Iroquois genes influence proximo-distal morphogenesis during rat lung development

Lung development is a highly regulated process directed by mesenchymal-epithelial interactions, which coordinate the temporal and spatial expression of multiple regulatory factors required for proper lung formation. The Iroquois homeobox (Irx) genes have been implicated in the patterning and specification of several Drosophila and vertebrate organs, including the heart. Herein, we investigated whether the Irx genes play a role in lung morphogenesis. We found that Irx1-3 and Irx5 expression was confined to the branching lung epithelium, whereas Irx4 was not expressed in the developing lung. Antisense knockdown of all pulmonary Irx genes together dramatically decreased distal branching morphogenesis and increased distention of the proximal tubules in vitro, which was accompanied by a reduction in surfactant protein C-positive epithelial cells and an increase in beta-tubulin IV and Clara cell secretory protein positive epithelial structures. Transmission electron microscopy confirmed the proximal phenotype of the epithelial structures. Furthermore, antisense Irx knockdown resulted in loss of lung mesenchyme and abnormal smooth muscle cell formation. Expression of fibroblast growth factors (FGF) 1, 7, and 10, FGF receptor 2, bone morphogenetic protein 4, and Sonic hedgehog (Shh) were not altered in lung explants treated with antisense Irx oligonucleotides. All four Irx genes were expressed in Shh- and Gli(2)-deficient murine lungs. Collectively, these results suggest that Irx genes are involved in the regulation of proximo-distal morphogenesis of the developing lung but are likely not linked to the FGF, BMP, or Shh signaling pathways.     

小鼠胎肺分支形态发生的分子机制

哺乳动物在早期胚胎发育过程中,肺发育经历了气管分支的形态发生、树样结构上皮管道的形成,并伴随着血管的发育而发生的气体通路和肺泡的分化等过程.肺发生涉及到许多复杂的分子机制.肺形态学的变化受到一系列持家基因、激素、核转录因子、生长因子及其他因素的综合调控.目前已经发现决定肺分支形态发生的许多重要因子.本文根据目前最新研究进展,阐述了小鼠胚胎肺在分支形态发生过程中,上皮与间充质之间诱导的信号通路之间的相互作用及其对呼吸树形态建成的调控机制.     

Axes establishment during eye morphogenesis in Xenopus by coordinate and antagonistic actions of BMP4, Shh,and RA

We have examined the roles of BMP4, Shh, and retinoic acid in establishing the proximal-distal and dorsal-ventral axes in the developing Xenopus eye. Misexpression of BMP4 caused the absence of an optic stalk and the expansion of dorsal and distal markers, tbx2/3/5, and pax6, at the expense of ventral and proximal markers vax2 and pax2. When Shh or Noggin, an antagonist of BMPs, was misexpressed, the reverse expression patterns of these marker genes were observed. These results suggest that BMP4 is involved in the specification of not only dorsal in the optic cup but also distal in the optic vesicle. Because Shh did not suppress bmp4 expression, unlike Noggin, Shh and BMP4 may antagonistically regulate common downstream genes in developing eye. We also found the difference between the effects of Shh and retinoic acid, another possible ventralizing factor, suggesting that Shh could promote ventralization independently of retinoic acid. These findings provide important clues to the coordinate and antagonistic actions of BMP4, Shh, and retinoic acid in axes specifications of Xenopus eyes.     

The epidemiology of supernumerary teeth and the associated molecular mechanism

Supernumerary teeth are common clinical dental anomalies. Although various studies have provided abundant information regarding genes and signaling pathways involved in tooth morphogenesis, which include Wnt, FGF, BMP, and Shh, the molecular mechanism of tooth formation, especially for supernumerary teeth, is still unclear. In the population, some cases of supernumerary teeth are sporadic, while others are syndrome-related with familial hereditary. The prompt and accurate diagnosis of syndrome related supernumerary teeth is quite important for some distinctive disorders. Mice are the most commonly used model system for investigating supernumerary teeth. The upregulation of Wnt and Shh signaling in the dental epithelium results in the formation of multiple supernumerary teeth in mice. Understanding the molecular mechanism of supernumerary teeth is also a component of understanding tooth formation in general and provides clinical guidance for early diagnosis and treatment in the future.     

乳腺癌耐药蛋白基因的转录调控机制

乳腺癌耐药蛋白(Breast cancer resistance protein, BCRP), 又名ABCG2, 是ATP结合盒(ATP-binding cas-sette, ABC)转运蛋白超家族成员之一, 在肿瘤多药耐药中具有十分重要的作用。BCRP基因启动子区无TATA盒, 含CAAT盒、AP1位点、AP2位点以及CpG岛下游的多个Sp-1位点。近年来的研究发现, 转录因子孕激素受体(PR)、雌激素受体(ER)、核因子-κB (NF-κB)、缺氧诱导因子(HIF)、Nrf2、芳香烃受体(AhR)、过氧化物酶体增殖活化受体(PPAR)和KLF5等可与BCRP启动子或增强子区的特定反应元件结合进而激活BCRP的转录。促炎细胞因子、生长因子、同源盒基因MSX2、Sonic hedgehog信号通路、Notch信号通路和RAR/RXR信号通路等均参与了BCRP的转录调控。此外, 启动子甲基化和组蛋白乙酰化在BCRP转录调控尤其是药物诱导BCRP表达中发挥重要作用。文章综述了这一研究领域的进展, 着重讨论了转录因子及表观遗传学在BCRP转录调控中的作用。     

Thrombin induces rapid PAR1-mediated non-classical FGF1 release

Thrombin induces cell proliferation and migration during vascular injury. We report that thrombin rapidly stimulated expression and release of the pro-angiogenic polypeptide fibroblast growth factor 1 (FGF1). Thrombin failed to induce FGF1 release from protease-activated receptor 1 (PAR1) null fibroblasts, indicating that this effect was dependent on PAR1. Similarly to thrombin, FGF1 expression and release were induced by TRAP, a specific oligopeptide agonist of PAR1. These results identify a novel aspect of the crosstalk between FGF and thrombin signaling pathways which both play important roles in tissue repair and angiogenesis.     

Hyperoxia reduces bone marrow, circulating, and lung endothelial progenitor cells in the developing lung: implications for the pathogenesis of bronchopulmonary dysplasia

Hyperoxia disrupts vascular and alveolar growth of the developing lung and contributes to the development of bronchopulmonary dysplasia (BPD). Endothelial progenitor cells (EPC) have been implicated in repair of the vasculature, but their role in lung vascular development is unknown. Since disruption of vascular growth impairs lung structure, we hypothesized that neonatal hyperoxia impairs EPC mobilization and homing to the lung, contributing to abnormalities in lung structure. Neonatal mice (1-day-old) were exposed to 80% O(2) at Denver's altitude (= 65% at sea level) or room air for 10 days. Adult mice were also exposed for comparison. Blood, lung, and bone marrow were harvested after hyperoxia. Hyperoxia decreased pulmonary vascular density by 72% in neonatal but not adult mice. In contrast to the adult, hyperoxia simplified distal lung structure neonatal mice. Moderate hyperoxia reduced EPCs (CD45-/Sca-1+/CD133+/VEGFR-2+) in the blood (55%; P < 0.03), bone marrow (48%; P < 0.01), and lungs (66%; P < 0.01) of neonatal mice. EPCs increased in bone marrow (2.5-fold; P < 0.01) and lungs (2-fold; P < 0.03) of hyperoxia-exposed adult mice. VEGF, nitric oxide (NO), and erythropoietin (Epo) contribute to mobilization and homing of EPCs. Lung VEGF, VEGF receptor-2, endothelial NO synthase, and Epo receptor expression were reduced by hyperoxia in neonatal but not adult mice. We conclude that moderate hyperoxia decreases vessel density, impairs lung structure, and reduces EPCs in the circulation, bone marrow, and lung of neonatal mice but increases EPCs in adults. This developmental difference may contribute to the increased susceptibility of the developing lung to hyperoxia and may contribute to impaired lung vascular and alveolar growth in BPD.     

Hypoxia-induced compensatory effect as related to Shh and HIF-1α in ischemia embryo rat heart

Chronic cardiac ischemia/hypoxia induces coronary collateral formation and cardiomyocyte proliferation. Hypoxia can induce cellular adaptive responses, such as synthesis of VEGF for angiogenesis and IGF-2 for proliferation. Both reduce apoptotic effects to minimize injury or damage. To investigate the mechanism of neoangiogenesis and proliferation of fetal heart under umbilical cord compression situation, we used H9c2 cardiomyoblast cell culture, and in vivo embryonic hearts as our study models. Results showed hypoxia induced not only the increase of IGF-2 and VEGF expression but also the activation of their upstream regulatory genes, HIF-1α and Shh. The relationship between HIF-1α and Shh was further studied by using cyclopamine and 2-ME2, inhibitor of Shh and HIF-1α signaling, respectively, in the cardiomyoblast cell culture under hypoxia. We found that the two inhibitors not only blocked their own signal pathway, but also inhibited each other. The observations revealed when fetal heart under hypoxia that HIF-1α and Shh pathways maybe involve in cell proliferation and neoangiogenesis to minimize injury or damage, whereas the complex cross-talk between the two pathways remains unknown. Pei-Cheng Lin, Chih-Yang Huang, and Wei-Wen Kuo contributed equally to this work.     

Fibroblast growth factor interactions in the developing lung.

Cellular activities that lead to organogenesis are mediated by epithelial-mesenchymal interactions, which ultimately result from local activation of complex gene networks. Fibroblast growth factor (FGF) signaling is an essential component of the regulatory network present in the embryonic lung, controlling proliferation, differentiation and pattern formation. However, little is known about how FGFs interact with other signaling molecules in these processes. By using cell and organ culture systems, we provide evidence that FGFs, Sonic hedgehog (Shh), bone morphogenetic protein 4 (BMP-4), and TGFbeta-1 form a regulatory circuit that is likely relevant for lung development in vivo. Our data show that FGF-10 and FGF-7, important for patterning and growth of the lung bud, are differentially regulated by FGF-1, -2 and Shh. In addition, we show that FGFs regulate expression of Shh, BMP-4 and other FGF family members. Our data support a model in which Shh, TGFbeta-1 and BMP-4 counteract the bud promoting effects of FGF-10, and where FGF levels are maintained throughout lung development by other FGFs and Shh.     

Fibroblast growth factors

Fibroblast growth factors (FGFs) make up a large family of polypeptide growth factors that are found in organisms ranging from nematodes to humans. In vertebrates, the 22 members of the FGF family range in molecular mass from 17 to 34 kDa and share 13-71% amino acid identity. Between vertebrate species, FGFs are highly conserved in both gene structure and amino-acid sequence. FGFs have a high affinity for heparan sulfate proteoglycans and require heparan sulfate to activate one of four cell-surface FGF receptors. During embryonic development, FGFs have diverse roles in regulating cell proliferation, migration and differentiation. In the adult organism, FGFs are homeostatic factors and function in tissue repair and response to injury. When inappropriately expressed, some FGFs can contribute to the pathogenesis of cancer. A subset of the FGF family, expressed in adult tissue, is important for neuronal signal transduction in the central and peripheral nervous systems.     

The Murine Bladder Supports a Population of Stromal Sca-1+/CD34+/lin- Mesenchymal Stem Cells

Bladder fibrosis is an undesired end point of injury of obstruction and often renders the smooth muscle layer noncompliant. In many cases, the long-term effect of bladder fibrosis is renal failure. Despite our understanding of the progression of this disease, little is known about the cellular mechanisms that lead to a remodeled bladder wall. Resident stem (progenitor) cells have been identified in various organs such as the brain, heart and lung. These cells function normally during organ homeostasis, but become dysregulated after organ injury. Here, we aimed to characterize a mesenchymal progenitor cell population as a first step in understanding its role in bladder fibrosis. Using fluorescence activated cell sorting (FACS), we identified a Sca-1⁺/ CD34⁺/ lin^- (PECAM^-: CD45^-: Ter119^-) population in the adult murine bladder. These cells were localized to the stromal layer of the adult bladder and appeared by postnatal day 1. Cultured Sca-1⁺/ CD34⁺/ lin^- bladder cells self-renewed, formed colonies and spontaneously differentiated into cells expressing smooth muscle genes. These cells differentiated into other mesenchymal lineages (chondrocytes, adipocytes and osteocytes) upon culture in induction medium. Both acute and partial obstruction of the bladder reduced expression of CD34 and changed localization of Sca-1 to the urothelium. Partial obstruction resulted in upregulation of fibrosis genes within the Sca-1⁺/CD34⁺/lin^- population. Our data indicate a resident, mesenchymal stem cell population in the bladder that is altered by bladder obstruction. These findings provide new information about the cellular changes in the bladder that may be associated with bladder fibrosis.     

Disruption of sonic hedgehog signaling alters growth and patterning of lingual taste papillae

Taste buds on the anterior part of the tongue develop in conjunction with epithelial-mesenchymal specializations in the form of gustatory (taste) papillae. Sonic hedgehog (Shh) and Bone Morphogenetic Protein 4 (BMP4) are expressed in developing taste papillae, but the roles of these signaling molecules in specification of taste bud progenitors and in papillary morphogenesis are unclear. We show here that BMP4 is not expressed in the early tongue, but is precisely coexpressed with Shh in papillary placodes, which serve as a signaling center for both gustatory and papillary development. To elucidate the role of Shh, we used an in vitro model of mouse fungiform papillary development to determine the effects of two functional inhibitors of Shh signaling: anti-Shh (5E1) antibody and cyclopamine. Cultured E11.5 tongue explants express Shh and BMP4(LacZ) in a pattern similar to that of intact embryos, localizing to developing papillary placodes after 2 days in culture. Tongues cultured with 5E1 antibody continue to express these genes in papillary patterns but develop more papillae that are larger and closer together than in controls. Tongues cultured with cyclopamine have a dose-dependent expansion of Shh and BMP4(LacZ) expression domains. Both antibody-treated and cyclopamine-treated tongue explants also are smaller than controls. Taken together, these results suggest that, although Shh is not involved in the initial specification of papillary placodes, Shh does play two key roles during pmcry development: (1) as a morphogen that directs cells toward a nonpapillary fate, and (2) as a mitogen, causing expansion of the interplacodal epithelium and underlying mesenchyme.     

A Highlights from MBoC Selection: Synergistic interaction between the fibroblast growth factor and bone morphogenetic protein signaling pathways in lens cells

Fibroblast growth factors (FGFs) play a central role in two processes essential for lens transparency—fiber cell differentiation and gap junction–mediated intercellular communication (GJIC). Using serum-free primary cultures of chick lens epithelial cells (DCDMLs), we investigated how the FGF and bone morphogenetic protein (BMP) signaling pathways positively cooperate to regulate lens development and function. We found that culturing DCDMLs for 6 d with the BMP blocker noggin inhibits the canonical FGF-to-ERK pathway upstream of FRS2 activation and also prevents FGF from stimulating FRS2- and ERK-independent gene expression, indicating that BMP signaling is required at the level of FGF receptors. Other experiments revealed a second type of BMP/FGF interaction by which FGF promotes expression of BMP target genes as well as of BMP4. Together these studies reveal a novel mode of cooperation between the FGF and BMP pathways in which BMP keeps lens cells in an optimally FGF-responsive state and, reciprocally, FGF enhances BMP-mediated gene expression. This interaction provides a mechanistic explanation for why disruption of either FGF or BMP signaling in the lens leads to defects in lens development and function.