Intrinsically disordered domain of transcription factor TCF-1 is required for T cell developmental fidelity.

In development, pioneer transcription factors access silent chromatin to reveal lineage-specific gene programs. The structured DNA-binding domains of pioneer factors have been well characterized, but whether and how intrinsically disordered regions affect chromatin and control cell fate is unclear. Here, we report that deletion of an intrinsically disordered region of the pioneer factor TCF-1 (termed L1) leads to an early developmental block in T cells. The few T cells that develop from progenitors expressing TCF-1 lacking L1 exhibit lineage infidelity distinct from the lineage diversion of TCF-1-deficient cells. Mechanistically, L1 is required for activation of T cell genes and repression of GATA2-driven genes, normally reserved to the mast cell and dendritic cell lineages. Underlying this lineage diversion, L1 mediates binding of TCF-1 to its earliest target genes, which are subject to repression as T cells develop. These data suggest that the intrinsically disordered N terminus of TCF-1 maintains T cell lineage fidelity.

Chromatin-enriched lncRNAs can act as cell-type specific activators of proximal gene transcription.

We recently described a new class of long noncoding RNAs (lncRNAs) that are distinguished by especially tight chromatin association and whose presence is strongly correlated to expression of nearby genes. Here, we examine the cis-enhancer mechanism of this class of chromatin-enriched RNA (cheRNA) across multiple human cell lines. cheRNAs are largely cell type specific and provide the most reliable chromatin signature to predict cis-gene transcription in every human cell type examined. Targeted depletion of three cheRNAs decreases expression of their neighboring genes, indicating potential co-activator function, and single-molecule fluorescence in situ hybridization (smFISH) of one cheRNA-distal target gene pair suggests a spatial overlap consistent with a role in chromosome looping. Additionally, the cheRNA HIDALGO stimulates the fetal hemoglobin subunit gamma 1 (HBG1) gene during erythroid differentiation by promoting contacts to a downstream enhancer. Our results suggest that multiple cheRNAs activate proximal lineage-specific gene transcription.

A Systematic Review and Comparison of Outcomes Following Simple Syndactyly Reconstruction With Skin Grafts or a Dorsal Metacarpal Advancement Flap.

PURPOSE: Many techniques exist for simple syndactyly reconstruction. The most commonly used techniques involve either skin grafts or a dorsal metacarpal advancement flap. Our aim was to review and compare the outcomes of these 2 techniques systematically. METHODS: We reviewed articles from PubMed, MEDLINE, EMBASE, and Google Scholar published between January 1966 and January 2016. We identified studies that reported outcomes after reconstruction of simple syndactyly using skin grafts and those using only a dorsal metacarpal advancement flap. Cases of complex syndactyly and those that were not clearly differentiated by technique or type of simple syndactyly were excluded. Outcomes were then stratified by technique and type of syndactyly (complete and incomplete). RESULTS: We identified 693 articles and selected 34 for inclusion. No standardized outcome measure was uniformly applied in the examined studies. Overall, skin grafting procedures were associated with more complications (eg, flap necrosis/graft failure, contracture, web creep, hypertrophic scarring) and a greater need for revision. When stratified by subtype, patients with simple, complete syndactyly who underwent skin grafting had a significantly higher rate of hypertrophic scarring than those who underwent reconstruction with a dorsal metacarpal advancement flap. CONCLUSIONS: Simple syndactyly reconstruction with a dorsal metacarpal advancement flap may lead to fewer complications than procedures using skin grafts. However, substantial limitations of currently available evidence do not allow for the recommendation of a specific technique. Future research should use a uniform reporting system for syndactyly classification and complications. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Pediatric Hand Injuries.

Pediatric hand injuries are extremely common. Although many hand injuries are adequately managed in the emergency department, some may need evaluation and treatment by a pediatric hand surgeon to ensure a good functional outcome. This article discusses the diagnosis and management of the most common pediatric hand maladies: fingertip injuries/amputation, tendon injuries, and phalangeal and metacarpal fractures. The plastic surgery nurse should be familiar with hand injuries that require intervention to facilitate efficient management and optimal postoperative care.

Congenital Hand Differences.

Congenital hand differences are frequently encountered by pediatric plastic surgeons. These anomalies may cause significant emotional and functional challenges for children. Pediatric plastic surgery nurses should have a basic understanding of common congenital hand differences and related treatment options to facilitate patient education and postoperative care. This article discusses clinical findings and management of 4 of the most common hand anomalies: syndactyly, polydactyly, thumb hypoplasia, and cleft hand. The goals of surgical treatment are to maximize hand function and aesthetics with minimal adverse outcomes.

Complex autonomous firing patterns of striatal low-threshold spike interneurons.

During sensorimotor learning, tonically active neurons (TANs) in the striatum acquire bursts and pauses in their firing based on the salience of the stimulus. Striatal cholinergic interneurons display tonic intrinsic firing, even in the absence of synaptic input, that resembles TAN activity seen in vivo. However, whether there are other striatal neurons among the group identified as TANs is unknown. We used transgenic mice expressing green fluorescent protein under control of neuronal nitric oxide synthase or neuropeptide-Y promoters to aid in identifying low-threshold spike (LTS) interneurons in brain slices. We found that these neurons exhibit autonomous firing consisting of spontaneous transitions between regular, irregular, and burst firing, similar to cholinergic interneurons. As in cholinergic interneurons, these firing patterns arise from interactions between multiple intrinsic oscillatory mechanisms, but the mechanisms responsible differ. Both neurons maintain tonic firing because of persistent sodium currents, but the mechanisms of the subthreshold oscillations responsible for irregular firing are different. In LTS interneurons they rely on depolarization-activated noninactivating calcium currents, whereas those in cholinergic interneurons arise from a hyperpolarization-activated potassium conductance. Sustained membrane hyperpolarizations induce a bursting pattern in LTS interneurons, probably by recruiting a low-threshold, inactivating calcium conductance and by moving the membrane potential out of the activation range of the oscillatory mechanisms responsible for single spiking, in contrast to the bursting driven by noninactivating currents in cholinergic interneurons. The complex intrinsic firing patterns of LTS interneurons may subserve differential release of classic and peptide neurotransmitters as well as nitric oxide.

Recurrent inhibitory network among striatal cholinergic interneurons.

The striatum plays a central role in sensorimotor learning and action selection. Tonically active cholinergic interneurons in the striatum give rise to dense axonal arborizations and significantly shape striatal output. However, it is not clear how the activity of these neurons is regulated within the striatal microcircuitry. In this study, using rat brain slices, we find that stimulation of intrastriatal cholinergic fibers evokes polysynaptic GABA(A) IPSCs in cholinergic interneurons. These polysynaptic GABA(A) IPSCs were abolished by general nicotinic acetylcholine receptor antagonists and also by a specific antagonist of nicotinic receptors containing beta2 subunits. Dopamine receptor antagonists or dopamine depletion failed to block polysynaptic IPSCs, indicating that phasic dopamine release does not directly mediate the polysynaptic transmission. Dual recording from pairs of cholinergic interneurons revealed that activation of a single cholinergic interneuron is capable of eliciting polysynaptic GABA(A) IPSCs both in itself and in nearby cholinergic interneurons. Although polysynaptic transmission arising from a single cholinergic interneuron was depressed during repetitive 2 Hz firing, intrastriatal stimulation reliably evoked large polysynaptic IPSCs by recruiting many cholinergic fibers. We also show that polysynaptic GABAergic inhibition leads to a transient suppression of tonic cholinergic interneuron firing. We propose a novel microcircuit in the striatum, in which cholinergic interneurons are connected to one another through GABAergic interneurons. This may provide a mechanism to convert activation of cholinergic interneurons into widespread recurrent inhibition of these neurons via nicotinic excitation of striatal GABAergic neurons.

Sindbis viral-mediated expression of eGFP-dopamine D1 receptors in situ with real-time two-photon microscopic detection.

Dopamine D1 receptors (D1DRs) mediate a major component of dopaminergic neurotransmission, and alterations in their synaptic and subcellular distribution may underlie a variety of neurological diseases. In order to monitor D1DR localization in real time, we subcloned a sindbis virus containing an enhanced-GFP coding region inserted at the C-terminal region of a dopamine D1 receptor (eGFP-D1DR). Two-photon excitation of expressed eGFP-D1DRs was monitored in a variety of viable neural preparations. Infection of primary cultured rat ventral striatal neurons, verified for neuronal phenotype using patch clamp electrophysiology, was induced by the simple addition of the virus to media. Parasagittal slice cultures, including the ventral tegmental area (VTA) and nucleus accumbens (NAc), were infected by manual injection below the glia surface. NAc-containing parasagittal slices prepared from mice in which the virus was administered via stereotaxic injection in vivo also displayed robust eGFP-D1DR expression. Expression of functional D1DRs following infection in baby hamster kidney (BHK) cells was monitored by DA-stimulated cAMP production that was also blocked by a selective D1 antagonist. Taken together, these findings provide the first demonstration of the functional expression and real-time imaging of eGFP-D1DRs, and indicate that sindbis virus is an effective method for D1 receptor expression in a variety of native neuronal preparations.