Biophysical characteristics reveal neural stem cell differentiation potential

Background

Distinguishing human neural stem/progenitor cell (huNSPC) populations that will predominantly generate neurons from those that produce glia is currently hampered by a lack of sufficient cell type-specific surface markers predictive of fate potential. This limits investigation of lineage-biased progenitors and their potential use as therapeutic agents. A live-cell biophysical and label-free measure of fate potential would solve this problem by obviating the need for specific cell surface markers.

Methodology/Principal Findings

We used dielectrophoresis (DEP) to analyze the biophysical, specifically electrophysiological, properties of cortical human and mouse NSPCs that vary in differentiation potential. Our data demonstrate that the electrophysiological property membrane capacitance inversely correlates with the neurogenic potential of NSPCs. Furthermore, as huNSPCs are continually passaged they decrease neuron generation and increase membrane capacitance, confirming that this parameter dynamically predicts and negatively correlates with neurogenic potential. In contrast, differences in membrane conductance between NSPCs do not consistently correlate with the ability of the cells to generate neurons. DEP crossover frequency, which is a quantitative measure of cell behavior in DEP, directly correlates with neuron generation of NSPCs, indicating a potential mechanism to separate stem cells biased to particular differentiated cell fates.

Conclusions/Significance

We show here that whole cell membrane capacitance, but not membrane conductance, reflects and predicts the neurogenic potential of human and mouse NSPCs. Stem cell biophysical characteristics therefore provide a completely novel and quantitative measure of stem cell fate potential and a label-free means to identify neuron- or glial-biased progenitors.     

Thermal ecology and baseline energetic requirements of a large‐bodied ectotherm suggest resilience to climate change

1. Most studies on how rising temperatures will impact terrestrial ectotherms have focused on single populations or multiple sympatric species. Addressing the thermal and energetic implications of climatic variation on multiple allopatric populations of a species will help us better understand how a species may be impacted by altered climates.
2. We used eight years of thermal and behavioral data collected from four populations of Pacific rattlesnakes (Crotalus oreganus) living in climatically distinct habitat types (inland and coastal) to determine the field‐active and laboratory‐preferred body temperatures, thermoregulatory metrics, and maintenance energetic requirements of snakes from each population.
3. Physical models showed that thermal quality was best at coastal sites, but inland snakes thermoregulated more accurately despite being in more thermally constrained environments. Projected increases of 1 and 2°C in ambient temperature result in an increase in overall thermal quality at both coastal and inland sites.
4. Population differences in modeled standard metabolic rate estimates were driven by body size and not field‐active body temperature, with inland snakes requiring 1.6× more food annually than coastal snakes.
5. All snakes thermoregulated with high accuracy, suggesting that small increases in ambient temperature are unlikely to impact the maintenance energetic requirements of individual snakes and that some species of large‐bodied reptiles may be robust to modest thermal perturbations under conservative climate change predictions.

​     

Okazaki fragment processing-independent role for human Dna2 enzyme during DNA replication

Dna2 is an essential helicase/nuclease that is postulated to cleave long DNA flaps that escape FEN1 activity during Okazaki fragment (OF) maturation in yeast. We previously demonstrated that the human Dna2 orthologue (hDna2) localizes to the nucleus and contributes to genomic stability. Here we investigated the role hDna2 plays in DNA replication. We show that Dna2 associates with the replisome protein And-1 in a cell cycle-dependent manner. Depletion of hDna2 resulted in S/G(2) phase-specific DNA damage as evidenced by increased γ-H2AX, replication protein A foci, and Chk1 kinase phosphorylation, a readout for activation of the ATR-mediated S phase checkpoint. In addition, we observed reduced origin firing in hDna2-depleted cells consistent with Chk1 activation. We next examined the impact of hDna2 on OF maturation and replication fork progression in human cells. As expected, FEN1 depletion led to a significant reduction in OF maturation. Strikingly, the reduction in OF maturation had no impact on replication fork progression, indicating that fork movement is not tightly coupled to lagging strand maturation. Analysis of hDna2-depleted cells failed to reveal a defect in OF maturation or replication fork progression. Prior work in yeast demonstrated that ectopic expression of FEN1 rescues Dna2 defects. In contrast, we found that FEN1 expression in hDna2-depleted cells failed to rescue genomic instability. These findings suggest that the genomic instability observed in hDna2-depleted cells does not arise from defective OF maturation and that hDna2 plays a role in DNA replication that is distinct from FEN1 and OF maturation.     

Donor milk intake and infant growth in a South African neonatal unit: a cohort study

Background

Implications of donor milk feedings on infant growth in resource limited settings remain uncertain. This knowledge gap includes the impact of donor milk availability on infant intake of mother’s own milk. Therefore, this investigation aimed to measure intake and growth in infants receiving donor milk when born to women from resource limited backgrounds with high rates of human immunodeficiency virus (HIV).

Methods

A retrospective cohort study enrolled eligible infants admitted to a South African combined neonatal intensive and secondary high care unit, within a one year admission period during 2015, with signed consent for donor milk feedings. A certified milk bank provided donor milk. Daily nutritional intake during the first month was recorded. Details included proportional intake of donor milk, mother’s own milk and infant formula. The primary outcome of infant growth velocity from day back to birth weight to discharge was calculated when length of stay was ≥14 days. Analyses primarily used T-tests; mixed effects models compared weekly calorie intake.

Results

One hundred five infants with donor milk consent were born at 30.9?±?3.6 weeks of gestation, weighing 1389?±?708 g. Forty percent of mothers had HIV. Infant growth velocity did not differ based on percent of feedings as donor milk (≥ 50%: 11.8?±?4.9 g/kg/d; <?50%: 13.5?±?5.3 g/kg/d; p?=?0.3). Percent of feedings from donor milk was similar based on maternal HIV status (positive: 31?±?25%; negative: 36?±?29%; p?=?0.4), as was percent of feedings as mother’s milk (positive: 53?±?35%; negative: 58?±?30%; p?=?0.4). Calorie intake increased markedly during the first two weeks and then plateaued (p?<?0.0001).

Conclusions

Donor milk feedings in higher proportions did not further impair growth of infants managed in a South African combined neonatal intensive and secondary high care unit with growth rates already below reference ranges. The provision of donor milk contributed to feedings being composed of primarily human milk during the first month. Increasing early calorie intake may improve infant growth in this center.

     

Glycosylation of a Fasciclin-Like Arabinogalactan-Protein (SOS5) Mediates Root Growth and Seed Mucilage Adherence via a Cell Wall Receptor-Like Kinase (FEI1/FEI2) Pathway in Arabidopsis

Fundamental processes that underpin plant growth and development depend crucially on the action and assembly of the cell wall, a dynamic structure that changes in response to both developmental and environmental cues. While much is known about cell wall structure and biosynthesis, much less is known about the functions of the individual wall components, particularly with respect to their potential roles in cellular signaling. Loss-of-function mutants of two arabinogalactan-protein (AGP)-specific galactosyltransferases namely, GALT2 and GALT5, confer pleiotropic growth and development phenotypes indicating the important contributions of carbohydrate moieties towards AGP function. Notably, galt2galt5 double mutants displayed impaired root growth and root tip swelling in response to salt, likely as a result of decreased cellulose synthesis. These mutants phenocopy a salt-overly sensitive mutant called sos5, which lacks a fasciclin-like AGP (SOS5/FLA4) as well as a fei1fei2 double mutant, which lacks two cell wall-associated leucine-rich repeat receptor-like kinases. Additionally, galt2gal5 as well as sos5 and fei2 showed reduced seed mucilage adherence. Quintuple galt2galt5sos5fei1fei2 mutants were produced and provided evidence that these genes act in a single, linear genetic pathway. Further genetic and biochemical analysis of the quintuple mutant demonstrated involvement of these genes with the interplay between cellulose biosynthesis and two plant growth regulators, ethylene and ABA, in modulating root cell wall integrity.     

The grant is what I eat: the politics of social security and disability in the post-apartheid South African state

In South Africa, disability grant allocation has been under review and tensions are evident in government rhetoric stressing welfare provision on the one hand, and encouraging 'rationalization' on the other. This ambiguity is traced down to the level of grant negotiations between doctors and 'clients' in a psychiatry clinic in Khayelitsha. Here 'having nerves' embodies the distress associated with harsh circumstances and is deemed by supplicants as sufficient to secure a grant. The paper illustrates how national discourses influence the presentation and experience of suffering and the way in which doctors mediate diagnoses. The implications of local understandings of 'health citizenship' for expectations of the post-apartheid state are explored.