Microglia, the resident immune cells of the central nervous system (CNS), are derived from yolk-sac macrophages that populate the developing CNS during early embryonic development. Once established, the microglia population is self-maintained throughout life by local proliferation. As a scalable source of microglia-like cells (MGLs), we here present a forward programming protocol for their generation from human pluripotent stem cells (hPSCs). The transient overexpression of PU.1 and C/EBPβ in hPSCs led to a homogenous population of mature microglia within 16 d. MGLs met microglia characteristics on a morphological, transcriptional, and functional level. MGLs facilitated the investigation of a human tauopathy model in cortical neuron–microglia cocultures, revealing a secondary dystrophic microglia phenotype. Single-cell RNA sequencing of microglia integrated into hPSC-derived cortical brain organoids demonstrated a shift of microglia signatures toward a more-developmental in vivo–like phenotype, inducing intercellular interactions promoting neurogenesis and arborization. Taken together, our microglia forward programming platform represents a tool for both reductionist studies in monocultures and complex coculture systems, including 3D brain organoids for the study of cellular interactions in healthy or diseased environments.

Background: ␥-Secretase is composed of four subunits with 19 transmembrane domains. Results: Transmembrane domain (TMD) 4 of presenilin 1 contains polar amino acids that are involved in ER retention, assembly, and stability. Conclusion: TMD4 is a crucial interaction site in the ␥-secretase complex. Significance: Understanding TMD-TMD interactions in molecular detail is crucial for understanding of ␥-secretase and other membrane protein complexes.

Edited by Tamas DalmayKeywords: Double-stranded RNA RNA-dependent RNA polymerase Conidia color switching Neurospora crassa a b s t r a c tIn the filamentous fungus Neurospora, the production of dsRNA can elicit a dsRNA-induced transcriptional response similar to the interferon response in vertebrates. However, how fungi sense the expression of dsRNA and activate gene expression is unknown. In this study, we established a dsRNA response reporter system in Neurospora crassa. Using the dsRNA-activated RNA-dependent RNA polymerase gene rrp-3 promoter, we created an expression construct (pRRP-3::Myc-Al-1) and introduced it into al-1 KO mutant. The test dsRNA efficiently induced pRRP-3::Myc-Al-1 expression in the al-1 KO mutant, resulting in conidia color switching from white to yellow. These results confirm that the dsRNA response is regulated at the transcriptional level and this reporter system can be used for future studies in dsRNA response in filamentous fungi. Crown