Lox System Research Articles

Development of genetic markers in Yarrowia lipolytica.

The oleaginous yeast Yarrowia lipolytica represents a potential microbial cell factory for the recombinant production of various valuable products. Currently, the commonly used selection markers for transformation in Y. lipolytica are limited, and successive genetic manipulations are often restricted by the number of available selection markers. In our study, we developed a dominant marker, dsdA, which encodes a D-serine deaminase for genetic manipulation in Y. lipolytica. In Y. lipolytica, this marker confers the ability to use D-serine as a nitrogen source. In addition, the selection conditions of several infrequently used dominant markers including bleoR (zeocin resistance), kanMX (G418 resistance), and guaB (mycophenolic acid resistance) were also analyzed. Our results demonstrated that these selection markers can be used for the genetic manipulation of Y. lipolytica and their selection conditions were different for various strains. Ultimately, the selection markers tested here will be useful to expand the genetic toolbox of Y. lipolytica. KEY POINTS: • The dsdA from Escherichia coli was developed as a dominant marker. • The applicability of several resistance markers in Y. lipolytica was determined. • We introduced the Cre/mutant lox system for marker recycling.

Abstract 12167: Cardiac-Specific Knockout of Myosin Phosphatase Targeting Subunit 2 Prevents Cardiac Fibrosis in a Connective Tissue Growth Factor-Dependent Manner in Mineralocorticoid Receptor-Related Hypertension Mice

Introduction: Myosin phosphatase targeting subunit 2 (MYPT2) is an important subunit of cardiac myosin light chain phosphatase (MLCP), which plays a crucial role in regulating the phosphorylation of MLC (p-MLC). Recent research has shown that cardiac MLCP plays an important role in cardiac fibrosis as a target of Rho kinase and protein kinase G. However, it is unclear how the loss of MYPT2 affects cardiac function and fibrosis. Methods: After the knockdown of MYPT2, HL-1 cells (murine cardiomyocytes) were incubated with aldosterone (ALDO) for 24h. Cardiac specific MYPT2 knockout (c-MYPT2 -/- ) mice were generated using the Cre lox system (αMHCMerCreMer; MYPT2 f/f ). Mineralocorticoid receptor (MR)-related hypertension mice were induced by the subcutaneous infusion of ALDO and 8% NaCl food for 4 weeks after uninephrectomy. Results: In HL-1 cells, ALDO increased connective tissue growth factor (CTGF) and MYPT2 and decreased the p-MLC in a dose-dependent manner. Knockdown of MYPT2 decreased CTGF. In mice model, the MYPT2 expression in the heart from MYPT2 -/- mice was decreased to less than 30% compared with MYPT2 +/+ mice. Heart rate, blood pressure, and cardiac systolic function were normal in c-MYPT2 -/- mice. Type 1 phosphatase catalytic subunit β was decreased and p-MLC was increased in c-MYPT2 -/- mice. Blood pressure elevation and left ventricular hypertrophy were observed in both MR-related hypertension mice, while no difference in heart size and the nuclear localization of MR in cardiomyocytes. However, ejection fraction and fractional shortening in echocardiography were higher in c-MYPT2 -/- than in MYPT2 +/+ in MR-related hypertension mice. After treatment of ALDO for 28 days, both global radial and longitudinal strain (GRS and DLS) were reduced in both c-MYPT2 -/- and MYPT2 +/+ mice, but the reduction in systolic and diastolic GRS and GLS strain rates were prevented in c-MYPT2 -/- mice compared with MYPT2 +/+ mice. Histopathology revealed fibrosis degree in c-MYPT2 -/- mice was lower than MYPT2 +/+ mice with decreased CTGF and increased p-MLC. Conclusions: Cardiac-specific deletion of MYPT2 resulted in a decrease of MLCP and an increase of p-MLC. MYPT2 deletion can prevent cardiac fibrosis and dysfunction in a MR-related hypertension model.

REGENERATION OF AGING LUNG TISSUE: A NOVEL WAY OF REOPENING THE PLASTICITY WINDOW OF POSTNATAL ALVEOLAR TYPE II CELLS

Abstract Prevalence of chronic lung diseases, such as pulmonary fibrosis and chronic obstructive pulmonary disease, have been found to increase with age. Pulmonary disease can occur from failure to maintain alveolar type (AT) 1 and alveolar type 2 cells located in the epithelium of the lung. It is currently known that AT2 cells are the facultative stem cells of the lung, and can transform into AT1 cells which make up the structure of the alveoli. This process happens throughout embryonic development, but AT2 cells can also replenish AT1 cell populations post lung injury. This research investigates whether this process that normally occurs during development can also occur in mature AT2 cells, and studies this question using genetically engineered mouse models at a postnatal stage. Using a double inhibition mechanism, we attempted to increase cellular proliferation by administering an agonist and conducted cellular lineage tracing with an SpcCreER lox system via tamoxifen-induced GFP expression. Through lineage labeling, we saw AT1 cells arising from AT2 cells that became plastic, mirroring the plasticity observed in development. Further research is needed to determine if this agonist can be used to epigenetically unlock mature AT2 cells. This result would provide a mechanism to temporarily induce plasticity in a patient’s own AT2 cells in an attempt to regenerate their lungs in disease.

CRISPR/Cas9 Editing of Duck Enteritis Virus Genome for the Construction of a Recombinant Vaccine Vector Expressing ompH Gene of Pasteurella multocida in Two Novel Insertion Sites.

Duck enteritis virus (DEV) and Pasteurella multocida, the causative agent of duck plague and fowl cholera, are acute contagious diseases and leading causes of morbidity and mortality in duck. The NHEJ-CRISPR/Cas9-mediated gene editing strategy, accompanied with the Cre–Lox system, have been employed in the present study to show that two new sites at UL55-LORF11 and UL44-44.5 loci in the genome of the attenuated Jansen strain of DEV can be used for the stable expression of the outer membrane protein H (ompH) gene of P. multocida that could be used as a bivalent vaccine candidate with the potential of protecting ducks simultaneously against major viral and bacterial pathogens. The two recombinant viruses, DEV-OmpH-V5-UL55-LORF11 and DEV-OmpH-V5-UL44-44.5, with the insertion of ompH-V5 gene at the UL55-LORF11 and UL44-44.5 loci respectively, showed similar growth kinetics and plaque size, compared to the wildtype virus, confirming that the insertion of the foreign gene into these did not have any detrimental effects on DEV. This is the first time the CRISPR/Cas9 system has been applied to insert a highly immunogenic gene from bacteria into the DEV genome rapidly and efficiently. This approach offers an efficient way to introduce other antigens into the DEV genome for multivalent vector.

Clonal sector analysis and cell ablation confirm a function for DORNROESCHEN-LIKE in founder cells and the vasculature in Arabidopsis

Main conclusionInducible lineage analysis and cell ablation via conditional toxin expression in cells expressing the DORNRÖSCHEN-LIKE transcription factor represent an effective and complementary adjunct to conventional methods of functional gene analysis.Classical methods of functional gene analysis via mutational and expression studies possess inherent limitations, and therefore, the function of a large proportion of transcription factors remains unknown. We have employed two complementary, indirect methods to obtain functional information for the AP2/ERF transcription factor DORNRÖSCHEN-LIKE (DRNL), which is dynamically expressed in flowers and marks lateral organ founder cells. An inducible, two-component Cre–Lox system was used to express beta-glucuronidase GUS in cells expressing DRNL, to perform a sector analysis that reveals lineages of cells that transiently expressed DRNL throughout plant development. In a complementary approach, an inducible system was used to ablate cells expressing DRNL using diphtheria toxin A chain, to visualise the phenotypic consequences. These complementary analyses demonstrate that DRNL functionally marks founder cells of leaves and floral organs. Clonal sectors also included the vasculature of the leaves and petals, implicating a previously unidentified role for DRNL in provasculature development, which was confirmed in cotyledons by closer analysis of drnl mutants. Our findings demonstrate that inducible gene-specific lineage analysis and cell ablation via conditional toxin expression represent an effective and informative adjunct to conventional methods of functional gene analysis.

Simultaneous Deletion of Virulence Factors and Insertion of Antigens into the Infectious Laryngotracheitis Virus Using NHEJ-CRISPR/Cas9 and Cre-Lox System for Construction of a Stable Vaccine Vector.

Infectious laryngotracheitis virus (ILTV) is a promising vaccine vector due to its heterologous gene accommodation capabilities, low pathogenicity, and potential to induce cellular and humoral arms of immunity. Owing to these characteristics, different gene-deletion versions of ILTVs have been successfully deployed as a vector platform for the development of recombinant vaccines against multiple avian viruses using conventional recombination methods, which are tedious, time-demanding, and error-prone. Here, we applied a versatile, and customisable clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 accompanied with Cre–Lox system to simultaneously delete virulence factors and to insert foreign genes in the ILTV genome. Using this pipeline, we successfully deleted thymidine kinase (TK) and unique short 4 (US4) genes and inserted fusion (F) gene of the Newcastle disease virus without adversely affecting ILTV replication and expression of the F protein. Taken together, the proposed approach offers novel tools to attenuate (by deletion of virulence factor) and to generate multivalent (by insertion of heterologous genes) vaccine vectors to protect chickens against pathogens of poultry and public health importance.

Murine Liver Organoids as a Genetically Flexible System to Study Liver Cancer In Vivo and In Vitro.

The rising incidence of cholangiocarcinoma (CCA) coupled with a low 5‐year survival rate that remains below 10% delineates the urgent need for more effective treatment strategies. Although several recent studies provided detailed information on the genetic landscape of this fatal malignancy, versatile model systems to functionally dissect the immediate clinical relevance of the identified genetic alterations are still missing. To enhance our understanding of CCA pathophysiology and facilitate rapid functional annotation of putative CCA driver and tumor maintenance genes, we developed a tractable murine CCA model by combining the cyclization recombination (Cre)‐lox system, RNA interference, and clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9 (CRISPR/Cas9) technology with liver organoids, followed by subsequent transplantation into immunocompetent, syngeneic mice. Histologically, resulting tumors displayed cytokeratin 19–positive ductal structures surrounded by a desmoplastic stroma—hallmark features of human CCAs. Despite their initial biliary phenotype in vitro, organoids retained the plasticity to induce a broader differentiation spectrum of primary liver cancers following transplantation into recipient mice, depending on their genetic context. Thus, the organoid system combines the advantage of using nontransformed, premalignant cells to recapitulate liver tumorigenesis as a multistep process, with the advantage of a reproducible and expandable cell culture system that abrogates the need for recurrent isolations of primary cells. Conclusion: Genetically modified liver organoids are able to transform into histologically accurate CCAs. Depending on the oncogenic context, they are also able to give rise to liver cancers that show features of hepatocellular carcinomas. The model can be used to functionally explore candidate cancer genes of primary liver cancers in immunocompetent animals and evaluate novel treatment regimens.

Pressure mode analysis of nonuniform cross-sectional pipes and preliminary evaluation of a pogo suppressor

The pogo phenomenon is a type of instability that arises when the longitudinal modes of a space launch vehicle fuselage resonate with the pressure modes of the feedline in its propulsion system, with such resonance re-exciting the fuselage structure. To analyze this phenomenon, this paper specifically focuses on an analysis of the pressure modes in the space shuttle interpump line included in the LOX engine system. Because the interpump line is connected to pipes in different cross-sectional areas, the pressure modes are analyzed as a nonuniform cross-sectional pipe. Further, by applying a pogo suppressor in the feedline system, the possibility of preventing the pogo phenomenon is demonstrated. In order to design the suppressor, the resistive accumulator inertance, compliance, and resistance are considered as variables. Resistive accumulator compliance and inertance are determined and the pressure perturbation of the engine is prevented by lowering the inlet pressure amplitude of the high-pressure oxidizer pump (HPOP) in the space shuttle LOX system interpump line. When the resistive accumulator resistance is increased, the pressure frequencies of the interpump line gradually decrease, avoiding the resonance region with the fuselage. As a result, the resonance region with the fuselage is prevented by varying the pressure amplitude and natural frequencies of the interpump line. In this way, the capability of the present pogo suppression is evaluated.

Abstract 2855: Identification of optimal treatment sequence and acquired resistance mechanisms of ALK inhibitors using EML4-ALK transgenic mouse model

Abstract Introduction: EML4-ALK is a distinct molecular entity that is highly sensitive to ALK tyrosine kinase inhibitors (TKIs). While many trials have showed the superiority of ALK TKIs over cytotoxic chemotherapy, the optimal sequencing of ALK TKIs is still obscure. Acquired resistance to ALK TKIs remains a key challenge, and unknown mechanisms of resistance need to be resolved. In this study, we aimed to identify optimal treatment sequence and acquired resistance mechanisms of ALK TKIs using EML4-ALK transgenic mice model that recapitulates human EML4-ALK lung adenocarcinoma. Methods: The tumorigenesis of EML4-ALK transgenic mice was based on Cre-ERT2/Lox system, and intraperitoneal injection with tamoxifen induced lung tumors. When tumor nodules were observed, EML4-ALK transgenic mice were treated with either crizotinib (150mg/kg) followed by ceritinib (75mg/kg) upon progression (N=13) or with ceritinib followed by crizotinib (N=12) upon progression. Tumor response was evaluated weekly using magnetic resonance imaging. Progression-free survival (PFS) was measured to compare the efficacy between two ALK TKIs. For the analysis of acquired resistance mechanism, whole-exome sequencing, RNA sequencing, and targeted sequencing of ALK gene were performed. Results: Head-to-head comparison of crizotinib and ceritinib was performed in the first-line setting. A total of 13 mice were treated with upfront crizotinib, and mice that showed progressive disease (PD) were crossed over to ceritinib (n=9). A total of 12 mice were treated with upfront ceritinib, and mice that showed PD (n=8) were crossed over to crizotinib. Four mice in each group were sacrificed for analysis of resistance mechanism at the time of PD. The PFS of ceritinib was significantly longer than that of crizotinib [24 weeks (95% CI, 21.4-26.5) vs. 8 weeks (95% CI, 6.5-9.0), P < 0.001]. Subsequent treatment with ceritinib following crizotinib resulted in significantly longer PFS than crizotinib following ceritinib [7 weeks (95% CI, 4.1-9.9) vs 3 weeks (95% CI, 2.5-3.5), P < 0.001]. Altogether, treatment with ceritinib followed by crizotinib showed a prolongation of PFS, compared to crizotinib followed by ceritinib (27 weeks vs. 15 weeks, P < 0.001). We noted that ALK-TKI resistant tumors harbored several copy number variations (CNVs), and nonsynonymous oncogenic mutations, but found no previously reported resistant mechanisms including secondary mutations, or CNVs. Wnt signaling related gene set was increased in both crizotinib- and ceritinib-resistant tumors, and Hippo signaling related gene set was increased in ceritinib-resistant tumors on KEGG pathway-based analysis. Conclusion: Our findings suggest that ceritinib is superior to crizotinib when used in the first-line setting. Novel mechanisms of acquired resistance such as increased Wnt and Hippo signaling need further validation. Citation Format: Kyoung-Ho Pyo, Lim Sun Min, Jae Hwan Kim, Ji Min Lee, Ha Ni Jo, Jae Soek Cho, Mi-Ran Yun, Sung Eun Kim, Hye Ryun Kim, Chun-Feng Xin, Tae-Min Kim, Byoung Chul Cho. Identification of optimal treatment sequence and acquired resistance mechanisms of ALK inhibitors using EML4-ALK transgenic mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2855.

Abstract 1570: Defective collagen production by mammary epithelia leads to increased breast cancer metastasis: a novel role of vacuolar ATPase

Abstract In cancer cells, vacuolar ATPase (V-ATPase), a multi-subunit enzyme, is expressed on the plasma as well as vesicular membranes and critically influences metastatic behavior. Recently, we have shown that by inhibiting a2 isoform of V-ATPase ‘a’ subunit (a2V) in cancer cells, in vivo tumor growth can be delayed through decreasing essential macrophage population in breast cancer. Here, we investigated whether the same tumor growth inhibition can be attain by deleting a2V in host tissue instead of cancer cell. For this purpose, we deleted a2V gene in the mouse mammary gland using MMTV-Cre lox system. Breast tumors were generated by inoculating E0771 mammary carcinoma in mammary fat pad of a2V knockout (KO) mice. We observed faster tumor growth in KO mice compared to wild type (WT). KO mice tumors showed more infiltration and metastasis of cancer cell as evident by the number of lung and liver lesions. KO mice did not display the characteristic solid tumor phenotype of breast cancer. Based on these observations, we evaluated expression and production of collagen protein which is an important component of the extra cellular matrix, in KO breast tissue. Trichrome staining showed less collagen protein in tumorous as well as in non-tumorous breast tissue of KO mice. Total collagen was measured by the hydroxyl proline assay and analysis showed that KO mice have significantly (P<0.05) less amount of hydroxyl proline compared to WT mice. (16.77 ± 3.74 vs 43.67 ± 6.89). To validate our observation, we knock down a2V in HMEpC mammary epithelial cell line to measure the effect on collagen production. After a2V inhibition, the production of collagen in culture media was reduced. The data show that for an efficient tumor growth, a2V is required in both cancer cell and host tissue. Citation Format: Gajendra K. Katara, Arpita Kulshrestha, Sahithi Pamarthy, Liqun Mao, Kenneth D. Beaman. Defective collagen production by mammary epithelia leads to increased breast cancer metastasis: a novel role of vacuolar ATPase. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1570.

Site-specific recombinatorics: in situ cellular barcoding with the Cre Lox system.

BackgroundCellular barcoding is a recently developed biotechnology tool that enables the familial identification of progeny of individual cells in vivo. In immunology, it has been used to track the burst-sizes of multiple distinct responding T cells over several adaptive immune responses. In the study of hematopoiesis, it revealed fate heterogeneity amongst phenotypically identical multipotent cells. Most existing approaches rely on ex vivo viral transduction of cells with barcodes followed by adoptive transfer into an animal, which works well for some systems, but precludes barcoding cells in their native environment such as those inside solid tissues.ResultsWith a view to overcoming this limitation, we propose a new design for a genetic barcoding construct based on the Cre Lox system that induces randomly created stable barcodes in cells in situ by exploiting inherent sequence distance constraints during site-specific recombination. We identify the cassette whose provably maximal code diversity is several orders of magnitude higher than what is attainable with previously considered Cre Lox barcoding approaches, exceeding the number of lymphocytes or hematopoietic progenitor cells in mice.ConclusionsIts high diversity and in situ applicability, make the proposed Cre Lox based tagging system suitable for whole tissue or even whole animal barcoding. Moreover, it can be built using established technology.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-016-0290-3) contains supplementary material, which is available to authorized users.

303. Deletion of Pdx1 in Mouse Pancreatic Ducts by CRISPR-Cas9 Mediated Gene Editing

Introduction: The homeodomain transcription factor Pdx1 is crucial for pancreas formation. Pdx1-expressing cells are first observed at embryonic day 8.5 (E8.5), prior even to the earliest indication of morphogenesis, in endodermal cells designated to give rise to the pancreas. In adult mouse, Pdx1 protein is transiently expressed when pancreas is injured, such as Langerhans islets damage in alloxan induced diabetic mice, implying Pdx1 may be necessary for the neogenetic formation of β-cells from mature ducts. In order to study the role of pdx1 in the pancreatic duct for pancreatic regeneration, most investigators use the Cre-lox system to generate duct-specific Pdx1 deletions in mice. This method is able to delete Pdx1specifically from tissue or cells with or without a tamoxifen-inducible (cre-ERT2) system; however, several caveats and limitations exist with tamoxifen-induced depletion. In addition, the cre-ERT2 system may be leaky, resulting in constitutive rather than inducible activation in some cells. To overcome these flaws from the Cre-ERT2/lox system, we decided to use a novel CRISPR-Cas9 gene editing technique to delete pdx1 in pancreatic ducts. Methods: We previously used a mouse short Sox9 promoter (468 bp) to generate a recombinant adeno-associated virus (AAV) carrying a reporter GFP (AAV6-Sox9-GFP), and this recombinant virus construct was infused into the pancreatic ducts, through the common bile/pancreatic duct, to specifically tag the duct cells. In order to address pancreatic duct specific deletion of Pdx1 after alloxan ablation of beta-cells, we first to applied the CRISPR-Cas9 gene editing technique on the HEK293-CMV-GFP cell line in vitro (Figure 2Figure 2) and ROSA26 LSL tomato reporter mice ex vivo (Figure 3Figure 3), and then employed AAV6 mediated CRISPR-SaCas9 under the control of the mouse sox9 short promoter, coupled with paired guide RNAs (gRNAs) flanking the Pdx1 exon2 (Figure 4Figure 4) through pancreatic duct infusion into the pancreas. RESULTS AND CONCLUSIONS: These CRISPR-SaCas9 and gRNAs AAV viruses were co-infused into pancreases of C57BL/6J mice 2 days after alloxan treatment. One week after AAV6-SaCas9+gRNAs infusion, it appeared that only the Pdx1 in pancreatic ductal cells were deleted. Comparatively, PBS or AAV6-CMV-GFP viral infused C57BL/6J mice and ROSA26 LSL tomato reporter mice expressed fluorescence in the entire pancreas as a result of the deleted loxP sites that removed the stop cassette, the Pdx1 is not deleted. Thus, we first report here a highly efficient and specific ablation of Pdx1 in adult mouse pancreatic ducts using the CRISPR-Cas9 technique. Figure 1Figure 1. Construction of AAV CRISPR-SaCas9 and gRNA vectors. Figure 2Figure 2. Deletion of ZsGeen in HEK293-CMV-GFP cells using SacCas9 and gRNA in vitro. Figure 3Figure 3. Valiation of SaCas9 and gRNA in vivo deletion of loxP sites in ROSA26-LSL tomato mice pancreas. Figure 4Figure 4. Deletion of Pdx1 exon2 in alloxan treated C57 pancreatic ducts.View Large Image | Download PowerPoint SlideView Large Image | Download PowerPoint SlideView Large Image | Download PowerPoint SlideView Large Image | Download PowerPoint Slide

Using the cre–lox system to randomize target gene expression states and generate diverse phenotypes

Modifying the expression of multiple genes enables both deeper understanding of their function and the engineering of complex multigenic cellular phenotypes. However, deletion or overexpression of multiple genes is typically laborious and involves multiple sequential genetic modifications. Here we describe a strategy to randomize the expression state of multiple genes in Saccharomyces cerevisiae using Cre-loxP recombination. By inserting promoters flanked by inverted loxP sites in front of a gene of interest we can randomly alter its expression by turning it OFF or ON, or between four distinct expression states. We show at least 6 genes can be randomized independently and argue that using orthogonal loxP sites should increase this number to at least 15. Finally, we show how combining this strategy with mating allows easy introduction of native regulation as an additional expression state and use this to probe the role of four different enzymes involved in base excision repair in tolerance to methyl methane sulfonate (MMS), a genotoxic DNA alkylating agent. The set of vectors developed here can be used to randomize the expression of both heterologous genes and endogenous genes, and could immediately prove useful for metabolic engineering in yeast. Because Cre-loxP recombination works in many organisms, this strategy should be readily extendable.

Gene amplification system based on double rolling-circle replication as a model for oncogene-type amplification

Gene amplification contributes to a variety of biological phenomena, including malignant progression and drug resistance. However, details of the molecular mechanisms remain to be determined. Here, we have developed a gene amplification system in yeast and mammalian cells that is based on double rolling-circle replication (DRCR). Cre-lox system is used to efficiently induce DRCR utilizing a recombinational process coupled with replication. This system shows distinctive features seen in amplification of oncogenes and drug-resistance genes: (i) intra- and extrachromosomal amplification, (ii) intensive chromosome rearrangement and (iii) scattered-type amplification resembling those seen in cancer cells. This system can serve as a model for amplification of oncogenes and drug-resistance genes, and improve amplification systems used for making pharmaceutical proteins in mammalian cells.

Sequential deletion of Pichia pastoris genes by a self-excisable cassette

A rapid and convenient method is presented for unmarked gene deletions in Pichia pastoris. Cre/mutated lox system, Zeocin(®) (Invitrogen) resistance marker and homologous arms were spliced together by fusion PCR to generate the gene disruption cassettes (homologous region-lox71-Cre-ZeoR-lox66-homologous region), which could be integrated into the P. pastoris genome via homologous recombination. After transferring double-cross-over recombinants to methanol induction medium, transient expression of Cre recombinase caused the recombination of lox71-Cre-ZeoR-lox66 fragment into a double-mutant lox72 site, thus excising the Cre-ZeoR cassette from the P. pastoris genome. As the double-mutant lox72 site displays strongly reduced binding affinity for Cre recombinase, this method could be used sequentially to disrupt P. pastoris genes without introducing selectable markers. The effectiveness of this strategy was verified by introducing both single and double gene deletions into the P. pastoris genome.

Ablation of LKB1 in the heart leads to energy deprivation and impaired cardiac function

Energy deprivation in the myocardium is associated with impaired heart function and increased morbidity. LKB1 is a kinase that is required for activation of AMP-activated protein kinase (AMPK) as well as 13 AMPK-related protein kinases. AMPK stimulates ATP production during ischemia and prevents post-ischemic dysfunction. We used the Cre–Lox system to generate mice where LKB1 was selectively knocked out in cardiomyocytes and muscle cells (LKB1-KO) to assess the role of LKB1 on cardiac function in these mice. Heart rates of LKB1-KO mice were reduced and ventricle diameter was increased. Ex vivo, cardiac function was impaired during aerobic perfusion of isolated working hearts, and recovery of function after ischemia was reduced. Although oxidative metabolism and mitochondrial function were normal, the AMP/ATP ratio was increased in LKB1-KO hearts. This was associated with a complete ablation of AMPKα2 activity, and a stimulation of signaling through the mammalian target of rapamycin. Our results establish a critical role for LKB1 for normal cardiac function under both aerobic conditions and during recovery after ischemia. Ablation of LKB1 leads to a decreased cardiac efficiency despite normal mitochondrial oxidative metabolism.

Exciting Challenges Ahead For Integrative And Regulatory Physiology

Exciting Challenges Ahead For Integrative And Regulatory Physiology

Differential Role of Class 1A PI 3-Kinase Regulatory Subunits in Mast Cell Growth, Maturation and Survival.

Abstract 77Stem cell factor (SCF) mediated c-Kit receptor activation plays a pivotal role in mast cell growth, maturation and survival. However, the signaling events downstream from c-Kit are poorly understood. Mast cells express multiple regulatory subunits of class 1A PI 3-kinase including p85α, p85β, p50α, and p55α. While it is known that PI 3-kinase plays an essential role in mast cells; the precise mechanism by which these regulatory subunits impact specific mast cell functions including maturation, growth, and survival are not known. Using mice deficient in the expression of p85α or p85β or combination of both p85α/p55α/p50α as well as all four subunits we have examined the role of these subunits in mast cell functions. We show that loss of p85α subunit alone results in impaired bone marrow derived mast cell (BMMC) maturation, growth, and survival compared to wild-type (WT) controls, in spite of the continuous expression of p85β, p55α, and p50α subunits in these cells. Restoring the expression of p85α in p85α deficient mast cells restores the maturation and growth defects. To assess the contribution of p50α and p55α subunits, we generated mice using the Cre lox system that were deficient in the expression of all three subunits (i.e. p85α/p55α/p50α). Deficiency of p85α/p55α/p50α subunits in bone marrow cells completely blocked mast cell maturation and growth, suggesting an essential role for the smaller subunits p50 and p55 in addition to the full length form of p85. Curiously, over-expression of p50α in p85α deficient BMMCs only marginally rescued mast cell maturation and growth, suggesting that the full length form of p85α functions with specificity in regulating mast cell functions. Since the major difference between the shorter isoforms and the full length form of p85α is the absence of the amino terminal SH3 and BH domains, we generated two mutants of p85α lacking either the SH3 or the BH domain and expressed them in p85α−/− BMMCs. While both these mutants completely restored the maturation defect associated with p85α deficiency and showed normal binding to the c-Kit receptor upon SCF stimulation as well as to the p110 catalytic subunits; none of these mutants completely rescued SCF induced proliferation (50% and 70% respectively, n=3, p<0.004). Biochemically, lack of SCF induced growth rescue in p85α−/− BMMCs expressing p85αΔSH3 and p85αΔBH mutants was associated with a lack of rescue in the activation of Akt and Erk, but complete rescue in the activation of JNK (n=3). Consistently, while transplantation of p85α deficient bone marrow cells transduced with p85α into mast cell deficient Wsh mice resulted in complete restoration of gastrointestinal mast cells as well as mast cells in the stomach and spleen, p85αΔSH3 and p85αΔBH mutants restored mast cells only partially. These results indicate that other domains (SH3 and BH) of p85α are required for mast cell growth. In contrast to p85α, deficiency of p85β alone resulted in increased BMMC maturation, growth and survival compared to controls (1.2 fold, n=3, p<0.003). Consistently, over-expression of p85β in WT bone marrow cells resulted in a profound reduction in the maturation of mast cells as well as proliferation. We studied whether reduced maturation and proliferation due to the loss or over-expression of p85β was a result of altered c-Kit receptor internalization and degradation. Our results revealed significantly more c-Kit receptor internalization and degradation in p85β expressing cells compared to p85α expressing cells (2 fold, n=5, p<0.001). Since Cbl family of ubiquitin ligases are involved in the down-regulation of tyrosine kinase receptors, we analyzed whether c-Cbl is involved in p85β mediated c-Kit receptor internalization and degradation. Phosphorylation of c-Cbl and ubiquitination of c-Kit receptor was more in p85β expressing cells compared to p85 expressing cells (n=3). In conclusion, while the current dogma in the field of PI3Kinase signaling suggests that all regulatory subunits of PI3Kinase function in a similar manner; we provide genetic and biochemical evidence to suggest that p85 regulatory subunits differentially regulate growth and maturation of mast cells. Disclosures:Munugalavadla:Genentech: Employment, Patents & Royalties.

Study on Agrobacterium-Mediated Transformation of Pepper with Barnase and Cre Gene

This study was designed to control plant fertility by cell lethal gene Barnase expressing at specific developmental stage and in specific tissue of male organ under the control of Cre/ lox system, for heterosis breeding of chili pepper ( Capsicum annuum L.). Chili pepper inbred lines (A, D, E, and I) were transformed with Cre gene and Barnase gene situated between loxp, separately, by means of Agrobacterium co-culture. In this study, we had established a high transformation system by extensive study of affecting factors including genotype, selection of marker, and lethal dose. Cotyledon with petiole from 9–11-day-old seeding was pre-cultured on media MR [MB (MS mineral +vitamine B5)+BA (6-Benzyladenine) 5.0 mg L −1 + IAA (indoleacetic acid) 1.0 mg L −1 + GA 3 (gibberellic acid) 1.0 mg L −1 + sucrose 3% + agar 6.5 g L −1] for 2 d. The explants were infected by Agrobacterium tumefaciens when their OD 600 (optical density at 600 nm) reached 0.6–0.9. After co-cultured for 4–5 d on media MC [MB + BA 5.0 mg L −1 + IAA 1.0 mg L −1 + GA 3 1.0 mg L −1 + sucrose 3% + agar 6.5 g L −1 + AS (acetosyringone) 200 μmol L −1], these cotyledons with petiole were cultured on selective differentiation medium in the media MT [MB medium supplemented with BA [5.0 mg L −1 + IAA 1.0 mg L −1 + GA 3 1.0 mg L −1 + AgNO 3 5.0 mg L −1 + CW (coconut water) 5% + Km (kanamycin) 65 mg L −1 + Cb (carbenicillin) 500 mg L −1 + 3% sucrose + agar 6.5 g L −1]. The Kmr (kanamycin resistant) bud rosettes were elongated on selective elongation medium and rooted on rooting medium. PCR and Southern blotting analysis of Kmr plantlet indicated that the foreign genes had been integrated into the genome of pepper. The transgenic plants with Cre gene developed well, blossomed out, and set fruit normally. The transgenic plants with Barnase gene grew well with normal appearance of flower, but they showed different fertility from complete sterility, partial sterility to complete fertility, and similar results were obtained from in vitro pollen germination experiments.

Retinal neuroprotection by hypoxic preconditioning is independent of hypoxia‐inducible factor‐1α expression in photoreceptors

Hypoxic preconditioning stabilizes hypoxia-inducible factor (HIF) 1 alpha in the retina and protects photoreceptors against light-induced cell death. HIF-1 alpha is one of the major transcription factors responding to low oxygen tension and can differentially regulate a large number of target genes. To analyse whether photoreceptor-specific expression of HIF-1 alpha is essential to protect photoreceptors by hypoxic preconditioning, we knocked down expression of HIF-1 alpha specifically in photoreceptor cells, using the cyclization recombinase (Cre)-lox system. The Cre-mediated knockdown caused a 20-fold reduced expression of Hif-1 alpha in the photoreceptor cell layer. In the total retina, RNA expression was reduced by 65%, and hypoxic preconditioning led to only a small increase in HIF-1 alpha protein levels. Accordingly, HIF-1 target gene expression after hypoxia was significantly diminished. Retinas of Hif-1 alpha knockdown animals did not show any pathological alterations, and tolerated hypoxic exposure in a comparable way to wild-type retinas. Importantly, the strong neuroprotective effect of hypoxic preconditioning against light-induced photoreceptor degeneration persisted in knockdown mice, suggesting that hypoxia-mediated survival of light exposure does not depend on an autocrine action of HIF-1 alpha in photoreceptor cells. Hypoxia-mediated stabilization of HIF-2 alpha and phosphorylation of signal transducer and activator of transcription 3 (STAT 3) were not affected in the retinas of Hif-1 alpha knockdown mice. Thus, these factors are candidates for regulating the resistance of photoreceptors to light damage after hypoxic preconditioning, along with several potentially neuroprotective genes that were similarly induced in hypoxic knockdown and control mice.