RESEARCH | REPORTS southern Spain turns into desert, deciduous 5. F. Médail, N. Myers, in Hotspots Revisited: Earth’s Biologically ACKNOWLEDGMENTS forestsinvademostofthemountains,andMe- Richest and Most Endangered Terrestrial Ecoregions, The authors are members of the Observatoire des Sciences de diterranean vegetation replaces most of the R. A. Mittermeier et al., Eds. (Conservation International, l’Univers Pytheas Institute and the ECCOREV network. This 2004), pp. 144–147. deciduous forests in a large part of the Mediter- research has been funded by Labex OT-Med (project ANR-11- 6. Materials and methods are available as supplementary LABEX-0061), the “Investissements d’Avenir” French government ranean basin. Figure 3H illustrates the variation materials on Science Online. project of the French National Research Agency (ANR), from areas without any changes, regardless of 7. E. Xoplaki, J. F. González-Rouco, J. Luterbacher, H. Wanner, AMidex (project 11-IDEX-0001-02), and the European – scenario (stable white areas), to areas in which Clim. Dyn. 23,63 78 (2004). Union FP7-ENVIRONMENT project OPERAs (grant 308393). 8. L. Maiorano et al., Philos. Trans. R. Soc. London Ser. B 366, We acknowledge the World Climate Research Programme’s changes from scenario RCP2.6 already appear – 2681 2692 (2011). Working Group on Coupled Modelling, which is responsible for (red areas). As expected, the most-sensitive areas 9. T. Keenan, J. Maria Serra, F. Lloret, M. Ninyerola, S. Sabate, CMIP, and we thank the climate modeling groups (table S2) for – are those located at the limit between two biomes— Glob. Change Biol. 17, 565 579 (2011). producing and making their model outputs available. For CMIP, 10. W. Thuiller, S. Lavorel, M. B. Araújo, Glob. Ecol. Biogeogr. 14, the U.S. Department of Energy’s Program for Climate Model for example, in the mountains at the transition – 347 357 (2005). Diagnosis and Intercomparison provides coordinating support between temperate and montane forest or in the – 11. B. Weninger et al., Doc. Praehist. 36,7 59 and led the development of software infrastructure, in southern Mediterranean at the transition between (2009). partnership with the Global Organization for Earth System forest and desert biomes. The map for 4700 yr 12. D. Kaniewski, E. Van Campo, H. Weiss, Proc. Natl. Acad. Sci. Science Portals. R. Suarez and S. Shi have extracted and – B.P., in which the past changes were among the U.S.A. 109, 3862 3867 (2012). preprocessed the model simulations. Holocene climate 13. N. Roberts, D. Brayshaw, C. Kuzucuoglu, R. Perez, L. Sadori, reconstructions are available at http://database.otmed.fr/ highest (Fig. 3B), has the largest changes in the – Holocene 21,3 13 (2011). geonetworkotmed/srv/eng/search - |54b9bf34-57ae-45ea-b455- southwest, eastern steppe areas, and the moun- 14. C. P. Kelley, S. Mohtadi, M. A. Cane, R. Seager, Y. Kushnir, 9f90351e538f. Future climate projections are available at – tains, but these changes are relatively sparse. Proc. Natl. Acad. Sci. U.S.A. 112, 3241 3246 (2015). http://cmip-pcmdi.llnl.gov/cmip5/. 15. B. I. Cook, K. J. Anchukaitis, R. Touchan, D. M. Meko, Our analysis shows that, in approximately one E. R. Cook, J. Geophys. Res. 121, 2060–2074 (2016). century, anthropogenic climate change without 16. G. Middleton, J. Archaeol. Res. 20, 257–307 (2012). SUPPLEMENTARY MATERIALS ambitious mitigation policies will likely alter 17. A. B. Knapp, S. W. Manning, Am. J. Archaeol. 120,99–149 www.sciencemag.org/content/354/6311/465/suppl/DC1 Downloaded from ecosystems in the Mediterranean in a way that (2016). Materials and Methods 18. C. B. Yackulc, J. D. Nichols, J. Reid, R. Der, Ecology 96,16–23 is without precedent during the past 10 millen- Table S1 and S2 (2015). References (21–28) nia. Despite known uncertainties in climate 19. C. Roumieux et al., Ecol. Mediterr. 36,17–24 models, GHG emission scenarios at the level (2010). 20. I. Harris, P. D. Jones, T. J. Osborn, D. H. Lister, Int. J. Climatol. 6 July 2016; accepted 21 September 2016 of country commitments before the UNFCCC 34, 623–642 (2014). 10.1126/science.aah5015 Paris Agreement will likely lead to the sub- stantial expansion of deserts in much of south- http://science.sciencemag.org/ ern Europe and northern Africa. The highly ambitiousRCP2.6scenarioseemstobetheonly GENE EXPRESSION possible pathway toward more limited impacts. Only the coldest RCP2.6L simulations, which correspond broadly to the 1.5°C target of the Paris Agreement, allow ecosystem shifts to re- Xist recruits the X chromosome to the main inside the limits experienced during the Holocene. nuclear lamina to enable This analysis does not account for other hu- man impacts on ecosystems, in addition to cli- chromosome-wide silencing mate change (i.e., land-use change, urbanization, on August 6, 2021 soil degradation, etc.), which have grown in Chun-Kan Chen,1 Mario Blanco,1 Constanza Jackson,1 Erik Aznauryan,1 importance after the mid-Holocene and have Noah Ollikainen,1 Christine Surka,1 Amy Chow,1 Andrea Cerase,2 become dominant during the past centuries. 3 1 Patrick McDonel, Mitchell Guttman * Many of these effects are likely to become even stronger in the future because of the expand- The Xist long noncoding RNA orchestrates X chromosome inactivation, a process that entails ing human population and economic activity. chromosome-wide silencing and remodeling of the three-dimensional (3D) structure of the Most land change processes reduce natural veg- X chromosome. Yet, it remains unclear whether these changes in nuclear structure are etation or they seal or degrade the soils, repre- mediated by Xist and whether they are required for silencing. Here, we show that Xist directly senting additional effects on ecosystems, which interacts with the Lamin B receptor, an integral component of the nuclear lamina, and that will enhance, rather than dampen, the biome this interaction is required for Xist-mediated silencing by recruiting the inactive X to the shifts toward a drier state than estimated by nuclear lamina and by doing so enables Xist to spread to actively transcribed genes across this analysis. This assessment shows that, with- the X. Our results demonstrate that lamina recruitment changes the 3D structure of DNA, out ambitious climate targets, the potential for enabling Xist and its silencing proteins to spread across the X to silence transcription. future managed or unmanaged ecosystems to host biodiversity or deliver services to society is likely to be greatly reduced by climate change he Xist long noncoding RNA (lncRNA) ini- tional silencing, called the A-repeat (10), leads to and direct local effects. tiates X chromosome inactivation (XCI), a a defect in Xist spreading (7) and spatial ex- process that entails chromosome-wide tran- clusion of active genes from the Xist-coated nu- scriptional silencing (1) and large-scale re- clear compartment (9). Whether these structural REFERENCES AND NOTES T modeling of the three-dimensional (3D) changes are required for, or merely a conse- 1. S. I. Seneviratne, M. G. Donat, A. J. Pitman, R. Knutti, structure of the X chromosome (2–4), by spread- quence of, transcriptional silencing mediated – R. L. Wilby, Nature 529, 477 483 (2016). ing across the future inactive X chromosome by the A-repeat of Xist remains unclear (7, 9). 2. W. Cramer et al., in Climate Change 2014: Impacts, Adaptation, 1 5 and Vulnerability. Part A: Global and Sectoral Aspects. and excluding RNA polymerase II (PolII) ( , ). Recently, we and others identified by means Contribution of Working Group II to the Fifth Assessment Report Xist initially localizes to genomic DNA regions of mass spectrometry the proteins that inter- of the Intergovernmental Panel on Climate Change, C. B. Field on the X chromosome that are not actively tran- act with Xist (11–13). One of these proteins is – et al., Eds. (Cambridge Univ. Press, 2014), pp. 979 1037. scribed (6–8), before spreading to actively tran- the Lamin B receptor (LBR) (11, 13), a trans- 3. C.-F. Schleussner et al., Earth Syst. Dyn. Discuss. 6, 7–9 2447–2505 (2015). scribed genes ( ). Deletion of a highly conserved membrane protein that is anchored in the 4. J. Guiot, D. Kaniewski, Front. Earth Sci. 3, 28 (2015). region of Xist that is required for transcrip- inner nuclear membrane, binds to Lamin B, 468 28 OCTOBER 2016 • VOL 354 ISSUE 6311 sciencemag.org SCIENCE RESEARCH | REPORTS and is required for anchoring chromatin to the membrane domains (DTM-LBR) (fig. S5) did not the observed silencing defect by reestablishing nuclear lamina (14)—a nuclear compartment that affect Xist binding (Fig. 1B) and was able to the DLBS-LBR interaction. To do this, we gener- helps shape the 3D structure of DNA (15) and rescue the silencing defect upon knockdown of ated an endogenous DLBS-BoxB Xist RNA (mate- is enriched for silencing proteins (14, 16). Be- LBR (Fig. 1C, figs. S1B and S6, and note 4). To rials and methods) and confirmed that expression cause induction of XCI leads to recruitment of ensure that DRS-LBR fails to silence X chromo- of LBR-lN, but not LBR fused to a different the inactive X-chromosome to the nuclear lamina some genes because of its RNA binding ability, RNA-binding domain (MS2-coat protein) (19), was (4), we hypothesized that the Xist-LBR interaction we fused three copies of the viral BoxB RNA able to rescue the silencing defect observed in might be required to shape nuclear structure and aptamer, which binds tightly to the viral lNcoat DLBS-BoxB cells (Fig. 2D, fig. S10, and materials regulate gene expression during XCI. protein (17), to the 3′ end of the endogenous and methods). In contrast, expression of other To test this, we knocked down LBR and mea- Xist RNA (Xist-BoxB) (fig.