Establishment of a human model of the blood-brain barrier has proven to be a difficult goal. To accomplish this, normal human brain endothelial cells were transduced by lentiviral vectors incorporating human telomerase or SV40 T antigen. Among the many stable immortalized clones obtained by sequential limiting dilution cloning of the transduced cells, one was selected for expression of normal endothelial markers, including CD31, VE cadherin, and von Willebrand factor. This cell line, termed hCMEC/D3, showed a stable normal karyotype, maintained contact-inhibited monolayers in tissue culture, exhibited robust proliferation in response to endothelial growth factors, and formed capillary tubes in matrix but no colonies in soft agar. hCMEC/D3 cells expressed telomerase and grew indefinitely without phenotypic dedifferentiation. These cells expressed chemokine receptors, up-regulated adhesion molecules in response to inflammatory cytokines, and demonstrated blood-brain barrier characteristics, including tight junctional proteins and the capacity to actively exclude drugs. hCMEC/D3 are excellent candidates for studies of blood-brain barrier function, the responses of brain endothelium to inflammatory and infectious stimuli, and the interaction of brain endothelium with lymphocytes or tumor cells. Thus, hCMEC/D3 represents the first stable, fully characterized, well-differentiated human brain endothelial cell line and should serve as a widely usable research tool.

Subcellular-sized, ultraflexible electrodes form seamless integration with the living brain and afford chronically reliable recording.

Basal stem cells (basal cells), located in the bronchi and trachea of the human lung epithelium, play a critical role in normal airway homeostasis and repair, and have been implicated in the development of diseases such as cancer [1][2][3][4] . Additionally, basal-like cells contribute to alveolar regeneration and fibrosis following severe injury [5][6][7][8] . However, the developmental origin of basal cells in humans is unclear. Previous work has shown that specialized progenitor cells exist at the tips of epithelial tubes during lung branching morphogenesis, and in mice, give rise to all alveolar and airway lineages 9,10 . These 'bud tip progenitor cells' have also been described in the developing human lung [11][12][13] , but the mechanisms controlling bud tip differentiation into specific cell lineages, including basal cells, are unknown. Here, we interrogated the bud tip-to-basal cell transition using human tissue specimens, bud tip progenitor organoid cultures 11 , and single-cell transcriptomics. We used single-cell mRNA sequencing (scRNAseq) of developing human lung specimens from 15-21 weeks gestation to identify molecular signatures and cell states in the developing human airway epithelium. We then inferred differentiation trajectories during bud tip-to-airway differentiation, which revealed a previously undescribed transitional cell state ('hub progenitors') and implicated SMAD signaling as a regulator of the bud tip-to-basal cell transition. We used bud tip progenitor organoids to show that TGFβ1 and BMP4 mediated SMAD signaling robustly induced the transition into functional basal-like cells, and these in vitro-derived basal cells exhibited clonal expansion, self-renewal and multilineage differentiation. This work provides a framework for deducing and validating key regulators of cell fate decisions using single cell transcriptomics and human organoid models. Further, the identification of SMAD signaling as a critical regulator .

No abstract

Ecological responses to climate change may depend on complex patterns of variability in weather and local microclimate that overlay global increases in mean temperature. Here, we show that high-resolution temporal and spatial variability in temperature drives the dynamics of range expansion for an exemplar species, the butterfly Hesperia comma. Using fine-resolution (5 m) models of vegetation surface microclimate, we estimate the thermal suitability of 906 habitat patches at the species' range margin for 27 years. Population and metapopulation models that incorporate this dynamic microclimate surface improve predictions of observed annual changes to population density and patch occupancy dynamics during the species' range expansion from 1982 to 2009. Our findings reveal how fine-scale, short-term environmental variability drives rates and patterns of range expansion through spatially localised, intermittent episodes of expansion and contraction. Incorporating dynamic microclimates can thus improve models of species range shifts at spatial and temporal scales relevant to conservation interventions.