Overview on mouse mutagenesis

Analyze Mouse Knockout Models of UPR Pathway Elements

Evidence from genetic studies in human and mice indicates that defective skeletal development is one of the major phenotypic outcomes for aberrant UPR signaling. Visualization of morphological alterations in whole-mount skeleton and protein secretion and UPR activation on tissue sections is the very first step to investigate skeletal phenotypes of UPR-related mouse models. In this chapter, we introduce the major techniques that have been frequently used in our laboratory to study UPR-induced skeletal disorders with genetically modified mice and provide descriptive directions of mouse genotyping, bone tissue grossing, whole-mount skeletal staining, immunostaining assays of matrix secretion, and UPR activation.

A novel strategy for a splice-variant selective gene ablation: the example of the versican V0/V2 knockout

The complete knockout of genes that give rise to alternative splice products can often provide only an integral view of the dominant function(s) of all the isoforms they encode. If one of these isoforms is indispensable for life, a constitutive and complete inactivation may even preclude any in vivo studies of later expressed splice-variants in mice. To explore function of the tissue-restricted versican V2 isoform during central nervous system maturation, for instance, we had to circumvent the early embryonic lethality of the complete knockout by employing a novel splice-variant-specific gene ablation approach. For this purpose, we introduced a preterm translational stop codon preceded by an ER-retention signal (KDEL) into the alternatively spliced exon 7 of the VCAN gene. This way the synthesis of the V2- and the V0-forms of the proteoglycan was entirely abolished in the mutant mice, most likely mediated by a KDEL-promoted intracellular degradation of the mutant fragment and by a nonsense-mediated decay mechanism. The expression of the vitally important V1-isoform and the smallest V3-variant remained, however, unaffected. Here we provide the details of our targeting strategy, the screening procedure, the generation of isoform-specific antibodies, and the transcript analysis and we supply the experimental protocols for the biochemical and immunohistological examinations of the mutant mouse strain Vcan(tm1.1Dzim).

Development of the piggyBac transposable system for Plasmodium berghei and its application for random mutagenesis in malaria parasites

BACKGROUND

The genome of a number of species of malaria parasites (Plasmodium spp.) has been sequenced in the hope of identifying new drug and vaccine targets. However, almost one-half of predicted Plasmodium genes are annotated as hypothetical and are difficult to analyse in bulk due to the inefficiency of current reverse genetic methodologies for Plasmodium. Recently, it has been shown that the transposase piggyBac integrates at random into the genome of the human malaria parasite P. falciparum offering the possibility to develop forward genetic screens to analyse Plasmodium gene function. This study reports the development and application of the piggyBac transposition system for the rodent malaria parasite P. berghei and the evaluation of its potential as a tool in forward genetic studies. P. berghei is the most frequently used malaria parasite model in gene function analysis since phenotype screens throughout the complete Plasmodium life cycle are possible both in vitro and in vivo.

RESULTS

We demonstrate that piggyBac based gene inactivation and promoter-trapping is both easier and more efficient in P. berghei than in the human malaria parasite, P. falciparum. Random piggyBac-mediated insertion into genes was achieved after parasites were transfected with the piggyBac donor plasmid either when transposase was expressed either from a helper plasmid or a stably integrated gene in the genome. Characterization of more than 120 insertion sites demonstrated that more than 70 most likely affect gene expression classifying their protein products as non-essential for asexual blood stage development. The non-essential nature of two of these genes was confirmed by targeted gene deletion one of which encodes P41, an ortholog of a human malaria vaccine candidate. Importantly for future development of whole genome phenotypic screens the remobilization of the piggyBac element in parasites that stably express transposase was demonstrated.

CONCLUSION

These data demonstrate that piggyBac behaved as an efficient and random transposon in P. berghei. Remobilization of piggyBac element shows that with further development the piggyBac system can be an effective tool to generate random genome-wide mutation parasite libraries, for use in large-scale phenotype screens in vitro and in vivo.

Unraveling the genetics of otitis media: from mouse to human and back again

Otitis media (OM) is among the most common illnesses of early childhood, characterised by the presence of inflammation in the middle ear cavity. Acute OM and chronic OM with effusion (COME) affect the majority of children by school age and have heritability estimates of 40-70%. However, the majority of genes underlying this susceptibility are, as yet, unidentified. One method of identifying genes and pathways that may contribute to OM susceptibility is to look at mouse mutants displaying a comparable phenotype. Single-gene mouse mutants with OM have identified a number of genes, namely, Eya4, Tlr4, p73, MyD88, Fas, E2f4, Plg, Fbxo11, and Evi1, as potential and biologically relevant candidates for human disease. Recent studies suggest that this "mouse-to-human" approach is likely to yield relevant data, with significant associations reported between polymorphisms at the FBXO11, TLR4, and PAI1 genes and disease in humans. An association between TP73 and chronic rhinosinusitis has also been reported. In addition, the biobanks of available mouse mutants provide a powerful resource for functional studies of loci identified by future genome-wide association studies of OM in humans. Mouse models of OM therefore are an important component of current approaches attempting to understand the complex genetic susceptibility to OM in humans, and which aim to facilitate the development of preventative and therapeutic interventions for this important and common disease.

Inhibition of the microRNA pathway in zebrafish by siRNA

The microRNA (miRNA) pathway and the phenomenon of RNA interference (RNAi), which have both been shown to involve targeting of mRNAs by small RNA molecules, are interconnected and depend partly on the same cellular machinery. RNAi in vertebrates was first reported in zebrafish (Danio rerio) 10 years ago. However, reliable RNAi-based gene silencing techniques, based on injection of small interfering RNAs (siRNAs) into zygotes, have not been established for this important vertebrate model because of unspecific developmental defects. We have recently shown that these side effects can be attributed to inhibition of the miRNA pathway by siRNAs at early embryonic stages. This review highlights these findings and the function of microRNAs in zebrafish development.

Towards better mouse models: enhanced genotypes, systemic phenotyping and envirotype modelling

The mouse is the leading mammalian model organism for basic genetic research and for studying human diseases. Coordinated international projects are currently in progress to generate a comprehensive map of mouse gene functions - the first for any mammalian genome. There are still many challenges ahead to maximize the value of the mouse as a model, particularly for human disease. These involve generating mice that are better models of human diseases at the genotypic level, systemic (assessing all organ systems) and systematic (analysing all mouse lines) phenotyping of existing and new mouse mutant resources, and assessing the effects of the environment on phenotypes.

Cell-intrinsic signals that regulate adult neurogenesis in vivo: insights from inducible approaches

The process by which adult neural stem cells generate new and functionally integrated neurons in the adult mammalian brain has been intensely studied, but much more remains to be discovered. It is known that neural progenitors progress through distinct stages to become mature neurons, and this progression is tightly controlled by cell-cell interactions and signals in the neurogenic niche. However, less is known about the cell-intrinsic signaling required for proper progression through stages of adult neurogenesis. Techniques have recently been developed to manipulate genes specifically in adult neural stem cells and progenitors in vivo, such as the use of inducible transgenic mice and viral-mediated gene transduction. A critical mass of publications utilizing these techniques has been reached, making it timely to review which molecules are now known to play a cell-intrinsic role in regulating adult neurogenesis in vivo. By drawing attention to these isolated molecules (e.g. Notch), we hope to stimulate a broad effort to understand the complex and compelling cascades of intrinsic signaling molecules important to adult neurogenesis. Understanding this process opens the possibility of understanding brain functions subserved by neurogenesis, such as memory, and also of harnessing neural stem cells for repair of the diseased and injured brain.