Multi-decadal to centennial-scale shifts in effective moisture over the past two millennia are inferred from sedimentary records from six lakes spanning a ~250 km region in northwest Ontario. This is the first regional application of a technique developed to reconstruct drought from drainage lakes (open lakes with surface outlets). This regional network of proxy drought records is based on individual within-lake calibration models developed using diatom assemblages collected from surface sediments across a water-depth gradient. Analysis of diatom assemblages from sediment cores collected close to the near-shore ecological boundary between benthic and planktonic diatom taxa indicated this boundary shifted over time in all lakes. These shifts are largely dependent on climate-driven influences, and can provide a sensitive record of past drought. Our lake-sediment records indicate two periods of synchronous signals, suggesting a common large-scale climate forcing. The first is a period of prolonged aridity during the Medieval Climate Anomaly (MCA, c. 900-1400 CE). Documentation of aridity across this region expands the known spatial extent of the MCA megadrought into a region that historically has not experienced extreme droughts such as those in central and western north America. The second synchronous period is the recent signal of the past ~100 years, which indicates a change to higher effective moisture that may be related to anthropogenic forcing on climate. This approach has the potential to fill regional gaps, where many previous paleo-lake depth methods (based on deeper centrally located cores) were relatively insensitive. By filling regional gaps, a better understanding of past spatial patterns in drought can be used to assess the sensitivity and realism of climate model projections of future climate change. This type of data is especially important for validating high spatial resolution, regional climate models.

In response to vascular injury, differentiated vascular smooth muscle cells (vSMCs) undergo a unique process known as "phenotype modulation," transitioning from a quiescent, "contractile" phenotype to a proliferative, "synthetic" state. We have demonstrated previously that the signaling pathway of bone morphogenetic proteins, members of the transforming growth factor ␤ family, play a role in the induction and maintenance of a contractile phenotype in human primary pulmonary artery smooth muscle cells. In this study, we show that a four-and-ahalf LIM domain protein 2 (FHL2) inhibits transcriptional activation of vSMC-specific genes mediated by the bone morphogenetic protein signaling pathway through the CArG box-binding proteins, such as serum response factor and members of the myocardin (Myocd) family. Interestingly, FHL2 does not affect recruitment of serum response factor or Myocd, however, it inhibits recruitment of a component of the SWI/SNF chromatin remodeling complex, Brg1, and RNA polymerase II, which are essential for the transcriptional activation. This is a novel mechanism of regulation of SMC-specific contractile genes by FHL2. Finally, aortic rings from homozygous FHL2-null mice display abnormalities in both endothelial-dependent and -independent relaxation, suggesting that FHL2 is essential for the regulation of vasomotor tone.Unlike skeletal and cardiac muscle cells, vSMCs 2 never terminally differentiate, but are capable of transitioning to a synthetic phenotype characterized by decreased vSMC marker gene expression, increased matrix deposition, and responsiveness to signals that lead to increased migration and growth (1).This plasticity is crucial for the normal development of vessels, homeostasis of blood pressure, and repair of injury, but it also contributes to the development of various vascular pathologies. Therefore, it is critical to understand the signaling pathways that modulate the phenotype of vSMCs to develop agents that can regulate aberrant vSMC responses in diseased vessels.Recently we demonstrated that the BMP signaling pathway plays an important role in the phenotype modulation of PASMCs. Activation of the BMP pathway is required not only for maintenance of the contractile phenotype in PASMCs, but also for induction of vSMC marker gene expression in nonSMCs, such as mouse mesenchymal C3H10T 1 ⁄ 2 (10T1/2) cells (2-4). BMPs are the largest group in the TGF ␤ superfamily of growth factors and play a crucial role in various physiological processes (5-7). During embryonic development, the BMP pathway participates in the induction of ventral mesoderm, cardiac myogenesis, and vasculogenesis (8). Heterozygous mutations in the gene encoding BMPRII, the type II subunit of the BMP receptor, were identified in patients with both familial and sporadic idiopathic pulmonary arterial hypertension (IPAH) (9, 10). IPAH is characterized by elevated pulmonary vascular resistance and pulmonary arterial pressure with increased muscularization of small arteries, thickening or fibrosis of the intima, ...

No abstract

The Winnipeg River Drainage Basin (WRDB), within the boreal forest region of northwest Ontario, is a region that is expected to be negatively affected by climate warming. Inferences of droughts over the past two millennia from Little Raleigh Lake were based on two nearshore sediment cores. The core locations were from depths of ~12 and 15 m and were based on sufficient nearshore sediment accumulation and distance from the modern benthic-to-planktonic diatom boundary, where a distinct shift from dominance of benthic taxa changed to dominance of planktonic taxa in surficial sediments at ~11.8 m. Diatom-inferred depth was based on a model developed from 60 surficial sediments within the study lake. Depth inferences indicate that prolonged periods of aridity occurred from ~ad 950 to 1300 (corresponds to ‘Medieval Climate Anomaly’) and from ~ad 1625 to 1750 (aridity during ‘Little Ice Age’). We found that the core collected from a depth closer to the benthic-to-planktonic diatom boundary was more sensitive to changes in lake level than the deeper core where planktonic diatoms dominated the assemblage. The inferred low-water stands of the past two millennia are well outside of the range of the past ~100 years, suggesting that recent drought history may not be a good estimate of future extremes.