Molecular analysis of smooth muscle development in the mouse

Primary cilia are critical for tracheoesophageal septation

INTRODUCTION

Primary cilia play pivotal roles in the patterning and morphogenesis of a wide variety of organs during mammalian development. Here we examined murine foregut septation in the cobblestone mutant, a hypomorphic allele of the gene encoding the intraflagellar transport protein IFT88, a protein essential for normal cilia function.

RESULTS

We reveal a crucial role for primary cilia in foregut division, since their dramatic decrease in cilia in both the foregut endoderm and mesenchyme of mutant embryos resulted in a proximal tracheoesophageal septation defects and in the formation of distal tracheo(broncho)esophageal fistulae similar to the most common congenital tracheoesophageal malformations in humans. Interestingly, the dorsoventral patterning determining the dorsal digestive and the ventral respiratory endoderm remained intact, whereas Hedgehog signaling was aberrantly activated.

CONCLUSIONS

Our results demonstrate the cobblestone mutant to represent one of the very few mouse models that display both correct endodermal dorsoventral specification but defective compartmentalization of the proximal foregut. It stands exemplary for a tracheoesophageal ciliopathy, offering the possibility to elucidate the molecular mechanisms how primary cilia orchestrate the septation process. The plethora of malformations observed in the cobblestone embryo allow for a deeper insight into a putative link between primary cilia and human VATER/VACTERL syndromes.

Direct modulation of TRPC ion channels by Gα proteins

GPCR-Gi protein pathways are involved in the regulation of vagus muscarinic pathway under physiological conditions and are closely associated with the regulation of internal visceral organs. The muscarinic receptor-operated cationic channel is important in GPCR-Gi protein signal transduction as it decreases heart rate and increases GI rhythm frequency. In the SA node of the heart, acetylcholine binds to the M2 receptor and the released Gβγ activates GIRK (I(K,ACh)) channel, inducing a negative chronotropic action. In gastric smooth muscle, there are two muscarinic acetylcholine receptor (mAChR) subtypes, M2 and M3. M2 receptor activates the muscarinic receptor-operated nonselective cationic current (mIcat, NSCC(ACh)) and induces positive chronotropic effect. Meanwhile, M3 receptor induces hydrolysis of PIP2 and releases DAG and IP3. This IP3 increases intracellular Ca2+ and then leads to contraction of GI smooth muscles. The activation of mIcat is inhibited by anti-Gi/o protein antibodies in GI smooth muscle, indicating the involvement of Gαi/o protein in the activation of mIcat. TRPC4 channel is a molecular candidate for mIcat and can be directly activated by constitutively active Gαi QL proteins. TRPC4 and TRPC5 belong to the same subfamily and both are activated by Gi/o proteins. Initial studies suggested that the binding sites for G protein exist at the rib helix or the CIRB domain of TRPC4/5 channels. However, recent cryo-EM structure showed that IYY58-60 amino acids at ARD of TRPC5 binds with Gi3 protein. Considering the expression of TRPC4/5 in the brain, the direct G protein activation on TRPC4/5 is important in terms of neurophysiology. TRPC4/5 channels are also suggested as a coincidence detector for Gi and Gq pathway as Gq pathway increases intracellular Ca2+ and the increased Ca2+ facilitates the activation of TRPC4/5 channels. More complicated situation would occur when GIRK, KCNQ2/3 (IM) and TRPC4/5 channels are co-activated by stimulation of muscarinic receptors at the acetylcholine-releasing nerve terminals. This review highlights the effects of GPCR-Gi protein pathway, including dopamine, μ-opioid, serotonin, glutamate, GABA, on various oragns, and it emphasizes the importance of considering TRPC4/5 channels as crucial players in the field of neuroscience.

Abnormally elevated expression of ACTA2 of circular smooth muscle leads to hyperactive contraction in aganglionic segments of HSCR

BACKGROUND

Actin Alpha 2 (ACTA2) is expressed in intestinal smooth muscle cells (iSMCs) and is associated with contractility. Hirschsprung disease (HSCR), one of the most common digested tract malformations, shows peristaltic dysfunction and spasm smooth muscles. The arrangement of the circular and longitudinal smooth muscle (SM) of the aganglionic segments is disorganized. Does ACTA2, as a marker of iSMCs, exhibit abnormal expression in aganglionic segments? Does the ACTA2 expression level affect the contraction function of iSMCs? What are the spatiotemporal expression trends of ACTA2 during different developmental stages of the colon?

METHODS

Immunohistochemical staining was used to detect the expression of ACTA2 in iSMCs of children with HSCR and Ednrb-/- mice, and the small interfering RNAs (siRNAs) knockdown technique was employed to investigate how Acta2 affected the systolic function of iSMCs. Additionally, Ednrb-/- mice were used to explore the changes in the expression level of iSMCs ACTA2 at different developmental stages.

RESULTS

The expression of ACTA2 is higher in circular SM in the aganglionic segments of HSCR patients and Ednrb-/- mice than in normal control children and mice. Down regulation of Acta2 weakens the contraction ability of intestinal smooth muscle cells. Abnormally elevated expression of ACTA2 of circular smooth muscle occurs since embryonic day 15.5 (E15.5d) in aganglionic segments of Ednrb-/- mice.

CONCLUSIONS

Abnormally elevated expression of ACTA2 in the circular SM leads to hyperactive contraction, which may cause the spasm of aganglionic segments in HSCR.

Physical organogenesis of the gut

The gut has been a central subject of organogenesis since Caspar Friedrich Wolff’s seminal 1769 work ‘De Formatione Intestinorum’. Today, we are moving from a purely genetic understanding of cell specification to a model in which genetics codes for layers of physical–mechanical and electrical properties that drive organogenesis such that organ function and morphogenesis are deeply intertwined. This Review provides an up-to-date survey of the extrinsic and intrinsic mechanical forces acting on the embryonic vertebrate gut during development and of their role in all aspects of intestinal morphogenesis: enteric nervous system formation, epithelium structuring, muscle orientation and differentiation, anisotropic growth and the development of myogenic and neurogenic motility. I outline numerous implications of this biomechanical perspective in the etiology and treatment of pathologies, such as short bowel syndrome, dysmotility, interstitial cells of Cajal-related disorders and Hirschsprung disease.

Mechanical forces directing intestinal form and function

The vertebrate intestine experiences a range of intrinsically generated and external forces during both development and adult homeostasis. It is increasingly understood how the coordination of these forces shapes the intestine through organ-scale folding and epithelial organization into crypt-villus compartments. Moreover, accumulating evidence shows that several cell types in the adult intestine can sense and respond to forces to regulate key cellular processes underlying adult intestinal functions and self-renewal. In this way, transduction of forces may direct both intestinal homeostasis as well as adaptation to external stimuli, such as food ingestion or injury. In this review, we will discuss recent insights from complementary model systems into the force-dependent mechanisms that establish and maintain the unique architecture of the intestine, as well as its homeostatic regulation and function throughout adult life.

Trigonella foenum-graecum L. and Psoralea corylifolia L. Improve Erectile Dysfunction in Streptozotocin-Induced Diabetic Rats through Suppression of Oxidative Stress

Background

Diabetes mellitus-induced erectile dysfunction (DMED) is one of the most common complications of diabetes and is mainly attributed to oxidative stress. Hu-Lu-Ba-Wan (HLBW) is a classic Chinese formulation consisting of Trigonella foenum-graecum L. (TFG) and Psoralea corylifolia L. (PC). HLBW has been used not only for the treatment of diabetes but also for the treatment of erectile dysfunction in clinics. This study aimed to explore the efficacy and underlying mechanism of HLBW in ameliorating erectile function in streptozotocin-induced diabetic rats.

Methods

The diabetic model was established by tail vein injection of streptozotocin (26 mg/kg), and then DMED rats screened by the apomorphine test were randomly divided into two groups: the model group and the HLBW group. The rats in the HLBW group were administered HLBW granules daily for 12 weeks. Fasting blood glucose and fasting insulin were tested by a commercial kit. Intracavernous pressure (ICP) and mean arterial pressure (MAP) were measured by cavernous nerve electrostimulation before the rats were killed. Erectile function was evaluated with ICP/MAP. The markers of oxidative stress in the corpus cavernosum (CC) were assayed by assay kits. Apoptosis in cavernosal tissue was detected by Western blotting (WB). The expression levels of vascular endothelial marker (vWF), α-smooth muscle actin (α-SMA), endothelial nitric oxide synthase (eNOS), and NADPH oxidase subunit P47^phox were determined by WB and PCR. Furthermore, the structure of the CC was further confirmed by Masson's trichrome staining.

Results

The results showed that HLBW significantly reduced blood glucose and increased insulin sensitivity. HLBW reduced oxidative stress and apoptosis. In addition, we observed that the expression levels of vWF, α-SMA, and eNOS as well as the ratio of smooth muscle to collagen increased in the HLBW group.

Conclusions

Our results demonstrated that HLBW could reduce oxidative stress damage in CC to improve diabetes mellitus-induced erectile dysfunction in rats by inhibiting NADPH oxidase.

The origin and mechanisms of smooth muscle cell development in vertebrates

Smooth muscle cells (SMCs) represent a major structural and functional component of many organs during embryonic development and adulthood. These cells are a crucial component of vertebrate structure and physiology, and an updated overview of the developmental and functional process of smooth muscle during organogenesis is desirable. Here, we describe the developmental origin of SMCs within different tissues by comparing their specification and differentiation with other organs, including the cardiovascular, respiratory and intestinal systems. We then discuss the instructive roles of smooth muscle in the development of such organs through signaling and mechanical feedback mechanisms. By understanding SMC development, we hope to advance therapeutic approaches related to tissue regeneration and other smooth muscle-related diseases.

The development and stem cells of the esophagus

The esophagus is derived from the anterior portion of the foregut endoderm, which also gives rise to the respiratory system. As it develops, the esophageal lining is transformed from a simple columnar epithelium into a stratified squamous cell layer, accompanied by the replacement of unspecified mesenchyme with layers of muscle cells. Studies in animal models have provided significant insights into the roles of various signaling pathways in esophageal development. More recent studies using human pluripotent stem cells (hPSCs) further demonstrate that some of these signaling pathways are conserved in human esophageal development. In addition, a combination of mouse genetics and hPSC differentiation approaches have uncovered new players that control esophageal morphogenesis. In this Review, we summarize these new findings and discuss how the esophagus is established and matures throughout different stages, including its initial specification, respiratory-esophageal separation, epithelial morphogenesis and maintenance. We also discuss esophageal muscular development and enteric nervous system innervation, which are essential for esophageal structure and function.

Histomorphometric analysis of the epithelial lumen, mesenchyme, smooth muscle cell layers, and mesentery of the mouse developing duodenum in relation with the macroscopic morphogenesis

Integral analysis of the development of the epithelium, mesenchyme, and smooth muscle cell (SMC) layers, i.e., the inner circular (IC) and outer longitudinal layers, as well as their relation with the mesentery is necessary to understand macroscopic gut development. We here focused on the proximal duodenum with the characteristic "C"-shaped loop and analyzed the duodenum down to the duodenojejunal flexure in C57BL/6J mouse embryos at embryonic days (E) 13.5, 15.5, and 17.5 by histomorphometric analysis. We examined the angle of the axis of the epithelial lumen, which was oval at E13.5 against the mesentery, along with the epithelial cell nuclear shape, the adjacent mesenchymal cell density in relation to the epithelial lumen axis, and the development of SMC layers. The luminal axis of the oval epithelial lumen at E13.5 rotated clockwise against the mesentery in the proximal duodenum. The shape of epithelial nuclei was longer and thinner at the long axis but shorter and broader at the short axis, whereas mesenchymal density was significantly lower in the area on the luminal long axis than that on the short axis. The number of SMC layers in the IC at E13.5, E15.5, and E17.5 showed a regional difference in relation to the mesentery, but no regional difference along the long axis of the duodenum. These findings suggest that epithelial lumen winding against the mesentery and the corresponding changes in the epithelial cell shape and surrounding mesenchymal density may be involved in the formation of the "C" loop of the proximal duodenum.

Generation of transgenic mice that conditionally express microRNA miR-145

MicroRNAs are modulators of cellular phenotypes and their functions contribute to development, homeostasis, and disease. miR-145 is a conserved microRNA that has been implicated in regulating an array of phenotypes. These include supporting smooth muscle differentiation, repression of stem cell pluripotency, and inhibition of tumor growth and metastasis. Previously, our lab demonstrated that miR-145 acts to suppress cardiac fibrosis through inhibition of the TGF-β signaling pathway. The range of effects that miR-145 has on different cell types makes it an attractive microRNA for further study. Here we describe the generation of transgenic mice that conditionally express miR-145 through Cre recombinase-mediated activation. Characterization of individual founder lines indicates that overexpression of miR-145 in the developing cardiovascular system has detrimental effects, with three independent miR-145 transgenic lines exhibiting Cre-dependent lethality. Expression analysis demonstrates that the transgene is robustly expressed and our analysis reveals a novel downstream target of miR-145, Tnnt2. The miR-145 transgenic mice represent a valuable tool to understand the role of miR-145 in diverse cell types and to address its potential as a therapeutic mediator for the treatment of disease.

Integrating Bioelectrical Currents and Ca2+ Signaling with Biochemical Signaling in Development and Pathogenesis

Roles of bioelectrical signals are increasingly recognized in excitable and nonexcitable non-neural tissues. Diverse ion-selective channels, pumps, and gap junctions participate in bioelectrical signaling, including those transporting calcium ions (Ca2+). Ca2+ is the most versatile transported ion, because it serves as an electrical charge carrier and a biochemical regulator for multiple molecular binding, enzyme, and transcription activities. We aspire to learn how bioelectrical signals crosstalk to biochemical/biomechanical signals. In this study, we review four recent studies showing how bioelectrical currents and Ca2+ signaling affect collective dermal cell migration during feather bud elongation, affect chondrogenic differentiation in limb development, couple with mechanical tension in aligning gut smooth muscle, and affect mitochondrial function and skeletal muscle atrophy. We observe bioelectrical signals involved in several developmental and pathological conditions in chickens and mice at multiple spatial scales: cellular, cellular collective, and subcellular. These examples inspire novel concept and approaches for future basic and translational studies.

Genetic and Mechanical Regulation of Intestinal Smooth Muscle Development

The gastrointestinal tract is enveloped by concentric and orthogonally aligned layers of smooth muscle; however, an understanding of the mechanisms by which these muscles become patterned and aligned in the embryo has been lacking. We find that Hedgehog acts through Bmp to delineate the position of the circumferentially oriented inner muscle layer, whereas localized Bmp inhibition is critical for allowing formation of the later-forming, longitudinally oriented outer layer. Because the layers form at different developmental stages, the muscle cells are exposed to unique mechanical stimuli that direct their alignments. Differential growth within the early gut tube generates residual strains that orient the first layer circumferentially, and when formed, the spontaneous contractions of this layer align the second layer longitudinally. Our data link morphogen-based patterning to mechanically controlled smooth muscle cell alignment and provide a mechanistic context for potentially understanding smooth muscle organization in a wide variety of tubular organs.

The absence of SOX2 in the anterior foregut alters the esophagus into trachea and bronchi in both epithelial and mesenchymal components

In the anterior foregut (AFG) of mouse embryos, the transcription factor SOX2 is expressed in the epithelia of the esophagus and proximal branches of respiratory organs comprising the trachea and bronchi, whereas NKX2.1 is expressed only in the epithelia of respiratory organs. Previous studies using hypomorphic Sox2 alleles have indicated that reduced SOX2 expression causes the esophageal epithelium to display some respiratory organ characteristics. In the present study, we produced mouse embryos with AFG-specific SOX2 deficiency. In the absence of SOX2 expression, a single NKX2.1-expressing epithelial tube connected the pharynx and the stomach, and a pair of bronchi developed in the middle of the tube. Expression patterns of NKX2.1 and SOX9 revealed that the anterior and posterior halves of SOX2-deficient AFG epithelial tubes assumed the characteristics of the trachea and bronchus, respectively. In addition, we found that mesenchymal tissues surrounding the SOX2-deficient NKX2.1-expressing epithelial tube changed to those surrounding the trachea and bronchi in the anterior and posterior halves, as indicated by the arrangement of smooth muscle cells and SOX9-expressing cells and by the expression of Wnt4 (esophagus specific), Tbx4 (respiratory organ specific), and Hoxb6 (distal bronchus specific). The impact of mesenchyme-derived signaling on the early stage of AFG epithelial specification has been indicated. Our study demonstrated an opposite trend where epithelial tissue specification causes concordant changes in mesenchymal tissues, indicating a reciprocity of epithelial-mesenchymal interactions.

Chick midgut morphogenesis

The gastrointestinal tract is an essential system of organs required for nutrient absorption. As a simple tube early in development, the primitive gut is patterned along its anterior-posterior axis into discrete compartments with unique morphologies relevant to their functions in the digestive process. These morphologies are acquired gradually through development as the gut is patterned by tissue interactions, both molecular and mechanical in nature, involving all three germ layers. With a focus on midgut morphogenesis, we review work in the chick embryo demonstrating how these molecular signals and mechanical forces sculpt the developing gut tube into its mature form. In particular, we highlight two mechanisms by which the midgut increases its absorptive surface area: looping and villification. Additionally, we review the differentiation and patterning of the intestinal mesoderm into the layers of smooth muscle that mechanically drive peristalsis and the villification process itself. Where relevant, we discuss the mechanisms of chick midgut morphogenesis in the context of experimental data from other model systems.

Embryogenesis of the peristaltic reflex

KEY POINTS

Neurogenic gut movements start after longitudinal smooth muscle differentiation in three species (mouse, zebrafish, chicken), and at E16 in the chicken embryo. The first activity of the chicken enteric nervous system is dominated by inhibitory neurons. The embryonic enteric nervous system electromechanically couples circular and longitudinal spontaneous myogenic contractions, thereby producing a new, rostro-caudally directed bolus transport pattern: the migrating motor complex. The response of the embryonic gut to mechanical stimulation evolves from a symmetric, myogenic response at E12, to a neurally mediated, polarized, descending inhibitory, 'law of the intestine'-like response at E16. High resolution, whole-mount 3D reconstructions are presented of the enteric nervous system of the chicken embryo at the neural-control stage E16 with the iDISCO+ tissue clarification technique.

ABSTRACT

Gut motility is a complex transport phenomenon involving smooth muscle, enteric neurons, glia and interstitial cells of Cajal. Because these different cells differentiate and become active at different times during embryo development, studying the ontogenesis of motility offers a unique opportunity to 'time-reverse-engineer' the peristaltic reflex. Working on chicken embryo intestinal explants in vitro, we found by spatio-temporal mapping and signal processing of diameter and position changes that motility follows a characteristic sequence of increasing complexity: (1) myogenic circular smooth muscle contractions from E6 to E12 that propagate as waves along the intestine, (2) overlapping and independent, myogenic, low-frequency, bulk longitudinal smooth muscle contractions around E14, and (3) tetrodotoxin-sensitive coupling of longitudinal and circular contractions by the enteric nervous system as from E16. Inhibition of nitric oxide synthase neurons shows that the coupling consists in nitric oxide-mediated relaxation of circular smooth muscle when the longitudinal muscle layer is contracted. This mechanosensitive coupling gives rise to a directional, cyclical, propagating bolus transport pattern: the migrating motor complex. We further reveal a transition to a polarized, descending, inhibitory reflex response to mechanical stimulation after neuronal activity sets in at E16. This asymmetric response is the elementary mechanism responsible for peristaltic transport. We finally present unique high-resolution 3D reconstructions of the chicken enteric nervous system at the neural-control stage based on confocal imaging of iDISCO+ clarified tissues. Our study shows that the enteric nervous system gives rise to new peristaltic transport patterns during development by coupling spontaneous circular and longitudinal smooth muscle contraction waves.

Epalrestat, an Aldose Reductase Inhibitor, Restores Erectile Function in Streptozocin-induced Diabetic Rats

Epalrestat, an aldose reductase inhibitor (ARI), was adopted to improve the function of peripheral nerves in diabetic patients. The aim of this study was to investigate whether epalrestat could restore the erectile function of diabetic erectile dysfunction using a rat model. From June 2016, 24 rats were given streptozocin (STZ) to induce the diabetic rat model, and epalrestat was administered to ten diabetic erectile dysfunction (DED) rats. Intracavernous pressure (ICP) and mean systemic arterial pressure (MAP), levels of aldose reductase (AR), nerve growth factor (NGF), neuronal nitric oxide synthase (nNOS), α-smooth muscle antigen (α-SMA), and von Willebrand factor (vWF) in the corpus cavernosum were analyzed. We discovered that epalrestat acted on cavernous tissue and partly restored erectile function. NGF and nNOS levels in the corpora were increased after treatment with epalrestat. We also found that the content of α-SMA-positive smooth muscle cells and vWF-positive endothelial cells in the corpora cavernosum were declined. Accordingly, epalrestat might improve erectile function by increasing the upregulation of NGF and nNOS to restore the function of the dorsal nerve of the penis.

Development and stem cells of the esophagus

The esophagus is derived from the anterior portion of the developmental intermediate foregut, a structure that also gives rise to other organs including the trachea, lung, and stomach. Genetic studies have shown that multiple signaling pathways (e.g. Bmp) and transcription factors (e.g. SOX2) are required for the separation of the esophagus from the neighboring respiratory system. Notably, some of these signaling pathways and transcription factors continue to play essential roles in the subsequent morphogenesis of the esophageal epithelium which undergoes a simple columnar-to-stratified squamous conversion. Reactivation of the relevant signaling pathways has also been associated with pathogenesis of esophageal diseases that affect the epithelium and its stem cells in adults. In this review we will summarize these findings. We will also discuss new data regarding the cell-of-origin for the striated and smooth muscles surrounding the esophagus and how they are differentiated from the mesenchyme during development.

Smooth Muscle-specific α Tropomyosin Is a Marker of Fully Differentiated Smooth Muscle in Lung

Tropomyosin (Tm) is one of the major components of smooth muscle. Currently it is impossible to easily distinguish the two major smooth muscle (sm) forms of Tm at a protein level by immunohistochemistry due to lack of specific antibodies. α-sm Tm contains a unique 2a exon not found in any other Tm. We have produced a polyclonal antibody to this exon that specifically detects α-sm Tm. We demonstrate here the utility of this antibody for the study of smooth muscle. The tissue distribution of α-sm Tm was shown to be highly specific to smooth muscle. α-sm Tm showed an identical profile and tissue colocalization with α-sm actin both by Western blotting and immunohistochemistry. Using lung as a model organ system, we examined the developmental appearance of α-sm Tm in comparison to α-sm actin in both the mouse and human. α-sm Tm is a late-onset protein, appearing much later than actin in both species. There were some differences in onset of appearance in vascular and airway smooth muscle with airway appearing earlier. α-sm Tm can therefore be used as a good marker of mature differentiated smooth muscle cells. Along with α-sm actin and sm-myosin antibodies, α-sm Tm is a valuable tool for the study of smooth muscle.

Smooth muscle cells largely develop independently of functional hemogenic endothelium

Vascular smooth muscle cells represent a major component of the cardiovascular system. In vitro studies have shown that FLK1(+) cells derived from embryonic stem (ES) cells can differentiate into both endothelial and smooth muscle cells. These FLK1(+) cells also contain a mesodermal precursor, the hemangioblast, able to produce endothelial, blood and smooth muscle cells. The generation of blood precursors from the hemangioblast was recently shown to occur through a transient cell population of specialised endothelium, a hemogenic endothelium. To date, the lineage relationship between this cell population and smooth muscle cell progenitors has not been investigated. In this study, we generated a reporter ES cell line in which expression of the fluorescent protein H2B-VENUS is driven by the α-smooth muscle actin (α-SMA) regulatory sequences. We demonstrated that this reporter cell line efficiently trace smooth muscle development during ES cell differentiation. Although some smooth muscle cells are associated with broad endothelial development, we established that smooth muscle cells are mostly generated independently from a specialised functional hemogenic endothelium. This study provides new and important insights into hematopoietic and vascular development, which may help in driving further progress towards the development of bioengineered vascular grafts for regenerative medicine.

Specific requirement of Gli transcription factors in Hedgehog-mediated intestinal development

Hedgehog (Hh) signaling is involved in multiple aspects of embryonic gut development, including mesenchymal growth and smooth muscle differentiation. The Gli family transcription factors is thought to collectively mediate Hh signaling in mammals. However, the function of different Gli proteins in gut development remains uncharacterized. Here, we genetically dissect the contribution of Gli transcriptional activation and de-repression in intestinal growth and patterning. We find that removal of the Gli3 repressor is dispensable for intestinal development and does not play a major role in Hh-controlled gut development. However, Gli2 activation is able to fully rescue the Smoothened (Smo)-null intestinal phenotype, suggesting that the Gli2 transcription factor is the main effector for Hh signaling in the intestine. To understand further the molecular mechanism underlying Hh/Gli function in the developing gut, we identify a subset of small leucine-rich glycoproteins (SLRPs) that may function downstream of Hh signaling in the mesenchyme. We show that osteoglycin, a SLRP, inhibits Hh-induced differentiation toward the smooth muscle lineage in C3H10T1/2 pluripotent mesenchymal cells. Taken together, our study reveals, for the first time, the distinct roles of Gli proteins in intestine development and suggests SLRPs as novel regulators of smooth muscle cell differentiation.

TSHZ3 and SOX9 regulate the timing of smooth muscle cell differentiation in the ureter by reducing myocardin activity

Smooth muscle cells are of key importance for the proper functioning of different visceral organs including those of the urogenital system. In the mouse ureter, the two transcriptional regulators TSHZ3 and SOX9 are independently required for initiation of smooth muscle differentiation from uncommitted mesenchymal precursor cells. However, it has remained unclear whether TSHZ3 and SOX9 act independently or as part of a larger regulatory network. Here, we set out to characterize the molecular function of TSHZ3 in the differentiation of the ureteric mesenchyme. Using a yeast-two-hybrid screen, we identified SOX9 as an interacting protein. We show that TSHZ3 also binds to the master regulator of the smooth muscle program, MYOCD, and displaces it from the coregulator SRF, thereby disrupting the activation of smooth muscle specific genes. We found that the initiation of the expression of smooth muscle specific genes in MYOCD-positive ureteric mesenchyme coincides with the down regulation of Sox9 expression, identifying SOX9 as a possible negative regulator of smooth muscle cell differentiation. To test this hypothesis, we prolonged the expression of Sox9 in the ureteric mesenchyme in vivo. We found that Sox9 does not affect Myocd expression but significantly reduces the expression of MYOCD/SRF-dependent smooth muscle genes, suggesting that down-regulation of Sox9 is a prerequisite for MYOCD activity. We propose that the dynamic expression of Sox9 and the interaction between TSHZ3, SOX9 and MYOCD provide a mechanism that regulates the pace of progression of the myogenic program in the ureter.

Comprehensive timeline of mesodermal development in the quail small intestine

BACKGROUND

To generate the mature intestine, splanchnic mesoderm diversifies into six different tissue layers each with multiple cell types through concurrent and complex morphogenetic events. Hindering the progress of research in the field is the lack of a detailed description of the fundamental morphological changes that constitute development of the intestinal mesoderm.

RESULTS

We used immunofluorescence and morphometric analyses of wild-type and Tg(tie1:H2B-eYFP) quail embryos to establish a comprehensive timeline of mesodermal development in the avian intestine. The following landmark features were analyzed from appearance of the intestinal primordium through generation of the definitive structure: radial compartment formation, basement membrane dynamics, mesothelial differentiation, mesenchymal expansion and growth patterns, smooth muscle differentiation, and maturation of the vasculature. In this way, structural relationships between mesodermal components were identified over time.

CONCLUSIONS

This integrated analysis presents a roadmap for investigators and clinicians to evaluate diverse experimental data obtained at individual stages of intestinal development within the longitudinal context of intestinal morphogenesis.

3-Dimensional morphometric analysis of murine bladder development and dysmorphogenesis

BACKGROUND

Disorders of the urinary tract represent a major cause of morbidity and impaired quality of life. To better understand the morphological events responsible for normal urinary tract development, we performed 3-D reconstructive analysis of developing mouse bladders in control, mgb-/-, and Fgfr2(Mes-/-) mice.

RESULTS

Detrusor smooth muscle differentiation initiated in the bladder dome and progressed caudally with the leading edge extending down the right posterior surface of the bladder. Gender-specific differences in detrusor smooth muscle development were observed during early embryonic development. Bladder trigone morphology transitioned from an isosceles to equilateral triangle during development due to the preferential lengthening of the urethra to ureter distance. The primary defect observed in mgb-/- bladders was a significant reduction in detrusor smooth muscle differentiation throughout development. Deviations from normal trigone morphology correlated best with VUR development in Fgfr2(Mes-/-) mice, while alterations in intravesicular tunnel length did not.

CONCLUSIONS

Multivariate morphometric analysis provides a powerful tool to quantify and assess urinary tract development.

Characterization of bacterial artificial chromosome transgenic mice expressing mCherry fluorescent protein substituted for the murine smooth muscle alpha-actin gene

Smooth muscle alpha actin (SMA) is a cytoskeletal protein expressed by mesenchymal and smooth muscle cell types, including mural cells (vascular smooth muscle cells and pericytes). Using Bacterial Artificial Chromosome (BAC) recombineering technology, we generated transgenic reporter mice that express a membrane localized cherry red fluorescent protein (mCherry), driven by the full-length SMA promoter and intronic sequences. We determined that the founders and F1 progeny of five independent lines contain 1-3 copies of the mCherry-substituted BAC vector. Furthermore, we characterized the expression of SMA-mCherry in relation to endogenous SMA in the embryo and in adult tissues, and found that the transgenic reporter in each line recapitulated endogenous SMA expression at all time points. We were also able to isolate SMA expressing cells from embryonic tissues using fluorescence-activated cell sorting (FACS). We demonstrated that this marker can be combined with other vital fluorescent reporters and it can be used for live imaging of embryonic cardiodynamics. Therefore, these transgenic mice will be useful for isolating live SMA-expressing cells via FACS and for studying the emergence, behavior, and regulation of SMA-expressing cells, including vascular smooth muscle cells and pericytes throughout embryonic and postnatal development.

Hedgehog signaling controls mesenchymal growth in the developing mammalian digestive tract

Homeostasis of the vertebrate digestive tract requires interactions between an endodermal epithelium and mesenchymal cells derived from the splanchnic mesoderm. Signaling between these two tissue layers is also crucial for patterning and growth of the developing gut. From early developmental stages, sonic hedgehog (Shh) and indian hedgehog (Ihh) are secreted by the endoderm of the mammalian gut, indicative of a developmental role. Further, misregulated hedgehog (Hh) signaling is implicated in both congenital defects and cancers arising from the gastrointestinal tract. In the mouse, only limited gastrointestinal anomalies arise following removal of either Shh or Ihh. However, given the considerable overlap in their endodermal expression domains, a functional redundancy between these signals might mask a more extensive role for Hh signaling in development of the mammalian gut. To address this possibility, we adopted a conditional approach to remove both Shh and Ihh functions from early mouse gut endoderm. Analysis of compound mutants indicates that continuous Hh signaling is dispensable for regional patterning of the gut tube, but is essential for growth of the underlying mesenchyme. Additional in vitro analysis, together with genetic gain-of-function studies, further demonstrate that Hh proteins act as paracrine mitogens to promote the expansion of adjacent mesenchymal progenitors, including those of the smooth muscle compartment. Together, these studies provide new insights into tissue interactions underlying mammalian gastrointestinal organogenesis and disease.

MicroRNA regulatory networks in cardiovascular development

The heart, more than any other organ, requires precise functionality on a second-to-second basis throughout the lifespan of the organism. Even subtle perturbations in cardiac structure or function have catastrophic consequences, resulting in lethal forms of congenital and adult heart disease. Such intolerance of the heart to variability necessitates especially robust regulatory mechanisms to govern cardiac gene expression. Recent studies have revealed central roles for microRNAs (miRNAs) as governors of gene expression during cardiovascular development and disease. The integration of miRNAs into the genetic circuitry of the heart provides a rich and robust array of regulatory interactions to control cardiac gene expression. miRNA regulatory networks also offer opportunities for therapeutically modulating cardiac function through the manipulation of pathogenic and protective miRNAs. We discuss the roles of miRNAs as regulators of cardiac form and function, unresolved questions in the field, and issues for the future.

Actin isoform expression patterns during mammalian development and in pathology: insights from mouse models

The dynamic actin cytoskeleton, consisting of six actin isoforms in mammals and a variety of actin binding proteins is essential for all developmental processes and for the viability of the adult organism. Actin isoform specific functions have been proposed for muscle contraction, cell migration, endo- and exocytosis and maintaining cell shape. However, these specific functions for each of the actin isoforms during development are not well understood. Based on transgenic mouse models, we will discuss the expression patterns of the six conventional actin isoforms in mammals during development and adult life. Ablation of actin genes usually leads to lethality and affects expression of other actin isoforms at the cell or tissue level. A good knowledge of their expression and functions will contribute to fully understand severe phenotypes or diseases caused by mutations in actin isoforms.

Six2 activity is required for the formation of the mammalian pyloric sphincter

The functional activity of Six2, a member of the so/Six family of homeodomain-containing transcription factors, is required during mammalian kidney organogenesis. We have now determined that Six2 activity is also necessary for the formation of the pyloric sphincter, the functional gate at the stomach-duodenum junction that inhibits duodenogastric reflux. Our data reveal that several genes known to be important for pyloric sphincter formation in the chick (e.g., Bmp4, Bmpr1b, Nkx2.5, Sox9, and Gremlin) also appear to be required for the formation of this structure in mammals. Thus, we propose that Six2 activity regulates this gene network during the genesis of the pyloric sphincter in the mouse.

The role of the visceral mesoderm in the development of the gastrointestinal tract

The gastrointestinal (GI) tract forms from the endoderm (which gives rise to the epithelium) and the mesoderm (which develops into the smooth muscle layer, the mesenchyme, and numerous other cell types). Much of what is known of GI development has been learned from studies of the endoderm and its derivatives, because of the importance of epithelial biology in understanding and treating human diseases. Although the necessity of epithelial-mesenchymal cross talk for GI development is uncontested, the role of the mesoderm remains comparatively less well understood. The transformation of the visceral mesoderm during development is remarkable; it differentiates from a very thin layer of cells into a complex tissue comprising smooth muscle cells, myofibroblasts, neurons, immune cells, endothelial cells, lymphatics, and extracellular matrix molecules, all contributing to the form and function of the digestive system. Understanding the molecular processes that govern the development of these cell types and elucidating their respective contribution to GI patterning could offer insight into the mechanisms that regulate cell fate decisions in the intestine, which has the unique property of rapid cell renewal for the maintenance of epithelial integrity. In reviewing evidence from both mammalian and nonmammalian models, we reveal the important role of the visceral mesoderm in the ontogeny of the GI tract.

Cell-cell interactions during remodeling of the intestine at metamorphosis in Xenopus laevis

Amphibian metamorphosis is accompanied by extensive intestinal remodeling. This process, mediated by thyroid hormone (TH) and its nuclear receptors, affects every cell type. Gut remodeling in Xenopus laevis involves epithelial and mesenchymal proliferation, smooth muscle thickening, neuronal aggregation, formation of intestinal folds, and shortening of its length by 75%. Transgenic tadpoles expressing a dominant negative TH receptor (TRDN) controlled by epithelial-, fibroblast-, and muscle-specific gene promoters were studied. TRDN expression in the epithelium caused abnormal development of virtually all cell types, with froglet guts displaying reduced intestinal folds, thin muscle and mesenchyme, absence of neurons, and reduced cell proliferation. TRDN expression in fibroblasts caused abnormal epithelia and mesenchyme development, and expression in muscle produced fewer enteric neurons and a reduced inter-muscular space. Gut shortening was inhibited only when TRDN was expressed in fibroblasts. Gut remodeling results from both cell-autonomous and cell-cell interactions.

Teashirt 3 is necessary for ureteral smooth muscle differentiation downstream of SHH and BMP4

Ureteric contractions propel foetal urine from the kidney to the urinary bladder. Here, we show that mouse ureteric smooth muscle cell (SMC) precursors express the transcription factor teashirt 3 (TSHZ3), and that Tshz3-null mutant mice have congenital hydronephrosis without anatomical obstruction. Ex vivo, the spontaneous contractions that occurred in proximal segments of wild-type embryonic ureter explants were absent in Tshz3 mutant ureters. In vivo, prior to the onset of hydronephrosis, mutant proximal ureters failed to express contractile SMC markers, whereas these molecules were detected in controls. Mutant embryonic ureters expressed Shh and Bmp4 transcripts as normal, with appropriate expression of Ptch1 and pSMAD1/5/8 in target SM precursors, whereas myocardin, a key regulator for SMC differentiation, was not expressed in Tshz3-null ureters. In wild-type embryonic renal tract explants, exogenous BMP4 upregulated Tshz3 and myocardin expression. More interestingly, in Tshz3 mutant renal tract explants, exogenous BMP4 did not improve the Tshz3 phenotype. Thus, Tshz3 is required for proximal ureteric SMC differentiation downstream of SHH and BMP4. Furthermore, the Tshz3 mutant mouse model of ;functional' urinary obstruction resembles congenital pelvi-ureteric junction obstruction, a common human malformation, suggesting that TSHZ, or related, gene variants may contribute to this disorder.

microRNA-133a regulates cardiomyocyte proliferation and suppresses smooth muscle gene expression in the heart

MicroRNAs (miRNAs) modulate gene expression by inhibiting mRNA translation and promoting mRNA degradation, but little is known of their potential roles in organ formation or function. miR-133a-1 and miR-133a-2 are identical, muscle-specific miRNAs that are regulated during muscle development by the SRF transcription factor. We show that mice lacking either miR-133a-1 or miR-133a-2 are normal, whereas deletion of both miRNAs causes lethal ventricular-septal defects in approximately half of double-mutant embryos or neonates; miR-133a double-mutant mice that survive to adulthood succumb to dilated cardiomyopathy and heart failure. The absence of miR-133a expression results in ectopic expression of smooth muscle genes in the heart and aberrant cardiomyocyte proliferation. These abnormalities can be attributed, at least in part, to elevated expression of SRF and cyclin D2, which are targets for repression by miR-133a. These findings reveal essential and redundant roles for miR-133a-1 and miR-133a-2 in orchestrating cardiac development, gene expression, and function and point to these miRNAs as critical components of an SRF-dependent myogenic transcriptional circuit.

Embryonic development of the striated muscle complex in rats with anorectal malformations

PURPOSE

Many patients with anorectal malformations (ARMs) continue to have postoperative anal dysfunction. The striated muscle complex (SMC) is one of the most important factors that influence defecation function. To explore the development of SMC in ARMs, the authors investigated the pelvic muscle development in rat embryos affected with ARMs.

METHODS

Anorectal malformation embryos were induced by ethylenethiourea on the 10th gestational day (E10). Normal rat embryos and embryos with ARMs from E13 to E21 were serial-sectioned in the sagittal, transverse, and coronal planes, stained with H&E and immunohistochemistry staining using specific antibodies to myogenin. Temporal and spatial sequence was carried out on SMC.

RESULTS

On E16, in normal group, SMC appeared fibroid structure in normal rats; SMC arose from bulbocavernosus muscle and ran backward, parallel to the perineal skin, and loosely surrounded the anal canal and urethra. Although in ARM rats the rectum was absent, the location and appearance of SMC were similar to the normal group. On E18, in normal group, SMC musculature became much thicker than on E16 and SMC gave off 2 branches outside anterior to the rectum. Striated muscle complex surrounded the rectum more tightly. However, in ARM rats, obvious changes of SMC could be noted. In detail, SMC in ARMs were characterized by abnormal location, appearance, and path. Striated muscle complex shifted obviously cephalad, ventrally, and medianward and converged inferior to the rectal terminus and posterior to the urethra. The distance between SMC musculature and the perineal skin increased. This structure surrounded the fiberlike tissue posterior to the urethra. Under high-power view, there was connective tissue among intermuscular bundles, and the structure was disordered. During the following gestational days, SMC in normal and ARM groups continued their own tendency, respectively.

CONCLUSIONS

This study illustrated the development of the SMC in normal and ARM rats. On E16, the location and appearance of SMC in ARM rats were similar to the normal rats, and at this time, the ectopic rectal orifice could be noted. From E18 on, the maldevelopment of SMC could be observed in ARM rats. These observations suggested that the morphological changes of SMC take place after the occurrence of abnormal anorectum.

Human and mouse enteric nervous system neurosphere transplants regulate the function of aganglionic embryonic distal colon

BACKGROUND & AIMS

Recent advances have raised the possibility of treating enteric nervous system (ENS) disorders with transplanted progenitor cells (ENSPC). Although these cells have been shown to migrate and differentiate after transplantation, no functional effects have been demonstrated. We therefore aimed to investigate whether embryonic mouse and neonatal human ENSPC can regulate the contractility of aganglionic bowel.

METHODS

Embryonic mouse and neonatal human ENSPC were grown as neurospheres before transplantation into aganglionic embryonic mouse hindgut explants and culture for 8-12 days. Engraftment and neural differentiation were confirmed using immunofluorescence and transmission electron microscopy. The contraction frequency of transplanted bowel was measured and compared with that of embryonic day 11.5 embryonic ganglionic and aganglionic bowel cultured for the same period. Calcium movement was measured at spatially defined points in bowel wall smooth muscle. Neural modulation of bowel contractility was assessed using tetrodotoxin.

RESULTS

Both mouse and human ENSPC migrated and differentiated after neurosphere transplantation. Transmission electron microscopy demonstrated the existence of synapses. Transplantation restored the high contraction frequency of aganglionic bowel to the lower rate of ganglionic bowel. Calcium imaging demonstrated that neurosphere transplantation coordinates intracellular free calcium levels. Both these effects were reversed by the addition of tetrodotoxin, indicating the functional effect of neurosphere-derived neurons.

CONCLUSIONS

Neonatal human gut is a source of ENSPC that can be transplanted to restore the contractile properties of aganglionic bowel by a neurally mediated mechanism. This may aid development of a stem cell-based treatment for Hirschsprung's disease.

Transcriptional profiling of the megabladder mouse: a unique model of bladder dysmorphogenesis

Recent studies in our lab identified a mutant mouse model of obstructive nephropathy designated mgb for megabladder. Homozygotic mgb mice (mgb-/-) develop lower urinary tract obstruction in utero due to a lack of bladder smooth muscle differentiation. This defect is the result of a random transgene insertion/translocation into chromosomes 11 and 16. Transcriptional profiling identified a significantly over-expressed cluster of gene products located on the translocated fragment of chromosome 16 including urotensin II-related peptide (Urp), which was shown to be preferentially over-expressed in developing mgb-/- bladders. Pathway analysis of mgb microarray data indicated dysregulation of at least 60 gene products associated with smooth muscle development. In conclusion, the results of this study indicate that the molecular pathways controlling normal smooth muscle development are severely altered in mgb-/- bladders, and provide the first evidence that Urp may play a critical role in bladder smooth muscle development.

Platelet-derived growth factor signals play critical roles in differentiation of longitudinal smooth muscle cells in mouse embryonic gut

In the development of mouse gut, longitudinal smooth muscle cells (LMC) and interstitial cells of Cajal (ICC) originate from common precursor cells expressing c-Kit. Recently, some gastrointestinal stromal tumours, which develop from smooth muscle layers of the gut and have gain-of-function mutations of c-kit, have been reported to have gain-of-function mutations of platelet-derived growth factor (PDGF) receptor alpha gene. These data raise the possibility that PDGF signalling might be involved in the development of LMC. Therefore, we examined the expression pattern of the PDGF signal family of embryonic gut by immunohistochemistry and in situ hybridization, and investigated the role of PDGF signals in the development of smooth muscle layers in mouse gut using a new organ culture system. During embryonic development, the circular muscle layer expressed PDGF-A, enteric neurons expressed PDGF-B and common precursor cells of LMC and ICC expressed both PDGF receptor alpha and beta. The selective PDGF receptor inhibitor AG1295 suppressed the differentiation of LMC in gut explants. We conclude that PDGF signals play critical roles in the differentiation of LMC in mouse embryonic gut.

Generation and characterization of Csrp1 enhancer-driven tissue-restricted Cre-recombinase mice

Cell type-specific genetic modification using the LoxP/Cre system is a powerful tool for genetic analysis of distinct cell lineages. Because of the unique arterial smooth muscle-restricted expression of a 5.0 kb cysteine-rich protein (Csrp1) enhancer (Lilly et al.,2001, Dev Biol 240:531-547), we hypothesized that a transgenic Cre line would prove useful for the smooth muscle lineage-specific genetic manipulation. Here we describe a transgenic mouse line, ECsrp1(Cre), where Cre is initially specifically expressed in arterial smooth muscle cells. Use of the ROSA26R reporter allele confirmed that Cre-mediated recombination in vascular smooth muscle cells began at approximately E10.0 and was highly proficient. Subsequently, Cre is expressed in restricted skeletal and nonvascular smooth muscle lineages. This lineage tracing data is important for future conditional knockout studies to understand where and when Cre-mediated deletion occurs and where Cre-expressing daughter cells finally localize. Additionally, we crossed the ECsrp1(Cre) mice to the ROSA26(-eGFP-DTA) diphtheria toxin A-expressing mice to genetically ablate ECsrp1(Cre) expressing cells. This ECsrp1(Cre) transgenic line should thus prove useful for genetic analysis of diverse aspects of cardiovascular morphogenesis and as a general smooth muscle lineage deletor line.

Morphogenetic lung defects of JSAP1-deficient embryos proceeds via the disruptions of the normal expressions of cytoskeletal and chaperone proteins

Recent studies have shown that JNK/stress-activated protein kinase-associated protein 1 (JSAP1)-deficient mice die from respiratory failure shortly after birth. To understand the underlying mechanism, we investigated the histological appearances and cell type changes in developing jsap1(-/-) lungs between E12.5 and E18.5. At the light microscopic level, no overt abnormality was detected in jsap1(-/-) until E16.5. However, alveoli and airway formations that normally occur after E16.5 were poorly advanced in jsap1(-/-). Despite these morphological defects, surfactant secreting cells labeled by anti-SP-B or anti-SP-C were present in normal ranges in jsap1(-/-) lungs. Smooth muscle alpha-actin expressing cells were also developed in jsap1(-/-) lungs, although actin expression was decreased. The expressions of transcriptional factors, such as, nuclear factor Ib (Nfib), N-myc, and octamer transcriptional factor 1 (Oct-1), which play a critical role in lung morphogenesis, were found to be down-regulated, whereas signal transducer and activator of transcription 3 (Stat3), sonic hedgehog (Shh), and smoothened (Smo) were up-regulated, in jsap1(-/-) lungs at E17.5-E18.5 compared with those in jsap1(+/+) lungs. Proteomics analysis of E17.5 lung identified 39 proteins with altered expressions, which included actin, tropomyosin, myosin light chain, vimentin, heat shock protein (Hsp27), and Hsp84. These results suggest that JSAP1 is required for the normal expressions of cytoskeletal and chaperone proteins in the developing lung, and that impaired expressions of these proteins might cause morphogenetic defects observed in jsap1(-/-) lungs.

Embryological origin of airway smooth muscle

Airway smooth muscle (SM) develops from local mesenchymal cells located around the tips of growing epithelial buds. These cells gradually displace from distal to proximal position alongside the bronchial tree, elongate, and begin to synthesize SM-specific proteins. Mechanical tension (either generated by cell spreading/elongation or stretch), as well as epithelial paracrine factors, regulates the process of bronchial myogenesis. The specific roles of many of these paracrine factors during normal lung development are currently unknown. It is also unknown how and if mechanical and paracrine signals integrate into a common myogenic pathway. Furthermore, as with vascular SM and other types of visceral SM, we are just beginning to elucidate the intracellular signaling pathways and the genetic program that controls lung myogenesis. Here we present what we have learned so far about the embryogenesis of bronchial muscle.

Sp1/Sp3 compound heterozygous mice are not viable: impaired erythropoiesis and severe placental defects

The ubiquitously expressed zinc finger transcription factors Sp1 and Sp3 play critical roles in embryonic development. Sp1 knockout mice die around embryonic day 10.5. Mice lacking Sp3 are postnatal lethal. Mice heterozygous for either Sp1 or Sp3 are apparently normal, although slightly smaller. Here, we show that compound heterozygosity of Sp1 and Sp3 results in embryonic lethality accompanied by a spectrum of developmental abnormalities, including growth retardation, morphological alterations of the lung, impaired ossification, anemia, and placental defects. Anemia in Sp1/Sp3 compound heterozygous mutant embryos is associated with impaired maturation of erythrocytes. Analyses of the placenta revealed a markedly reduced spongiotrophoblast layer and a severe disorganization of the labyrinth layer in Sp1/Sp3 compound heterozygous as well as in Sp3-deficient mutant embryos. Our findings demonstrate that a threshold of Sp1 and Sp3 activity is required for normal embryonic development, suggesting that Sp1 and Sp3 act cooperatively to regulate downstream targets.

Spatiotemporal expression of smooth muscle markers in developing zebrafish gut

Smooth muscle is important for the contractility and elasticity of visceral organs. The zebrafish is an excellent model for understanding embryonic development, yet due to a lack of appropriate markers, visceral smooth muscle development remains poorly characterized. Here, we develop markers and trace the development of gut and swim bladder smooth muscle in embryonic and juvenile fish. The first smooth muscle marker we detect in the vicinity of the gut is the myoblast marker nonmuscle myosin heavy chain-b at 50 hours postfertilization (hpf), followed by the early smooth muscle markers SM22alpha-b, and alpha-smooth muscle actin at 56 and 60 hpf, respectively. Markers of more differentiated smooth muscle, smoothelin-b and cpi-17, appear by 3 days postfertilization (dpf). Tropomyosin, a relatively late marker, is first expressed at 4 dpf. We find that smooth muscle marker expression in the swim bladder follows the same sequence of marker expression as the gut, but markers have a temporal delay reflecting the later formation of swim bladder smooth muscle.

Urothelial sonic hedgehog signaling plays an important role in bladder smooth muscle formation

During bladder development, primitive mesenchyme differentiates into smooth muscle (SM) under the influence of urothelium. The gene(s) responsible for this process have not been elucidated. We propose that the Sonic hedgehog (Shh) signaling pathway is critical in bladder SM formation. Herein, we examine the role of the Shh-signaling pathway during SM differentiation in the embryonic mouse bladder. Genes in the Shh pathway and SM expression in mouse embryonic (E) bladders (E12.5, 13.5, and 14.5) were examined by immunohistochemistry (IHC), in situ hybridization, and reverse transcription polymerase chain reaction (RT-PCR). To examine the effects of disrupting Shh signaling, bladder tissues were isolated at E12.5 and E14.5, that is, before and after bladder SM induction. The embryonic bladders were cultured on membranes floating on medium with and without 10 muM of cyclopamine, an Shh inhibitor. After 3 days, SM expression was examined by assessing the following: SM alpha-actin (SMAA), SM gamma-actin (SMGA), SM-myosin heavy chain (SM-MHC), Patched, GLI1, bone morphogenic protein 4 (BMP4), and proliferating cell nuclear antigen (PCNA) by IHC and RT-PCR. SM-related genes and proteins were not expressed in E12.5 mouse embryonic bladder before SM differentiation, but were expressed by E13.5 when SM differentiation was initiated. Shh was expressed in the urothelium in E12.5 bladders. Shh-related gene expression at E12.5 was significantly higher than at E14.5. In cyclopamine-exposed cultures of E12.5 tissue, SMAA, SMGA, GLI1, and BMP4 gene expression was significantly decreased compared with controls, but PCNA gene expression did not change. In cyclopamine-exposed E14.5 cultures, SMGA and SM-MHC gene expression did not change compared with controls. Using an in vitro embryonic bladder culture model, we were able to define the kinetics of SM- and Shh-related gene expression. Cyclopamine inhibited detrusor SM actin induction, but did not inhibit SM-MHC induction. SMAA and SMGA genes appear to be induced by Shh-signaling pathways, but the SM-MHC gene is not. Based on Shh expression by urothelium and the effects of Shh inhibition on bladder SM induction, we hypothesize that urothelial-derived Shh orchestrates induction of SM in the fetal mouse bladder.

Identification of a Unique Transgenic Mouse Line That Develops Megabladder, Obstructive Uropathy, and Renal Dysfunction

Urinary tract malformations, obstructive uropathy, and hypoplasia/dysplasia are extremely important in terms of pediatric health care costs, with end-stage renal failure in children estimated to cost >$15 billion annually in the United States alone. Even so, little is known regarding the mechanisms that control these processes. Identified was a unique mutant mouse model that develops in utero megabladder, resulting in variable hydroureteronephrosis and chronic renal failure secondary to obstructive uropathy. These animals, designated mgb for megabladder, possess a primary defect in bladder smooth muscle development that is apparent by embryonic day 15. The mgb mouse represents an excellent model for the study of normal and pathogenic bladder development, including the postnatal progression of chronic renal failure that results from the development of in utero obstructive uropathy.

Chronic effects of mechanical force on airways

Airways are embedded in the mechanically dynamic environment of the lung. In utero, this mechanical environment is defined largely by fluid secretion into the developing airway lumen. Clinical, whole lung, and cellular studies demonstrate pivotal roles for mechanical distention in airway morphogenesis and cellular behavior during lung development. In the adult lung, the mechanical environment is defined by a dynamic balance of surface, tissue, and muscle forces. Diseases of the airways modulate both the mechanical stresses to which the airways are exposed as well as the structure and mechanical behavior of the airways. For instance, in asthma, activation of airway smooth muscle abruptly changes the airway size and stress state within the airway wall; asthma also results in profound remodeling of the airway wall. Data now demonstrate that airway epithelial cells, smooth muscle cells, and fibroblasts respond to their mechanical environment. A prominent role has been identified for the epithelium in transducing mechanical stresses, and in both the fetal and mature airways, epithelial cells interact with mesenchymal cells to coordinate remodeling of tissue architecture in response to the mechanical environment.

Serum response factor, its cofactors, and epithelial-mesenchymal signaling in urinary bladder smooth muscle formation

Little is known about the mechanism of bladder smooth muscle differentiation. We hypothesize that epithelial-mesenchymal signaling induces the expression of smooth muscle proteins in bladder mesenchyme resulting in smooth muscle differentiation. We confirmed that smooth muscle differentiation in the mouse urinary bladder occurs first at gestational day 14 (E14) based upon immunohistochemical localization of smooth muscle alpha-actin (SMAA). To investigate murine bladder smooth muscle differentiation and epithlelial-mesenchymal signaling in the developing bladder, we analyzed gene expression profiles of intact embryonic murine bladders and separated epithelial and mesenchymal components at embryonic days E13, E14, E15, E16, and postnatal day 1 (P1). Using cDNA microarray, we identified regulators of vascular smooth muscle differentiation in bladder mesenchyme, including serum response factor (SRF) and its cofactors, ELK1 and SRF accessory protein (SAP)1, as well as two SRF-associated pathways, angiotension receptor II and transforming growth factor- beta2. Immunohistochemistry showed diffuse expression of SRF in the bladder at E12 with localization of expression to the peripheral mesenchyme at E13 and E14. Our results suggest that bladder smooth muscle differentiation may share a similar gene expression program as occurs during vascular smooth muscle differentiation. The unique structure of the urinary bladder makes it an ideal model for studies of smooth muscle differentiation and epithelial-mesenchymal signaling.

Nox1 Overexpression Potentiates Angiotensin II-Induced Hypertension and Vascular Smooth Muscle Hypertrophy in Transgenic Mice

BACKGROUND

Reactive oxygen species (ROS) have been implicated in the development of cardiovascular pathologies. NAD(P)H oxidases (Noxes) are major sources of reactive oxygen species in the vessel wall, but the importance of individual Nox homologues in specific layers of the vascular wall is unclear. Nox1 upregulation has been implicated in cardiovascular pathologies such as hypertension and restenosis.

METHODS AND RESULTS

To investigate the pathological role of Nox1 upregulation in vascular smooth muscle, transgenic mice overexpressing Nox1 in smooth muscle cells (TgSMCnox1) were created, and the impact of Nox1 upregulation on the medial hypertrophic response during angiotensin II (Ang II)-induced hypertension was studied. These mice have increased expression of Nox1 protein in the vasculature, which is accompanied by increased superoxide production. Infusion of Ang II (0.7 mg/kg per day) into these mice for 2 weeks led to a potentiation of superoxide production compared with similarly treated negative littermate controls. Systolic blood pressure and aortic hypertrophy were also markedly greater in TgSMCnox1 mice than in their littermate controls. To confirm that this potentiation of vascular hypertrophy and hypertension was due to increased ROS formation, additional groups of mice were coinfused with the antioxidant Tempol. Tempol decreased the level of Ang II-induced aortic superoxide production and partially reversed the hypertrophic and hypertensive responses in these animals.

CONCLUSIONS

These data indicate that smooth muscle-specific Nox1 overexpression augments the oxidative, pressor, and hypertrophic responses to Ang II, supporting the concept that medial Nox1 participates in the development of cardiovascular pathologies.