Sea lamprey enlightens the origin of the coupling of retinoic acid signaling to vertebrate hindbrain segmentation.

Retinoic acid (RA) is involved in antero-posterior patterning of the chordate body axis and, in jawed vertebrates, has been shown to play a major role at multiple levels of the gene regulatory network (GRN) regulating hindbrain segmentation. Knowing when and how RA became coupled to the core hindbrain GRN is important for understanding how ancient signaling pathways and patterning genes can evolve and generate diversity. Hence, we investigated the link between RA signaling and hindbrain segmentation in the sea lamprey Petromyzon marinus, an important jawless vertebrate model providing clues to decipher ancestral vertebrate features. Combining genomics, gene expression, and functional analyses of major components involved in RA synthesis (Aldh1as) and degradation (Cyp26s), we demonstrate that RA signaling is coupled to hindbrain segmentation in lamprey. Thus, the link between RA signaling and hindbrain segmentation is a pan vertebrate feature of the hindbrain and likely evolved at the base of vertebrates.

Reducing wait times and avoiding unnecessary use of high-cost mental health services through a Rapid Access and Stabilization Program: protocol for a program evaluation study.

BACKGROUND: Emergency psychiatric care, unplanned hospital admissions, and inpatient health care are the costliest forms of mental health care. According to Statistics Canada (2018), almost 18% (5.3 million) of Canadians reported needing mental health support. However, just above half of this figure (56.2%) have reported their needs were fully met. In light of this evidence there is a pressing need to provide accessible mental health services in flexible yet cost-effective ways. To further expand capacity and access to mental health care in the province, Nova Scotia Health has launched a novel mental health initiative for people in need of mental health care without requiring emergency department visits or hospitalization. This new service is referred to as the Rapid Access and Stabilization Program (RASP). This study evaluates the effectiveness and impact of the RASP on high-cost health services utilization (e.g. ED visits, mobile crisis visits, and inpatient treatments) and related costs. It also assesses healthcare partners' (e.g. healthcare providers, policymakers, community leaders) perceptions and patient experiences and satisfaction with the program and identifies sociodemographic characteristics, psychological conditions, recovery, well-being, and risk measures in the assisted population. METHOD: This is a hypothesis-driven program evaluation study that employs a mixed methods approach. A within-subject comparison (pre- and post-evaluation study) will examine health services utilization data from patients attending RASP, one year before and one year after their psychiatry assessment at the program. A controlled between-subject comparison (cohort study) will use historical data from a control population will examine whether possible changes in high-cost health services utilization are associated with the intervention (RASP). The primary analysis involves extracting secondary data from provincial information systems, electronic medical records, and regular self-reported clinical assessments. Additionally, a qualitative sub-study will examine patient experience and satisfaction, and health care partners' impressions. DISCUSSION: We expect that RASP evaluation findings will demonstrate a minimum 10% reduction in high-cost health services utilization and corresponding 10% cost savings, and also a reduction in the wait times for patient consultations with psychiatrists to less than 30 calendar days, in both within-subject and between-subject comparisons. In addition, we anticipate that patients, healthcare providers and healthcare partners would express high levels of satisfaction with the new service. CONCLUSION: This study will demonstrate the results of the Mental Health and Addictions Program (MHAP) efforts to provide stepped-care, particularly community-based support, to individuals with mental illnesses. Results will provide new insights into a novel community-based approach to mental health service delivery and contribute to knowledge on how to implement mental health programs across varying contexts.

Chromatin accessibility in the Drosophila embryo is determined by transcription factor pioneering and enhancer activation.

Chromatin accessibility is integral to the process by which transcription factors (TFs) read out cis-regulatory DNA sequences, but it is difficult to differentiate between TFs that drive accessibility and those that do not. Deep learning models that learn complex sequence rules provide an unprecedented opportunity to dissect this problem. Using zygotic genome activation in Drosophila as a model, we analyzed high-resolution TF binding and chromatin accessibility data with interpretable deep learning and performed genetic validation experiments. We identify a hierarchical relationship between the pioneer TF Zelda and the TFs involved in axis patterning. Zelda consistently pioneers chromatin accessibility proportional to motif affinity, whereas patterning TFs augment chromatin accessibility in sequence contexts where they mediate enhancer activation. We conclude that chromatin accessibility occurs in two tiers: one through pioneering, which makes enhancers accessible but not necessarily active, and the second when the correct combination of TFs leads to enhancer activation.

Pan-Canadian study of psychiatric care (PCPC): protocol for a mixed-methods study.

INTRODUCTION: The Canadian population has poor and inequitable access to psychiatric care despite a steady per-capita supply of psychiatrists in most provinces. There is some quantitative evidence that practice style and characteristics vary substantially among psychiatrists. However, how this compares across jurisdictions and implications for workforce planning require further study. A qualitative exploration of psychiatrists' preferences for practice style and the practice choices that result is also lacking. The goal of this study is to inform psychiatrist workforce planning to improve access to psychiatric care by: (1) developing and evaluating comparable indicators of supply of psychiatric care across provinces, (2) analysing variations and changes in the characteristics of the psychiatrist workforce, including demographics and practice style and (3) studying psychiatrist practice choices and intentions, and the factors that lead to these choices. METHODS AND ANALYSIS: A cross-provincial mixed-methods study will be conducted in the Canadian provinces of British Columbia, Manitoba, Ontario and Nova Scotia. We will analyse linked-health administrative data within three of the four provinces to develop comparable indicators of supply and characterise psychiatric services at the regional level within provinces. We will use latent profile analysis to estimate the probability that a psychiatrist is in a particular practice style and map the geographical distribution of psychiatrist practices overlayed with measures of need for psychiatric care. We will also conduct in-depth, semistructured qualitative interviews with psychiatrists in each province to explore their preferences and practice choices and to inform workforce planning. ETHICS AND DISSEMINATION: This study was approved by Ontario Tech University Research Ethics Board (16637 and 16795) and institutions affiliated with the study team. We built a team comprising experienced researchers, psychiatrists, medical educators and policymakers in mental health services and workforce planning to disseminate knowledge that will support effective human resource policies to improve access to psychiatric care in Canada.

Pharmacist Administration of Long-Acting Injectable Antipsychotics to Community-Dwelling Patients: A Scoping Review.

Long-acting injectable antipsychotics (LAIAs) have demonstrated positive outcomes for people with serious mental illnesses. They are underused, and access to LAIAs can be challenging. Pharmacies could serve as suitable environments for LAIA injection by pharmacists. To map and characterize the literature regarding the administration of LAIAs by pharmacists, a scoping review was conducted. Electronic-database searches (e.g., PsycINFO, Ovid Medline, Scopus, and Embase) and others including ProQuest Dissertations & Theses Global and Google, were conducted. Citation lists and cited-reference searches were completed. Zotero was used as the reference-management database. Covidence was used for overall review management. Two authors independently screened articles and performed full-text abstractions. From all sources, 292 studies were imported, and 124 duplicates were removed. After screening, 13 studies were included for abstraction. Most articles were published in the US since 2010. Seven studies used database and survey methods, with adherence and patient satisfaction as the main patient-outcomes assessed. Reporting of pharmacists' and patients' perspectives surrounding LAIA administration was minimal and largely anecdotal. Financial analyses for services were also limited. The published literature surrounding pharmacist administration of LAIAs is limited, providing little-to-no guidance for the development and implementation of this service by others.

Cell-type profiling of the sympathetic nervous system using spatial transcriptomics and spatial mapping of mRNA.

BACKGROUND: The molecular identification of neural progenitor cell populations that connect to establish the sympathetic nervous system (SNS) remains unclear. This is due to technical limitations in the acquisition and spatial mapping of molecular information to tissue architecture. RESULTS: To address this, we applied Slide-seq spatial transcriptomics to intact fresh frozen chick trunk tissue transversely cryo-sectioned at the developmental stage prior to SNS formation. In parallel, we performed age- and location-matched single cell (sc) RNA-seq and 10× Genomics Visium to inform our analysis. Downstream bioinformatic analyses led to the unique molecular identification of neural progenitor cells within the peripheral sympathetic ganglia (SG) and spinal cord preganglionic neurons (PGNs). We then successfully applied the HiPlex RNAscope fluorescence in situ hybridization and multispectral confocal microscopy to visualize 12 gene targets in stage-, age- and location-matched chick trunk tissue sections. CONCLUSIONS: Together, these data demonstrate a robust strategy to acquire and integrate single cell and spatial transcriptomic information, resulting in improved resolution of molecular heterogeneities in complex neural tissue architectures. Successful application of this strategy to the developing SNS provides a roadmap for functional studies of neural connectivity and platform to address complex questions in neural development and regeneration.

Augmenting Mental Health Support for Patients Accessing Different Degrees of Formal Psychiatric Care through a Supportive Text Messaging Program: Protocol for a Randomized Controlled Trial.

Patients feel more vulnerable when accessing community mental health programs for the first time or after being discharged from psychiatric inpatient units. Long wait times for follow-up appointments, shortage of mental health professionals, lack of service integration, and scarcity of tailored support can weaken their connection to the health care system. As a result, patients can present low adherence, dissatisfaction with treatment, and recurrent hospitalizations. Finding solutions to avoid unnecessary high-cost services and providing tailored and cost-effective mental health interventions may reduce the health system burden and augment patient support. We propose implementing an add-on, supportive text messaging service (Text4Support), developed using cognitive-behavioural therapy (CBT) principles to augment mental health support for patients attending to or being discharged from psychiatric care in Nova Scotia, Canada. This randomized controlled trial aims to investigate the effectiveness of Text4Support in improving mental health outcomes and overall mental well-being compared with usual care. We also will examine the intervention's impact on health services utilization and patient satisfaction. The results from this study will provide evidence on stepped and technology-based mental health care, which will contribute to generating new knowledge about mental health innovations in various clinical contexts, which is not only helpful for the local context but to other jurisdictions in Canada and abroad that are seeking to improve their health care.

A multiple baseline trial of adapted prolonged exposure psychotherapy for individuals with early phase psychosis, comorbid substance misuse, and a history of adversity: A study protocol.

Background: Adversity is prevalent among people with psychotic disorders, especially those within the first 5 years of a psychotic disorder, called early phase psychosis. Although adversity can lead to many negative outcomes (e.g., posttraumatic stress symptoms), very few treatments for adversity-related sequelae have been tested with individuals with psychotic disorders, and even fewer studies have specifically tested interventions for people in early phase psychosis. Furthermore, people who misuse substances are commonly excluded from adversity treatment trials, which is problematic given that individuals with early phase psychosis have high rates of substance misuse. For the first time, this trial will examine the outcomes of an adapted 15-session prolonged exposure protocol (i.e., PE+) to observe whether reductions in adversity-related psychopathology occurs among people with early phase psychosis and comorbid substance misuse. Methods: This study will use a multiple-baseline design with randomization of participants to treatment start time. Participants will complete baseline appointments prior to therapy, engage in assessments between each of the five therapy modules, and complete a series of follow-up appointments 2 months after the completion of therapy. Primary hypothesized outcomes include clinically significant reductions in (1) negative psychotic symptoms measured using the Positive and Negative Syndrome Scale, (2) adversity-related sequelae measured using the Trauma Symptom Checklist-40, and (3) substance use frequency and overall risk score measured with the Alcohol, Smoking, and Substance Involvement Screening Test. We also anticipate that clinically significant reductions in hopelessness and experiential avoidance, measured with the Beck Hopelessness Scale and Brief Experiential Avoidance Questionnaire, the theorized mechanisms of change of PE+, will also be observed. A secondary outcome is a hypothesized improvement in functioning, measured using the Clinical Global Impression and Social and Occupational Functioning Assessment scales. Discussion: The results of this treatment trial will contribute to the advancement of treatment research for individuals in early phase psychosis who have current substance misuse and a history of adversity, and the findings may provide evidence supporting the use of hopelessness and experiential avoidance as mechanisms of change for this treatment. Clinical trial registration: Clinicaltrials.gov, NCT04546178; registered August 28, 2020, https://clinicaltrials.gov/ct2/show/NCT04546178?term=NCT04546178&draw=2&rank=1.

The Text4HealthyAging Program: An Evidence-Based Text Messaging Innovation to Support Healthy Urban Aging in Canada and Australia.

Age-friendly cities are crucial to achieve the WHO goal of healthy aging. Such cities promote opportunities for health, participation, and security, thus enhancing quality of life as people age. Older people commonly experience psychosocial challenges such as anxiety, depression, substance abuse, loss of autonomy, grief, fear, and loneliness. Australian and Canadian cities continue to seek innovation to improve healthy urban aging and create more age-friendly environments for older adults. There is increasing evidence on the effectiveness and feasibility of mobile technology in health promotion and closing psychological treatment gaps. Older adults have been demonstrated to engage frequently with mobile devices, particularly text messaging. In this article, we conceptualize the Text4HealthyAging, an evidence-based text messaging innovation to support healthy urban aging in Canadian and Australian cities.

Three-dimensional Movement and Distribution of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) Adults in Stored Wheat Under Constant Temperatures and Moisture Contents.

Understanding the movement and distribution of insects inside a grain bin is crucial to develop an effective stored grain management protocol. The three-dimensional movement and distribution of adult Cryptolestes ferrugineus (Stephens) at 20 and 30°C were determined in a 0.7 × 0.7 × 0.7 m3 (internal dimensions) wooden box filled with wheat of uniform moisture contents (12.5 ± 0.1%, 14.5 ± 0.1%, and 16.5 ± 0.1% wet basis). The wheat at a constant moisture content was filled into 343 mesh cubes (0.1 × 0.1 × 0.1 m3) and placed inside the wooden box. The center mesh cube in the box had one hundred adult insects introduced at the beginning of the movement. After 24 h, the 343 mesh cubes were removed from the wooden box in less than 45 min. Finally, the contents of each mesh cube were sieved, and the insects counted. Each experiment was replicated three times. A maximum of 17% of insects stayed at the introduced cube (center of the wooden box). About 50-88% of the introduced adults moved downward from the introduction location at the studied temperatures and moisture contents. This 24 h study showed that C. ferrugineus movements in three dimensions follow a diffusion pattern in the horizontal direction and move downward due to the 'drift' effect and geotaxis in the vertical direction.

The embryonic trunk neural crest microenvironment regulates the plasticity and invasion of human neuroblastoma via TrkB signaling.

Mistakes in trunk neural crest (NC) cell migration may lead to birth defects of the sympathetic nervous system (SNS) and neuroblastoma (NB) cancer. Receptor tyrosine kinase B (TrkB) and its ligand BDNF critically regulate NC cell migration during normal SNS development and elevated expression of TrkB is correlated with high-risk NB patients. However, in the absence of a model with in vivo interrogation of human NB cell and gene expression dynamics, the mechanistic role of TrkB in NB disease progression remains unclear. Here, we study the functional relationship between TrkB, cell invasion and plasticity of human NB cells by taking advantage of our validated in vivo chick embryo transplant model. We find that LAN5 (high TrkB) and SHSY5Y (moderate TrkB) human NB cells aggressively invade host embryos and populate typical NC targets, however loss of TrkB function significantly reduces cell invasion. In contrast, NB1643 (low TrkB) cells remain near the transplant site, but over-expression of TrkB leads to significant cell invasion. Invasive NB cells show enhanced expression of genes indicative of the most invasive host NC cells. In contrast, transplanted human NB cells down-regulate known NB tumor initiating and stem cell markers. Human NB cells that remain within the dorsal neural tube transplant also show enhanced expression of cell differentiation genes, resulting in an improved disease outcome as predicted by a computational algorithm. These in vivo data support TrkB as an important biomarker and target to control NB aggressiveness and identify the chick embryonic trunk neural crest microenvironment as a source of signals to drive NB to a less aggressive state, likely acting at the dorsal neural tube.

Examination of the impact of COVID-19 public health quarantine measures on acute mental health care services: A retrospective observational study.

This study assesses for the impact of Covid-19 public health quarantine measures on acute care psychiatric admissions, by comparing admission data from the quarantine period to a comparator period. A chart review was conducted for all admissions to an urban acute care psychiatric centre from Mar 22 - June 5 2020 (quarantine) and January 5 - Mar 21 2020 (comparator). Data was collected on the number of admissions, demographics, patients' psychiatric history, characteristics of admissions, discharge information, patients' substance use and social factors. Data was analyzed using a student's t-test for continuous variables and Chi squared analyses for categorical variables. Results demonstrated 185 admissions during quarantine and 190 during the comparator, with no significant differences in the distribution of admissions across time periods. There was a significantly greater frequency of admissions in the 35-44 age bracket and admissions involving substance use during quarantine. Additionally, admissions during quarantine were significantly shorter, with increased frequency of involuntary status and use of seclusion. The data suggests a vulnerability specific to individuals in their 30-40s during quarantine and demonstrates a need to better understand factors impacting this group. It also suggests that quarantine is associated with changes to substance use, potentiating high acuity illness requiring admission.

Modelling Cell Invasion: A Review of What JD Murray and the Embryo Can Teach Us.

Cell invasion and cell plasticity are critical to human development but are also striking features of cancer metastasis. By distributing a multipotent cell type from a place of birth to distal locations, the vertebrate embryo builds organs. In comparison, metastatic tumor cells often acquire a de-differentiated phenotype and migrate away from a primary site to inhabit new microenvironments, disrupting normal organ function. Countless observations of both embryonic cell migration and tumor metastasis have demonstrated complex cell signaling and interactive behaviors that have long confounded scientist and clinician alike. James D. Murray realized the important role of mathematics in biology and developed a unique strategy to address complex biological questions such as these. His work offers a practical template for constructing clear, logical, direct and verifiable models that help to explain complex cell behaviors and direct new experiments. His pioneering work at the interface of development and cancer made significant contributions to glioblastoma cancer and embryonic pattern formation using often simple models with tremendous predictive potential. Here, we provide a brief overview of advances in cell invasion and cell plasticity using the embryonic neural crest and its ancestral relationship to aggressive cancers that put into current context the timeless aspects of his work.

Single-cell reconstruction with spatial context of migrating neural crest cells and their microenvironments during vertebrate head and neck formation.

The dynamics of multipotent neural crest cell differentiation and invasion as cells travel throughout the vertebrate embryo remain unclear. Here, we preserve spatial information to derive the transcriptional states of migrating neural crest cells and the cellular landscape of the first four chick cranial to cardiac branchial arches (BA1-4) using label-free, unsorted single-cell RNA sequencing. The faithful capture of branchial arch-specific genes led to identification of novel markers of migrating neural crest cells and 266 invasion genes common to all BA1-4 streams. Perturbation analysis of a small subset of invasion genes and time-lapse imaging identified their functional role to regulate neural crest cell behaviors. Comparison of the neural crest invasion signature to other cell invasion phenomena revealed a shared set of 45 genes, a subset of which showed direct relevance to human neuroblastoma cell lines analyzed after exposure to the in vivo chick embryonic neural crest microenvironment. Our data define an important spatio-temporal reference resource to address patterning of the vertebrate head and neck, and previously unidentified cell invasion genes with the potential for broad impact.

Leaf: an open-source, model-agnostic, data-driven web application for cohort discovery and translational biomedical research.

OBJECTIVE: Academic medical centers and health systems are increasingly challenged with supporting appropriate secondary use of clinical data. Enterprise data warehouses have emerged as central resources for these data, but often require an informatician to extract meaningful information, limiting direct access by end users. To overcome this challenge, we have developed Leaf, a lightweight self-service web application for querying clinical data from heterogeneous data models and sources. MATERIALS AND METHODS: Leaf utilizes a flexible biomedical concept system to define hierarchical concepts and ontologies. Each Leaf concept contains both textual representations and SQL query building blocks, exposed by a simple drag-and-drop user interface. Leaf generates abstract syntax trees which are compiled into dynamic SQL queries. RESULTS: Leaf is a successful production-supported tool at the University of Washington, which hosts a central Leaf instance querying an enterprise data warehouse with over 300 active users. Through the support of UW Medicine (https://uwmedicine.org), the Institute of Translational Health Sciences (https://www.iths.org), and the National Center for Data to Health (https://ctsa.ncats.nih.gov/cd2h/), Leaf source code has been released into the public domain at https://github.com/uwrit/leaf. DISCUSSION: Leaf allows the querying of single or multiple clinical databases simultaneously, even those of different data models. This enables fast installation without costly extraction or duplication. CONCLUSIONS: Leaf differs from existing cohort discovery tools because it does not specify a required data model and is designed to seamlessly leverage existing user authentication systems and clinical databases in situ. We believe Leaf to be useful for health system analytics, clinical research data warehouses, precision medicine biobanks, and clinical studies involving large patient cohorts.

Neural crest cells bulldoze through the microenvironment using Aquaporin 1 to stabilize filopodia.

Neural crest migration requires cells to move through an environment filled with dense extracellular matrix and mesoderm to reach targets throughout the vertebrate embryo. Here, we use high-resolution microscopy, computational modeling, and in vitro and in vivo cell invasion assays to investigate the function of Aquaporin 1 (AQP-1) signaling. We find that migrating lead cranial neural crest cells express AQP-1 mRNA and protein, implicating a biological role for water channel protein function during invasion. Differential AQP-1 levels affect neural crest cell speed and direction, as well as the length and stability of cell filopodia. Furthermore, AQP-1 enhances matrix metalloprotease activity and colocalizes with phosphorylated focal adhesion kinases. Colocalization of AQP-1 with EphB guidance receptors in the same migrating neural crest cells has novel implications for the concept of guided bulldozing by lead cells during migration.

Predicting neuroblastoma using developmental signals and a logic-based model.

Genomic information from human patient samples of pediatric neuroblastoma cancers and known outcomes have led to specific gene lists put forward as high risk for disease progression. However, the reliance on gene expression correlations rather than mechanistic insight has shown limited potential and suggests a critical need for molecular network models that better predict neuroblastoma progression. In this study, we construct and simulate a molecular network of developmental genes and downstream signals in a 6-gene input logic model that predicts a favorable/unfavorable outcome based on the outcome of the four cell states including cell differentiation, proliferation, apoptosis, and angiogenesis. We simulate the mis-expression of the tyrosine receptor kinases, trkA and trkB, two prognostic indicators of neuroblastoma, and find differences in the number and probability distribution of steady state outcomes. We validate the mechanistic model assumptions using RNAseq of the SHSY5Y human neuroblastoma cell line to define the input states and confirm the predicted outcome with antibody staining. Lastly, we apply input gene signatures from 77 published human patient samples and show that our model makes more accurate disease outcome predictions for early stage disease than any current neuroblastoma gene list. These findings highlight the predictive strength of a logic-based model based on developmental genes and offer a better understanding of the molecular network interactions during neuroblastoma disease progression.

NGF reprograms metastatic melanoma to a bipotent glial-melanocyte neural crest-like precursor.

Melanoma pathogenesis from normal neural crest-derived melanocytes is often fatal due to aggressive cell invasion throughout the body. The identification of signals that reprogram de-differentiated, metastatic melanoma cells to a less aggressive and stable phenotype would provide a novel strategy to limit disease progression. In this study, we identify and test the function of developmental signals within the chick embryonic neural crest microenvironment to reprogram and sustain the transition of human metastatic melanoma to a neural crest cell-like phenotype. Results reveal that co-culture of the highly aggressive and metastatic human melanoma cell line C8161 upregulate a marker of melanosome formation (Mart-1) in the presence of embryonic day 3.5 chick trunk dorsal root ganglia. We identify nerve growth factor (NGF) as the signal within this tissue driving Mart-1 re-expression and show that NGF receptors trkA and p75 cooperate to induce Mart-1 re-expression. Furthermore, Mart-1 expressing C8161 cells acquire a gene signature of poorly aggressive C81-61 cells. These data suggest that targeting NGF signaling may yield a novel strategy to reprogram metastatic melanoma toward a benign cell type.

Epilepsy as a Network Disorder (2): What can we learn from other network disorders such as dementia and schizophrenia, and what are the implications for translational research?

There is common agreement that many disorders of the central nervous system are 'complex', that is, there are many potential factors that influence the development of the disease, underlying mechanisms, and successful treatment. Most of these disorders, unfortunately, have no cure at the present time, and therapeutic strategies often have debilitating side effects. Interestingly, some of the 'complexities' of one disorder are found in another, and the similarities are often network defects. It seems likely that more discussions of these commonalities could advance our understanding and, therefore, have clinical implications or translational impact. With this in mind, the Fourth International Halifax Epilepsy Conference and Retreat was held as described in the prior paper, and this companion paper focuses on the second half of the meeting. Leaders in various subspecialties of epilepsy research were asked to address aging and dementia or psychosis in people with epilepsy (PWE). Commonalities between autism, depression, aging and dementia, psychosis, and epilepsy were the focus of the presentations and discussion. In the last session, additional experts commented on new conceptualization of translational epilepsy research efforts. Here, the presentations are reviewed, and salient points are highlighted.

Single-cell transcriptome analysis of avian neural crest migration reveals signatures of invasion and molecular transitions.

Neural crest cells migrate throughout the embryo, but how cells move in a directed and collective manner has remained unclear. Here, we perform the first single-cell transcriptome analysis of cranial neural crest cell migration at three progressive stages in chick and identify and establish hierarchical relationships between cell position and time-specific transcriptional signatures. We determine a novel transcriptional signature of the most invasive neural crest Trailblazer cells that is consistent during migration and enriched for approximately 900 genes. Knockdown of several Trailblazer genes shows significant but modest changes to total distance migrated. However, in vivo expression analysis by RNAscope and immunohistochemistry reveals some salt and pepper patterns that include strong individual Trailblazer gene expression in cells within other subregions of the migratory stream. These data provide new insights into the molecular diversity and dynamics within a neural crest cell migratory stream that underlie complex directed and collective cell behaviors.