Dynamic Localization of the C. elegans GoLoco Proteins GPR-1/2 Mediates Mitotic Spindle Orientation in Response to Extrinsic Signals

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  • March 20, 2019
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  • Werts, Adam David
    • Affiliation: College of Arts and Sciences, Department of Biology
Abstract
  • Normal regulation of mitotic spindle orientation plays key roles in development and contributes to preventing tumorigenesis. In many cases, cell divisions are oriented by signals from neighboring cells. However, very little is known about how mitotic spindle orientation is established by signaling between cells. GoLoco-domain proteins (C. elegans GPR-1/2, Drosophila Pins, vertebrate LGN and AGS3) are good candidates for mediating spindle orientation in response to extrinsic signals, as they are key players in cell-autonomous mitotic spindle orientation, linking plasma membrane-associated Galpha proteins to microtubule-associated proteins. In C. elegans, the GoLoco-domain protein pair GPR-1/2 has been implicated in orienting the spindle of an endomesodermal precursor cell, EMS, toward an accumulation of GPR-1/2 at the point of contact between EMS and its neighbor, the germline precursor cell P2. Because it is difficult to resolve the cell of origin for such cortically-distributed proteins, I generated mosaic embryos with different fluorescent tags on GPR-1/2 in different cells. Using this system, I found that GPR-1/2 is surprisingly uniform in the EMS cell, but that it is asymmetrically distributed in the neighbor cell, P2. Indeed, P2 depended on cortically-tethered GPR-1/2 for normal division orientation. I demonstrate that intercellular signaling via MES-1 plays an instructive role in localizing GPR-1/2 asymmetrically in P2. I ruled out a model suggesting that cortical GPR-1/2 localization in P2 occurred through inhibition of LET-99, a GPR-1/2 antagonist. Instead, my investigations suggested that GPR-1/2 accumulated through diffusion and preferential trapping at one cell contact, coupled with destabilization at another cell contact. Once the mitotic spindle of P2 is oriented normally, microtubule-dependent removal of GPR-1/2 prevented excess accumulation. I conclude that the dynamic localization of GPR-1/2 can serve as a key intermediate relaying positional information from one cell to the alignment of a mitotic spindle in the neighboring cell. Together with previous findings, my results demonstrate that GoLocodomain proteins are localized by multiple signaling pathways. I propose that orientation of mitotic spindles by intercellular signaling via GoLoco-domain protein localization may be a fundamental and widespread mechanism in animal development.
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  • In Copyright
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  • "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biology."
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  • Goldstein, Robert P.
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  • Chapel Hill, NC
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  • Open access
Date uploaded
  • March 18, 2013

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