Curr Opin Pediatr 1999 Jun;11(3):188-92
Current concepts on lung development.
Warburton D, Lee MK
Childrens Hospital Los Angeles Research Institute, CA 90027, USA. email@example.com
Recent molecular genetic and embryonic organ culture studies have implicated several novel regulatory processes in the coordination of lung development. Failure of pulmonary initiation results from interruptions of the sonic hedgehog/patched/Gli and Nl alpha 2.1 signaling pathways. Sonic hedgehog null mutants and Gli2/Gli3 compound null mutants each exhibited failed tracheoesophageal septation. However, proximodistal epithelial differentiation is disrupted by compound Gli mutation, but is preserved in sonic hedgehog mutants. Null mutation of Nl alpha 2.1 also abrogates tracheoesophageal septation in association with thyroid and pituitary agenesis. Primary tracheal branching is regulated by fibroblast growth factor-10 signaling; in the murine fibroblast growth factor-10 null phenotype, the lung fails to separate from the foregut and morphogenesis is arrested distal to the trachea. Several genes in the fibroblast growth factor-10 pathway have homologous roles in fruit fly tracheal organogenesis, and corresponding Drosophila mutations yield strikingly similar phenotypes. Recent data also indicate that airway branching can be regulated by vascular endothelial growth factor, suggesting mutual regulation of airway and vascular development. The bases of pulmonary left-right asymmetry and laterality have also been investigated. The transforming growth factor-beta superfamily members Lefty-1, Lefty-2, and nodal comprise a regulatory pathway whose function is required for the development of left-right asymmetry, whereas left-right laterality is dependent on regulation of dynein expression by the transcription factor hepatocyte nuclear factor-4. Terminal lung differentiation is modulated by yet another set of signals. Hoxa5 null mutants exhibit tracheal occlusion and surfactant protein deficiency, whereas fibroblast growth factor receptor-2 and -4 compound null phenotypes include abrogated neonatal alveolization, perturbed alveolar myofibroblast differentiation, and persistent neonatal elastin deposition. These new contributions represent substantial advances toward a comprehensive molecular model of pulmonary development.
PMID: 10349094, UI: 99278711
Am J Physiol 1999 May;276(5 Pt 1):L697-704
Molecular embryology of the lung: then, now, and in the future.
Warburton D, Zhao J, Berberich MA, Bernfield M
Developmental Biology Program and Department of Surgery, Childrens Hospital Los Angeles Research Institute, Los Angeles, California 90027, USA. firstname.lastname@example.org
Complementary molecular and genetic approaches are yielding information about gain- versus loss-of-function phenotypes of specific genes and gene families in the embryonic, fetal, neonatal, and adult lungs. New insights are being derived from the conservation of function between genes regulating branching morphogenesis of the respiratory organs in Drosophila and in the mammalian lung. The function of specific morphogenetic genes in the lung are now placed in context with pattern-forming functions in other, better understood morphogenetic fields such as the limb bud. Initiation of lung morphogenesis from the floor of the primitive foregut requires coordinated transcriptional activation and repression involving hepatocyte nuclear factor-3beta, Sonic hedgehog, patched, Gli2, and Gli3 as well as Nkx2.1. Subsequent inductive events require epithelial-mesenchymal interaction mediated by specific fibroblast growth factor ligand-receptor signaling as well as modulation by other peptide growth factors including epidermal growth factor, platelet-derived growth factor-A and transforming growth factor-beta and by extracellular matrix components. A scientific rationale for developing new therapeutic approaches to urgent questions of human pulmonary health such as bronchopulmonary dysplasia is beginning to emerge from work in this field.
PMID: 10330024, UI: 99261910
Curr Biol 1998 Sep 24;8(19):1083-6
Sonic hedgehog regulates branching morphogenesis in the mammalian lung.
Pepicelli CV, Lewis PM, McMahon AP
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
The mammalian lung, like many other organs, develops by branching morphogenesis of an epithelium . Development initiates with evagination of two ventral buds of foregut endoderm into the underlying splanchnic mesoderm. As the buds extend, they send out lateral branches at precise, invariant positions, establishing the primary airways and the lobes of each lung. Dichotomous branching leads to further extension of the airways. Grafting studies have demonstrated the importance of bronchial mesenchyme in inducing epithelial branching, but the significance of epithelial signaling has largely been unstudied. The morphogen Sonic hedgehog (Shh) is widely expressed in the foregut endoderm and is specifically upregulated in the distal epithelium of the lung where branching is occurring . Ectopic expression of Shh disrupts branching and increases proliferation, suggesting that local Shh signaling regulates lung development . We report here that Shh is essential for development of the respiratory system. In Shh null mutants, we found that the trachea and esophagus do not separate properly and the lungs form a rudimentary sac due to failure of branching and growth after formation of the primary lung buds. Interestingly, normal proximo-distal differentiation of the airway epithelium occurred, indicating that Shh is not needed for differentiation events. In addition, the transcription of several mesenchymally expressed downstream targets of Shh is abolished. These results highlight the importance of epithelially derived Shh in regulating branching morphogenesis of the lung.
PMID: 9768363, UI: 98441477
Biochem Cell Biol 1998;76(6):971-95
Commitment and differentiation of lung cell lineages.
Warburton D, Wuenschell C, Flores-Delgado G, Anderson K
Department of Surgery, Developmental Biology Program, Childrens Hospital Los Angeles Research Institute, University of Southern California Schools of Medicine and Dentistry 90027, USA. email@example.com
[Medline record in process]
To form a large diffusible interface capable of conducting respiratory gases to and from the circulation, the lung must undergo extensive cell proliferation, branching morphogenesis, and alveolar saccule formation, to generate sufficient surface area. In addition, the cells must differentiate into at least 40 distinct lung cell lineages. Specific transcriptional factors, peptide growth factor receptor-mediated signaling pathways, extracellular matrix components, and integrin-signaling pathways interact to direct lung morphogenesis and lung cell lineage differentiation. Branching mutants of the respiratory tracheae in Drosophila have identified several functionally conserved genes in the fibroblast growth factor signaling pathway that also regulate pulmonary organogenesis in mice and probably also in man. Key transcriptional factors including Nkx2.1, hepatocyte nuclear factor family forkhead homologues, GATA family zinc finger factors, pou and homeodomain proteins, as well as basic helix-loop-helix factors, serve as master genes to integrate the developmental genetic instruction of lung morphogenesis and cell lineage determination. Lung mesenchyme serves as a 'compleat' inducer of lung morphogenesis by secreting soluble peptide growth factors. In general, peptide growth factors signaling through cognate receptors with tyrosine kinase intracellular signaling domains such as epidermal growth factor receptor, fibroblast growth factor receptors, hepatocyte growth factor/scatter factor receptor, c-met, insulin-like growth factor receptor, and platelet-derived growth factor receptor, stimulate lung morphogenesis, while the cognate receptors with serine/threonine kinase intracellular signaling domains, such as the transforming growth factor-beta receptor family are inhibitory. The extracellular matrix also plays a key role in determining branching morphogenesis. Pulmonary neuroendocrine (PNE) cells differentiate earliest in gestation among lung epithelial cells. PNE cells are principally derived from endoderm and not neural crest. PNE cells have been proposed to function as airway chemoreceptors, while PNE cell secretory granules contain many bioactive substances such as GRP which may direct proliferation of adjacent epithelial cells. Mammalian achaete-schute homolog-1 null mutant mice do not develop PNE cells. Candidate molecular switches in the transition from a quiescent to a proliferative alveolar epithelial cell (AEC) phenotype and back again following acute hyperoxia, include autocrine peptide growth factor signaling pathways and cell cycle regulatory elements. AEC type 2 also appear capable of reversible transdifferentiation into AEC type 1 and intermediate phenotypes in response to cues from extracellular matrix and cell shape, as well as soluble factors. Evidence for expression of telomerase by alveolar epithelial stem cells, which correlates with self-renewal potential, is now beginning to emerge. Lung regeneration following lobectomy in juvenile rodents is associated with co-ordinated cell proliferation, re-expression of elastin and formation of alveoli. Retinoic acid has recently shown promise as a stimulator of alveolization in juvenile rats.Our future goal is to devise new rational and gene therapeutic strategies to stimulating lung growth and maturation, ameliorating lung injury, augmenting lung repair, and inducing lung regeneration. The ideal agent or agents would therefore mimic the instructive role of lung mesenchyme, correctly inducing the temporospatial pattern of lung cell lineages necessary to restore pulmonary gas diffusing capacity.
PMID: 10392710, UI: 99319881
Dev Biol 1996 Nov 25;180(1):273-83
Sonic hedgehog differentially regulates expression of GLI and GLI3 during limb development.
Marigo V, Johnson RL, Vortkamp A, Tabin CJ
Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
Sonic hedgehog is a secreted factor regulating patterning of the anterior-posterior axis in the developing limb. The signaling pathway mediating the transduction of the signal is still poorly understood. In Drosophila several genes are known to act downstream of hedgehog, the fly homolog of Sonic hedgehog. An important gene epistatic to hedgehog is cubitus interruptus, which encodes the fly homolog of a family of vertebrate putative transcription factors, the GLI genes. We have isolated two members of the GLI family from chick, called GLI and GLI3. Their expression patterns in a variety of tissues during embryogenesis suggest that these genes may be targets of the Sonic hedgehog signal. We demonstrate that the two GLI genes are differentially regulated by Sonic hedgehog during limb development. Sonic hedgehog up-regulates GLI transcription, while down-regulating GLI3 expression in the mesenchymal cells of the developing limb bud. Finally, we demonstrate that an activated form of GLI can induce expression of Patched, a known target of Sonic hedgehog, thus implicating GLI as a key transcription factor in the vertebrate hedgehog signaling pathway. In conjunction with evidence from a mouse Gli3 mutant, our data suggest that GLI and GLI3 may have taken two different functions of their Drosophila homolog cubitus interruptus.
PMID: 8948590, UI: 97105842
Dev Biol 1997 Aug 15;188(2):337-48
Evidence for the involvement of the Gli gene family in embryonic mouse lung development.
Grindley JC, Bellusci S, Perkins D, Hogan BL
Department of Cell Biology, Vanderbilt University Medical Center, Nashville, Tennessee, 37232-2175, USA.
Murine Gli, Gli2, and Gli3 are zinc finger genes related to Drosophila cubitus interuptus, a component of the hedgehog signal transduction pathway. In the embryonic lung, all three Gli genes are strongly expressed at the pseudoglandular stage, in distinct but overlapping domains of the mesoderm. Expression of Gli and Gli3, but not of Gli2, is subsequently downregulated at the canalicular stage, coincident with a decline in the expression of sonic hedgehog (Shh) and the hedgehog receptor gene, patched (Ptc). Overexpression of Shh in the lung results in increased levels of Ptc mRNA. Gli, but not Gli2, is also upregulated, suggesting a differential involvement of the Gli genes in the regulation of Ptc by SHH during lung development. Gli3 is not upregulated by Shh overexpression. However, its importance for lung development is shown by the finding that Gli3XtJ embryos, homozygous for a mutation involving a deletion of the Gli3 gene, have a stereotypic pattern of abnormalities in lung morphogenesis. The pulmonary defects in these embryos, consisting of localized shape changes and size reductions, correlate with normal Gli3 expression. Thus, our data indicate that one of the Gli genes, Gli3, is essential for normal lung development, and that another, Gli, can be placed downstream of Shh signaling in the lung.
PMID: 9268579, UI: 97415704
Curr Opin Pediatr 1996 Jun;8(3):202-8
New insights into lung growth and development.
Price WA, Stiles AD
Department of Pediatrics, University of North Carolina at Chapel Hill 27599, USA.
Lung development requires a complex series of developmentally controlled interactions that involve mechanical forces, genetic and endocrine influences, and cell-cell communication. At each step, cell-matrix or cell-cell signaling mediated by peptide growth factors and extracellular matrix components is crucial in directing cell proliferation, differentiation, and migration. Although a comprehensive understanding of how these components interact to guide lung organogenesis has been elusive, the action and control of peptide growth factors in autocrine and paracrine signaling, mesenchymal-epithelial interactions in controlling branching morphogenesis, cell-cell communication in the regulation of cellular differentiation, and factors regulating pattern formation are being clarified.
PMID: 8814395, UI: 96409413
Dev Biol 1998 Sep 15;201(2):125-34
FGF-10 is a chemotactic factor for distal epithelial buds during lung development.
Park WY, Miranda B, Lebeche D, Hashimoto G, Cardoso WV
Pulmonary Center, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Fibroblast growth factor (FGF) signaling is required for normal epithelial branching in the respiratory system of several species. Recent studies have shown that FGF-10 may be a key regulator of lung branching morphogenesis, based on its pattern of expression in the early lung and its ability to induce epithelial budding in vitro. In this study we investigate whether FGF-10 is able to direct lung epithelial buds to proper positions during development . We maintained localized high levels of FGF-10 in cultured lungs using FGF-10-soaked heparin beads. FGF-10 exerts a powerful chemoattractant effect on the distal but not on proximal lung epithelium. Epithelial buds grow toward an FGF-10 source within 24 h, and subsequently form concentric layers of epithelium around the bead. BrdU incorporation analysis suggests that FGF-10, in contrast to FGF-7, is a modest proliferation factor for the lung epithelium. In the absence of mesenchyme FGF-10 requires an associated proliferative signal to induce bud migration. This can be provided by extract from lung mesenchyme, or by FGF-7, a growth factor also present in the early embryonic lung. FGF-10 does not seem to interfere with early epithelial cell differentiation. The chemoattractant effect of FGF-10 in the lung epithelium is reminiscent of the patterning effect of the Drosophila FGF ortholog branchless in the developing tracheal epithelium, suggesting that the function of these genes has been conserved during evolution. Copyright 1998 Academic Press.
PMID: 9740653, UI: 98414459
Pediatr Pulmonol 1998 Apr;25(4):244-56
Influence of epidermal growth factor and transforming growth factor beta-1 on patterns of fetal mouse lung branching morphogenesis in organ culture.
Chinoy MR, Zgleszewski SE, Cilley RE, Blewett CJ, Krummel TM, Reisher SR, Feinstein SI
Department of Surgery, The Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, Hershey 17033-0850, USA.
Transforming growth factor-beta (TGF-beta), a potent inhibitor of epithelial cell proliferation, and epidermal growth factor (EGF), a mitogenic polypeptide that binds to cell surface receptors, are important regulators of cell differentiation; however, their distinct role(s) in lung development and their mechanisms of action are not well understood. We evaluated the effects of these factors on lung morphogenesis in murine fetal lungs at gestational day 14 (time:zero) and again after 7 days in culture. Baseline controls were cultured after tracheal transection in supplemented BGJb medium, and other tracheally transected lungs were cultured following addition of EGF (10 ng/ml BGJb), TGF-beta1 (2 ng/ml BFJb), or with both in combination added to the medium. The control lungs in culture had poorly developed airways and an absence of defined acinar structures. The addition of EGF resulted in hyperplasia of primary airways with stunted outgrowths, monopodial branching, and absence of distinct acinar structures. Addition of TGF-beta1 alone, led to significant elongation of primary airways, without normal airway branching; however, terminal dipodial branching was seen and the prospective pulmonary acini were well defined. Combination of these growth factors (GF) resulted in a more normal branching pattern and differentiation, suggesting their epigenetic role in lung morphogenesis and mutual interactive mechanisms that regulate lung development. These lungs had more abundant and larger lamellar bodies than those after other treatments. Control lungs remained immature with prominent glycogen aggregates with occasional dense lamellar bodies. The total protein and DNA contents were highest with EGF treatment, followed by combination treatment; these observations were supported by immunohistochemical localization of proliferating cell nuclear antigen, an indication of the proliferative state of tissues. All the surfactant proteins were relatively unaltered and their messages were up-regulated for SP-A, but down-regulated for SP-B and SP-C in the lungs treated with growth factors. In conclusion, we have demonstrated enhanced biochemical and structural development of lungs treated in vitro with GF, and propose that further research in this area may lead to therapeutic uses of GF alone or in combination with other agents for the treatment of newborn respiratory distress due to lung immaturity or hypoplastic lung development.
PMID: 9590485, UI: 98250367
Annu Rev Physiol 1996;58:51-71
Mechanisms of gene expression and cell fate determination in the developing pulmonary epithelium.
Hackett BP, Bingle CD, Gitlin JD
Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
The pulmonary epithelium is a derivative of the foregut endoderm. Proliferation and differentiation of the primitive pulmonary epithelium result in an array of epithelial cell phenotypes that determine lung function and the response of the lung to injury, infection, or neoplastic transformation. The establishment of a cell phenotype requires the presence of transcription factors that activate or repress expression of specific genes. Members of the forkhead family of transcription factors, in particular HNF-3 alpha, HNF-3 beta, HFH-4; the homeodomain protein TTF-1; and N-myc, are all expressed in the developing pulmonary epithelium and may play important regulatory roles during development. Two genes specific to the pulmonary epithelium, the surfactant protein A and Clara cell secretory protein genes, serve as useful paradigms for understanding the mechanisms regulating cell-specific gene expression in the pulmonary epithelium.
PMID: 8815806, UI: 96254669
Nat Genet 1998 Sep;20(1):54-7
Essential function of Gli2 and Gli3 in the formation of lung, trachea and oesophagus.
Motoyama J, Liu J, Mo R, Ding Q, Post M, Hui CC
Programs in Developmental Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada.
Foregut malformations (oesophageal atresia, tracheo-oesophageal fistula, lung anomalies and congenital stenosis of the oesophagus and trachea) are relatively common anomalies occurring in 1 in 2,000-5,000 live births, although their aetiology is poorly understood. The secreted glycoprotein Sonic hedgehog (Shh) has been suggested to act as an endodermal signal that controls hindgut patterning and lung growth. In mice, three zinc-finger transcription factors, Gli1, Gli2 and Gli3, have been implicated in the transduction of Shh signal. We report here that mutant mice lacking Gli2 function exhibit foregut defects, including stenosis of the oesophagus and trachea, as well as hypoplasia and lobulation defects of the lung. A reduction of 50% in the gene dosage of Gli3 in a Gli2-/- background resulted in oesophageal atresia with tracheo-oesophageal fistula and a severe lung phenotype. Mutant mice lacking both Gli2 and Gli3 function did not form oesophagus, trachea and lung. These results indicate that Gli2 and Gli3 possess specific and overlapping functions in Shh signalling during foregut development, and suggest that mutations in GLI genes may be involved in human foregut malformations.
PMID: 9731531, UI: 98400257
J Biol Chem 1999 Jul 23;274(30):21180-5
Lung Kruppel-like factor, a zinc finger transcription factor, is essential for normal lung development.
Wani MA, Wert SE, Lingrel JB
Department of Molecular Genetics, Biochemistry and Microbiology College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA.
Lung Kruppel-like factor (LKLF) is a member of the Kruppel-like factor family of transcription factors and is highly expressed in lung with limited distribution in other tissues. Mice lacking LKLF due to inactivation of LKLF by gene targeting die in utero at midgestation around day 12.5 due to severe hemorrhage, making it difficult to study the role of this transcription factor in lung development and function. However, in vitro organ culture of lung buds removed from 11.5-day-old LKLF(-/-) embryos show normal tracheobronchial tree formation. To examine later stages of lung development, the embryonic lethality due to germ line LKLF null mutation was circumvented by constructing LKLF homozygous null mouse embryonic stem cells, using a two-step gene targeting procedure, and determining whether these cells give rise to lung tissue. The targeted cells were used to produce chimeric animals, and the contribution of LKLF-deficient cells to the formation of various internal organs was analyzed. In chimeric mice that survived after birth, null embryonic stem cells contributed significantly to all of the major organs except the lungs. On the other hand, some highly chimeric animals died at birth, and histopathological examination of their lungs suggested abnormalities in their lung development. These studies show that LKLF plays an important role in normal lung development.
PMID: 10409672, UI: 99340054
Am J Physiol 1995 Oct;269(4 Pt 1):L429-42
Transcription factors and pattern formation in the developing lung.
Department of Medicine, Boston University School of Medicine, Massachusetts 02118, USA.
During development of the respiratory tract embryonic cells are instructed to organize themselves along an axis and differentiate, such that proximal structures (trachea) greatly differ from those in distal alveoli. Pattern formation relates to this process of organization, and it is believed to be transcriptionally regulated in many developmental systems. Although the lung is the site of expression of many transcription factors, such as Hox, retinoid receptors, hepatocyte nuclear factors, and myc, among others, little information is available on how they influence lung pattern. Functional studies so far have directly implicated the product of the protooncogene N-myc and the retinoic acid receptors as transcriptional regulators of lung patterning, and it is likely that tissue-specific homeobox genes, such as the thyroid transcription factor-1, play an important role in distal lung formation. This review describes several aspects of transcription factors possibly involved in lung patterning, including structure, spatial distribution, and their putative functions.
PMID: 7485515, UI: 96043427
Development 1997 Jan;124(1):53-63
Involvement of Sonic hedgehog (Shh) in mouse embryonic lung growth and morphogenesis.
Bellusci S, Furuta Y, Rush MG, Henderson R, Winnier G, Hogan BL
Department of Cell Biology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-2175, USA.
Branching morphogenesis of the embryonic lung requires interactions between the epithelium and the mesenchyme. Previously, we reported that Sonic hedgehog (Shh) transcripts are present in the epithelium of the developing mouse lung, with highest levels in the terminal buds. Here, we report that transcripts of mouse patched (Ptc), the homologue of a Drosophila gene encoding a putative transmembrane protein required for hedgehog signaling, are expressed at high levels in the mesenchyme adjacent to the end buds. To investigate the function of SHH in lung development, Shh was overexpressed throughout the distal epithelium, using the surfactant protein-C (SP-C)-enhancer/promoter. Beginning around 16.5 dpc, when Shh and Ptc RNA levels are normally both declining, this treatment caused an increase in the ratio of interstitial mesenchyme to epithelial tubules in transgenic compared to normal lungs. Transgenic newborn mice die soon after birth. Histological analysis of the lungs at the light and electron microscope level shows an abundance of mesenchyme and the absence of typical alveoli. In vivo BrdU labeling indicates that Shh overexpression results in increased mesenchymal and epithelial cell proliferation at 16.5 and 17.5 dpc. However, analysis of CC-10 and SP-C expression reveals no significant inhibition in the differentiation of proximal and distal epithelial cells. The expression of genes potentially regulated by SHH was also examined. No difference could be observed between transgenic and control lungs in either the level or distribution of Bmp4, Wnt2 and Fgf7 RNA. By contrast, Ptc is clearly upregulated in the transgenic lung. These results thus establish a role for SHH in lung morphogenesis, and suggest that SHH normally regulates lung mesenchymal cell proliferation in vivo.
PMID: 9006067, UI: 97158707
New insights into lung growth and development. Price WA, Stiles ADCurr Opin Pediatr 1996 Jun;8(3):202-8