Mutated fukutin-related protein (FKRP) localises as wild type in differentiated muscle cells

The mechanism of disease in forms of congenital and limb girdle muscular dystrophy linked to mutations in the gene encoding for Fukutin-related protein (FKRP) has previously been associated with the mis-localisation of FKRP from the Golgi apparatus. In the present report, we have transfected V5-tagged Fukutin-related protein expression constructs into differentiated C2C12 myotubes and the tibialis anterior of normal mice. The transfection of either wild type (WT) or several mutant constructs (P448L, C318Y, L276I) into myotubes consistently showed clear co-localisation with GM130, a Golgi marker. In contrast, whilst WT and the L276I localised to the Golgi of Cos-7 cells, the P448L and C318Y was mis-localised in the majority of these undifferentiated cells. The injection of the same constructs into the tibialis anterior of mice resulted in similar localisation of both the WT and all the mutants. Immunolabelling of FKRP in the muscle of MDC1C and LGMD2I patients was found to be indistinguishable from normal controls. Overall, these data suggest that retention in the endoplasmic reticulum of FKRP is not the main mechanism of disease but that this may instead relate to a disruption of the functional activity of this putative enzyme with its substrate(s) in the Golgi.     

A versatile transgenic allele for mouse overexpression studies

For the analysis of gene function in vivo, gene overexpression in the mouse provides an alternative to loss-of-function knock-out approaches and can help reveal phenotypes where compensatory mechanisms are at play. Furthermore, when multiple lines overexpressing a gene-of-interest at varying levels are studied, the consequences of differences in gene dosage can be explored. Despite these advantages, inherent shortcomings in the methodologies used for the generation of gain-of-function transgenic mouse models have limited their application to functional gene analysis, and the necessity for multiple lines comes at a significant animal and financial cost. The targeting of transgenic overexpression constructs at single copy into neutral genomic loci is the preferred method for the generation of such models, which avoids the unpredictable outcomes associated with conventional random integration. However, despite the increased reliability that targeted transgenic methodologies provide, only one expression level results, as defined by the promoter used. Here, we report a new versatile overexpression allele, the promoter-switch allele, which couples PhiC31 integrase-targeted transgenesis with Flp recombinase promoter switching and Cre recombinase activation. These recombination switches allow the conversion of different overexpression alleles, combining the advantages of transgenic targeting with tunable transgene expression. With this approach, phenotype severity can be correlated with transgene expression in a single mouse model, providing a cost-effective solution amenable to systematic gain-of-function studies.

     

A fear-inducing odor alters PER2 and c-Fos expression in brain regions involved in fear memory

Evidence demonstrates that rodents learn to associate a foot shock with time of day, indicating the formation of a fear related time-stamp memory, even in the absence of a functioning SCN. In addition, mice acquire and retain fear memory better during the early day compared to the early night. This type of memory may be regulated by circadian pacemakers outside of the SCN. As a first step in testing the hypothesis that clock genes are involved in the formation of a time-stamp fear memory, we exposed one group of mice to fox feces derived odor (TMT) at ZT 0 and one group at ZT 12 for 4 successive days. A separate group with no exposure to TMT was also included as a control. Animals were sacrificed one day after the last exposure to TMT, and PER2 and c-Fos protein were quantified in the SCN, amygdala, hippocampus, and piriform cortex. Exposure to TMT had a strong effect at ZT 0, decreasing PER2 expression at this time point in most regions except the SCN, and reversing the normal rhythm of PER2 expression in the amygdala and piriform cortex. These changes were accompanied by increased c-Fos expression at ZT0. In contrast, exposure to TMT at ZT 12 abolished the rhythm of PER2 expression in the amygdala. In addition, increased c-Fos expression at ZT 12 was only detected in the central nucleus of the amygdala in the TMT12 group. TMT exposure at either time point did not affect PER2 or c-Fos in the SCN, indicating that under a light-dark cycle, the SCN rhythm is stable in the presence of repeated exposure to a fear-inducing stimulus. Taken together, these results indicate that entrainment to a fear-inducing stimulus leads to changes in PER2 and c-Fos expression that are detected 24 hours following the last exposure to TMT, indicating entrainment of endogenous oscillators in these regions. The observed effects on PER2 expression and c-Fos were stronger during the early day than during the early night, possibly to prepare appropriate systems at ZT 0 to respond to a fear-inducing stimulus.     

The neuroprotective effects of heat shock protein 27 overexpression in transgenic animals against kainate-induced seizures and hippocampal cell death

The 27-kDa heat shock protein (HSP27) has a potent ability to increase cell survival in response to a wide range of cellular challenges. In order to investigate the mode of action of HSP27 in vivo, we have developed transgenic lines, which express human HSP27 at high levels throughout the brain, spinal cord, and other tissues. In view of the particular property of HSP27 compared with other HSPs to protect neurons against apoptosis, we have tested these transgenic lines in a well established in vivo model of neurotoxicity produced by kainic acid, where apoptotic cell death occurs. Our results demonstrate for the first time the marked protective effects of HSP27 overexpression in vivo, which significantly reduces kainate-induced seizure severity and mortality rate (>50%) in two independent lines and markedly reduces neuronal cell death in the CA3 region of hippocampus. This reduced seizure severity in HSP27 transgenic animals was associated with a marked attenuation of caspase 3 induction and apoptotic features. These studies clearly demonstrate that HSP27 has a major neuroprotective effect in the central nervous system in keeping with its properties demonstrated in culture and highlight an early stage in the cell death pathway that is affected by HSP27.