The development expression of the rat alpha-vascular and gamma-enteric smooth muscle isoactins: isolation and characterization of a rat gamma-enteric actin cDNA

Mfge8 is expressed by pericytes in gastric antrum submucosa from patients with obesity

The main function of the stomach is to digest ingested food. Gastric antrum muscular contractions mix ingested food with digestive enzymes and stomach acid and propel the chyme through the pyloric sphincter at a rate in which the small intestine can process the chyme for optimal nutrient absorption. Mfge8 binding to α8β1 integrins helps regulate gastric emptying by reducing the force of antral smooth muscle contractions. The source of Mfge8 within gastric muscles is unclear. Since Mfge8 is a secreted protein, Mfge8 could be delivered via the circulation, or be locally secreted by cells within the muscle layers. In this study, we identify a source of Mfge8 within human gastric antrum muscles using spatial transcriptomic analysis. We show that Mfge8 is expressed in subpopulations of Mef2c+ perivascular cells within the submucosa layer of the gastric antrum. Mef2c is expressed in subpopulations of NG2+ and PDGFRB+ pericytes. Mfge8 is expressed in NG2+/Mef2c+ pericytes, but not in NG2+/Mef2c-, PDGFRB+/Mef2c-, or PDGFRB+/Mef2c+ pericytes. Mfge8 is absent from CD34+ endothelial cells but is expressed in a small population of perivascular ACTA2+ cells. We also show that α8 integrin is not expressed by interstitial cells of Cajal (ICC), supporting the findings that Mfge8 attenuates gastric antrum smooth muscle contractions by binding to α8β1 integrins on enteric smooth muscle cells. These findings suggest a novel, supplementary mechanism of regulation of gastric antrum motility by cellular regulators of capillary blood flow, in addition to the regulation of gastric antrum motility by the enteric nervous system and the SMC, ICC, and PDGFRα+ cell (SIP) syncytium.

Biliary Atresia Remnants Revisited: Myogenesis, Hepatic Duct-Like Structures, and Fate of Peribiliary Glands

PURPOSE AND CONTEXT

Proximal levels of excised remnants from youngest infants may reveal early features of biliary atresia (BA).

METHOD

A targeted IHC survey was applied to 34 most proximal 2 levels in 17 BA remnants excised at age 10-74 days including 7 = <30 days old and 6 control hepatic ducts (HD).

KEY RESULTS

Severity of inflammation and extent of active fibroplasia do not distinguish proximal remnants in younger (n = 7) and older (n = 10) infants. In 27/34 levels of 14/17 remnants, reactive stroma is focally SM-MHC-2 (+), marking smooth muscle myosin, termed reactive myogenesis (RM), that is absent in controls. RM facilitates identification of 3 novel hepatic duct remnants (HDR): an HD-like collagen collar lined by degenerating cholangiocytes (n = 5); erosion defects in loose reactive stroma (n = 14); solitary foci of hyperplastic squamoid epithelium (n = 4). Peribiliary glands are either hyperplastic or atretic and typically lack RM.

CONCLUSION

Minimally inflammed end-stage lesions in BA remnants occur at youngest ages favoring prenatal onset. Three novel HDR are defined. RM, a useful surrogate for HDR, is a prevalent inappropriate stromal reaction in proximal remnants of uncertain biological significance. RM is the source of mature smooth muscle in BA remnants.

Mfge8 attenuates human gastric antrum smooth muscle contractions

Coordinated gastric smooth muscle contraction is critical for proper digestion and is adversely affected by a number of gastric motility disorders. In this study we report that the secreted protein Mfge8 (milk fat globule-EGF factor 8) inhibits the contractile responses of human gastric antrum muscles to cholinergic stimuli by reducing the inhibitory phosphorylation of the MYPT1 (myosin phosphatase-targeting subunit (1) subunit of MLCP (myosin light chain phosphatase), resulting in reduced LC20 (smooth muscle myosin regulatory light chain (2) phosphorylation. Mfge8 reduced the agonist-induced increase in the F-actin/G-actin ratios of β-actin and γ-actin1. We show that endogenous Mfge8 is bound to its receptor, α8β1 integrin, in human gastric antrum muscles, suggesting that human gastric antrum muscle mechanical responses are regulated by Mfge8. The regulation of gastric antrum smooth muscles by Mfge8 and α8 integrin functions as a brake on gastric antrum mechanical activities. Further studies of the role of Mfge8 and α8 integrin in regulating gastric antrum function will likely reveal additional novel aspects of gastric smooth muscle motility mechanisms.

Generation of an enteric smooth muscle cell line from the pig ileum

Smooth muscle cells (SMCs) play an important role in physiology and production in farm animals such as pigs. Here, we report the generation of a pig SMC line. Our original objective was to establish an enteroendocrine cell line from the pig ileum epithelium through lentiviral transduction of the Simian Virus (SV) 40 large T antigen. However, an initial expression analysis of marker genes in nine cell clones revealed that none of them were enteroendocrine cells or absorptive enterocytes, goblet cells, or Paneth cells, some of the major cell types existing in the ileum epithelium. A more detailed characterization of one clone named PIC7 by RNA-seq showed that these cells expressed many of the known smooth muscle-specific or -enriched genes, including smooth muscle actin alpha 2, calponin 1, calponin 3, myosin heavy chain 11, myosin light chain kinase, smoothelin, tenascin C, transgelin, tropomyosin 1, and tropomyosin 2. Both quantitative PCR and RNA-seq analyses showed that the PIC7 cells had a high expression of mRNA for smooth muscle actin gamma 2, also known as enteric smooth muscle actin. A Western blot analysis confirmed the expression of SV40 T antigen in the PIC7 cells. An immunohistochemical analysis demonstrated the expression of smooth muscle actin alpha 2 filaments in the PIC7 cells. A collagen gel contraction assay showed that the PIC7 cells were capable of both spontaneous contraction and contraction in response to serotonin stimulation. We conclude that the PIC7 cells are derived from an enteric SMC from the pig ileum. These cells may be a useful model for studying the cellular and molecular physiology of pig enteric SMCs. Because pigs are similar to humans in anatomy and physiology, the PIC7 cells may be also used as a model for human intestinal SMCs.

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.

A role for actin polymerization in persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is defined as the failure of normal pulmonary vascular relaxation at birth. Hypoxia is known to impede postnatal disassembly of the actin cytoskeleton in pulmonary arterial myocytes, resulting in elevation of smooth muscle α-actin and γ-actin content in elastic and resistance pulmonary arteries in PPHN compared with age-matched controls. This review examines the original histological characterization of PPHN with attention to cytoskeletal structural remodeling and actin isoform abundance, reviews the existing evidence for understanding the biophysical and biochemical forces at play during neonatal circulatory transition, and specifically addresses the role of the cortical actin architecture, primarily identified as γ-actin, in the transduction of mechanical force in the hypoxic PPHN pulmonary circuit.

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.

In vivo GSH depletion induces c-myc expression by modulation of chromatin protein complexes

We hypothesize that glutathione (GSH) fluctuations could have a prominent role in the modulation of c-myc expression through a mechanism affecting chromatin remodeling complexes. This could lead to an open chromatin structure accessible to transcription factors. We studied the in vivo effect of GSH depletion on these complexes bound to the c-myc promoter in the liver of l-buthionine-(S,R)-sulfoximine (BSO)-treated rats. Using chromatin immunoprecipitation we found that 3 h after BSO treatment the repressing complexes Id2 and Sin3A (part of a histone-deacetylase complex) were released from the c-myc promoter. STAT3 was phosphorylated and associated with its coactivator p300 with intrinsic acetyltransferase activity. Consequently, STAT3 was acetylated and bound to the c-myc promoter and histone H3 became hyperacetylated. At the same time, the RNApol II paused on the c-myc promoter was released, and the gene was overexpressed. After 6 h of BSO treatment, Id2/Sin3A returned to the c-myc promoter and the gene expression was down-regulated. Moreover, we observed a second peak of c-myc expression 48 h after BSO treatment, although at this time histone H3 was hypoacetylated and RNApol II paused, suggesting that this second peak was not subject to transcriptional control, but to posttranscriptional modulation. On the whole, our experiments suggest a novel mechanism for the effect of GSH on gene expression involving chromatin changes from a repressive to an open structure accessible to transcription factors such as STAT3.

Defining α-skeletal and α-cardiac actin expression in human heart and skeletal muscle explains the absence of cardiac involvement in ACTA1 nemaline myopathy

Mutations in alpha-skeletal actin (ACTA1) underlie several congenital muscle disorders including nemaline myopathy (NM). Almost all ACTA1-NM patients have normal cardiac function, and, even lethally affected congenital NM patients exhibit an unremarkable gestation with decreased foetal movement just prior to birth. Although alpha-skeletal actin is thought to be the predominant sarcomeric actin in human heart (Boheler KR, Carrier L, de la Bastie D, et al. Skeletal actin mRNA increases in the human heart during ontogenic development and is the major isoform of control and failing adult hearts. J Clin Invest 1991;88:323-30 ), ACTA1-NM patients almost never exhibit a cardiac phenotype. In this study, we define the relative expression of skeletal and cardiac actin proteins in human heart and skeletal muscle. We show that alpha-cardiac actin is the predominant sarcomeric isoform in human donor hearts and in early foetal skeletal muscle development. Skeletal actin is the predominant isoform from 25 to 27 weeks gestation and is the exclusive isoform expressed in muscle from infancy through to adulthood. These findings are consistent with clinical observations of NM patients and assist us to better understand the pathogenesis of inherited myopathies and cardiomyopathies with mutations in actin.

Proteomics of the rat gut: Analysis of the myenteric plexus-longitudinal muscle preparation

The enteric nervous system (ENS)--present all along the gastrointestinal tract - is the largest and most complicated division of the peripheral nervous system that can function independently of the brain. The peripheral nerve cells are organized in two separate but interconnected meshworks, called the myenteric and submucous plexus. The nervous control of intestinal motility is primarily governed by the myenteric plexus (MP), which lies in-between the longitudinal- (LM) and circular-muscle layers and regulates their functions. To determine whether the proteomic technology is adapted to the analysis of specific gut tissues, we dissected the MP-LM layers from the jejunum, ileum, and colon of Long Evans rats, homogenized them, and separated the proteins using two-dimensional gel electrophoresis. A subset of all the visualized protein spots, covering the entire range of molecular weights and isoelectric points, was then selected and further analyzed by matrix-assisted laser desorption/ionization-time of flight and liquid chromatography mass spectrometry. We identified around 80 proteins in each gut segment, and among those, five were segment-specific. Most of the proteins identified were derived from muscle cells, but we also detected some neuron-specific proteins. This study represents, to our knowledge, the first extensive protein catalog of a neuromuscular layer of the rat intestine and it may constitute the basis to understand pathophysiological mechanisms related to the ENS.

Urogenital Tract Expression of Enhanced Green Fluorescent Protein in Transgenic Mice Driven by a Smooth Muscle γ-Actin Promoter

PURPOSE

Our understanding of urogenital tract development and its response to disease or injury is hindered by complex interactions between epithelial and mesenchymal cells, and the difficulties in studying either component in isolation. We investigated whether transgenic mice could be generated to express enhanced green fluorescent protein (EGFP) in smooth muscle cells (SMCs) and whether such cells could then be purified using flow cytometric sorting to isolate RNA to be used in future gene expression assays.

MATERIALS AND METHODS

A 13.7 kb mouse smooth muscle gamma-actin promoter fragment was ligated to an EGFP reporter gene and microinjected into male mouse pronuclei. Adult transgenic mice were sacrificed and urogenital tissues were removed for histological and immunohistochemical studies. In other animals conditions were determined for dissociating bladder cells and the subsequent purification of bladder SMCs by sorting.

RESULTS

Six lines of transgenic mice were generated (transgene copy numbers 1 to 30). EGFP was expressed in all smooth muscle beds examined except those associated with small blood vessels. EGFP levels appeared to correlate with transgene copy number. Histological and immunohistochemical analysis confirmed that reporter gene expression was restricted to SMCs of all tissues examined. Parameters for generating bladder cell suspensions were established and EGFP labeled bladder SMCs were identified by flow cytometric analysis.

CONCLUSIONS

Several lines of transgenic mice have been generated in which SMCs of urogenital tissues have been labeled with EGFP and pure populations of SMCs have been obtained. The methods established for the rapid dissociation and purification of bladder SMCs should minimize degradative changes. These approaches may enable us to address issues involving bladder SMC development and differentiation as well as the response to injury and disease by performing transcriptome wide analyses on purified SMC populations.

Molecular and functional analyses of the contractile apparatus in lymphatic muscle

Lymphatics are necessary for the generation and regulation of lymph flow. Lymphatics use phasic contractions and extrinsic compressions to generate flow; tonic contractions alter resistance. Lymphatic muscle exhibits important differences from typical vascular smooth muscle. In this study, the thoracic duct exhibited significant functional differences from mesenteric lymphatics. To understand the molecular basis for these differences, we examined the profiles of contractile proteins and their messages in mesenteric lymphatics, thoracic duct, and arterioles. Results demonstrated that mesenteric lymphatics express only SMB smooth muscle myosin heavy chain (SM-MHC), whereas thoracic duct and arterioles expressed both SMA and SMB isoforms. Both SM1 and SM2 isoforms of SM-MHC were detected in arterioles and mesenteric and thoracic lymphatics. In addition, the fetal cardiac/skeletal slow-twitch muscle-specific beta-MHC message was detected only in mesenteric lymphatics. All four actin messages, cardiac alpha-actin, vascular alpha-actin, enteric gamma-actin, and skeletal alpha-actin, were present in both mesenteric lymphatics and arterioles. However, in thoracic duct, predominantly cardiac alpha-actin and vascular alpha-actin were found. Western blot and immunohistochemical analyses corroborated the mRNA studies. However, in arterioles only vascular alpha-actin protein was detected. These data indicate that lymphatics display genotypic and phenotypic characteristics of vascular, cardiac, and visceral myocytes, which are needed to fulfill the unique roles of the lymphatic system.

Contractile effects and intracellular Ca2+ signalling induced by motilin and erythromycin in the circular smooth muscle of human colon

Motilin has excitatory effects on the colon of the rabbit and the dog, but little is known of its effect on the human colon. The aim of this study was to investigate the effects induced by motilin and erythromycin A (EMA) on muscle strips and on single cells from primary cultures from human colon. Isotonic contraction was recorded in circular muscle strips from macroscopically normal resection specimens of patients operated on for colonic neoplasm. Agonist-induced intracellular Ca2+ ([Ca2+]i) signalling was studied in primary cultures of colonic smooth-muscle cells using the ratiometric Ca2+ indicator Indo 1, on a laser-scanning confocal epifluorescence microscope. In circular muscle strips, norleucine13-porcine motilin ([Nle13]-pm)and EMA induced tonic contractions with an EC50 of 92 +/- 21 nmol L(-1) and 31 +/- 16 micromol L(-1), respectively. The maximal contraction was 21 +/- 4% (motilin) and 33 +/- 12% (EMA) of the response to 10(-4) mol L(-1) acetylcholine (ACh). The motilin antagonist OHM-11526 (10(-5.5) mol L(-1)) abolished the effects of both [Nle13]-pm and EMA. Neither tetrodotoxin (10(-5.5) mol L(-1)), L-nitro-D-arginine methyl ester (L-NAME) (10(-3.5) mol L(-1)) nor guanethidine (10(-5) mol L(-1)) interfered with the effects of [Nle13]-pm or EMA. [Nle13]-pm (10(-11)-10(-6) mol L(-1)) induced rises of [Ca2+]i in cultured colonic myocytes. At 10(-6) mol L-1, 94% of the cells responded, and half of the cells responded at 1.4 nmol L(-1) [Nle13]-pm. 81% (35/43) and 95% (75/79) responded to EMA (10(-6) mol L(-1)) and acetylcholine (ACh, 10(-4) mol L(-1)), respectively. The motilin antagonist GM-109 inhibited motilin- and EMA-induced [Ca2+]i rises. In the absence of extracellular Ca2+, only 13% (7/52) of the cells responded to [Nle13]-pm (10(-6) mol L(-1)) vs. 90% (47/52) to ACh (10(-4) mol L(-1)). Motilin and EMA have direct excitatory effects on circular smooth muscle from the human colon and these effects are mediated via a smooth-muscle motilin receptor. These findings suggest that motilin may regulate colonic motility and that motilides may have therapeutic potential for the treatment of colonic hypomotility.

Impaired vascular contractility and blood pressure homeostasis in the smooth muscle alpha-actin null mouse

The smooth muscle (SM) alpha-actin gene activated during the early stages of embryonic cardiovascular development is switched off in late stage heart tissue and replaced by cardiac and skeletal alpha-actins. SM alpha-actin also appears during vascular development, but becomes the single most abundant protein in adult vascular smooth muscle cells. Tissue-specific expression of SM alpha-actin is thought to be required for the principal force-generating capacity of the vascular smooth muscle cell. We wanted to determine whether SM alpha-actin gene expression actually relates to an actin isoform's function. Analysis of SM alpha-actin null mice indicated that SM alpha-actin is not required for the formation of the cardiovascular system. Also, SM alpha-actin null mice appeared to have no difficulty feeding or reproducing. Survival in the absence of SM alpha-actin may result from other actin isoforms partially substituting for this isoform. In fact, skeletal alpha-actin gene, an actin isoform not usually expressed in vascular smooth muscle, was activated in the aortas of these SM alpha-actin null mice. However, even with a modest increase in skeletal alpha-actin activity, highly compromised vascular contractility, tone, and blood flow were detected in SM alpha-actin-defective mice. This study supports the concept that SM alpha-actin has a central role in regulating vascular contractility and blood pressure homeostasis, but is not required for the formation of the cardiovascular system.

A systematic analysis of 40 random genes in cultured vascular smooth muscle subtypes reveals a heterogeneity of gene expression and identifies the tight junction gene zonula occludens 2 as a marker of epithelioid "pup" smooth muscle cells and a participant in carotid neointimal formation

An accumulation of evidence suggests that vascular smooth muscle is composed of cell subpopulations with distinct patterns of gene expression. Much of this evidence has come from serendipitous discoveries of genes marking phenotypically distinct aortic cultures derived from 12-day-old and 3-month-old rats. To identify more systematic differences, we isolated 40 genes at random from libraries of these 2 cultures and examined message expression patterns. To determine consistency of differential expression, we measured mRNA levels in 4 sets of cultures in 6 phenotypically distinct aortic cell clones and in balloon injured rat carotid arteries to determine the relevance of these differences in vitro to in vivo biology. The following 5 consistently differentially expressed genes were identified in vitro: zonula occludens 2 (ZO-2); peroxisome proliferator-activated receptor delta (PPARdelta); secreted protein, acidic and rich in cysteine (SPARC); alpha1(I)collagen; and A2, an uncharacterized gene. We examined these 5 clones during carotid artery injury and an inconsistently differentially expressed clone Krox-24 because, as an early response transcription factor, it could be involved in the injury response. PPARdelta, A2, and Krox-24 mRNAs were upregulated during the day after injury. ZO-2 and alpha1(I)collagen messages were modulated for up to a month, whereas SPARC message showed no consistent change. An analysis of ZO-2 and other tight junction genes indicates that tight junctions may play a role in smooth muscle biology. These data suggest that a systematic analysis of these libraries is likely to identify a very large number of differentially expressed genes. ZO-2 is particularly intriguing both because of this tight junction gene's pattern of prolonged over-expression after injury and because of its potential role in determining the distinctive epithelioid phenotype of smooth muscle cells identified in rat and other species.

Characteristics of inflammation-induced hypertrophy of rat intestinal smooth muscle cell

Inflammation of the human intestine causes thickening of the smooth muscle layers, and studies in rats infected with Trichinella spiralis (Tsp) have shown hyperplasia of the intestinal smooth muscle cells (ISMC). We have shown that Tsp-induced inflammation caused a fivefold increase in total protein per ISMC over control, while ISMC from the noninflamed distal ileum also showed a threefold increase. The amount of alpha-smooth muscle (SM) actin per ISMC increased nearly 500% over control by postinfection (PI) day 6. The proportion of alpha-SM actin in the total cellular protein increased 200% by day 6 PI, indicating a higher density of alpha-SM actin in the hypertrophied ISMC. Gamma-SM actin mRNA increased sharply and was matched by an increased fractional content of gamma-SM actin protein. These increases in the smooth muscle-specific actins may affect force production and further demonstrate the plasticity of smooth muscle in the inflamed intestine.

Neurotransmitters modulate cytokine-stimulated interleukin 6 secretion in rat intestinal smooth muscle cells

BACKGROUND & AIMS

Cytokine production by resident cells of the richly innervated muscularis externa may contribute to neuromuscular changes observed during intestinal inflammation. This study investigated neurotransmitter modulation of cytokine production by intestinal smooth muscle.

METHODS

We measured interleukin (IL)-6 messenger RNA expression by reverse-transcription polymerase chain reaction, IL-6 by bioassay, and cyclic adenosine monophosphate by enzyme immunoassay in rat cultured intestinal smooth muscle cells exposed to IL-1beta, in the presence or absence of neurotransmitters.

RESULTS

IL-1beta significantly increased IL-6 messenger RNA and protein. This was dose-dependently enhanced by vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), and norepinephrine and inhibited by [LYS1,PRO2,5,ARG3,4,TYR6]VIP and propranolol, respectively. Forskolin mimicked the stimulatory effects of these neurotransmitters on IL-6 secretion, and the protein kinase inhibitor6-22 amide abolished the actions of VIP, CGRP, and norepinephrine, but not that of human recombinant IL-1beta, on IL-6 secretion. These agents each increased cyclic adenosine monophosphate activity in muscle substance P, and the neurokinin 1 agonist Ac-[Arg6,Sar9,Met(O2)11] substance P(6-11) inhibited the IL-1beta-induced IL-6 release.

CONCLUSIONS

This study shows neuropeptide and sympathetic modulation of IL-1beta-induced IL-6 production by intestinal smooth muscle. These interactions may contribute to altered muscle function during intestinal inflammation.

Growing and differentiating characterization of aortic smooth muscle cell line, p53LMAC01 obtained from p53 knock out mice

Recently we have established an aortic smooth muscle cell line, p53LMAC01 obtained from p53 knockout mice. This cell line showed some differentiated properties which were accelerated by 5-azacytidine treatment [1]. In this study, further characterization of p53LMAC01 cell line was investigated according to cell growth and differentiation, and especially focused into the changes of cell feature, actin filaments' formation, and changes of intracellular calcium concentrations to sympathetic nerve transmitter, norepinephrine. While the cell feature was changed from flattened shape to extended form during 4 days, actin filaments were developing, arranging in parallel to longitudinal direction, and gathering under the surface membrane. In 11 days many cells died and detached from substrate, while actin filaments became poor except for the surface membrane in the remained cells. Appearance of calcium response to noradrenalin needed several days after passage as well as a morphological change of the cells for the extended form and development of actin filaments. The calcium response was maintained on 11 days, which coincided with the result that the cells hold actin filaments under the surface membrane. These results suggest that p53LMAC01 cell line maintains several differentiated characters of adult smooth muscle cell and that their expression needs several days after passage.

Antisense fosB RNA inhibits thrombin-induced hypertrophy in cultured pulmonary arterial smooth muscle cells

BACKGROUND

We have previously reported that fosB mRNA is induced by hypertrophic stimuli (thrombin, angiotensin II) but not proliferative stimuli (platelet-derived growth factor, basic fibroblast growth factor) in pulmonary arterial smooth muscle cells (PASMCs) (J Biol Chem. 1994;9:6399-6404). Our aim in the present study was to investigate the potential role of FosB in PASMC hypertrophy.

METHODS AND RESULTS

Adenoviruses carrying sense or antisense fosB RNA expression cassettes were used to infect cultured PASMCs with the aim of increasing or inhibiting fosB expression, respectively. We examined whether fosB expression modification affected the growth of quiescent PASMCs, thrombin-induced hypertrophy, or platelet-derived growth factor-induced proliferation. PASMC growth was assessed by daily cell number count, determination of [3H]leucine incorporation, and quantification of total cellular protein. Neither an increase nor a decrease in FosB protein expression caused a significant change in the growth of quiescent PASMCs over a period of 96 hours, indicating that FosB alone is not sufficient to induce hypertrophy. Modification of FosB levels did not affect platelet-derived growth factor-induced PASMC proliferation. An increase in FosB expression did not augment thrombin-induced hypertrophy; however, inhibition of FosB expression resulted in a diminution of thrombin-induced hypertrophy by 58+/-6% (P<0.005).

CONCLUSIONS

These results suggest that FosB is necessary but not sufficient for thrombin-induced hypertrophy in cultured PASMCs.

Smooth muscle actin and myosin expression in cultured airway smooth muscle cells

In this study, the expression of smooth muscle actin and myosin was examined in cultures of rat tracheal smooth muscle cells. Protein and mRNA analyses demonstrated that these cells express alpha- and gamma-smooth muscle actin and smooth muscle myosin and nonmuscle myosin-B heavy chains. The expression of the smooth muscle specific actin and myosin isoforms was regulated in the same direction when growth conditions were changed. Thus, at confluency in 1 or 10% serum-containing medium as well as for low-density cells (50-60% confluent) deprived of serum, the expression of the smooth muscle forms of actin and myosin was relatively high. Conversely, in rapidly proliferating cultures at low density in 10% serum, smooth muscle contractile protein expression was low. The expression of nonmuscle myosin-B mRNA and protein was more stable and was upregulated only to a small degree in growing cells. Our results provide new insight into the molecular basis of differentiation and contractile function in airway smooth muscle cells.

Molecular marker for development of interstitial cystitis in rat model: isoactin gene expression

PURPOSE

To determine whether the differential expression of bladder smooth muscle isoactin can be used as a molecular marker for the development of interstitial cystitis (IC).

METHODS

Three groups of five female Sprague-Dawley rats each underwent urethral catheterization and intravesical instillation of 0.5 ml. of 0.4N HCl. One group was sacrificed one, two and four weeks after the application of HCl, and their bladders harvested for histologic examination and evaluation using Northern blot analysis of bladder smooth muscle isoactins. Five control animals were sacrificed and their bladders harvested to establish isoactin gene expression of bladder smooth muscle in the normal state. The bladders of the rats in each group were excised, immediately frozen in liquid nitrogen, pooled, then stored -70 degrees C until needed for RNA isolation. Isoactin cDNA probes have been developed, therefore isoactin specific cDNA insert fragments were isolated and insert DNA was purified by gel electrophoresis. Total cellular RNA was isolated from 1.0 gm. of bladder smooth muscle from each group. After spectrophotometric quantification, Northern Blot analysis was performed using 2% agarose-formaldehyde gels and Biotrans nylon membranes. Two complete Northern Blot series were run on a single gel and blotted to a single membrane to eliminate gel and blotting discrepancies.

RESULTS

Microscopic histologic analysis revealed detrusor mastocystosis and eosinophilia as has been noted in humans with chronic interstitial cystitis. Two weeks after the intravesical application of hydrochloric acid, the relative expression of gamma-smooth muscle isoactin was noted to increase by 1.7-fold, while alpha-smooth muscle isoactin expression increased by a factor of 9. These effects were seen to stabilize four weeks after acid application.

CONCLUSIONS

The intravesical application of dilute HCl in rats results in a histologic appearance which mimics that seen in humans with interstitial cystitis. The appearance of detrusor mastocytosis and eosinophilia was accompanied by a relative decrease in the expression of gamma- and a relative increase in alpha-smooth muscle isoactin gene expression. This pattern of smooth muscle isoactin expression is consistent with a more immature and possibly synthetic smooth muscle phenotype, which may be responsible for the clinical presentation of those with IC. Northern blot analysis of bladder smooth muscle cells may serve as an effective marker for the development of interstitial cystitis in humans.

Neuromuscular regulation of T-cell activation

Recent investigations in our laboratory have shown that murine intestinal smooth muscle cells (ISMCs) can exert an immunomodulatory effect on T-cells. Therefore, we examined the effects of substance P, calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) on the ability of ISMCs to modulate T-cell proliferation and lymphokine generation. T-cell proliferation was observed when these cells were co-cultured with IFN-pretreated C57/BL6 ISMCs which expressed major histocompatibility complex II (MHC II), but not during T-cell co-culture with C2D (MHC II -/-) ISMCs pretreated in the same manner. T-cell proliferation during co-culture with C57/BL6 ISMCs was also associated with significantly enhanced T-cell synthesis of IFN. When CGRP (at 10(-9) M), but not substance P or VIP, was added to C57/BL6 ISMCs during the IFN-pretreatment period. T-cell proliferation was significantly increased. However, increased T-cell proliferation was not observed if the concentration of CGRP was increased to 10(-6) M. At the higher concentration, addition of substance P or VIP during the pretreatment period significantly inhibited the subsequent T-cell proliferation. Pretreatment of C57/BL6 ISMCs with any of the three neuropeptides and IFN resulted in the diminished production of IL-4 and IFN by co-cultured T-cells. A similar pattern of cytokine secretion was observed during T-cell co-culture with IFN- and neuropeptide-pretreated C2D ISMCs except when 10(-6) M substance P was added; IFN secretion by co-cultured T-cells was increased 4-fold under these conditions. Taken together, these data show a direct modulatory role for neuropeptides in the interaction between ISMCs and T-cells and suggest that, in general, neuropeptides may dampen immune responses in the neuromuscular layers of the inflamed intestine.

Muscle isoactin expression during in vitro differentiation of murine embryonic stem cells

Embryonic stem (ES) cells are pluripotent cells derived from mouse blastocysts. ES cells can differentiate into complex embryoid bodies (EBs) which exhibit many of the characteristics of 4-10-d embryos, including areas which rhythmically contract. The expression of the four muscle isoactins was examined in EBs by using transcript-specific probes for each of the muscle actin mRNAs and selectively reactive MAbs to muscle actins. Northern blot analyses from undifferentiated ES cells and EBs after 5, 10, 15, and 20 d in suspension culture demonstrated that no muscle actin transcripts could be detected in the undifferentiated cells, whereas during differentiation, the vascular and enteric smooth muscle isoactin mRNAs were easily detected. To further define the pattern of expression polymerase chain reaction analyses were carried out on RNA isolated from individual EBs. The data indicated that all four muscle-specific actin genes are transcribed. We also demonstrated the presence of muscle actins in at least two distinct cell populations within the EBs using selectively reactive MAbs. Fibroblast-like cells exhibit significant levels of the two smooth muscle actins (vascular and enteric) localized to stress fibers. In addition, one or both of the striated muscle actins (cardiac and skeletal) are expressed in cardiomyocyte-like cells. As is the case in embryonic heart, alpha-smooth muscle actin and the striated muscle actin(s) are incorporated into well organized sarcomeres in these cardiomyocyte-like cells. Thus, differentiating EBs provide an in vitro system to study both striated and smooth muscle cell gene expression.

Tissue and developmental specific expression of murine smooth muscle gamma-actin fusion genes in transgenic mice

Smooth muscle gamma-actin (SMGA) is an excellent marker of smooth muscle differentiation because it is essentially restricted to smooth muscle. As a first step toward unraveling the mechanisms underlying smooth muscle development and differentiation, we have examined the tissue-specific and developmental expression patterns of six constructs carrying portions of the murine SMGA gene linked to chloramphenicol acetyltransferase (CAT) in stable lines of transgenic mice. Based on the transgenic studies most, if not all, of the regulatory elements necessary for proper spatial and temporal expression of SMGA are present within a 13.7 kb segment of the SMGA gene containing 4.9 kb of upstream sequence, exon 1, intron 1, and a portion of exon 2 up to the start codon for translation. A second construct (SMGA11.6CAT) that lacks the distal 2.1 kb of upstream sequence but is otherwise identical to SMGA13.7CAT shows a similar level of smooth muscle-specific CAT activity. However, SMGA9.3CAT fusion gene containing only 571 bp of 5' flanking sequence, but otherwise identical to SMGA13.7CAT, and SMGA6.0CAT containing only the 4.9 kb upstream sequence, exon 1, and a miniintron 1 show a more than a 100-fold reduction of CAT activity in most smooth muscle-rich tissues. Furthermore, removal of most or all of intron 1 from a transgene with 571 bp of upstream sequence (SMGA2.0 CAT and SMGA0.6CAT) results in a near-complete or complete loss of activity, respectively, in all tissues. Overall, the studies suggest that upstream elements between -2.7 kb and -571 bp and elements within intron 1 are required for high levels of SMGA gene expression in an appropriate temporal-spatial fashion.

Placental villous stroma as a model system for myofibroblast differentiation

Different subtypes of myofibroblasts have been described according to their cytoskeletal protein patterns. It is quite likely that these different subtypes represent distinct steps of differentiation. We propose the human placental stem villi as a particularly suitable model to study this differentiation process. During the course of pregnancy, different types of placental villi develop by differentiation of the mesenchymal stroma surrounding the fetal blood vessels. In order to characterise the differentiation of placental stromal cells in the human placenta, the expression patterns of the cytoskeletal proteins vimentin, desmin, alpha- and gamma-smooth muscle actin, pan-actin, smooth muscle myosin, and the monoclonal antibody GB 42, a marker of myofibroblasts, were investigated on placental tissue of different gestational age (7th-40th week of gestation). Proliferation patterns were assessed with the proliferation markers MIB 1 and PCNA. Additionally, dipeptidyl peptidase IV distribution was studied in term placenta and the ultrastructure of placental stromal cells was assessed by electron microscopy. Different subpopulations of extravascular stromal cells were distinguished according to typical co-expression patterns of cytoskeletal proteins. Around the fetal stem vessels in term placental villi they were arranged as concentric layers with increasing stage of differentiation. A variable layer of extravascular stromal cells lying beneath the trophoblast expressed vimentin (V) or vimentin and desmin (VD). They were mitotically active. The next layer co-expressed vimentin, desmin, and alpha-smooth muscle actin (VDA). More centrally towards the fetal vessels, extravascular stromal cells co-expressed vimentin, desmin, alpha- and gamma-smooth muscle actin, and GB 42 (VDAG). Cells close to the fetal vessels additionally co-expressed smooth muscle myosin (VDAGM). Ultrastructurally, V cells resembled typical mesenchymal cells. VD cells corresponded to fibroblasts, while VDA and VDAG cells developed features of myofibroblasts. Cells of the VDAGM-type revealed a smooth muscle cell-related ultrastructure. In earlier stages of pregnancy, stromal cell types with less complex expression patterns prevailed. The media smooth muscle cells of the fetal vessels showed a mixture of different co-expression patterns. These cells were separated from extravascular stromal cells by a layer of collagen fibres. The results obtained indicate a clearly defined spatial differentiation gradient with increasing cytoskeletal complexity in human placental stromal cells from the superficial trophoblast towards the blood vessels in the centre of the stem villi. The spatial distribution of the various stages of differentiation suggests that human placental villi could be a useful model for the study of the differentiation of myofibroblasts.

In postmeiotic male germ cells poly (A) shortening accompanies translation of mRNA encoding gamma enteric actin but not cytoplasmic beta and gamma actin mRNAs

In the mammalian testis the cytoplasmic beta and gamma actins are expressed in all stages of germ-cell differentiation, whereas gamma enteric actin is expressed in germ cells solely in postmeiotic stages. Northern blot analysis of mouse testicular RNAs reveals actin mRNAs of about 2.1, 1.5, and 1.4 kB. The 2.1-kB mRNAs encode the cytoplasmic beta and gamma actins, whereas the two faster-migrating actin mRNAs encode gamma enteric actin. When postmitochondrial mouse testis extracts are fractionated by sucrose gradient centrifugation, the 1.5-kB gamma enteric actin mRNA is primarily found in the nonpolysomal fraction, whereas the 1.4-kB gamma enteric actin is polysomal. When the poly (A) tails are removed, the nonpolysomal and polysomal gamma enteric actin mRNAs both migrate at 1.3 kB, indicating that the difference in electrophoretic mobilities of the two gamma enteric actin mRNAs is caused by poly (A) length differences. The nonpolysomal and polysomal forms of the cytoplasmic beta and gamma actins show similar electrophoretic mobilities before and after deadenylation. Sequence comparison of the 3' untranslated region of the mouse gamma enteric actin to the 3' untranslated regions of other testicular mRNAs that undergo partial deadenylation reveals three highly-conserved sequence elements. These data demonstrate that the poly (A) shortening of polysomal mRNAs previously seen only with testis-specific mRNAs that are stored as mRNPs also occurs with mRNAs of widely-expressed genes that are expressed in postmeiotic male germ cells. The mRNAs all contain specific conserved sequence elements in their 3' untranslated regions.

Regulation of expression of contractile proteins with cardiac hypertrophy and failure

Transitions in sarcomeric alpha-actin and cardiac myosin heavy chain (MHC) gene expression have been useful as molecular markers for the development of cardiac hypertrophy and failure. In simpler model systems, alpha-actin expression has been useful in delineating some of the molecular pathways responsible for its induction following growth stimulation in vitro. In this study, we report that the effects of adrenergic agonists on alpha-actin expression in neonatal cardiocytes is dependent upon the culture conditions. In cardiocytes plated at 5 x 10(4) cells/cm2, skeletal alpha-actin mRNA levels represent 47%, 37% or 42% of total sarcomeric alpha-actin accumulations following administrations of 4 microM norepinephrine (NE), isoproterenol (Iso), or phenylephrine (PE), respectively. Cultured cardiocytes treated with vehicle (ascorbate) only accumulated 19% skeletal alpha-actin. Under these tissue culture conditions, in contrast to data reported previously, skeletal alpha-actin expression is regulated by both alpha- and beta-adrenergic agonist stimulation. Furthermore, we present data showing that an endogenous anti-beta-MHC transcript is regulated by both pressure-overload- or thyroxine-induced cardiac hypertrophy. Although anti-beta-MHC transcripts do not play a major role in regulating beta-MHC gene expression, the presence of this antisense transcript is associated with a novel set of beta-MHC degradation products. In vitro studies, where oligonucleotides complementary to beta-MHC have been introduced into cardiomyocytes, show that the mRNA levels of beta-MHC are decreased by 14-21% within 72 h after addition of the oligonucleotides. This result together with the presence of beta-MHC degradation products suggest that endogenous anti-beta-MHC transcripts may be involved in a post-transcriptional regulatory mechanism affecting the steady-state levels of beta-MHC expression.

Computer-assisted stereological analysis of gastric volume during the human embryonic period

Morphometric data concerning human embryos and fetuses have become more clinically informative since ultrasound was employed to make prenatal measurements and software preprocessing techniques improved the previous fuzzy ultrasound signals (Mahoney, 1992). The aim of this study was to determine the volume of the human stomach during the embryonic period and to compare its rate of growth with that during the early fetal period. To calculate gastric volume, computer imaging techniques were applied on cross sections of a graded series of human embryos (from Carnegie stage 11) and fetuses. Gastric volume increased progressively, except for a decrease between stages 12 and 13 due principally to the reduction of the right gastric wall. The growth of the left wall of the stomach was predominant over that of the right. Until stage 20 the stomach volume increased due to the predominant growth of the walls, after this stage the gastric cavity volume increased rapidly, and the rate of growth of the gastric volume reached similar values to that of the early fetal period. We concluded that in the beginning the human stomach grows due to the predominant growth of its walls, chiefly of the left, and from stage 20 because of the predominant expansion of its cavity, which may be related to the capacity to swallow amniotic fluid at the end of the embryonic period. The diminution of the right gastric wall volume (stages 12-13) is consistent with an extension of the omental bursa into the mesodermal anlage of the stomach.

Molecular analysis of smooth muscle development in the mouse

Little is currently known regarding the ontogeny of smooth muscle tissues during normal mammalian development. The alpha-smooth muscle and gamma-smooth muscle isoactins have been shown to be excellent molecular markers of smooth muscle cell phenotype. This study characterizes both the temporal and spatial patterns of alpha-smooth muscle and gamma-smooth muscle isoactin expression in the developing mouse. In situ analysis was performed on serial sections of whole mouse embryos on embryonic day 9, 11, 13, 15, and 17 using alpha-smooth muscle and gamma-smooth muscle isoactin-specific riboprobes. Distinct temporal and spatial patterns of alpha-smooth muscle and gamma-smooth muscle isoactin gene expression were observed in the developing gastrointestinal tract, urogenital tract, respiratory tract, and vascular system. Independent expression of the alpha-smooth muscle isoactin was observed during the early stages of skeletal, cardiac, and smooth muscle myogenesis as well as in a novel subset of distinct organs including the postnatal component of the hindgut, allantois, and primitive placenta. The results of this study indicate that distinct cellular phenotypes are involved in smooth muscle myogenesis and suggest that organ-specific mechanisms might exist for the initiation of smooth muscle development in vivo. In addition, the pattern of independent alpha-smooth muscle isoactin expression observed in this study provides novel information regarding the early stages of hindgut and placental development, and suggests that a common functional phenotype may be associated with the early stages of skeletal, cardiac, and smooth muscle myogenesis.

The monoclonal antibody GB 42--a useful marker for the differentiation of myofibroblasts

The expression patterns of a variety of cytoskeletal antigens were studied in normal human tissues (placenta, umbilical cord, myometrium, colon, mammary gland, testis, skeletal muscle, myocardium) as well as in abnormal human tissues (palmar fibromatosis, fibrocystic disease of the mammary gland, mammary carcinoma). The immunohistochemical binding patterns of the monoclonal antibody GB 42 were compared to those of commercial antibodies directed against vimentin, desmin, smooth muscle myosin, pan actin, alpha-smooth muscle actin and gamma-smooth muscle actin. Methods applied comprised immunohistochemistry on cryostat sections and paraffin sections. Immunogold immunocytochemistry was performed on Lowicryl sections. The patterns of GB 42-binding were confirmed biochemically by SDS-PAGE and Western-blotting, and quantitative amino acid analysis. Our data suggest that the monoclonal antibody GB 42 recognizes an actin isoform which is identical to, or closely related to, gamma-smooth muscle actin. Unlike the commercially available antibody against gamma-smooth muscle actin, GB 42 does not cross-react with alpha-skeletal or alpha-cardiac actins. The GB 42-antigen is expressed in smooth muscle cells, myoepithelial cells and in later stages of differentiation of myofibroblasts, in all the tissues investigated. Throughout the development of smooth muscle cells and myofibroblasts, the appearance of the GB 42-antigen occurs after the expression of vimentin, desmin and alpha-smooth muscle actin, but prior to the expression of smooth muscle myosin. GB 42 is a reliable marker for higher stages of differentiation of smooth muscle cells and myofibroblasts.

A retinoic acid-induced clonal cell line derived from multipotential P19 embryonal carcinoma cells expresses smooth muscle characteristics

Despite intense interest in understanding the differentiation of vascular smooth muscle, very little is known about the cellular and molecular mechanisms that control differentiation of this cell type. Progress in this field has been hampered by the lack of an inducible in vitro system for study of the early steps of smooth muscle differentiation. In this study, we describe a model system in which multipotential mouse P19 embryonal carcinoma cells (P19s) can be induced to express multiple characteristics of differentiated smooth muscle. Treatment of P19s with retinoic acid was associated with profound changes in cell morphology and with the appearance at high frequency of smooth muscle alpha-actin-positive cells that were absent or present at extremely low frequency in parental P19s. A clonal line derived from retinoic acid-treated P19s (9E11G) stably expressed multiple characteristics of differentiated smooth muscle, including smooth muscle-specific isoforms of alpha-actin and myosin heavy chain, as well as functional responses to the contractile agonists phenylephrine, angiotensin II, ATP, bradykinin, histamine, platelet-derived growth factor (PDGF)-AA, and PDGF-BB. Additionally, 9E11G cells expressed transcripts for MHox, a muscle homeobox gene expressed in smooth, cardiac, and skeletal muscles, but not the skeletal muscle-specific regulatory factors, MyoD and myogenin. Results demonstrate that retinoic acid treatment of multipotential P19 cells is associated with formation of cell lines that stably express multiple properties of differentiated smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of alpha-actin mRNA and immunoreactive protein in brain microvascular pericytes and smooth muscle cells

Hypertension has been linked to opening of the blood-brain barrier and may be related to the expression of the smooth muscle alpha-actin gene in contractile cells at the brain microvasculature. However, the cellular origin (i.e., endothelial cells, pericytes, smooth muscle cells) of the alpha-actin mRNA in the brain microvasculature is not clearly identified. Therefore, we investigated the abundance of actin mRNA by Northern blot analysis in isolated brain microvessels and in brain microvascular endothelial or pericytes in tissue culture. All samples showed the characteristic 2.1 kb transcript corresponding to cytoplasmic beta and gamma isoform mRNA. The 1.7 kb transcript corresponding to smooth muscle alpha-actin was detected in freshly isolated bovine brain microvessels, in primary cultures of brain microvascular pericytes, or endothelial cells; the latter cultures contain both endothelial cells and pericytes. The alpha-actin mRNA was absent in a cloned bovine brain endothelial cell line. The relative abundance of the alpha/(beta + gamma) actin transcript ratio was: cultured pericytes > freshly isolated microvessels > endothelial primary. The cellular distribution of the smooth muscle alpha-actin immunoreactive protein was studied by immunocytochemistry in cytospun/methanol-fixed isolated bovine brain microvessels with a monoclonal antibody directed to the amino-terminal decapeptide of the smooth muscle alpha-actin isoform. This antibody reacted strongly with precapillary arterioles of isolated microvessels, whereas no immunostaining was observed in either capillary endothelial cells or in pericytes. In conclusion, the alpha-actin mRNA is expressed in brain microvascular pericytes in tissue culture, but the immunoreactive alpha-actin protein is not expressed in brain microvascular pericytes in vivo. These data suggest that either 1) alpha-actin gene expression is induced in capillary pericytes in tissue culture or 2) alpha-actin mRNA in brain capillary pericytes in vivo is subject to translational repression resulting in no detectable alpha-actin protein under normal conditions.

Characterization of cloned aortic smooth muscle cells from young rats

Clones were derived by dilute plating from cultured aortic smooth muscle cells of 12-day-old rats. Clones Pup I to III resemble uncloned smooth muscle cultures from aortas of rat pups and from adult rat neointimas. They have a cobblestone morphology and proliferate in plasma-derived serum. By Northern analysis they contain platelet-derived growth factor B chain (PDGF-B) mRNA and high levels of CYPIA1, elastin, and osteopontin mRNAs, and they lack platelet-derived growth factor alpha-receptor (PDGF-alpha R) mRNA. In contrast, Pup V resembles smooth muscle cultures derived from uninjured adult rat arteries. It has an elongated morphology and proliferates poorly in plasma-derived serum. This clone expresses PDGF-alpha R mRNA, low levels of elastin and osteopontin mRNAs, and lacks CYPIA1 and PDGF-B mRNAs. Pup IV and VI have most of the properties of Pup I to III. We conclude that uncloned pup cultures are heterogeneous, but that the growth properties and gene expression pattern described for the uncloned culture is characteristic of individual clones within the population.

Alterations in the expression of the beta-cytoplasmic and the gamma-smooth muscle actins in hypertrophied urinary bladder smooth muscle

The obstruction of the bladder outlet induces a marked increase in bladder mass, and this is accompanied by reduced contractility of bladder smooth muscle and alteration in the cellular architecture. In this study, we show that the composition of various isoforms of actin, a major component of the contractile apparatus and the cytoskeletal structure of smooth muscle, is altered in response to the obstruction-induced bladder hypertrophy. Northern blot analysis of the total RNA isolated from hypertrophied urinary bladder muscle, using a cDNA probe specific for smooth muscle gamma-actin, shows over 200% increase in the gamma-actin mRNA. However, the estimate of the amount of actin from the 2D gel reveals only a 16% increase in gamma-actin, since the 2D gel electrophoresis does not distinguish gamma-smooth muscle actin from gamma-cytoplasmic actin. The bladder smooth muscle alpha-actin and the smooth muscle alpha-actin mRNA are not altered in response to the hypertrophy. The obstructed bladder also reveals a decrease in the beta-cytoplasmic actin (37%) and a concomitant diminution in the beta-cytoplasmic actin mRNA (29%). Hence, the composition of the actin isoforms in bladder smooth muscle is altered in response to the obstruction-induced hypertrophy. This alteration of the actin isoforms is observed at both the protein and mRNA levels.

Altered isoactin gene expression in the affected bowel segments of the lethal spotted mouse

BACKGROUND

Actin is a key contractile protein associated with the normal differentiation and function of gastrointestinal smooth muscle cells. Distinct changes in gastrointestinal smooth muscle cell morphology and function have been reported for the aganglionic rectum and megacolon of the adult lethal spotted mouse. This study examines what effect these changes in smooth muscle cell morphology and function have on the expression of the actin multigene family in both the aganglionic rectum and megacolon of the lethal spotted mouse.

METHODS

Expression of the smooth muscle and cytoplasmic isoactins was examined by Northern blot analysis of the aganglionic rectum and megacolon of the homozygotic lethal spotted mouse and the equivalent bowel segments of control animals.

RESULTS

The megacolon of the lethal spotted mouse showed a significant increase in gamma-smooth muscle isoactin expression. The aganglionic rectum of the lethal spotted mouse displayed a complex pattern of altered isoactin gene expression that included changes in both gamma-smooth muscle and beta-cytoplasmic isoactin expression. Strain-specific differences in the quantitative levels of isoactin gene expression were observed for the various bowel segments examined in this study.

CONCLUSIONS

These results show that the changes in smooth muscle cell morphology and function observed in the lethal spotted mutant mouse are accompanied by significant alterations in isoactin gene expression.

Heterogeneous isoactin gene expression in the adult rat gastrointestinal tract

BACKGROUND

Normal gastrointestinal development is a complex process involving the precise integration of multiple cell types. To gain a better understanding of these processes, the present study examined isoactin gene expression in the adult rat gastrointestinal tract.

METHODS

Northern blot analysis was performed on specified segments of the adult rat esophagus, stomach, small intestine, cecum, colon, rectum, and anus using actin isoform-specific complementary DNAs for all six vertebrate isoactins.

RESULTS

Smooth muscle and cytoplasmic isoactins were heterogeneously coexpressed in a segment-specific manner throughout the gastrointestinal tract. In addition, striated muscle isoactin expression was also detected in segments of the adult rat esophagus, stomach, colon, cecum, rectum, and anus. Histological analysis indicated that the adult rat esophagus, stomach, and anus contained significant quantities of skeletal muscle, providing a source for the striated muscle isoactins detected in these gut segments. A similar source of striated muscle isoactin expression in the cecum, colon, and rectum was not identified. Both coordinate and independent regulation of isoactin gene expression was observed in the gastrointestinal tract, although distinct patterns of autoregulation were absent.

CONCLUSIONS

This study represents the first complete analysis of isoactin gene expression in the adult rat gastrointestinal tract and provides the basis for future studies designed to investigate the factors responsible for these processes.

Molecular cloning and expression of the chicken smooth muscle gamma-actin mRNA

We have investigated the expression of chicken smooth muscle gamma-actin mRNA by isolation and characterization of cDNAs representing this actin isoform and utilizing the cDNA to probe RNA from adult and developing cells. Nucleotide sequence elucidated from an apparent full length smooth muscle gamma-actin cDNA revealed that it contained 94 bp of 5' non-translated sequence, an open reading frame of 1131 bp, and 97 bp of 3' non-translated sequence. Within the 376 amino acid sequence deduced from the chicken cDNA were diagnostic amino acids at the NH2- and COOH-terminal regions which provided unequivocal identification of the gamma-enteric smooth muscle actin isoform. In addition, the chicken gamma-enteric actin deduced from our cDNA clones was found to differ from the sequence reported in earlier protein studies [J. Vandekerckhove and K. Weber, FEBS Lett. 102:219, 1979] by containing a proline rather than a glutamine at position 359 of the protein, indicating that the avian gamma-enteric actin isoform is identical to its mammalian counterpart. Comparison of the 5' and 3' non-translated sequence determined from the chicken cDNA to that elucidated for rat, mouse, and human showed that there is not a high degree of cross-species sequence conservation outside of the coding regions among these mRNAs. Northern hybridization analyses demonstrated that the gamma-enteric actin mRNA is expressed in adult aorta and oviduct tissues but not in adult skeletal muscle, cardiac muscle, liver, brain, and spleen tissues. The gamma-enteric actin mRNA was first observed in measurable quantities in gizzard tissue from 4-5 day embryos and increased in content in developing smooth muscle cells through 16-17 embryonic days. Following this initial increase during embryonic development, the gamma-enteric actin mRNA exhibits a decline in content until approximately 7 days posthatching, after which there is an increase in content to maximal levels found in adult gizzard tissue. In general, the developmental appearance of the gamma-enteric mRNA parallels that observed for this protein in previous studies indicating that the developmental expression of smooth muscle gamma-actin is regulated, in part, by an increased content of mRNA in chicken visceral smooth muscle cells during myogenesis.

Development and characterization of a cloned rat pulmonary arterial smooth muscle cell line that maintains differentiated properties through multiple subcultures

BACKGROUND

Pulmonary hypertension is associated with abnormal pulmonary arterial contractility and growth. The mechanisms for these abnormalities are largely unknown. To study these processes, we sought to develop an in vitro system. Even though cultured aortic and pulmonary artery smooth muscle cells (SMCs) have been of considerable value in studying smooth muscle biology, one drawback of this system has been that these cells often lose differentiated properties in an unpredictable manner when they are passaged in culture. In addition, there appear to be significant differences in physiological and pathological responses between the systemic and pulmonary circulations, many of which could be directly related to the smooth muscle. We therefore established a cloned population of rat pulmonary arterial SMCs (PASMCs) that maintain differentiated properties through multiple subcultures.

METHODS AND RESULTS

PASMCs were obtained initially by enzymatic dissociation from pulmonary arteries of adult Sprague-Dawley rats. From these cells, clones were isolated. The cloned cells retained expression of functional surface receptors for angiotensin II, norepinephrine, and alpha-thrombin and high levels of the smooth muscle isoforms of alpha-actin, myosin heavy chain, myosin regulatory light chain, and alpha-tropomyosin mRNAs even after multiple passages. The cells could also be transfected and processed exogenous transcripts in a smooth muscle-specific fashion.

CONCLUSIONS

These cloned PASMCs retain many differentiated characteristics and should be valuable for future studies of pulmonary vascular smooth muscle cell biology.

Expression of the sarcomeric actin isogenes in the rat heart with development and senescence

Sarcomeric actin genes, alpha-cardiac and alpha-skeletal, are coexpressed in neonatal rodent hearts and are regulated in response to hormonal and hemodynamic stimuli; however, their precise developmental pattern of expression has not been determined, and it is unknown whether they are coexpressed during senescence. We have, therefore, investigated the accumulation of sarcomeric actin transcripts in rat heart during fetal and postnatal development and with senescence by two different techniques: primer extension analysis with an oligonucleotide common to both sarcomeric actins and RNA hybridization with specific cardiac alpha-actin cRNA probes. We found that at 17-19 days in utero both isogenes are coexpressed and alpha-skeletal actin mRNAs represent 28.0 +/- 0.8% of the sarcomeric actin mRNA total. Skeletal actin mRNAs increase to 40% of the total 1 week after birth (NS, p = 0.15), remain constant for 3 weeks, and decrease to less than 20% of the total in ventricles and atria of 1-month-old rats. The alpha-skeletal actin transcripts further decline to less than 5% of the total at 2 months of age and do not reaccumulate in senescent animals. There was no significant difference between male and female rat ventricles. By comparison with the known accumulations of alpha- and beta-myosin heavy chain mRNAs, our results demonstrate that whatever the developmental stage the kinetics of expression for the sarcomeric myosin and actin multigene families are independent.

A comprehensive analysis of the developmental and tissue-specific expression of the isoactin multigene family in the rat

The present study represents the first comprehensive analysis of isoactin gene expression in the developing rat. Our results clearly demonstrate that the developmental and tissue-specific expression of the actin multigene family is a highly integrated and complex process involving a variety of regulatory paradigms. The distinct temporal patterns of expression reported in this study indicate that there are three key phases in the regulation of expression of the actin multigene family during development. These include early embryonic development, late fetal development, and early postnatal development. The specific spatial patterns of expression observed in this study demonstrate that the expression of the actin multigene family is much more permissive than previously reported. This permissive expression includes a wide range of "ectopic" expression of the striated muscle isoactins as well as an extended expression of the alpha-smooth muscle isoactin. These findings expand our current understanding of the expression of the actin multigene family in development and provide a fundamental basis for future studies directed at investigating these processes.

Distribution of actin isoforms within cells of the seminiferous epithelium of the rat testis: evidence for a muscle form of actin in spermatids

Recently, a cDNA that coded for an enteric smooth muscle gamma-actin (SMGA) that was expressed in post-meiotic mouse testicular cells was identified. To determine the cellular location(s) of the protein encoded by this cDNA, this SMGA was probed for by immunocytochemistry in the cells of the seminiferous epithelium with two different monoclonal antibodies (Mabs), B4 and HUC 1-1, known to be muscle actin selective. As a control, we also examined the immunoreactivity of a third Mab, C4, that reacts with all non-muscle and muscle vertebrate isoactins. Using light and electron microscopy, a progressive increase in immunolabeling was observed with the muscle selective HUC 1-1 Mab over a loose actin filamentous network distributed throughout the cytoplasm of steps 4-16 spermatids. Thereafter, the labeling decreased such that at step 17 spermatids, only cytoplasmic labeling in the tail of the spermatids was observed. No labeling of this network was noted with the C4 or B4 Mabs. However, myoid cells enveloping seminiferous tubules and smooth muscle cells of interstitial blood vessels demonstrated comparable intense labeling with each of the three Mabs. The C4 Mab intensely labeled actin filaments of the Sertoli-Sertoli and Sertoli-spermatid ectoplasmic specializations. Also well labeled were numerous actin filaments found in the apical Sertoli cell processes encapsulating the heads of late step 19 spermatids at stage VII of the cycle of the seminiferous epithelium. In addition, actin filamentous bundles enveloping tubulobulbar complexes of the late spermatids within the Sertoli cell apical processes were intensely labeled. The actin filaments in the Sertoli apical processes and surrounding the tubulobulbar complexes were also strongly immunolabeled with the HUC 1-1 Mab. The C4 Mab but not the B4 or HUC 1-1 Mabs, recognized actin in the subacrosomal space of steps 4-18 spermatids. This study suggests that there are muscle isoforms of actin within the cytoplasm of developing spermatids and within apical processes of Sertoli cells.

Smooth muscle actin expression during rat gut development and induction in fetal skin fibroblastic cells associated with intestinal embryonic epithelium

Cytodifferentiation of smooth muscle cells has been analyzed immunocytochemically during rat intestinal development and in chimaeric intestines by using monoclonal antibodies reacting specifically with smooth muscle actin species (CGA7 [10] and anti-alpha SM-1 [40]). As development proceeds, the various intestinal muscle layers differentiate in the following order: (1) cells expressing smooth muscle actin appear within the mesenchyme of the 15-day fetal rat intestine, in the circular muscle-forming area, the differentiation of cells in the presumptive longitudinal muscle layer starting with a 48-h delay; (2) smooth muscle fibers appear within the connective tissue core of the villi shortly after birth, in parallel with a progressive formation of the muscularis mucosae, which becomes clear-cut only in the course of the 2nd week after birth; (3) a distinct cell layer in the innermost part of the circular muscle layer arises during the perinatal period. Thereafter, the fluorescence pattern remains unchanged until the adult stage. Chimaeric intestines were constructed by the association of 14-day fetal intestinal epithelium and cultured fetal rat or human skin fibroblasts. These fibroblastic cells did not express actin at the time at which they were associated. The immunocytochemical analysis of smooth muscle actin in the hybrid intestines, which had developed as intracoelomic grafts for 12 days, revealed that the skin fibroblastic cells had been induced by the intestinal epithelial cells to differentiate into smooth muscle cells. Such a result was also obtained with allantoic endoderm. It was not obvious in cocultures of intestinal epithelium with skin fibroblastic cells. However, when intestinal epithelial cells were cocultured with intestinal mesenchymal cells, actin expression was stimulated in the latter cell population.