): A novel conserved protein that is required for Gqa signaling in the C. elegans nervous system. Neuron 27(2), 289-299. PMID: 10985349. See Adventures > 1996-2000.
Prior to our study, a pioneering Cell paper from Ron Plasterk's lab provided the first evidence that G proteins were involved in mitotic spindle alignments during early embryogenesis by showing that GPB-1 (G beta) mutants had embryonic lethality and mitotic spindle misalignments. However, the G alpha subunit is thought to be the main signaling switch of G protein pathways, and no study prior to ours had identified a G alpha protein involved in mitotic spindle alignment. In addition to being the first study to show that the newly discovered RIC-8 protein was also required for the function of this pathway, our study was also the first to generalize the G protein pathway function in the early embryo by noting that all G alpha pathway functions could be described in terms of regulation of centrosome movements. We did this by showing that the G alpha signaling pathway regulates one-cell posterior centrosome rocking, P1 centrosome flattening, and nuclear migration in addition to the centrosome movements that determine mitotic spindle alignments.
Zwaal, R. R., J. Ahringer, H. G. A. M. van Luenen, A. Rushforth, P. Anderson et al., 1996 G proteins are required for spatial orientation of early cell cleavages in C. elegans embryos. Cell 86: 619-629.
While our Genetics paper was out for review, two papers were published in Cell and Current Biology showing that a protein called Pins (Partner of Inscuteable) was required for mitotic spindle alignment in Drosophila neuroblasts and that a protein identified as either Go or Gi physically interacts with Pins. However, a requirement for the unidentified G alpha protein, or any G alpha protein, in mitotic spindle alignment was not demonstrated until our study.
Schaefer, M., Shevchenko, A., Shevchenko, A., and Knoblich, J.A. (2000). A protein complex containing Inscuteable and the Galpha-binding protein Pins orients asymmetric cell divisions in Drosophila. Curr Biol 10, 353-362.
Yu, F., Morin, X., Cai, Y., Yang, X., and Chia, W. (2000). Analysis of partner of inscuteable, a novel player of Drosophila asymmetric divisions, reveals two distinct steps in inscuteable apical localization. Cell 100, 399-409.
Three months after our Genetics paper was published, Julie Ahringer's lab at Cambridge published a Nature Cell Biology paper that also identified GOA-1 (Go) as the relevant G alpha subunit for centrosome movements during early embryogenesis. Although they did not investigate the role of the newly discovered RIC-8 protein like we did, their paper broke new ground by showing that another closely related G alpha protein, GPA-16, acts redundantly with GOA-1. This nicely explained our finding that embryonic lethality was only 11% in goa-1 null mutants, but 100% in goa-1+; ric-8/ric-8 mutants. Their paper also confirmed our immunolocalization of GOA-1 (Go), our finding that PAR polarity is not disrupted in G protein signaling mutants, and our findings that one-cell posterior centrosome rocking, P1, centrosome flattening, and nuclear migration are also disrupted in the G protein signaling mutants. Interestingly, and perhaps mistakenly, I had tipped off their lead author, Monica Gotta, about all of these phenotypes months before our paper was published, and our paper was not cited by them. Their paper also claimed evidence that the G alpha phenotypes were caused by excess G beta gamma activity, and this conclusion contributed to the paper's title. However, they did not provide a strong genetic test of that hypothesis and, in a 2005 review by the lead author, that early hypothesis was not even mentioned as a possibility.
Gotta, M., and Ahringer, J. (2001). Distinct roles for G alpa and G beta gamma in regulating spindle position and orientation in Caenorhabditis elegans. Nature Cell Biology 3, 297-300.
Bellaiche, Y., and Gotta, M. (2005). Heterotrimeric G proteins and regulation of size asymmetry during cell division. Curr Opin Cell Biol 17, 658-663. [Review]
A year after our paper was published, Juergen Knoblich's group published a Cell paper identifying the relevant Drosophila G protein as Gi (a protein closely related to Go) and confirmed that reducing its function caused defects in mitotic spindle alignments in neuroblasts and sensory organ precursor cells. This paper was also the first to propose that Pins could be a receptor-independent activator of Go.
Schaefer, M., Petronczki, M., Dorner, D., Forte, M., and Knoblich, J.A. (2001). Heterotrimeric G proteins direct two modes of asymmetric cell division in the Drosophila nervous system. Cell 107, 183-194.
Over the next 4 years, this little field treally exploded, with many papers confirming our foundational work and identifying other components in the embryonic G protein pathway.
In 2003, 3 studies from the labs of Pierre Gonczy, Sander van den Heuvel, and Julie Ahringer's lab showed that GPR-1 and GPR-2, which are the C. elegans homologs of Pins, function in the same pathway as GOA-1 (Go) and are enriched at the posterior membrane of the one-cell embryo, suggesting that they could be involved in the positional activation of the GOA-1 (Go) pathway.
Colombo, K., Grill, S.W., Kimple, R.J., Willard, F.S., Siderovski, D.P., and Gonczy, P. (2003). Translation of polarity cues into asymmetric spindle positioning in Caenorhabditis elegans embryos. Science 300, 1957-1961.
Gotta, M., Dong, Y., Peterson, Y.K., Lanier, S.M., and Ahringer, J. (2003). Asymmetrically distributed C. elegans homologs of AGS3/PINS control spindle position in the early embryo. Curr Biol 13, 1029-1037.
Srinivasan, D.G., Fisk, R.M., Xu, H., and van den Heuvel, S. (2003). A complex of LIN-5 and GPR proteins regulates G protein signaling and spindle function in C elegans. Genes Dev 17, 1225-1239.
In 2003, Greg Tall in Al Gilman's lab published his paper showing that mouse RIC-8 could act as a GDP-GTP exchange factor (a "GEF") for G alpha proteins and proposed that it could contribute to "receptor-independent" activation of G alpha proteins. However, Greg and others later showed that RIC-8 can also function as a molecular chaperone for G protein alpha subunits that is necessary for G alpha stability. It is still not clear whether RIC-8 functions mainly as a chaperone, or whether it can also function as a receptor-independent GEF in some contexts.
Tall, G. G.. Ric-8 Regulation of Heterotrimeric G Proteins. 2013. J Recept Signal Transduct Res. 33(3): 139-143 [Excellent review of Ric-8]
In 2004, 3 groups published papers in Cell and Current Biology that basically confirmed our results published in our 2000 Genetics paper that ric-8 mutants have defects in centrosome movements during early embryogenesis and that further confirmed Greg Tall's results that RIC-8 directly interacts with G alpha proteins and stimulates GDP-GTP exchange. The paper from Michael Koelle's group further identified RGS-7 as the relevant RGS protein (GTPase activating protein) for Go during early embryogenesis.
Afshar, K., Willard, F.S., Colombo, K., Johnston, C.A., McCudden, C.R., Siderovski, D.P., and Gonczy, P. (2004). RIC-8 is required for GPR-1/2-dependent Ga function during asymmetric division of C. elegans embryos. Cell 119, 219-230.
Couwenbergs, C., Spilker, A.C., and Gotta, M. (2004). Control of embryonic spindle positioning and Ga activity by C. elegans RIC-8. Curr Biol 14, 1871-1876.
Hess, H.A., Roper, J.C., Grill, S.W., and Koelle, M.R. (2004). RGS-7 completes a receptor-independent heterotrimeric G protein cycle to asymmetrically regulate mitotic spindle positioning in C. elegans. Cell 119, 209-218.
In 2005, three Drosophila groups caught up with C. elegans researchers and published 3 papers in Nature Cell Biology confirming that RIC-8 and Gi/o are also required for the orientation and positioning of mitotic spindles (and the centrosomes from which they grow) during asymmetric cell divisions of neural progenitors (neuroblasts) and sensory precursor cells in Drosophila embryos. Further emphasizing the fundamental roles of RIC-8 and Gi/o in guiding centrosome movements throughout the animal kingdom, Greg Tall in Al Gilman's lab also demonstrated similar biochemical interactions using the mammalian orthologs of the fly and worm embryonic G protein pathway, and a 2010 study from John Kehl's lab at NIH demonstrated that the mammalian orthologs of RIC-8 and Gi/o help orient the mitotic spindle in adherent mammalian cells and in polarized MDCK cells.
David, N.B., Martin, C.A., Segalen, M., Rosenfeld, F., Schweisguth, F., and Bellaiche, Y. (2005). Drosophila Ric-8 regulates Galphai cortical localization to promote Galphai-dependent planar orientation of the mitotic spindle during asymmetric cell division. Nat Cell Biol 7, 1083-1090.
Hampoelz, B., Hoeller, O., Bowman, S.K., Dunican, D., and Knoblich, J.A. (2005). Drosophila Ric-8 is essential for plasma-membrane localization of heterotrimeric G proteins. Nat Cell Biol 7, 1099-1105.
Matsuzaki, F. (2005). Drosophila G-protein signalling: intricate roles for Ric-8? Nat Cell Biol 7, 1047-1049. [News and Views]
Tall, G.G., and Gilman, A.G. (2005). Resistance to inhibitors of cholinesterase 8A catalyzes release of Galphai-GTP and nuclear mitotic apparatus protein (NuMA) from NuMA/LGN/Galphai-GDP complexes. Proc Natl Acad Sci U S A 102, 16584-16589.
Wang, H., Ng, K.H., Qian, H., Siderovski, D.P., Chia, W., and Yu, F. (2005). Ric-8 controls Drosophila neural progenitor asymmetric division by regulating heterotrimeric G proteins. Nat Cell Biol 7, 1091-1098.
Woodard, G.E., Huang, N.N., Cho, H., Miki, T., Tall, G.G., and Kehrl, J.H. (2010). Ric-8A and Gi alpha recruit LGN, NuMA, and dynein to the cell cortex to help orient the mitotic spindle. Mol Cell Biol 30, 3519-3530.
Fun Factoids about this Study
This was one of our most foundational studies. Even so, we chose not to pursue follow up studies because we wanted to focus on the nervous system. There were lots of "firsts" in this study:
-First study to identify a G alpha protein with a role in mitotic spindle alignments.
-First study to show that RIC-8 has a role in centrosome movements/ mitotic spindle alignments.
-First study to show stereotyped nuclear migrations in the large cells of young embryos where nuclear position at the time of cell division is critical for determining the sizes and shapes of the daughter cells.
-We not only made the first published observations of stereotyped nuclear migrations in young embryos, but we also identified the first signal transduction pathway that regulates the migrations.
-As we noted in the paper, the times required for the first 3 cell divisions in the G alpha and ric-8 mutants took 10 - 18% longer than wild type, and this was a statistically significant increase. We hypothesize that this is because there are checkpoints that monitor centrosome and/ or nuclear position, and centrosomes and nuclei were often out of position in the mutants. However, since there was only an 18% delay, and since divisions often occurred in the wrong plane in the mutants, other signals can over-ride the checkpoint after a certain amount of time.
-First study to identify a G alpha protein with a role in mitotic spindle alignments.
-First study to show that RIC-8 has a role in centrosome movements/ mitotic spindle alignments.
-First study to show stereotyped nuclear migrations in the large cells of young embryos where nuclear position at the time of cell division is critical for determining the sizes and shapes of the daughter cells.
-We not only made the first published observations of stereotyped nuclear migrations in young embryos, but we also identified the first signal transduction pathway that regulates the migrations.
-As we noted in the paper, the times required for the first 3 cell divisions in the G alpha and ric-8 mutants took 10 - 18% longer than wild type, and this was a statistically significant increase. We hypothesize that this is because there are checkpoints that monitor centrosome and/ or nuclear position, and centrosomes and nuclei were often out of position in the mutants. However, since there was only an 18% delay, and since divisions often occurred in the wrong plane in the mutants, other signals can over-ride the checkpoint after a certain amount of time.