Sinisa Hrvatin

Functional beta-cell maturation is marked by an increased glucose threshold and by expression of urocortin 3

Insulin-expressing cells that have been differentiated from human pluripotent stem cells in vitro lack the glucose responsiveness characteristic of mature beta cells. Beta-cell maturation in mice was studied to find genetic markers that enable screens for factors that induce bona fide beta cells in vitro. We find that functional beta-cell maturation is marked by an increase in the glucose threshold for insulin secretion and by expression of the gene urocortin 3.

Differentiated human stem cells resemble fetal, not adult, β cells

Significance Human pluripotent stem cells (hPSCs) can be produced from any person and have the potential to differentiate into any cell type in the body. This study focuses on the generation of insulin-expressing cells from hPSCs and compares their gene expression, as assayed by transcriptional gene products, to that of insulin-expressing β cells from human fetal and adult samples. We employ a new method to isolate and profile insulin-expressing cells and conclude that several different hPSC lines generate very similar insulin-expressing cells, cells whose transcripts resemble fetal rather than adult β cells. This study advances the possibility of directing the differentiation of stem cells into functional β cells by comparing and cataloging differences between hPSC-derived insulin-expressing cells and human β cells. Human pluripotent stem cells (hPSCs) have the potential to generate any human cell type, and one widely recognized goal is to make pancreatic β cells. To this end, comparisons between differentiated cell types produced in vitro and their in vivo counterparts are essential to validate hPSC-derived cells. Genome-wide transcriptional analysis of sorted insulin-expressing (INS+) cells derived from three independent hPSC lines, human fetal pancreata, and adult human islets points to two major conclusions: (i) Different hPSC lines produce highly similar INS+ cells and (ii) hPSC-derived INS+ (hPSC-INS+) cells more closely resemble human fetal β cells than adult β cells. This study provides a direct comparison of transcriptional programs between pure hPSC-INS+ cells and true β cells and provides a catalog of genes whose manipulation may convert hPSC-INS+ cells into functional β cells.

Cloning and characterization of the biosynthetic gene cluster for kutznerides

Kutznerides, actinomycete-derived cyclic depsipetides, consist of six nonproteinogenic residues, including a highly oxygenated tricyclic hexahydropyrroloindole, a chlorinated piperazic acid, 2-(1-methylcyclopropyl)-glycine, a β-branched-hydroxy acid, and 3-hydroxy glutamic acid, for which biosynthetic logic has not been elucidated. Herein we describe the biosynthetic gene cluster for the kutzneride family, identified by degenerate primer PCR for halogenating enzymes postulated to be involved in biosyntheses of these unusual monomers. The 56-kb gene cluster encodes a series of six nonribosomal peptide synthetase (NRPS) modules distributed over three proteins and a variety of tailoring enzymes, including both mononuclear nonheme iron and two flavin-dependent halogenases, and an array of oxygen transfer catalysts. The sequence and organization of NRPS genes support incorporation of the unusual monomer units into the densely functionalized scaffold of kutznerides. Our work provides insight into the formation of this intriguing class of compounds and provides a foundation for elucidating the timing and mechanisms of their biosynthesis.

DeCoN: genome-wide analysis of in vivo transcriptional dynamics during pyramidal neuron fate selection in neocortex

UNLABELLED Neuronal development requires a complex choreography of transcriptional decisions to obtain specific cellular identities. Realizing the ultimate goal of identifying genome-wide signatures that define and drive specific neuronal fates has been hampered by enormous complexity in both time and space during development. Here, we have paired high-throughput purification of pyramidal neuron subclasses with deep profiling of spatiotemporal transcriptional dynamics during corticogenesis to resolve lineage choice decisions. We identified numerous features ranging from spatial and temporal usage of alternative mRNA isoforms and promoters to a host of mRNA genes modulated during fate specification. Notably, we uncovered numerous long noncoding RNAs with restricted temporal and cell-type-specific expression. To facilitate future exploration, we provide an interactive online database to enable multidimensional data mining and dissemination. This multifaceted study generates a powerful resource and informs understanding of the transcriptional regulation underlying pyramidal neuron diversity in the neocortex. VIDEO ABSTRACT

Widespread occurrence and genomic context of unusually small polyketide synthase genes in microbial consortia associated with marine sponges.

ABSTRACT Numerous marine sponges harbor enormous amounts of as-yet-uncultivated bacteria in their tissues. There is increasing evidence that these symbionts play an important role in the synthesis of protective metabolites, many of which are of great pharmacological interest. In this study, genes for the biosynthesis of polyketides, one of the most important classes of bioactive natural products, were systematically investigated in 20 demosponge species from different oceans. Unexpectedly, the sponge metagenomes were dominated by a ubiquitously present, evolutionarily distinct, and highly sponge-specific group of polyketide synthases (PKSs). Open reading frames resembling animal fatty acid genes were found on three corresponding DNA regions isolated from the metagenomes of Theonella swinhoei and Aplysina aerophoba. Their architecture suggests that methyl-branched fatty acids are the metabolic product. According to a phylogenetic analysis of housekeeping genes, at least one of the PKSs belongs to a bacterium of the Deinococcus-Thermus phylum. The results provide new insights into the chemistry of sponge symbionts and allow inference of a detailed phylogeny of the diverse functional PKS types present in sponge metagenomes. Based on these qualitative and quantitative data, we propose a significantly simplified strategy for the targeted isolation of biomedically relevant PKS genes from complex sponge-symbiont associations.

MARIS: method for analyzing RNA following intracellular sorting.

Transcriptional profiling is a key technique in the study of cell biology that is limited by the availability of reagents to uniquely identify specific cell types and isolate high quality RNA from them. We report a Method for Analyzing RNA following Intracellular Sorting (MARIS) that generates high quality RNA for transcriptome profiling following cellular fixation, intracellular immunofluorescent staining and FACS. MARIS can therefore be used to isolate high quality RNA from many otherwise inaccessible cell types simply based on immunofluorescent tagging of unique intracellular proteins. As proof of principle, we isolate RNA from sorted human embryonic stem cell-derived insulin-expressing cells as well as adult human β cells. MARIS is a basic molecular biology technique that could be used across several biological disciplines.

Single-cell transcriptomics of the developing lateral geniculate nucleus reveals insights into circuit assembly and refinement

Significance Neurons and nonneuronal cells in the developing brain dynamically regulate gene expression as neural connectivity is established. However, the specific gene programs activated in distinct cell populations during the assembly and refinement of many intact neuronal circuits have not been thoroughly characterized. In this study, we take advantage of recent advances in transcriptomic profiling techniques to characterize gene expression in the postnatal developing lateral geniculate nucleus (LGN) at single-cell resolution. Our data reveal that genes involved in brain development are dynamically regulated in all major cell types of the LGN, suggesting that the establishment of neural connectivity depends upon functional collaboration between multiple neuronal and nonneuronal cell types in this brain region. Coordinated changes in gene expression underlie the early patterning and cell-type specification of the central nervous system. However, much less is known about how such changes contribute to later stages of circuit assembly and refinement. In this study, we employ single-cell RNA sequencing to develop a detailed, whole-transcriptome resource of gene expression across four time points in the developing dorsal lateral geniculate nucleus (LGN), a visual structure in the brain that undergoes a well-characterized program of postnatal circuit development. This approach identifies markers defining the major LGN cell types, including excitatory relay neurons, oligodendrocytes, astrocytes, microglia, and endothelial cells. Most cell types exhibit significant transcriptional changes across development, dynamically expressing genes involved in distinct processes including retinotopic mapping, synaptogenesis, myelination, and synaptic refinement. Our data suggest that genes associated with synapse and circuit development are expressed in a larger proportion of nonneuronal cell types than previously appreciated. Furthermore, we used this single-cell expression atlas to identify the Prkcd-Cre mouse line as a tool for selective manipulation of relay neurons during a late stage of sensory-driven synaptic refinement. This transcriptomic resource provides a cellular map of gene expression across several cell types of the LGN, and offers insight into the molecular mechanisms of circuit development in the postnatal brain.

Publisher Correction: Single-cell analysis of experience-dependent transcriptomic states in the mouse visual cortex

In the version of this article initially published, the x-axis labels in Fig. 3c read Vglut, Gad1/2, Aldh1l1 and Pecam1; they should have read Vglut+, Gad1/2+, Aldh1l1+ and Pecam1+. In Fig. 4, the range values were missing from the color scales; they are, from left to right, 4–15, 0–15, 4–15 and 0–15 in Fig. 4a and 4–15, 4–15 and 4–8 in Fig. 4h. In the third paragraph of the main text, the phrase reading “Previous approaches have analyzed a limited number of inhibitory cell types, thus masking the full diversity of excitatory populations” should have read “Previous approaches have analyzed a limited number of inhibitory cell types and masked the full diversity of excitatory populations.” In the second paragraph of Results section “Diversity of experience-regulated ERGs,” the phrase reading “thus suggesting considerable divergence within the gene expression program responding to early stimuli” should have read “thus suggesting considerable divergence within the early stimulus-responsive gene expression program.” In the fourth paragraph of Results section “Excitatory neuronal LRGs,” the sentence reading “The anatomical organization of these cell types into sublayers, coupled with divergent transcriptional responses to a sensory stimulus, suggested previously unappreciated functional subdivisions located within the laminae of the mouse visual cortex and resembling the cytoarchitecture in higher mammals” should have read “The anatomical organization of these cell types into sublayers, coupled with divergent transcriptional responses to a sensory stimulus, suggests previously unappreciated functional subdivisions located within the laminae of the mouse visual cortex, resembling the cytoarchitecture in higher mammals.” In the last sentence of the Results, “sensory-responsive genes” should have read “sensory-stimulus-responsive genes.” The errors have been corrected in the HTML and PDF versions of the article.

Catching the Brain in the Act

Understanding how genes within cells, and cells within circuits, function together to produce the extraordinary repertoire of animal behaviors is arguably one of the most challenging undertakings in neuroscience. Two papers in this issue move toward this goal via 3D imaging of active neurons across the entire mouse brain.