The mechanisms whereby cells and organisms are able to compensate for Mg2+ limitation have only begun to be explored. This is an important area of research, because Mg2+ deficiency is a common human health condition (10-30% of the human population) and also because the growth and division of cells within certain microenvironments (e.g., tumors) occurs under conditions of limited Mg2+ availability. We are using the C. elegans gonad as a model for understanding how developing systems cope with Mg2+ starvation.
In the newly-hatched C. elegans L1 larva, the gonad primordium comprises two somatic gonad precursor cells (Z1 and Z4, aka the SGPs) and two germ cells (Z2 and Z3). Germ cell growth and division are strictly dependent upon signals and nutrients provided by the SGPs; therefore, the somatic cells are considered to be of primary importance with regard to regulation of gonadogenesis. When L1s are provided with an E. coli food source, the SGPs commence divisions midway through the 1st larval stage and proceed to generate a total of twelve descendants by the beginning of the 2nd larval stage (within about 5 hours, at 20 degrees).
The postembryonic divisions of the SGPs are blocked by mutations that reduce the activity of gon-2, which encodes a non-specific cation channel protein orthologous to mammalian TRMP6/7. GON-2 is permeable to Mg2+ and the gonadogenesis defect can be largely suppressed by Mg2+ supplementation. Through mosaic analysis and targeted expression experiments we have established that GON-2 function within the SGPs is necessary and sufficient for gonadogenesis. Thus, by searching for modifiers of GON-2 function, we can identify cellular components that mediate adaptation to low-Mg2+ conditions. In genetic interactor screens, we have interrogated ~107 mutagenized genomes for candidate molecular regulators and collaborators of GON-2. These led us to the identifcation of mutations in: a) two paralogs of gon-2 (gtl-1 and gtl-2) which modulate gonadogenesis by regulating systemic Mg2+ levels, b) two transporter proteins, GEM-1 (SLC16A monocarboxylate transporter) and CATP-6 (P5B ATPase polyamine transporter), which act in parallel to GON-2 to promote division of the SGPs, and c) A calcium-dependent phospholipid binding protein (GEM-4 copine), which antagonizes GON-2 activity. We isolated multiple alleles of each of these genes, indicating that our screen is approaching saturation with respect to loss-of-function mutations in “typical” protein-coding genes.
We are currently seeking to dissect the functional significance of these genetic interactions, as well as exploring the mechanisms of action of novel gain-of-function alleles in additional loci.
Selected publications:
1: Vrijsen S, Besora-Casals L, van Veen S, Zielich J, Van den Haute C, Hamouda NN, Fischer C, Ghesquière B, Tournev I, Agostinis P, Baekelandt V, Eggermont J, Lambie E, Martin S, Vangheluwe P. ATP13A2-mediated endo-lysosomal polyamine export counters mitochondrial oxidative stress. Proc Natl Acad Sci U S A. 2020 Dec 8;117(49):31198-31207.
2: van Veen S, Martin S, Van den Haute C, Benoy V, Lyons J, Vanhoutte R, Kahler JP, Decuypere JP, Gelders G, Lambie E, Zielich J, Swinnen JV, Annaert W, Agostinis P, Ghesquière B, Verhelst S, Baekelandt V, Eggermont J, Vangheluwe P. ATP13A2 deficiency disrupts lysosomal polyamine export. Nature. 2020 Feb;578(7795):419-424.
3: Mangal S, Zielich J, Lambie E, Zanin E. Rapamycin-induced protein dimerization as a tool for C. elegans research. MicroPubl Biol. 2018 Mar 20;2018:10.17912/W2BH3H.
4: Zielich J, Tzima E, Schröder EA, Jemel F, Conradt B, Lambie EJ. Overlapping expression patterns and functions of three paralogous P5B ATPases in Caenorhabditis elegans. PLoS One. 2018 Mar 16;13(3):e0194451.
5: Lambie EJ, Bruce RD 3rd, Zielich J, Yuen SN. Novel Alleles of gon-2, a C. elegans Ortholog of Mammalian TRPM6 and TRPM7, Obtained by Genetic Reversion Screens. PLoS One. 2015 Nov 25;10(11):e0143445.
6: Lambie EJ, Tieu PJ, Lebedeva N, Church DL, Conradt B. CATP-6, a C. elegans ortholog of ATP13A2 PARK9, positively regulates GEM-1, an SLC16A transporter. PLoS One. 2013 Oct 9;8(10):e77202.
7: Teramoto T, Sternick LA, Kage-Nakadai E, Sajjadi S, Siembida J, Mitani S, Iwasaki K, Lambie EJ. Magnesium excretion in C. elegans requires the activity of the GTL-2 TRPM channel. PLoS One. 2010 Mar 8;5(3):e9589.
8: Kemp BJ, Church DL, Hatzold J, Conradt B, Lambie EJ. Gem-1 encodes an SLC16 monocarboxylate transporter-related protein that functions in parallel to the gon-2 TRPM channel during gonad development in Caenorhabditis elegans. Genetics. 2009 Feb;181(2):581-91.
9: Teramoto T, Lambie EJ, Iwasaki K. Differential regulation of TRPM channels governs electrolyte homeostasis in the C. elegans intestine. Cell Metab. 2005 May;1(5):343-54.
10: Church DL, Lambie EJ. The promotion of gonadal cell divisions by the Caenorhabditis elegans TRPM cation channel GON-2 is antagonized by GEM-4 copine. Genetics. 2003 Oct;165(2):563-74.
11: West RJ, Sun AY, Church DL, Lambie EJ. The C. elegans gon-2 gene encodes a putative TRP cation channel protein required for mitotic cell cycle progression. Gene. 2001 Mar 21;266(1-2):103-10.
12: Sun AY, Lambie EJ. gon-2, a gene required for gonadogenesis in Caenorhabditis elegans. Genetics. 1997 Nov;147(3):1077-89.
The Conradt and Lambie Lab 