BackgroundDue to their ability to limitlessly proliferate and specialize into almost any cell type, human induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to generate human brain microvascular endothelial cells (BMECs), which compose the blood–brain barrier (BBB), for research purposes. Unfortunately, the time, expense, and expertise required to differentiate iPSCs to purified BMECs precludes their widespread use. Here, we report the use of a defined medium that accelerates the differentiation of iPSCs to BMECs while achieving comparable performance to BMECs produced by established methods.MethodsInduced pluripotent stem cells were seeded at defined densities and differentiated to BMECs using defined medium termed E6. Resultant purified BMEC phenotypes were assessed through trans-endothelial electrical resistance (TEER), fluorescein permeability, and P-glycoprotein and MRP family efflux transporter activity. Expression of endothelial markers and their signature tight junction proteins were confirmed using immunocytochemistry. The influence of co-culture with astrocytes and pericytes on purified BMECs was assessed via TEER measurements. The robustness of the differentiation method was confirmed across independent iPSC lines.ResultsThe use of E6 medium, coupled with updated culture methods, reduced the differentiation time of iPSCs to BMECs from thirteen to 8 days. E6-derived BMECs expressed GLUT-1, claudin-5, occludin, PECAM-1, and VE-cadherin and consistently achieved TEER values exceeding 2500 Ω × cm2 across multiple iPSC lines, with a maximum TEER value of 4678 ± 49 Ω × cm2 and fluorescein permeability below 1.95 × 10−7 cm/s. E6-derived BMECs maintained TEER above 1000 Ω × cm2 for a minimum of 8 days and showed no statistical difference in efflux transporter activity compared to BMECs differentiated by conventional means. The method was also found to support long-term stability of BMECs harboring biallelic PARK2 mutations associated with Parkinson’s Disease. Finally, BMECs differentiated using E6 medium responded to inductive cues from astrocytes and pericytes and achieved a maximum TEER value of 6635 ± 315 Ω × cm2, which to our knowledge is the highest reported in vitro TEER value to date.ConclusionsGiven the accelerated differentiation, equivalent performance, and reduced cost to produce BMECs, our updated methods should make iPSC-derived in vitro BBB models more accessible for a wide variety of applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s12987-017-0059-0) contains supplementary material, which is available to authorized users.

This article addresses theoretical and empirical issues relevant for the development and evaluation of language learning progressions. The authors explore how learning progressions aligned with new content standards can form a central basis of efforts to describe the English language needed in school contexts for learning, instruction, and assessment. Learning progressions, in contrast with standards, can articulate incremental growth and are positioned to support teachers' formative assessment practices with K-12 students who are acquiring English as an additional language. Extending learning progressions that have taken hold in other areas of student learning to language learning and development requires conceptualizing (1) in what ways language progresses, and (2) how language growth can be supported by educators. The authors illustrate both considerations with the example of a new language learning progression and formative assessment initiative that are based on the characterization of explanations generated by students with a wide range of experiences with English.

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For parents to provide effective support for their children’s language development, they must be attuned to their child’s changing abilities. This study presents a theoretically driven strategy that addresses a methodological challenge present when tracking longitudinally the cessation or ‘fading’ of behaviors by capturing withdrawal of maternal assistance over time relative to change in child participation. Data are the co-constructed narratives of 31 mother–child dyads when the children were 3, 4, and 5 years old. Responsibility for providing narrative macrostructure shifted from children relying on maternal prompts to contributing them spontaneously, while maternal contributions showed a gradual cessation. The findings support the notion of bidirectionality in co-construction and are interpreted using a dose-effect model of the shift in responsibility for the narration over time with implications for intervention.