Hybridization Chain Reaction for mRNA Localization in Single Cells from Mouse and Human Cryosections

In situ hybridization has been a robust method for detection of mRNA expression in whole-mount samples or tissue sections for more than 50 years. Recent technical advances for in situ hybridization have incorporated oligo-based probes that attain greater tissue penetration and signal amplification steps with restricted localization for visualization of specific mRNAs within single cells. One such method is third-generation in situ hybridization chain reaction (V3HCR). Here, we report an optimized protocol for V3HCR detection of gene expression using sectioned frozen tissues from mouse and human on microscope slides. Our methods and modifications for cryosectioning, tissue fixation, and processing over a three-day V3HCR protocol are detailed along with recommendations for aliquoting and storing V3HCR single-stranded DNA probes and hairpin amplifiers. In addition, we describe a method for blocking background signal from lipofuscin, a highly autofluorescent material that is widespread in human neurons and often complicates imaging efforts. After testing multiple strategies for reduction of lipofuscin, we determined that application of a lipofuscin quencher dye is compatible with V3HCR, in contrast to other methods like cupric sulfate quenching or Sudan Black B blocking that cause V3HCR signal loss. This adaptation enables application of V3HCR for in situ detection of gene expression in human neuronal populations that are otherwise problematic due to lipofuscin autofluorescence. © 2022 Wiley Periodicals LLC. Basic Protocol: Mouse and human fresh-frozen tissue in situ hybridization chain reaction on microscope slides Support Protocol: Aliquoting of HCR probes and hairpins.

5-HT3 Signaling Alters Development of Sacral Neural Crest Derivatives That Innervate the Lower Urinary Tract

The autonomic nervous system derives from the neural crest (NC) and supplies motor innervation to the smooth muscle of visceral organs, including the lower urinary tract (LUT). During fetal development, sacral NC cells colonize the urogenital sinus to form pelvic ganglia (PG) flanking the bladder neck. The coordinated activity of PG neurons is required for normal urination; however, little is known about the development of PG neuronal diversity. To discover candidate genes involved in PG neurogenesis, the transcriptome profiling of sacral NC and developing PG was performed, and we identified the enrichment of the type 3 serotonin receptor (5-HT3, encoded by Htr3a and Htr3b). We determined that Htr3a is one of the first serotonin receptor genes that is up-regulated in sacral NC progenitors and is maintained in differentiating PG neurons. In vitro cultures showed that the disruption of 5-HT3 signaling alters the differentiation outcomes of sacral NC cells, while the stimulation of 5-HT3 in explanted fetal pelvic ganglia severely diminished neurite arbor outgrowth. Overall, this study provides a valuable resource for the analysis of signaling pathways in PG development, identifies 5-HT3 as a novel regulator of NC lineage diversification and neuronal maturation in the peripheral nervous system, and indicates that the perturbation of 5-HT3 signaling in gestation has the potential to alter bladder function later in life.

Altered sacral neural crest development in Pax3 spina bifida mutants underlies deficits of bladder innervation and function

Mouse models of Spina bifida (SB) have been instrumental for identifying genes, developmental processes, and environmental factors that influence neurulation and neural tube closure. Beyond the prominent neural tube defects, other aspects of the nervous system can be affected in SB with significant changes in essential bodily functions such as urination. SB patients frequently experience bladder dysfunction and SB fetuses exhibit reduced density of bladder nerves and smooth muscle although the developmental origins of these deficits have not been determined. The Pax3 Splotch-delayed (Pax3^Sp-d) mouse model of SB is one of a very few mouse SB models that survives to late stages of gestation. Through analysis of Pax3^Sp-d mutants we sought to define how altered bladder innervation in SB might arise by tracing sacral neural crest (NC) development, pelvic ganglia neuronal differentiation, and assessing bladder nerve fiber density. In Pax3^Sp-d/Sp-d fetal mice we observed delayed migration of Sox10+ NC-derived progenitors (NCPs), deficient pelvic ganglia neurogenesis, and reduced density of bladder wall innervation. We further combined NC-specific deletion of Pax3 with the constitutive Pax3^Sp-d allele in an effort to generate viable Pax3 mutants to examine later stages of bladder innervation and postnatal bladder function. Neural crest specific deletion of a Pax3 flox allele, using a Sox10-cre driver, in combination with a constitutive Pax3^Sp-d mutation produced postnatal viable offspring that exhibited altered bladder function as well as reduced bladder wall innervation and altered connectivity between accessory ganglia at the bladder neck. Combined, the results show that Pax3 plays critical roles within sacral NC that are essential for initiation of neurogenesis and differentiation of autonomic neurons within pelvic ganglia.

Combinatorial Transcriptional Profiling of Mouse and Human Enteric Neurons Identifies Shared and Disparate Subtypes In Situ

BACKGROUND & AIMS

The enteric nervous system (ENS) coordinates essential intestinal functions through the concerted action of diverse enteric neurons (ENs). However, integrated molecular knowledge of EN subtypes is lacking. To compare human and mouse ENs, we transcriptionally profiled healthy ENS from adult humans and mice. We aimed to identify transcripts marking discrete neuron subtypes and visualize conserved EN subtypes for humans and mice in multiple bowel regions.

METHODS

Human myenteric ganglia and adjacent smooth muscle were isolated by laser-capture microdissection for RNA sequencing. Ganglia-specific transcriptional profiles were identified by computationally subtracting muscle gene signatures. Nuclei from mouse myenteric neurons were isolated and subjected to single-nucleus RNA sequencing, totaling more than 4 billion reads and 25,208 neurons. Neuronal subtypes were defined using mouse single-nucleus RNA sequencing data. Comparative informatics between human and mouse data sets identified shared EN subtype markers, which were visualized in situ using hybridization chain reaction.

RESULTS

Several EN subtypes in the duodenum, ileum, and colon are conserved between humans and mice based on orthologous gene expression. However, some EN subtype-specific genes from mice are expressed in completely distinct morphologically defined subtypes in humans. In mice, we identified several neuronal subtypes that stably express gene modules across all intestinal segments, with graded, regional expression of 1 or more marker genes.

CONCLUSIONS

Our combined transcriptional profiling of human myenteric ganglia and mouse EN provides a rich foundation for developing novel intestinal therapeutics. There is congruency among some EN subtypes, but we note multiple species differences that should be carefully considered when relating findings from mouse ENS research to human gastrointestinal studies.

Sox10-cre BAC transgenes reveal temporal restriction of mesenchymal cranial neural crest and identify glandular Sox10 expression

Diversity of neural crest derivatives has been studied with a variety of approaches during embryonic development. In mammals Cre-LoxP lineage tracing is a robust means to fate map neural crest relying on cre driven from regulatory elements of early neural crest genes. Sox10 is an essential transcription factor for normal neural crest development. A variety of efforts have been made to label neural crest derivatives using partial Sox10 regulatory elements to drive cre expression. To date published Sox10-cre lines have focused primarily on lineage tracing in specific tissues or during early fetal development. We describe two new Sox10-cre BAC transgenes, constitutive (cre) and inducible (cre/ER^T2), that contain the complete repertoire of Sox10 regulatory elements. We present a thorough expression profile of each, identifying a few novel sites of Sox10 expression not captured by other neural crest cre drivers. Comparative mapping of expression patterns between the Sox10-cre and Sox10-cre/ER^T2 transgenes identified a narrow temporal window in which Sox10 expression is present in mesenchymal derivatives prior to becoming restricted to neural elements during embryogenesis. In more caudal structures, such as the intestine and lower urinary tract, our Sox10-cre BAC transgene appears to be more efficient in labeling neural crest-derived cell types than Wnt1-cre. The analysis reveals consistent expression of Sox10 in non-neural crest derived glandular epithelium, including salivary, mammary, and urethral glands of adult mice. These Sox10-cre and Sox10-cre/ER^T2 transgenic lines are verified tools that will enable refined temporal and cell-type specific lineage analysis of neural crest derivatives as well as glandular tissues that rely on Sox10 for proper development and function.

Insights into olfactory ensheathing cell development from a laser-microdissection and transcriptome-profiling approach

Olfactory ensheathing cells (OECs) are neural crest-derived glia that ensheath bundles of olfactory axons from their peripheral origins in the olfactory epithelium to their central targets in the olfactory bulb. We took an unbiased laser microdissection and differential RNA-seq approach, validated by in situ hybridization, to identify candidate molecular mechanisms underlying mouse OEC development and differences with the neural crest-derived Schwann cells developing on other peripheral nerves. We identified 25 novel markers for developing OECs in the olfactory mucosa and/or the olfactory nerve layer surrounding the olfactory bulb, of which 15 were OEC-specific (that is, not expressed by Schwann cells). One pan-OEC-specific gene, Ptprz1, encodes a receptor-like tyrosine phosphatase that blocks oligodendrocyte differentiation. Mutant analysis suggests Ptprz1 may also act as a brake on OEC differentiation, and that its loss disrupts olfactory axon targeting. Overall, our results provide new insights into OEC development and the diversification of neural crest-derived glia.

RNA-seq of Isolated Chromaffin Cells Highlights the Role of Sex-Linked and Imprinted Genes in Adrenal Medulla Development

Adrenal chromaffin cells and sympathetic neurons synthesize and release catecholamines, and both cell types are derived from neural crest precursors. However, they have different developmental histories, with sympathetic neurons derived directly from neural crest precursors while adrenal chromaffin cells arise from neural crest-derived cells that express Schwann cell markers. We have sought to identify the genes, including imprinted genes, which regulate the development of the two cell types in mice. We developed a method of separating the two cell types as early as E12.5, using differences in expression of enhanced yellow fluorescent protein driven from the tyrosine hydroxylase gene, and then used RNA sequencing to confirm the characteristic molecular signatures of the two cell types. We identified genes differentially expressed by adrenal chromaffin cells and sympathetic neurons. Deletion of a gene highly expressed by adrenal chromaffin cells, NIK-related kinase, a gene on the X-chromosome, results in reduced expression of adrenaline-synthesizing enzyme, phenyl-N-methyl transferase, by adrenal chromaffin cells and changes in cell cycle dynamics. Finally, many imprinted genes are up-regulated in chromaffin cells and may play key roles in their development.

Olfactory ensheathing cells abutting the embryonic olfactory bulb express Frzb, whose deletion disrupts olfactory axon targeting

We and others previously showed that in mouse embryos lacking the transcription factor Sox10, olfactory ensheathing cell (OEC) differentiation is disrupted, resulting in defective olfactory axon targeting and fewer gonadotropin‐releasing hormone (GnRH) neurons entering the embryonic forebrain. The underlying mechanisms are unclear. Here, we report that OECs in the olfactory nerve layer express Frzb—encoding a secreted Wnt inhibitor with roles in axon targeting and basement membrane breakdown—from embryonic day (E)12.5, when GnRH neurons first enter the forebrain, until E16.5, the latest stage examined. The highest levels of Frzb expression are seen in OECs in the inner olfactory nerve layer, abutting the embryonic olfactory bulb. We find that Sox10 is required for Frzb expression in OECs, suggesting that loss of Frzb could explain the olfactory axon targeting and/or GnRH neuron migration defects seen in Sox10‐null mice. At E16.5, Frzb‐null embryos show significant reductions in both the volume of the olfactory nerve layer expressing the maturation marker Omp and the number of Omp‐positive olfactory receptor neurons in the olfactory epithelium. As Omp upregulation correlates with synapse formation, this suggests that Frzb deletion indeed disrupts olfactory axon targeting. In contrast, GnRH neuron entry into the forebrain is not significantly affected. Hence, loss of Frzb may contribute to the olfactory axon targeting phenotype, but not the GnRH neuron phenotype, of Sox10‐null mice. Overall, our results suggest that Frzb secreted from OECs in the olfactory nerve layer is important for olfactory axon targeting.

Frzb is expressed by olfactory ensheathing cells abutting the embryonic mouse olfactory bulb.

Frzb expression requires Sox10. Deletion of Frzb disrupts olfactory receptor neuron maturation, likely reflecting a defect in olfactory axon targeting.

Void spot assay procedural optimization and software for rapid and objective quantification of rodent voiding function, including overlapping urine spots

Mouse urinary behavior is quantifiable and is used to pinpoint mechanisms of voiding dysfunction and evaluate potential human therapies. Approaches to evaluate mouse urinary function vary widely among laboratories, however, complicating cross-study comparisons. Here, we describe development and multi-institutional validation of a new tool for objective, consistent, and rapid analysis of mouse void spot assay (VSA) data. Void Whizzard is a freely available software plugin for FIJI (a distribution of ImageJ) that facilitates VSA image batch processing and data extraction. We describe its features, demonstrate them by evaluating how specific VSA method parameters influence voiding behavior, and establish Void Whizzard as an expedited method for VSA analysis. This study includes control and obese diabetic mice as models of urinary dysfunction to increase rigor and ensure relevance across distinct voiding patterns. In particular, we show that Void Whizzard is an effective tool for quantifying nonconcentric overlapping void spots, which commonly confound analyses. We also show that mouse genetics are consistently more influential than assay design parameters when it comes to VSA outcomes. None of the following procedural modifications to reduce overlapping spots masked these genetic-related differences: reduction of VSA testing duration, water access during the assay period, placement of a wire mesh cage bottom on top of or elevated over the filter paper, treatment of mesh with a hydrophobic spray, and size of wire mesh opening. The Void Whizzard software and rigorous validation of VSA methodological parameters described here advance the goal of standardizing mouse urinary phenotyping for comprehensive urinary phenome analyses.

Optimization of Laser-Capture Microdissection for the Isolation of Enteric Ganglia from Fresh-Frozen Human Tissue

The purpose of this method is to obtain high-integrity RNA samples from enteric ganglia collected from unfixed, freshly-resected human intestinal tissue using laser capture microdissection (LCM). We have identified five steps in the workflow that are crucial for obtaining RNA isolates from enteric ganglia with sufficiently high quality and quantity for RNA-seq. First, when preparing intestinal tissue, each sample must have all excess liquid removed by blotting prior to flattening the serosa as much as possible across the bottom of large base molds. Samples are then quickly frozen atop a slurry of dry ice and 2-methylbutane. Second, when sectioning the tissue, it is important to position cryomolds so that intestinal sections parallel the full plane of the myenteric plexus, thereby yielding the greatest surface area of enteric ganglia per slide. Third, during LCM, polyethylene napthalate (PEN)-membrane slides offer the greatest speed and flexibility in outlining the non-uniform shapes of enteric ganglia when collecting enteric ganglia. Fourth, for distinct visualization of enteric ganglia within sections, ethanol-compatible dyes, like Cresyl Violet, offer excellent preservation of RNA integrity relative to aqueous dyes. Finally, for the extraction of RNA from captured ganglia, we observed differences between commercial RNA extraction kits that yielded superior RNA quantity and quality, while eliminating DNA contamination. Optimization of these factors in the current protocol greatly accelerates the workflow and yields enteric ganglia samples with exceptional RNA quality and quantity.

Serotonin Receptor 5-HT3A Affects Development of Bladder Innervation and Urinary Bladder Function

The autonomic and sensory nervous systems are required for proper function of all visceral organs, including the lower urinary tract (LUT). Despite the wide prevalence of bladder dysfunction, effective treatment options remain limited. Pelvic innervation regenerative strategies are promising, but surprisingly little is known about the molecular factors driving the development of bladder innervation. Given prior evidence that serotonin receptor 5-HT3A is expressed early in LUT development and is an important mediator of adult bladder function, we sought to determine if 5-HT3A is required for the development of autonomic innervation of the bladder. We found that 5-HT3A is expressed early in fetal mouse pelvic ganglia and is maintained through adulthood. Htr3a knockout male mice, but not females, exhibit increased urinary voiding frequency compared to wild type littermates. Analysis of LUT function via anesthetized cystometry revealed decreased voiding efficiency in male Htr3a mutants. Htr3a^−/− mutant animals exhibit a transient disturbance of autonomic neuronal subtype markers (tyrosine hydroxylase and choline acetyl transferase) within the fetal pelvic ganglia, although the imbalance of neuronal subtype markers assayed is no longer apparent in adulthood. Loss of 5-HT3A activity results in a higher density of autonomic and sensory neuronal fibers supplying bladder smooth muscle in both fetal and adult mice. Collectively, our findings highlight 5-HT3A as a critical component in the autonomic control of micturition and identify a novel role for this serotonin receptor in peripheral nervous system development.

Adult enteric nervous system in health is maintained by a dynamic balance between neuronal apoptosis and neurogenesis

According to current dogma, there is little or no ongoing neurogenesis in the fully developed adult enteric nervous system. This lack of neurogenesis leaves unanswered the question of how enteric neuronal populations are maintained in adult guts, given previous reports of ongoing neuronal death. Here, we confirm that despite ongoing neuronal cell loss because of apoptosis in the myenteric ganglia of the adult small intestine, total myenteric neuronal numbers remain constant. This observed neuronal homeostasis is maintained by new neurons formed in vivo from dividing precursor cells that are located within myenteric ganglia and express both Nestin and p75NTR, but not the pan-glial marker Sox10. Mutation of the phosphatase and tensin homolog gene in this pool of adult precursors leads to an increase in enteric neuronal number, resulting in ganglioneuromatosis, modeling the corresponding disorder in humans. Taken together, our results show significant turnover and neurogenesis of adult enteric neurons and provide a paradigm for understanding the enteric nervous system in health and disease.

Migration pathways of sacral neural crest during development of lower urogenital tract innervation

The migration and fate of cranial and vagal neural crest-derived progenitor cells (NCPCs) have been extensively studied; however, much less is known about sacral NCPCs particularly in regard to their distribution in the urogenital system. To construct a spatiotemporal map of NCPC migration pathways into the developing lower urinary tract, we utilized the Sox10-H2BVenus transgene to visualize NCPCs expressing Sox10. Our aim was to define the relationship of Sox10-expressing NCPCs relative to bladder innervation, smooth muscle differentiation, and vascularization through fetal development into adulthood. Sacral NCPC migration is a highly regimented, specifically timed process, with several potential regulatory mileposts. Neuronal differentiation occurs concomitantly with sacral NCPC migration, and neuronal cell bodies are present even before the pelvic ganglia coalesce. Sacral NCPCs reside within the pelvic ganglia anlagen through 13.5 days post coitum (dpc), after which they begin streaming into the bladder body in progressive waves. Smooth muscle differentiation and vascularization of the bladder initiate prior to innervation and appear to be independent processes. In adult bladder, the majority of Sox10+ cells express the glial marker S100β, consistent with Sox10 being a glial marker in other tissues. However, rare Sox10+ NCPCs are seen in close proximity to blood vessels and not all are S100β+, suggesting either glial heterogeneity or a potential nonglial role for Sox10+ cells along vasculature. Taken together, the developmental atlas of Sox10+ NCPC migration and distribution profile of these cells in adult bladder provided here will serve as a roadmap for future investigation in mouse models of lower urinary tract dysfunction.

Dynamic Expression of Serotonin Receptor 5-HT3A in Developing Sensory Innervation of the Lower Urinary Tract

Sensory afferent signaling is required for normal function of the lower urinary tract (LUT). Despite the wide prevalence of bladder dysfunction and pelvic pain syndromes, few effective treatment options are available. Serotonin receptor 5-HT3A is a known mediator of visceral afferent signaling and has been implicated in bladder function. However, basic expression patterns for this gene and others among developing bladder sensory afferents that could be used to inform regenerative efforts aimed at treating deficiencies in pelvic innervation are lacking. To gain greater insight into the molecular characteristics of bladder sensory innervation, we conducted a thorough characterization of Htr3a expression in developing and adult bladder-projecting lumbosacral dorsal root ganglia (DRG) neurons. Using a transgenic Htr3a-EGFP reporter mouse line, we identified 5-HT3A expression at 10 days post coitus (dpc) in neural crest derivatives and in 12 dpc lumbosacral DRG. Using immunohistochemical co-localization we observed Htr3a-EGFP expression in developing lumbosacral DRG that partially coincides with neuropeptides CGRP and Substance P and capsaicin receptor TRPV1. A majority of Htr3a-EGFP+ DRG neurons also express a marker of myelinated Aδ neurons, NF200. There was no co-localization of 5-HT3A with the TRPV4 receptor. We employed retrograde tracing in adult Htr3a-EGFP mice to quantify the contribution of 5-HT3A+ DRG neurons to bladder afferent innervation. We found that 5-HT3A is expressed in a substantial proportion of retrograde traced DRG neurons in both rostral (L1, L2) and caudal (L6, S1) axial levels that supply bladder innervation. Most bladder-projecting Htr3a-EGFP+ neurons that co-express CGRP, Substance P, or TRPV1 are found in L1, L2 DRG, whereas Htr3a-EGFP+, NF200+ bladder-projecting neurons are from the L6, S1 axial levels. Our findings contribute much needed information regarding the development of LUT innervation and highlight the 5-HT3A serotonin receptor as a candidate for future studies of neurally mediated bladder control.

Mouse models of Hirschsprung disease and other developmental disorders of the enteric nervous system: Old and new players

Hirschsprung disease (HSCR, intestinal aganglionosis) is a multigenic disorder with variable penetrance and severity that has a general population incidence of 1/5000 live births. Studies using animal models have contributed to our understanding of the developmental origins of HSCR and the genetic complexity of this disease. This review summarizes recent progress in understanding control of enteric nervous system (ENS) development through analyses in mouse models. An overview of signaling pathways that have long been known to control the migration, proliferation and differentiation of enteric neural progenitors into and along the developing gut is provided as a framework for the latest information on factors that influence enteric ganglia formation and maintenance. Newly identified genes and additional factors beyond discrete genes that contribute to ENS pathology including regulatory sequences, miRNAs and environmental factors are also introduced. Finally, because HSCR has become a paradigm for complex oligogenic diseases with non-Mendelian inheritance, the importance of gene interactions, modifier genes, and initial studies on genetic background effects are outlined.

Sox10 Regulates Stem/Progenitor and Mesenchymal Cell States in Mammary Epithelial Cells

To discover mechanisms that mediate plasticity in mammary cells, we characterized signaling networks that are present in the mammary stem cells responsible for fetal and adult mammary development. These analyses identified a signaling axis between FGF signaling and the transcription factor Sox10. Here, we show that Sox10 is specifically expressed in mammary cells exhibiting the highest levels of stem/progenitor activity. This includes fetal and adult mammary cells in vivo and mammary organoids in vitro. Sox10 is functionally relevant, as its deletion reduces stem/progenitor competence whereas its overexpression increases stem/progenitor activity. Intriguingly, we also show that Sox10 overexpression causes mammary cells to undergo a mesenchymal transition. Consistent with these findings, Sox10 is preferentially expressed in stem- and mesenchymal-like breast cancers. These results demonstrate a signaling mechanism through which stem and mesenchymal states are acquired in mammary cells and suggest therapeutic avenues in breast cancers for which targeted therapies are currently unavailable.

LRIG1 Regulates Ontogeny of Smooth Muscle-Derived Subsets of Interstitial Cells of Cajal in Mice

BACKGROUND & AIMS

Interstitial cells of Cajal (ICC) control intestinal smooth muscle contraction to regulate gut motility. ICC within the plane of the myenteric plexus (ICC-MY) arise from KIT-positive progenitor cells during mouse embryogenesis. However, little is known about the ontogeny of ICC associated with the deep muscular plexus (ICC-DMP) in the small intestine and ICC associated with the submucosal plexus (ICC-SMP) in the colon. Leucine-rich repeats and immunoglobulin-like domains protein 1 (LRIG1) marks intestinal epithelial stem cells, but the role of LRIG1 in nonepithelial intestinal cells has not been identified. We sought to determine the ontogeny of ICC-DMP and ICC-SMP, and whether LRIG1 has a role in their development.

METHODS

Lrig1-null mice (homozygous Lrig1-CreERT2) and wild-type mice were analyzed by immunofluorescence and transit assays. Transit was evaluated by passage of orally administered rhodamine B-conjugated dextran. Lrig1-CreERT2 mice or mice with CreERT2 under control of an inducible smooth muscle promoter (Myh11-CreERT2) were crossed with Rosa26-LSL-YFP mice for lineage tracing analysis.

RESULTS

In immunofluorescence assays, ICC-DMP and ICC-SMP were found to express LRIG1. Based on lineage tracing, ICC-DMP and ICC-SMP each arose from LRIG1-positive smooth muscle progenitors. In Lrig1-null mice, there was loss of staining for KIT in DMP and SMP regions, as well as for 2 additional ICC markers (anoctamin-1 and neurokinin 1 receptor). Lrig1-null mice had significant delays in small intestinal transit compared with control mice.

CONCLUSIONS

LRIG1 regulates the postnatal development of ICC-DMP and ICC-SMP from smooth muscle progenitors in mice. Slowed small intestinal transit observed in Lrig1-null mice may be due, at least in part, to loss of the ICC-DMP population.

A Phox2b BAC Transgenic Rat Line Useful for Understanding Respiratory Rhythm Generator Neural Circuitry

The key role of the respiratory neural center is respiratory rhythm generation to maintain homeostasis through the control of arterial blood pCO₂/pH and pO₂ levels. The neuronal network responsible for respiratory rhythm generation in neonatal rat resides in the ventral side of the medulla and is composed of two groups; the parafacial respiratory group (pFRG) and the pre-Bötzinger complex group (preBötC). The pFRG partially overlaps in the retrotrapezoid nucleus (RTN), which was originally identified in adult cats and rats. Part of the pre-inspiratory (Pre-I) neurons in the RTN/pFRG serves as central chemoreceptor neurons and the CO₂ sensitive Pre-I neurons express homeobox gene Phox2b. Phox2b encodes a transcription factor and is essential for the development of the sensory-motor visceral circuits. Mutations in human PHOX2B cause congenital hypoventilation syndrome, which is characterized by blunted ventilatory response to hypercapnia. Here we describe the generation of a novel transgenic (Tg) rat harboring fluorescently labeled Pre-I neurons in the RTN/pFRG. In addition, the Tg rat showed fluorescent signals in autonomic enteric neurons and carotid bodies. Because the Tg rat expresses inducible Cre recombinase in PHOX2B-positive cells during development, it is a potentially powerful tool for dissecting the entire picture of the respiratory neural network during development and for identifying the CO₂/O₂ sensor molecules in the adult central and peripheral nervous systems.

Differences in CART expression and cell cycle behavior discriminate sympathetic neuroblast from chromaffin cell lineages in mouse sympathoadrenal cells

Adrenal medullary chromaffin cells and peripheral sympathetic neurons originate from a common sympathoadrenal (SA) progenitor cell. The timing and phenotypic changes that mark this lineage diversification are not fully understood. The present study investigated the expression patterns of phenotypic markers, and cell cycle dynamics, in the adrenal medulla and the neighboring suprarenal ganglion of embryonic mice. The noradrenergic marker, tyrosine hydroxylase (TH), was detected in both presumptive adrenal medulla and sympathetic ganglion cells, but with significantly stronger immunostaining in the former. There was intense cocaine and amphetamine-regulated transcript (CART) peptide immunostaining in most neuroblasts, whereas very few adrenal chromaffin cells showed detectable CART immunostaining. This phenotypic segregation appeared as early as E12.5, before anatomical segregation of the two cell types. Cell cycle dynamics were also examined. Initially, 88% of Sox10 positive (+) neural crest progenitors were proliferating at E10.5. Many SA progenitor cells withdrew from the cell cycle at E11.5 as they started to express TH. Whereas 70% of neuroblasts (TH+/CART+ cells) were back in the cell cycle at E12.5, only around 20% of chromaffin (CART negative) cells were in the cell cycle at E12.5 and subsequent days. Thus, chromaffin cell and neuroblast lineages showed differences in proliferative behavior from their earliest appearance. We conclude that the intensity of TH immunostaining and the expression of CART permit early discrimination of chromaffin cells and sympathetic neuroblasts, and that developing chromaffin cells exhibit significantly lower proliferative activity relative to sympathetic neuroblasts.

An illustrated anatomical ontology of the developing mouse lower urogenital tract

Malformation of the urogenital tract represents a considerable paediatric burden, with many defects affecting the lower urinary tract (LUT), genital tubercle and associated structures. Understanding the molecular basis of such defects frequently draws on murine models. However, human anatomical terms do not always superimpose on the mouse, and the lack of accurate and standardised nomenclature is hampering the utility of such animal models. We previously developed an anatomical ontology for the murine urogenital system. Here, we present a comprehensive update of this ontology pertaining to mouse LUT, genital tubercle and associated reproductive structures (E10.5 to adult). Ontology changes were based on recently published insights into the cellular and gross anatomy of these structures, and on new analyses of epithelial cell types present in the pelvic urethra and regions of the bladder. Ontology changes include new structures, tissue layers and cell types within the LUT, external genitalia and lower reproductive structures. Representative illustrations, detailed text descriptions and molecular markers that selectively label muscle, nerves/ganglia and epithelia of the lower urogenital system are also presented. The revised ontology will be an important tool for researchers studying urogenital development/malformation in mouse models and will improve our capacity to appropriately interpret these with respect to the human situation.

Enteric neuron imbalance and proximal dysmotility in ganglionated intestine of the Sox10Dom/+ Hirschsprung mouse model

BACKGROUND & AIMS

In Hirschsprung disease (HSCR), neural crest-derived progenitors (NCPs) fail to completely colonize the intestine so that the enteric nervous system (ENS) is absent from distal bowel. Despite removal of the aganglionic region, many HSCR patients suffer from residual intestinal dysmotility. To test the hypothesis that inappropriate lineage segregation of NCPs in proximal ganglionated regions of the bowel could contribute to such postoperative disease, we investigated neural crest (NC)-derived lineages and motility in ganglionated, postnatal intestine of the Sox10Dom/+ HSCR mouse model.

METHODS

Cre-mediated fate-mapping was applied to evaluate relative proportions of NC-derived cell types. Motility assays were performed to assess gastric emptying and small intestine motility while colonic inflammation was assessed by histopathology for Sox10Dom/+ mutants relative to wildtype controls.

RESULTS

Sox10Dom/+ mice showed regional alterations in neuron and glia proportions as well as Calretinin+ and nNOS+ neuronal subtypes. In the colon, imbalance of enteric NC derivatives correlated with the extent of aganglionosis. All Sox10Dom/+ mice exhibited reduced small intestinal transit at 4-weeks of age, and at 6-weeks, Sox10Dom/+ males had increased gastric emptying rates. Sox10Dom/+ mice surviving to 6-weeks of age had little or no colonic inflammation when compared to wildtype littermates, suggesting that these changes in GI motility are neurally mediated.

CONCLUSIONS

The Sox10Dom mutation disrupts the balance of NC-derived lineages and affects GI motility in the proximal, ganglionated intestine of adult animals. This is the first report identifying alterations in enteric neuronal classes in Sox10Dom/+ mutants, which suggests a previously unrecognized role for Sox10 in neuronal subtype specification.

A Uchl1-Histone2BmCherry:GFP-gpi BAC transgene for imaging neuronal progenitors

Uchl1 encodes the protein gene product 9.5 antigen (PGP9.5) that is a widely used to identify migrating neural progenitors in the PNS, mature neurons of the central and peripheral nervous systems, as well as neuroendocrine cells. To facilitate analysis of developing peripheral neurons, we linked regulatory regions of Uchl1 carried within a 160kb bacterial artificial chromosome (BAC) to the dual fluorescent reporter H2BmCherry:GFP-gpi. The Uchl1-H2BmCherry:GFP-gpi transgene exhibits robust expression and allows clear discrimination of individual cells and cellular processes in cranial ganglia, sympathetic chain, the enteric nervous system (ENS), and autonomic ganglia of the urogenital system. The transgene also labels subsets of cells in endocrine tissues where earlier in situ hybridization (ISH) studies have previously identified expression of this deubiquinating enzyme. The Uchl1-H2BmCherry:GFP-gpi transgene will be a powerful tool for static and live imaging, as well as isolation of viable neural progenitors to investigate processes of autonomic neurogenesis.

Balancing on the crest - Evidence for disruption of the enteric ganglia via inappropriate lineage segregation and consequences for gastrointestinal function

Normal enteric nervous system (ENS) development relies on numerous factors, including appropriate migration, proliferation, differentiation, and maturation of neural crest (NC) derivatives. Incomplete rostral to caudal migration of enteric neural crest-derived progenitors (ENPs) down the gut is at least partially responsible for the absence of enteric ganglia that is a hallmark feature of Hirschsprung disease (HSCR). The thought that ganglia proximal to aganglionosis are normal has guided surgical procedures for HSCR patients. However, chronic gastrointestinal dysfunction suffered by a subset of patients after surgery as well as studies in HSCR mouse models suggest that aberrant NC segregation and differentiation may be occurring in ganglionated regions of the intestine. Studies in mouse models that possess enteric ganglia throughout the length of the intestine (non-HSCR) have also found that certain genetic alterations affect neural crest lineage balance and interestingly many of these mutants also have functional gastrointestinal (GI) defects. It is possible that many GI disorders can be explained in part by imbalances in NC-derived lineages. Here we review studies evaluating ENS defects in HSCR and non-HSCR mouse models, concluding with clinical implications while highlighting areas requiring further study.

A genome-wide screen to identify transcription factors expressed in pelvic Ganglia of the lower urinary tract

Relative positions of neurons within mature murine pelvic ganglia based on expression of neurotransmitters have been described. However the spatial organization of developing innervation in the murine urogenital tract (UGT) and the gene networks that regulate specification and maturation of neurons within the pelvic ganglia of the lower urinary tract (LUT) are unknown. We used whole-mount immunohistochemistry and histochemical stains to localize neural elements in 15.5 days post coitus (dpc) fetal mice. To identify potential regulatory factors expressed in pelvic ganglia, we surveyed expression patterns for known or probable transcription factors (TF) annotated in the mouse genome by screening a whole-mount in situ hybridization library of fetal UGTs. Of the 155 genes detected in pelvic ganglia, 88 encode TFs based on the presence of predicted DNA-binding domains. Neural crest (NC)-derived progenitors within the LUT were labeled by Sox10, a well-known regulator of NC development. Genes identified were categorized based on patterns of restricted expression in pelvic ganglia, pelvic ganglia and urethral epithelium, or pelvic ganglia and urethral mesenchyme. Gene expression patterns and the distribution of Sox10+, Phox2b+, Hu+, and PGP9.5+ cells within developing ganglia suggest previously unrecognized regional segregation of Sox10+ progenitors and differentiating neurons in early development of pelvic ganglia. Reverse transcription-PCR of pelvic ganglia RNA from fetal and post-natal stages demonstrated that multiple TFs maintain post-natal expression, although Pax3 is extinguished before weaning. Our analysis identifies multiple potential regulatory genes including TFs that may participate in segregation of discrete lineages within pelvic ganglia. The genes identified here are attractive candidate disease genes that may now be further investigated for their roles in malformation syndromes or in LUT dysfunction.

An optimized procedure for fluorescence-activated cell sorting (FACS) isolation of autonomic neural progenitors from visceral organs of fetal mice

During development neural crest (NC)-derived neuronal progenitors migrate away from the neural tube to form autonomic ganglia in visceral organs like the intestine and lower urinary tract. Both during development and in mature tissues these cells are often widely dispersed throughout tissues so that isolation of discrete populations using methods like laser capture micro-dissection is difficult. They can however be directly visualized by expression of fluorescent reporters driven from regulatory regions of neuron-specific genes like Tyrosine hydroxylase (TH). We describe a method optimized for high yields of viable TH+ neuronal progenitors from fetal mouse visceral tissues, including intestine and lower urogenital tract (LUT), based on dissociation and fluorescence-activated cell sorting (FACS). The Th gene encodes the rate-limiting enzyme for production of catecholamines. Enteric neuronal progenitors begin to express TH during their migration in the fetal intestine and TH is also present in a subset of adult pelvic ganglia neurons . The first appearance of this lineage and the distribution of these neurons in other aspects of the LUT, and their isolation has not been described. Neuronal progenitors expressing TH can be readily visualized by expression of EGFP in mice carrying the transgene construct Tg(Th-EGFP)DJ76Gsat/Mmnc. We imaged expression of this transgene in fetal mice to document the distribution of TH+ cells in the developing LUT at 15.5 days post coitus (dpc), designating the morning of plug detection as 0.5 dpc, and observed that a subset of neuronal progenitors in the coalescing pelvic ganglia express EGFP. To isolate LUT TH+ neuronal progenitors, we optimized methods that were initially used to purify neural crest stem cells from fetal mouse intestine. Prior efforts to isolate NC-derived populations relied upon digestion with a cocktail of collagenase and trypsin to obtain cell suspensions for flow cytometry. In our hands these methods produced cell suspensions from the LUT with relatively low viability. Given the already low incidence of neuronal progenitors in fetal LUT tissues, we set out to optimize dissociation methods such that cell survival in the final dissociates would be increased. We determined that gentle dissociation in Accumax (Innovative Cell Technologies, Inc), manual filtering, and flow sorting at low pressures allowed us to achieve consistently greater survival (>70% of total cells) with subsequent yields of neuronal progenitors sufficient for downstream analysis. The method we describe can be broadly applied to isolate a variety of neuronal populations from either fetal or adult murine tissues.

Enteric nervous system specific deletion of Foxd3 disrupts glial cell differentiation and activates compensatory enteric progenitors

The enteric nervous system (ENS) arises from the coordinated migration, expansion and differentiation of vagal and sacral neural crest progenitor cells. During development, vagal neural crest cells enter the foregut and migrate in a rostro-to-caudal direction, colonizing the entire gastrointestinal tract and generating the majority of the ENS. Sacral neural crest contributes to a subset of enteric ganglia in the hindgut, colonizing the colon in a caudal-to-rostral wave. During this process, enteric neural crest-derived progenitors (ENPs) self-renew and begin expressing markers of neural and glial lineages as they populate the intestine. Our earlier work demonstrated that the transcription factor Foxd3 is required early in neural crest-derived progenitors for self-renewal, multipotency and establishment of multiple neural crest-derived cells and structures including the ENS. Here, we describe Foxd3 expression within the fetal and postnatal intestine: Foxd3 was strongly expressed in ENPs as they colonize the gastrointestinal tract and was progressively restricted to enteric glial cells. Using a novel Ednrb-iCre transgene to delete Foxd3 after vagal neural crest cells migrate into the midgut, we demonstrated a late temporal requirement for Foxd3 during ENS development. Lineage labeling of Ednrb-iCre expressing cells in Foxd3 mutant embryos revealed a reduction of ENPs throughout the gut and loss of Ednrb-iCre lineage cells in the distal colon. Although mutant mice were viable, defects in patterning and distribution of ENPs were associated with reduced proliferation and severe reduction of glial cells derived from the Ednrb-iCre lineage. Analyses of ENS-lineage and differentiation in mutant embryos suggested activation of a compensatory population of Foxd3-positive ENPs that did not express the Ednrb-iCre transgene. Our findings highlight the crucial roles played by Foxd3 during ENS development including progenitor proliferation, neural patterning, and glial differentiation and may help delineate distinct molecular programs controlling vagal versus sacral neural crest development.

The GUDMAP database--an online resource for genitourinary research

The GenitoUrinary Development Molecular Anatomy Project (GUDMAP) is an international consortium working to generate gene expression data and transgenic mice. GUDMAP includes data from large-scale in situ hybridisation screens (wholemount and section) and microarray gene expression data of microdissected, laser-captured and FACS-sorted components of the developing mouse genitourinary (GU) system. These expression data are annotated using a high-resolution anatomy ontology specific to the developing murine GU system. GUDMAP data are freely accessible at www.gudmap.org via easy-to-use interfaces. This curated, high-resolution dataset serves as a powerful resource for biologists, clinicians and bioinformaticians interested in the developing urogenital system. This paper gives examples of how the data have been used to address problems in developmental biology and provides a primer for those wishing to use the database in their own research.

Isolation and live imaging of enteric progenitors based on Sox10-Histone2BVenus transgene expression

To facilitate dynamic imaging of neural crest (NC) lineages and discrimination of individual cells in the enteric nervous system (ENS) where close juxtaposition often complicates viewing, we generated a mouse BAC transgenic line that drives a Histone2BVenus (H2BVenus) reporter from Sox10 regulatory regions. This strategy does not alter the endogenous Sox10 locus and thus facilitates analysis of normal NC development. Our Sox10-H2BVenus BAC transgene exhibits temporal, spatial, and cell-type specific expression that reflects endogenous Sox10 patterns. Individual cells exhibiting nuclear-localized fluorescence of the H2BVenus reporter are readily visualized in both fixed and living tissue and are amenable to isolation by fluorescence activated cell sorting (FACS). FACS-isolated H2BVenus+ enteric NC-derived progenitors (ENPs) exhibit multipotency, readily form neurospheres, self-renew in vitro and express a variety of stem cell genes. Dynamic live imaging as H2BVenus+ ENPs migrate down the fetal gut reveals cell fragmentation suggesting that apoptosis occurs at a low frequency during normal development of the ENS. Confocal imaging both during population of the fetal intestine and in postnatal gut muscle strips revealed differential expression between individual cells consistent with down-regulation of the transgene as progression towards non-glial fates occurs. The expression of the Sox10-H2BVenus transgene in multiple regions of the peripheral nervous system will facilitate future studies of NC lineage segregation as this tool is expressed in early NC progenitors and maintained in enteric glia.

Genetic background impacts developmental potential of enteric neural crest-derived progenitors in the Sox10Dom model of Hirschsprung disease

Abnormalities in the development of enteric neural crest-derived progenitors (ENPs) that generate the enteric nervous system (ENS) can lead to aganglionosis in a variable portion of the distal gastrointestinal tract. Cumulative evidence suggests that variation of aganglionosis is due to gene interactions that modulate the ability of ENPs to populate the intestine; however, the developmental processes underlying this effect are unknown. We hypothesized that differences in enteric ganglion deficits could be attributable to the effects of genetic background on early developmental processes, including migration, proliferation, or lineage divergence. Developmental processes were investigated in congenic Sox10(Dom) mice, an established Hirschsprung disease (HSCR) model, on distinct inbred backgrounds, C57BL/6J (B6) and C3HeB/FeJ (C3Fe). Immuno-staining on whole-mount fetal gut tissue and dissociated cell suspensions was used to assess migration and proliferation. Flow cytometry utilizing the cell surface markers p75 and HNK-1 was used to isolate live ENPs for analysis of developmental potential. Frequency of ENPs was reduced in Sox10(Dom) embryos relative to wild-type embryos, but was unaffected by genetic background. Both migration and developmental potential of ENPs in Sox10(Dom) embryos were altered by inbred strain background with the most highly significant differences seen for developmental potential between strains and genotypes. In vivo imaging of fetal ENPs and postnatal ganglia demonstrates that altered lineage divergence impacts ganglia in the proximal intestine. Our analysis demonstrates that genetic background alters early ENS development and suggests that abnormalities in lineage diversification can shift the proportions of ENP populations and thus may contribute to ENS deficiencies in vivo.

A Histone2BCerulean BAC transgene identifies differential expression of Phox2b in migrating enteric neural crest derivatives and enteric glia

The mammalian enteric nervous system (ENS) derives from migratory enteric neural crest-derived cells (ENCC) that express the transcription factor Phox2b. Studies of these enteric progenitors have typically relied on immunohistochemical (IHC) detection. To circumvent complicating factors of IHC, we have generated a mouse BAC transgenic line that drives a Histone2BCerulean (H2BCFP) reporter from Phox2b regulatory regions. This construct does not alter the endogenous Phox2b locus and enables studies of normal neural crest (NC) derivatives. The Phox2b-H2BCFP transgene expresses the H2BCFP reporter in patterns that recapitulate expression of endogenous Phox2b. Our studies reveal Phox2b expression in mature enteric glia at levels below that of enteric neurons. Moreover, we also observe differential expression of the transgene reporter within the leading ENCC that traverse the gut. Our findings indicate that the wavefront of migrating enteric progenitors is not homogeneous, and suggest these cells may be fate-specified before expression of mature lineage markers appears.

Fate mapping using Cited1-CreERT2 mice demonstrates that the cap mesenchyme contains self-renewing progenitor cells and gives rise exclusively to nephronic epithelia

Classic tissue recombination and in vitro lineage tracing studies suggest that condensed metanephric mesenchyme (MM) gives rise to nephronic epithelium of the adult kidney. However, these studies do not distinguish between cap mesenchyme and pre-tubular aggregates comprising the condensed MM, nor do they establish whether these cells have self-renewing capacity. To address these questions, we generated Cited1-CreER(T2) BAC transgenic mice, which express tamoxifen-regulated Cre recombinase exclusively in the cap mesenchyme. Fate mapping was performed by crossing these mice with the Rosa26R(LacZ) reporter line and evaluating the location and cellular characteristics of LacZ positive cells at different time points following tamoxifen injection. These studies confirmed expected results from previous in vitro analysis of MM cell fate, and provide in vivo evidence that the cap mesenchyme does not contribute to collecting duct epithelium in the adult. Furthermore, by exploiting the temporally regulated Cre recombinase, these studies show that nephronic epithelium arising at different stages of nephrogenesis has distinct spatial distribution in the adult kidney, and demonstrate for the first time that the cap mesenchyme includes a population of self-renewing epithelial progenitor cells.

Relevance of BAC transgene copy number in mice: transgene copy number variation across multiple transgenic lines and correlations with transgene integrity and expression

Bacterial artificial chromosomes (BACs) are excellent tools for manipulating large DNA fragments and, as a result, are increasingly utilized to engineer transgenic mice by pronuclear injection. The demand for BAC transgenic mice underscores the need for careful inspection of BAC integrity and fidelity following transgenesis, which may be crucial for interpreting transgene function. Thus, it is imperative that reliable methods for assessing these parameters are available. However, there are limited data regarding whether BAC transgenes routinely integrate in the mouse genome as intact molecules, how BAC transgenes behave as they are passed through the germline across successive generations, and how variation in BAC transgene copy number relates to transgene expression. To address these questions, we used TaqMan real-time PCR to estimate BAC transgene copy number in BAC transgenic embryos and lines. Here we demonstrate the reproducibility of copy number quantification with this method and describe the variation in copy number across independent transgenic lines. In addition, polymorphic marker analysis suggests that the majority of BAC transgenic lines contain intact molecules. Notably, all lines containing multiple BAC copies also contain all BAC-specific markers. Three of 23 founders analyzed contained BAC transgenes integrated into more than one genomic location. Finally, we show increased BAC transgene copy number correlates with increased BAC transgene expression. In sum, our efforts have provided a reliable method for assaying BAC transgene integrity and fidelity, and data that should be useful for researchers using BACs as transgenic vectors.

Distant regulatory elements in a Sox10-beta GEO BAC transgene are required for expression of Sox10 in the enteric nervous system and other neural crest-derived tissues

Sox10 is an essential transcription factor required for development of neural crest-derived melanocytes, peripheral glia, and enteric ganglia. Multiple transcriptional targets regulated by Sox10 have been identified; however, little is known regarding regulation of Sox10. High sequence conservation surrounding 5' exons 1 through 3 suggests these regions might contain functional regulatory elements. However, we observed that these Sox10 genomic sequences do not confer appropriate cell-specific transcription in vitro when linked to a heterologous reporter. To identify elements required for expression of Sox10 in vivo, we modified bacterial artificial chromosomes (BACs) to generate a Sox10betaGeoBAC transgene. Our approach leaves endogenous Sox10 loci unaltered, circumventing haploinsufficiency issues that arise from gene targeting. Sox10betaGeoBAC expression closely approximates Sox10 expression in vivo, resulting in expression in anterior dorsal neural tube at embryonic day (E) 8.5 and in cranial ganglia, otic vesicle, and developing dorsal root ganglia at E10.5. Characterization of Sox10betaGeoBAC expression confirms the presence of essential regulatory regions and additionally identifies previously unreported expression in thyroid parafollicular cells, thymus, salivary, adrenal, and lacrimal glands. Fortuitous deletions in independent Sox10betaGeoBAC lines result in loss of transgene expression in peripheral nervous system lineages and coincide with evolutionarily conserved regions. Our analysis indicates that Sox10 expression requires the presence of distant cis-acting regulatory elements. The Sox10betaGeoBAC transgene offers one avenue for specifically testing the role of individual conserved regions in regulation of Sox10 and makes possible analysis of Sox10+ derivatives in the context of normal neural crest development.

The X chromosome in quantitative trait locus mapping

The X chromosome requires special treatment in the mapping of quantitative trait loci (QTL). However, most QTL mapping methods, and most computer programs for QTL mapping, have focused exclusively on autosomal loci. We describe a method for appropriate treatment of the X chromosome for QTL mapping in experimental crosses. We address the important issue of formulating the null hypothesis of no linkage appropriately. If the X chromosome is treated like an autosome, a sex difference in the phenotype can lead to spurious linkage on the X chromosome. Further, the number of degrees of freedom for the linkage test may be different for the X chromosome than for autosomes, and so an X chromosome-specific significance threshold is required. To address this issue, we propose a general procedure to obtain chromosome-specific significance thresholds that controls the genomewide false positive rate at the desired level. We apply our methods to data on gut length in a large intercross of mice carrying the Sox10Dom mutation, a model of Hirschsprung disease. We identified QTL contributing to variation in gut length on chromosomes 5 and 18. We found suggestive evidence of linkage to the X chromosome, which would be viewed as strong evidence of linkage if the X chromosome was treated as an autosome. Our methods have been implemented in the package R/qtl.

Genetic evidence does not support direct regulation of EDNRB by SOX10 in migratory neural crest and the melanocyte lineage

Mutations in the transcription factor Sox10 or Endothelin Receptor B (Ednrb) result in Waardenburg Syndrome Type IV (WS-IV), which presents with deficiencies of neural crest derived melanocytes (hypopigmentation) and enteric ganglia (hypoganglionosis). As Sox10 and Ednrb are expressed in mouse migratory neural crest cells and melanoblasts, we investigated the possibility that SOX10 and EDNRB function through a hierarchical relationship during melanocyte development. However, our results support a distinct rather than hierarchical relationship. First, SOX10 expression continues in Ednrb null melanoblasts, demonstrating that SOX10 expression is not dependent on EDNRB function. Second, Ednrb expression persists in E10.5 Sox10null embryos, demonstrating that Ednrb is not dependent on SOX10 for expression in migratory neural crest cells. Third, over-expression of SOX10 in melanoblasts of mice that harbor null or hypomorphic Ednrb alleles does not rescue hypopigmentation, suggesting that SOX10 overexpression can neither complement a lack of EDNRB function nor increase Ednrb expression. Fourth, mice that are double heterozygous for loss-of-function mutations in Sox10 and Ednrb do not demonstrate synergistically increased hypopigmentation compared to mice that are single heterozygotes for either mutation alone, suggesting a lack of direct genetic interaction between these genes. Our results suggest that SOX10 does not directly activate Ednrb transcription in the melanocyte lineage. Given that SOX10 directly activates Ednrb in the enteric nervous system, our results suggest that SOX10 may differentially activate target genes based on the particular cellular context.

Genome-wide linkage identifies novel modifier loci of aganglionosis in the Sox10Dom model of Hirschsprung disease

Hirschsprung disease (HSCR) is a complex disorder that exhibits incomplete penetrance and variable expressivity due to interactions among multiple susceptibility genes. Studies in HSCR families have identified RET-dependent modifiers for short-segment HSCR (S-HSCR), but epistatic effects in long-segment (L-HSCR) and syndromic cases have not been fully explained. SOX10 mutations contribute to syndromic HSCR cases and Sox10 alleles in mice exhibit aganglionosis and pigmentary anomalies typical of a subset of HSCR patients categorized as Waardenburg-Shah syndrome (WS4, OMIM 277580). Sox10 mutant alleles in mice exhibit strain-dependent variation in penetrance and expressivity of aganglionic megacolon analogous to the variation observed in patients with aganglionosis. In this study, we focused on enteric ganglia deficits in Sox10Dom mice and defined aganglionosis as a quantitative trait in Sox10Dom intercross progeny to investigate the contribution of strain background to variation in enteric nervous system deficits. We observe that the phenotype of Sox10Dom/+ mutants ranges over a continuum from severe aganglionosis to no detectable phenotype in the gut. To systematically identify genes that modulate Sox10-dependent aganglionosis, we performed a single nucleotide polymorphism-based genome scan in Sox10Dom/+ F1 intercross progeny. Our analysis reveals modifier loci on mouse chromosomes 3, 5, 8, 11 and 14 with distinct effects on penetrance and severity of aganglionosis. Three of these loci on chromosomes 3, 8 and 11 do not coincide with previously known aganglionosis susceptibility genes or modifier loci and offer new avenues for elucidating the genetic network that modulates this complex neurocristopathy.

Interactions between Sox10 and EdnrB modulate penetrance and severity of aganglionosis in the Sox10Dom mouse model of Hirschsprung disease

Cumulative evidence suggests that Hirschsprung disease (HSCR) is the consequence of multiple gene interactions that modulate the ability of enteric neural crest (NC) cells to populate the developing gut. One of the essential genes for this process is the NC transcription factor Sox10. Sox10Dom mice on a mixed genetic background show variation in penetrance and expressivity of enteric aganglionosis that are analogous to the variable aganglionosis seen in human HSCR families. The phenotype of Sox10Dom mice in congenic lines indicates this variation arises from modifiers in the genetic background. To determine whether known HSCR susceptibility loci are acting as modifiers of Sox10, we tested for association between genes in the endothelin signaling pathway (EdnrB, Edn3, Ece1) and severity of aganglionosis in an extended pedigree of B6C3FeLe.Sox10Dom mice. Single locus association analysis in this pedigree identifies interaction between EdnrB and Sox10. Additional analysis of F2 intercross progeny confirms a highly significant effect of EdnrB alleles on the Sox10Dom/+ phenotype. The presence of C57BL/6J alleles at EdnrB is associated with increased penetrance and more severe aganglionosis in Sox10Dom mutants. Crosses between EdnrB and Sox10 mutants corroborate this gene interaction with double mutant progeny exhibiting significantly more severe aganglionosis. The background strain of the EdnrB mutant further influences the phenotype of Sox10/EdnrB double mutant progeny implying the action of additional modifiers on this phenotype. Our data demonstrates that Sox10-EdnrB interactions can influence development of the enteric nervous system in mouse models and suggests that this interaction could contribute to the epistatic network producing variation between patients with aganglionosis.

Spatiotemporal regulation of endothelin receptor-B by SOX10 in neural crest-derived enteric neuron precursors

Hirschsprung disease (HSCR) is a multigenic, congenital disorder that affects 1 in 5,000 newborns and is characterized by the absence of neural crest-derived enteric ganglia in the colon. One of the primary genes affected in HSCR encodes the G protein-coupled endothelin receptor-B (EDNRB). The expression of Ednrb is required at a defined time period during the migration of the precursors of the enteric nervous system (ENS) into the colon. In this study, we describe a conserved spatiotemporal ENS enhancer of Ednrb. This 1-kb enhancer is activated as the ENS precursors approach the colon, and partial deletion of this enhancer at the endogenous Ednrb locus results in pigmented mice that die postnatally from megacolon. We identified binding sites for SOX10, an SRY-related transcription factor associated with HSCR, in the Ednrb ENS enhancer, and mutational analyses of these sites suggested that SOX10 may have multiple roles in regulating Ednrb in the ENS.

Analysis of SOX10 function in neural crest-derived melanocyte development: SOX10-dependent transcriptional control of dopachrome tautomerase

SOX10 is a high-mobility-group transcription factor that plays a critical role in the development of neural crest-derived melanocytes. At E11.5, mouse embryos homozygous for the Sox10(Dom) mutation entirely lack neural crest-derived cells expressing the lineage marker KIT, MITF, or DCT. Moreover, neural crest cell cultures derived from homozygous embryos do not give rise to pigmented cells. In contrast, in Sox10(Dom) heterozygous embryos, melanoblasts expressing KIT and MITF do occur, albeit in reduced numbers, and pigmented cells eventually develop in nearly normal numbers both in culture and in vivo. Intriguingly, however, Sox10(Dom)/+ melanoblasts transiently lack Dct expression both in culture and in vivo, suggesting that during a critical developmental period SOX10 may serve as a transcriptional activator of Dct. Indeed, we found that SOX10 and DCT colocalized in early melanoblasts and that SOX10 is capable of transactivating the Dct promoter in vitro. Our data suggest that during early melanoblast development SOX10 acts as a critical transactivator of Dct, that MITF, on its own, is insufficient to stimulate Dct expression, and that delayed onset of Dct expression is not deleterious to the melanocyte lineage.

The Sox10(Dom) mouse: modeling the genetic variation of Waardenburg-Shah (WS4) syndrome

Hirschsprung disease (HSCR) is a multigenic neurocristopathy clinically recognized by aganglionosis of the distal gastrointestinal tract. Patients presenting with aganglionosis in association with hypopigmentation are classified as Waardenburg syndrome type 4 (Waardenburg-Shah, WS4). Variability in the disease phenotype of WS4 patients with equivalent mutations suggests the influence of genetic modifier loci in this disorder. Sox10(Dom)/+ mice exhibit variability of aganglionosis and hypopigmentation influenced by genetic background similar to that observed in WS4 patients. We have constructed Sox10(Dom)/+ congenic lines to segregate loci that modify the neural crest defects in these mice. Consistent with previous studies, increased lethality of Sox10(Dom)/+ animals resulted from a C57BL/6J locus(i). However, we also observed an increase in hypopigmentation in conjunction with a C3HeB/FeJLe-a/a locus(i). Linkage analysis localized a hypopigmentation modifier of the Dom phenotype to mouse chromosome 10 in close proximity to a previously reported modifier of hypopigmentation for the endothelin receptor B mouse model of WS4. To evaluate further the role of SOX10 in development and disease, we have performed comparative genomic analyses. An essential role for this gene in neural crest development is supported by zoo blot hybridizations that reveal extensive conservation throughout vertebrate evolution and by similar Northern blot expression profiles between mouse and man. Comparative sequence analysis of the mouse and human SOX10 gene have defined the exon-intron boundaries of SOX10 and facilitated mutation analysis leading to the identification of two new SOX10 mutations in individuals with WS4. Structural analysis of the HMG DNA-binding domain was performed to evaluate the effect of human mutations in this region.

The Sox10Dom Mouse: Modeling the Genetic Variation of Waardenburg-Shah (WS4) Syndrome

Hirschsprung disease (HSCR) is a multigenic neurocristopathy clinically recognized by aganglionosis of the distal gastrointestinal tract. Patients presenting with aganglionosis in association with hypopigmentation are classified as Waardenburg syndrome type 4 (Waardenburg-Shah, WS4). Variability in the disease phenotype of WS4 patients with equivalent mutations suggests the influence of genetic modifier loci in this disorder. Sox10Dom/+ mice exhibit variability of aganglionosis and hypopigmentation influenced by genetic background similar to that observed in WS4 patients. We have constructed Sox10Dom/+ congenic lines to segregate loci that modify the neural crest defects in these mice. Consistent with previous studies, increased lethality ofSox10Dom/+ animals resulted from a C57BL/6J locus(i). However, we also observed an increase in hypopigmentation in conjunction with a C3HeB/FeJLe-a/a locus(i). Linkage analysis localized a hypopigmentation modifier of the Dom phenotype to mouse chromosome 10 in close proximity to a previously reported modifier of hypopigmentation for the endothelin receptor B mouse model of WS4. To evaluate further the role of SOX10 in development and disease, we have performed comparative genomic analyses. An essential role for this gene in neural crest development is supported by zoo blot hybridizations that reveal extensive conservation throughout vertebrate evolution and by similar Northern blot expression profiles between mouse and man. Comparative sequence analysis of the mouse and humanSOX10 gene have defined the exon–intron boundaries ofSOX10 and facilitated mutation analysis leading to the identification of two new SOX10 mutations in individuals with WS4. Structural analysis of the HMG DNA-binding domain was performed to evaluate the effect of human mutations in this region.

Sox10 mutation disrupts neural crest development in Dom Hirschsprung mouse model

Hirschsprung disease (HSCR, MIM #142623) is a multigenic neurocristopathy (neural crest disorder) characterized by absence of enteric ganglia in a variable portion of the distal colon. Subsets of HSCR individuals also present with neural crest-derived melanocyte deficiencies (Hirschsprung-Waardenburg, HSCR-WS, MIM #277580). Murine models have been instrumental in the identification and analysis of HSCR disease genes. These include mice with deficiencies of endothelin B receptor (Ednrb(s-l); refs 1,2) endothelin 3 (Edn3(ls): refs 1,3) the tyrosine kinase receptor cRet and glial-derived neurotrophic factor. Another mouse model of HSCR disease, Dom, arose spontaneously at the Jackson Laboratory. While Dom/+ heterozygous mice display regional deficiencies of neural crest-derived enteric ganglia in the distal colon, Dom/Dom homozygous animals are embryonic lethal. We have determined that premature termination of Sox10, a member of the SRY-like HMG box family of transcription factors, is responsible for absence of the neural crest derivatives in Dom mice. We demonstrate expression of Sox10 in normal neural crest cells, disrupted expression of both Sox10 and the HSCR disease gene Ednrb in Dom mutant embryos, and loss of neural crest derivatives due to apoptosis. Our studies suggest that Sox10 is essential for proper peripheral nervous system development. We propose SOX10 as a candidate disease gene for individuals with HSCR whose disease does not have an identified genetic origin.

Coordinate control and variation in X-linked gene expression among female mice

In normal female mammals, one of the two X Chromosome (Chr) homologs per cell is silenced coordinately during early embryogenesis. The genes located on the inactivated X homolog are predicted to be influenced by the same underlying repression mechanism. To test the uniformity of cis-acting gene repression, 32 genetically identical F1 female mice were analyzed for differential expression of homologous alleles at three X-linked genes-Otc, Atp7a (= Mottled), and Hprt. Gene expression was assayed by the single-nucleotide primer extension (SNuPE) method, thereby allowing the three genes to be quantitated from the same RNA sample. Although variable between individual animals, the relative expression of the two alleles (allelic expression ratio) of the genes is significantly correlated within each steady-state RNA pool. When examined by animal age (3 months to 12 months), no statistically significant differences were observed in the mean or variance of allelic expression ratio. Together, the results confirm that X inactivation is coordinately controlled and is stable across the early- to mid-adult life span.

Disparate tissue-specific expression of members of the tissue kallikrein multigene family of the rat

To understand the regulatory diversity of the rat family of linked kallikrein genes, we have assayed the expression of family members in 20 major organs. Reverse transcription-polymerase chain reaction analysis using primers and hybridization probes specific for each of the 10 expressed kallikrein genes showed that no two family members share the same organ-specific pattern of expression. The only common site of expression for all 10 known active genes is the submandibular gland. The presence of the mRNA for at least one family member is detected in 19 of these 20 organs (liver excepted), from as few as three organs to as many as 18 for individual family members. For individual genes there can be more than a 10(5)-fold variation in mRNA levels among organs, from a limit of detection of slightly less than 1 mRNA molecule/10 cells to more than 10,000 mRNA molecules/cell. Despite high sequence conservation and close linkage, the members of this family are expressed in very different and complex patterns. A gradient of diversity of expression corresponds to the order of the genes within the kallikrein family locus.