Distal element(s) is(are) required for position-independent expression of the goat α-lactalbumin gene in transgenic mice. Potential relationship with the location of the cyclin T1 locus

We recently reported the site-independent and copy-number-related expression in mice of a goat α-lactalbumin gene with 150 kb and 10 kb of 5'- and 3'-flanking sequences, respectively. In the present study, we observed that the resection of the 5'-flanking region, leaving only 70 kb, resulted in a site-dependent expression of this milk protein-encoding transgene. This suggests that important cis-regulatory elements are located within the distal-deleted sequence. Within this region, we localised the promoter of the cyclin T1 gene, an ubiquitously expressed gene. So far, no other gene has been located between these two loci. Since these two genes are differentially expressed, our data suggest the potential location of an insulator within the deleted region that allows the two genes to be independently regulated

Overexpression of the Mitochondrial T3 Receptor p43 Induces a Shift in Skeletal Muscle Fiber Types

In previous studies, we have characterized a new hormonal pathway involving a mitochondrial T3 receptor (p43) acting as a mitochondrial transcription factor and consequently stimulating mitochondrial activity and mitochondrial biogenesis. We have established the involvement of this T3 pathway in the regulation of in vitro myoblast differentiation.We have generated mice overexpressing p43 under control of the human α-skeletal actin promoter. In agreement with the previous characterization of this promoter, northern-blot and western-blot experiments confirmed that after birth p43 was specifically overexpressed in skeletal muscle. As expected from in vitro studies, in 2-month old mice, p43 overexpression increased mitochondrial genes expression and mitochondrial biogenesis as attested by the increase of mitochondrial mass and mt-DNA copy number. In addition, transgenic mice had a body temperature 0.8°C higher than control ones and displayed lower plasma triiodothyronine levels. Skeletal muscles of transgenic mice were redder than wild-type animals suggesting an increased oxidative metabolism. In line with this observation, in gastrocnemius, we recorded a strong increase in cytochrome oxidase activity and in mitochondrial respiration. Moreover, we observed that p43 drives the formation of oxidative fibers: in soleus muscle, where MyHC IIa fibers were partly replaced by type I fibers; in gastrocnemius muscle, we found an increase in MyHC IIa and IIx expression associated with a reduction in the number of glycolytic fibers type IIb. In addition, we found that PGC-1α and PPARδ, two major regulators of muscle phenotype were up regulated in p43 transgenic mice suggesting that these proteins could be downstream targets of mitochondrial activity. These data indicate that the direct mitochondrial T3 pathway is deeply involved in the acquisition of contractile and metabolic features of muscle fibers in particular by regulating PGC-1α and PPARδ

Prominent and Persistent Extraneural Infection in Human PrP Transgenic Mice Infected with Variant CJD

Background. The evolution of the variant Creutzfeldt-Jakob disease (vCJD) epidemic is hazardous to predict due to uncertainty in ascertaining the prevalence of infection and because the disease might remain asymptomatic or produce an alternate, sporadic-like phenotype. Methodology/Principal Findings. Transgenic mice were produced that overexpress human prion protein with methionine at codon 129, the only allele found so far in vCJD-affected patients. These mice were infected with prions derived from variant and sporadic CJD (sCJD) cases by intracerebral or intraperitoneal route, and transmission efficiency and strain phenotype were analyzed in brain and spleen. We showed that i) the main features of vCJD infection in humans, including a prominent involvement of the lymphoid tissues compared to that in sCJD infection were faithfully reproduced in such mice; ii) transmission of vCJD agent by intracerebral route could lead to the propagation of either vCJD or sCJD-like prion in the brain, whereas vCJD prion was invariably propagated in the spleen, iii) after peripheral exposure, inefficient neuroinvasion was observed, resulting in an asymptomatic infection with life-long persistence of vCJD prion in the spleen at stable and elevated levels. Conclusion/Significance. Our findings emphasize the possibility that human-to-human transmission of vCJD might produce alternative neuropathogical phenotypes and that lymphoid tissue examination of CJD cases classified as sporadic might reveal an infection by vCJD-type prions. They also provide evidence for the strong propensity of this agent to establish long-lasting, subclinical vCJD infection of lymphoreticular tissues, thus amplifying the risk for iatrogenic transmission

Effect of fluoxetine on neuromuscular function in acetylcholinesterase (AChe) knockout mice

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p28, a truncated form of TR alpha 1 regulates mitochondrial physiology

We have previously identified in mitochondria two truncated forms of the T3 nuclear receptor TR alpha 1, with molecular weights of 43kDa (p43) and 28kDa (p28) respectively located in the matrix and in the inner membrane. Previously, we have demonstrated that p43 stimulates mitochondrial transcription and protein synthesis in the presence of T3. Here we report that p28 is targeted into the organelle in a T3-dependent manner and displays an affinity for T3 higher than the nuclear receptor. We tried to generate mice overexpressing p28 using the human alpha-skeletal actin promoter, however we found an early embryonic lethality that was probably linked to a transient expression of p28 in trophoblast giant cells. This could be partly explained by the observation that overexpression of p28 in human fibroblasts induced alterations of mitochondrial physiology

Hyposensitivity to the amnesic effects of scopolamine or amyloid beta25-35 peptide in heterozygous acetylcholinesterase knockout (AchE+/-) mice

International audienceAcetylcholinesterase (AChE) is the main catabolic enzyme of acetylcholine, responsible for the synaptic clearance of the neurotransmitter from the synaptic cleft. Decrease in AChE expression, or activity, results in increased cholinergic tonus in the brain or periphery, with concomittant regulations of nicotinic and muscarinic receptors expression. We generated AChE knockout mice and characterized the behavioral phenotype of heterozygous animals, particularly focusing on learning and memory functions. Male and female, AChE+/- and AChE+/+ littermate controls (129sv strain), tested at 5-9 weeks of age, failed to show any difference in terms of locomotion, exploration and anxiety parameters in the open-field test. Animals were then tested for place learning in the water-maze. They were trained using a 'sustained acquisition' protocol (3 swims/day during 5 days) or a 'mild acquisition' protocol (2 swims/day during 9 days) to locate an invisible platform in fixed position (reference memory procedure). Then, during 3 days, they were trained to locate the platform in a variable position (working memory procedure). Learning profiles and probe test performances were unchanged in AChE+/- mice as compared with AChE+/+. Mice were then treated with the muscarinic M1 antagonist scopolamine (0.5, 5 mg/kg sc) 20 min before each training session (3 swims/day during 5 days). Scopolamine impaired learning at both doses in AChE+/+ mice, but only at the highest dose in AChE+/- mice. Moreover, the central injection of amyloid beta25-35 peptide (9 nmol) failed to induce learning deficits in AChE+/- mice, contrarily to AChE+/+ controls. These behavioral study shows that the increase in cholinergic tonus did not result in increased memory abilities in these heterozygous AChE+/- mice, but allowed a significant prevention of the deleterious effects of muscarinic blockade or amyloid toxicity

Hyposensitivity to the amnesic effects of scopolamine or amyloid β25–35 peptide in heterozygous acetylcholinesterase knockout (AChE+/−) mice

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