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RtTA toxicity limits the usefulness of the SP-C-rtTA transgenic mouse.

ABSTRACT: The doxycycline (DOX)-inducible gene expression systems allow tight temporal and spatial control of transgene expression, invaluable in studies of organ development and disease pathogenesis. Transgenic mice using the human Surfactant Protein C promoter to drive the expression of the reverse tetracycline transactivator (SP-C-rtTA) enabled functional analysis of essential gene function during lung development. Here we report that DOX-fed SP-C-rtTA mice during the period in which Type II cells differentiate results in cellular toxicity that may have confounded the interpretation of previous reports using this line. These effects included impaired alveologenesis, loss/reduction in expression of surfactant-associated proteins, and death. Severity was dependent on genetic background: outbred mice or those on a CD1 background are highly susceptible, whereas the C57BL/6 background appeared resistant by morphological criteria. However, quantitative analysis reveled that DOX-fed, SP-C-rtTA C57BL/6 pups had reduced surfactant mRNA accumulation that could contribute to synthetic lethality when combined with other genetic alterations. We conclude that the combination of genetic backgrounds, length of DOX exposure and the presence of the SP-C-rtTA transgene contributed more than previously appreciated to the similarities seen in the phenotypes reported by investigators using the SP-C-rtTA, (tetO)(7)-Cre. These studies demonstrate the importance of using appropriate SP-C-rtTA only controls in all experiments.

SUBMITTER: Morimoto M

PROVIDER: S-EPMC2955437 | biostudies-literature | 2009 Jan

REPOSITORIES: biostudies-literature

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rtTA toxicity limits the usefulness of the SP-C-rtTA transgenic mouse.

Morimoto Mitsuru M Kopan Raphael R

Developmental biology 20081101 1

The doxycycline (DOX)-inducible gene expression systems allow tight temporal and spatial control of transgene expression, invaluable in studies of organ development and disease pathogenesis. Transgenic mice using the human Surfactant Protein C promoter to drive the expression of the reverse tetracycline transactivator (SP-C-rtTA) enabled functional analysis of essential gene function during lung development. Here we report that DOX-fed SP-C-rtTA mice during the period in which Type II cells diff ...[more]

PMID: 19013447

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Project description:The anti-angiogenic soluble fms-like tyrosine kinase 1 (sFLT1) is one of the candidates in the progression of preeclampsia, often associated with fetal growth restriction (FGR). Therapeutic agents against preeclampsia with/without FGR, as well as adequate transgenic sFLT1 mouse models for testing such agents, are still missing. Much is known about sFLT1-mediated endothelial dysfunction in several tissues; however, the influence of sFLT1 on placental and fetal development is currently unknown. We hypothesize that sFLT1 is involved in the progression of FGR by influencing placental differentiation and vascularization and is a prime candidate for interventional strategies. Therefore, we generated transgenic inducible human sFLT1/reverse tetracycline-controlled transactivator (hsFLT1/rtTA) mice, in which hsFLT1 is ubiquitously overexpressed during pregnancy in dams and according to the genetics in hsFLT1/rtTA homozygous and heterozygous fetuses. Induction of hsFLT1 led to elevated hsFLT1 levels in the serum of dams and on mRNA level in all placentas and hetero-/homozygous fetuses, resulting in FGR in all fetuses at term. The strongest effects in respect to FGR were observed in the hsFLT1/rtTA homozygous fetuses, which exhibited the highest hsFLT1 levels. Only fetal hsFLT1 expression led to impaired placental morphology characterized by reduced placental efficiency, enlarged maternal sinusoids, reduced fetal capillaries, and impaired labyrinthine differentiation, associated with increased apoptosis. Besides impaired placental vascularization, the expression of several transporter systems, such as glucose transporter 1 and 3 (Glut-1; Glut-3); amino acid transporters, solute carrier family 38, member one and two (Slc38a1; Slc38a2); and most severely the fatty acid translocase Cd36 and fatty acid binding protein 3 (Fabp3) was reduced upon hsFLT1 expression, associated with an accumulation of phospholipids in the maternal serum. Moreover, the Vegf pathway showed alterations, resulting in reduced Vegf, Vegfb, and Plgf protein levels and increased Bad and Caspase 9 mRNA levels. We suggest that hsFLT1 exerts an inhibitory influence on placental vascularization by reducing Vegf signaling, which leads to apoptosis in fetal vessels, impairing placental differentiation, and the nutrient exchange function of the labyrinth. These effects were more pronounced when both the dam and the fetus expressed hsFLT1 and ultimately result in FGR and resemble the preeclamptic phenotype in humans.

Project description:BackgroundSelf-assembly of the amyloid-β (Aβ) peptide into aggregates, from small oligomers to amyloid fibrils, is fundamentally linked with Alzheimer's disease (AD). However, it is clear that not all forms of Aβ are equally harmful and that linking a specific aggregate to toxicity also depends on the assays and model systems used (Haass et al., J Biol. Chem 269:17741-17748, 1994; Borchelt et al., Neuron 17:1005-1013, 1996). Though a central postulate of the amyloid cascade hypothesis, there remain many gaps in our understanding regarding the links between Aβ deposition and neurodegeneration.MethodsIn this study, we examined familial mutations of Aβ that increase aggregation and oligomerization, E22G and ΔE22, and induce cerebral amyloid angiopathy, E22Q and D23N. We also investigated synthetic mutations that stabilize dimerization, S26C, and a phospho-mimetic, S8E, and non-phospho-mimetic, S8A. To that end, we utilized BRI2-Aβ fusion technology and rAAV2/1-based somatic brain transgenesis in mice to selectively express individual mutant Aβ species in vivo. In parallel, we generated PhiC31-based transgenic Drosophila melanogaster expressing wild-type (WT) and Aβ40 and Aβ42 mutants, fused to the Argos signal peptide to assess the extent of Aβ42-induced toxicity as well as to interrogate the combined effect of different Aβ40 and Aβ42 species.ResultsWhen expressed in the mouse brain for 6 months, Aβ42 E22G, Aβ42 E22Q/D23N, and Aβ42WT formed amyloid aggregates consisting of some diffuse material as well as cored plaques, whereas other mutants formed predominantly diffuse amyloid deposits. Moreover, while Aβ40WT showed no distinctive phenotype, Aβ40 E22G and E22Q/D23N formed unique aggregates that accumulated in mouse brains. This is the first evidence that mutant Aβ40 overexpression leads to deposition under certain conditions. Interestingly, we found that mutant Aβ42 E22G, E22Q, and S26C, but not Aβ40, were toxic to the eye of Drosophila. In contrast, flies expressing a copy of Aβ40 (WT or mutants), in addition to Aβ42WT, showed improved phenotypes, suggesting possible protective qualities for Aβ40.ConclusionsThese studies suggest that while some Aβ40 mutants form unique amyloid aggregates in mouse brains, they do not exacerbate Aβ42 toxicity in Drosophila, which highlights the significance of using different systems for a better understanding of AD pathogenicity and more accurate screening for new potential therapies.

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RtTA toxicity limits the usefulness of the SP-C-rtTA transgenic mouse.

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rtTA toxicity limits the usefulness of the SP-C-rtTA transgenic mouse.

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