Author ORCID Identifier
https://orcid.org/0000-0002-6477-1571
Date of Award
Summer 7-12-2024
Document Type
Thesis (Ph.D.)
Department or Program
Biological Sciences
First Advisor
Erik Griffin
Second Advisor
James Moseley
Third Advisor
Sharon Bickel
Abstract
During asymmetric cell division, cell polarity and cell cycle are tightly coupled to ensure robust segregation of cell fate determinants and generation of cellular diversity. In the one-cell C. elegans embryo, multiple cell cycle kinases regulate cell polarization and posterior segregation of germline fate determinants (germplasm). For example, PLK-1 kinase inhibits the retention of its germplasm substrate POS-1 in the anterior, driving POS-1 segregation to the posterior (Han et al., 2018). Additionally, MBK-2 kinase disassembles P granules in the anterior through phosphorylation of the P granule scaffold MEG-3, helping to drive P granule segregation to the posterior (Wang et al., 2014). However, the equally exciting role of cell cycle phosphatases has been less explored. Recently, two classes of phosphatases PP1 and PP2A-B56, were shown to regulate cell polarity. PP1 promotes PAR-2 dephosphorylation and asymmetric cortical loading (Calvi et al., 2022). PP2A-B56 counteracts MBK-2 by dephosphorylating MEG-3 and favoring its assembly in the posterior (Wang et al., 2014).
Using a combination of genetics and microscopy techniques my work has uncovered a new role for PP1 phosphatase and its regulator SDS-22 in polarizing the germplasm in the C. elegans embryo. In sds-22(RNAi)embryos, germplasm proteins POS-1 and PIE-1 are retained properly in the posterior. Additionally, many P granule proteins fail to stably form granules in the sds-22(RNAi) embryos, suggesting that SDS-22 is critical for global germplasm organization. Indeed, my work provides evidence that SDS-22 downregulates PLK-1 kinase activity and possibly upregulates PP2A-B56 phosphatase activity to promote germplasm retention. First, PLK-1 activity-dependent processes are exaggerated in sds-22(RNAi) embryos. Second, inhibition of PLK-1 activity partially rescues germplasm organization, suggesting that SDS-22 might be downregulating PLK-1 activity. We also show genetic evidence indicating that PP1 binding motif on PP2A-B56 is necessary for its ability to stabilize granules. Finally, I also assessed the dynamics of PLK-1 anterior-rich gradient formation, an event critical for its downstream regulation of germplasm, collaboratively. My thesis contributes to the growing understanding of the coupling between cell cycle and cell polarity.
Original Citation
Barbieri S, Nurni Ravi A, Griffin EE, Gotta M. Modeling protein dynamics in Caenorhabditis elegans embryos reveals that the PLK-1 gradient relies on weakly coupled reaction-diffusion mechanisms. Proc Natl Acad Sci U S A. 2022 Mar 15;119(11):e2114205119. doi: 10.1073/pnas.2114205119. Epub 2022 Mar 8. PMID: 35259017; PMCID: PMC8931239.
Recommended Citation
Nurni Ravi, Aparna, "Role of SDS-22/PP1 phosphatase in polarizing the germplasm of Caenorhabditis elegans embryo" (2024). Dartmouth College Ph.D Dissertations. 296.
https://digitalcommons.dartmouth.edu/dissertations/296
Included in
Biochemistry Commons, Biology Commons, Developmental Biology Commons, Education Commons, Laboratory and Basic Science Research Commons, Molecular Genetics Commons
