The biosynthesis of most secondary metabolites in different bacteria is strongly depressed by inorganic phosphate. The twocomponent phoR-phoP system of Streptomyces lividans has been cloned and characterized. PhoR showed all of the characteristics of the membrane-bound sensor proteins, whereas PhoP is a member of the DNA-binding OmpR family. Deletion mutants lacking phoP or phoR-phoP, were unable to grow in minimal medium at low phosphate concentration (10 M). Growth was fully restored by complementation with the phoR-phoP genes. Both S. lividans ⌬phoP and ⌬phoR-phoP deletion mutants were unable to synthesize extracellular alkaline phosphatase (AP) as shown by immunodetection with anti-AP antibodies and by enzymatic analysis, suggesting that the PhoR-PhoP system is required for expression of the AP gene (phoA). Synthesis of AP was restored by complementation of the deletion mutants with phoR-phoP. The biosynthesis of two secondary metabolites, actinorhodin and undecylprodigiosin, was significantly increased in both solid and liquid medium in the ⌬phoP or ⌬phoR-phoP deletion mutants. Negative phosphate control of both secondary metabolites was restored by complementation with the phoR-phoP cluster. These results prove that expression of both phoA and genes implicated in the biosynthesis of secondary metabolites in S. lividans is regulated by a mechanism involving the two-component PhoR-PhoP system. P hosphate control of the biosynthesis of antibiotics and many other types of secondary metabolites is a well known phenomenon (1-5), although the molecular mechanism by which this control is exerted is unknown (6, 7). Expression of genes encoding enzymes for the biosynthesis of secondary metabolites is negatively regulated by phosphate, and formation of the corresponding transcripts occurs only under phosphate-limiting conditions (8-10); but, surprisingly, nothing is known about the molecular mechanism of phosphate control of expression of the corresponding biosynthetic genes (11).In Escherichia coli and Bacillus subtilis the genes belonging to the pho regulon, including the alkaline phosphatase (AP) gene (phoA) and the phosphate-specific transport (pst) genes, are regulated by a two-protein system consisting of a phosphatesensor protein, PhoR, and a transcriptional activator protein, PhoB (named PhoP in B. subtilis;. The sensor kinase PhoR is self-phosphorylated under phosphate starvation conditions (forming PhoR-P) that transfer its phosphate group to dephosphorylated PhoB. The phosphorylated PhoB transcriptional factor (PhoB-P) activates the expression of Ϸ30 different genes by binding to the pho boxes located upstream of the phosphate-regulated genes (12). Expression of phoA and other members of the pho regulon occurs under phosphate limitation when the transcriptional activator is available in its phosphorylated form.An important question is whether the control of the biosynthesis of secondary metabolites in actinomycetes is exerted by the same mechanism as the control of AP and other genes involved in phosphate ...

BackgroundFibroblast growth factors (FGF) are essential key players during embryonic development. Through their specific cognate receptors (FGFR) they activate intracellular cascades, finely regulated by modulators such as Sprouty. Several FGF ligands (FGF1, 2, 7, 9, 10 and 18) signaling through the four known FGFRs, have been implicated in lung morphogenesis. Although much is known about mammalian lung, so far, the avian model has not been explored for lung studies.Methodology/Principal FindingsIn this study we provide the first description of fgf10, fgfr1-4 and spry2 expression patterns in early stages of chick lung development by in situ hybridization and observe that they are expressed similarly to their mammalian counterparts. Furthermore, aiming to determine a role for FGF signaling in chick lung development, in vitro FGFR inhibition studies were performed. Lung explants treated with an FGF receptor antagonist (SU5402) presented an impairment of secondary branch formation after 48 h of culture; moreover, abnormal lung growth with a cystic appearance of secondary bronchi and reduction of the mesenchymal tissue was observed. Branching and morphometric analysis of lung explants confirmed that FGFR inhibition impaired branching morphogenesis and induced a significant reduction of the mesenchyme.Conclusions/SignificanceThis work demonstrates that FGFRs are essential for the epithelial-mesenchymal interactions that determine epithelial branching and mesenchymal growth and validate the avian embryo as a good model for pulmonary studies, namely to explore the FGF pathway as a therapeutic target.

Background Lung branching morphogenesis is characterized by epithelial-mesenchymal interactions that ultimately define the airway conducting system. Throughout this process, energy and structural macromolecules are necessary to sustain the high proliferative rates. The extensive knowledge of the molecular mechanisms underlying pulmonary development contrasts with the lack of data regarding the embryonic lung metabolic requirements. Here, we studied the metabolic profile associated with the early stages of chicken pulmonary branching. Methods In this study, we used an ex vivo lung explant culture system and analyzed the consumption/production of extracellular metabolic intermediates associated with glucose catabolism (alanine, lactate, and acetate) by 1H-NMR spectroscopy in the culture medium. Then, we characterized the transcript levels of metabolite membrane transporters (glut1, glut3, glut8, mct1, mct3, mct4, and mct8) and glycolytic enzymes (hk1, hk2, pfk1, ldha, ldhb, pdha, and pdhb) by qPCR. ldha and ldhb mRNA spatial localization was determined by in situ hybridization. Proliferation was analyzed by directly assessing DNA synthesis using an EdU-based assay. Additionally, we performed western blot to analyze LDHA and LDHT protein levels. Finally, we used a Clark-Type Electrode to assess the lung explant's respiratory capacity. Results Glucose consumption decreases, whereas alanine, lactate, and acetate production progressively increase as branching morphogenesis proceeds. mRNA analysis revealed variations in the expression levels of key enzymes and transporters from the glycolytic pathway. ldha and ldhb displayed a compartment-specific expression pattern that resembles proximal–distal markers. In addition, high proliferation levels were detected at active branching sites. LDH protein expression levels suggest that LDHB may account for the progressive rise in lactate. Concurrently, there is a stable oxygen consumption rate throughout branching morphogenesis. Conclusions This report describes the temporal metabolic changes that accompany the early stages of chicken lung branching morphogenesis. Overall, the embryonic chicken lung seems to shift to a glycolytic lactate-based metabolism as pulmonary branching occurs. Moreover, this metabolic rewiring might play a crucial role during lung development.

The canonical hedgehog (HH) signaling pathway is of major importance during embryonic development. HH is a key regulatory morphogen of numerous cellular processes, namely, cell growth and survival, differentiation, migration, and tissue polarity. Overall, it is able to trigger tissue-specific responses that, ultimately, contribute to the formation of a fully functional organism. Of all three HH proteins, Sonic Hedgehog (SHH) plays an essential role during lung development. In fact, abnormal levels of this secreted protein lead to severe foregut defects and lung hypoplasia. Canonical SHH signal transduction relies on the presence of transmembrane receptors, such as Patched1 and Smoothened, accessory proteins, as Hedgehog-interacting protein 1, and intracellular effector proteins, like GLI transcription factors. Altogether, this complex signaling machinery contributes to conveying SHH response. Pulmonary morphogenesis is deeply dependent on SHH and on its molecular interactions with other signaling pathways. In this review, the role of SHH in early stages of lung development, specifically in lung specification, primary bud formation, and branching morphogenesis is thoroughly reviewed.