Production of p53 gene knockout rats by homologous recombination in embryonic stem cells. Nature. 2010;467:211-213. [PMID: 20703227 PMCID: PMC2937076 DOI: 10.1038/nature09368]

Rat blastocyst-derived stem cells are precursors of embryonic and extraembryonic lineages

Despite recent advances in the derivation of rat embryonic stem cells, clear comprehension of the timing and mechanisms underlying rat early embryo lineage selection is lacking. We have previously shown the in vivo contribution of rat embryonic stem-like cells exclusively to developing extraembryonic tissues. To elucidate possible mechanisms governing the in vitro and in vivo behaviors of these rat blastocyst-derived stem cells, we evaluated their developmental capacity by using several approaches. Molecular marker analysis demonstrated the expression profile of genes characterizing not only pluripotency but also extraembryonic endoderm and trophoblast. In vitro differentiation through embryoid body formation showed in vitro pluripotent capacity through differentiation into derivatives of all three embryonic germ layers. Following either blastocyst injection, diploid or tetraploid aggregation, and embryo transfer, these rat blastocyst-derived stem cells also demonstrated in vivo multipotency through contribution to multiple developmentally distinct extraembryonic lineages. Features of phenotypic heterogeneity were revealed following examination of cell line morphology and culture behavior, as well as quantitative analysis of marker expression in discrete undifferentiated and differentiated populations of cells by flow cytometry. We demonstrate for the first time that stem cells derived from the rat blastocyst have the ability to contribute to the embryonic and extraembryonic lineages. Together, these results provide a valuable new model for rat stem cell biology and for the elucidation of early lineage selection in the embryo.

Using zebrafish to unravel the genetics of complex brain disorders

The zebrafish has been prominently utilized in developmental biology for the past three decades and numerous genetic tools have been developed for it. Due to the accumulated genetic knowledge the zebrafish has now been considered an excellent research tool in other disciplines of biology too, including behavioral neuroscience and behavior genetics. Given the complexity of the vertebrate brain in general and the large number of human brain disorders whose mechanisms remain mainly unmapped in particular, there is a substantial need for appropriate laboratory research organisms that may be utilized to model such diseases and facilitate the analysis of their mechanisms. The zebrafish may have a bright future in this research field. It offers a compromise between system complexity (it is a vertebrate similar in many ways to our own species) and practical simplicity (it is small, easy to keep, and it is prolific). These features have made zebrafish an excellent choice, for example, for large scale mutation and drug screening. Such approaches may have a chance to tackle the potentially large number of molecular targets and mechanisms involved in complex brain disorders. However, although promising, the zebrafish is admittedly a novel research tool and only few empirical examples exist to support this claim. In this chapter, first I briefly review some of the rapidly evolving genetic methods available for zebrafish. Second, I discuss some promising examples for how zebrafish have been used to model and analyze molecular mechanisms of complex brain disorders. Last, I present some recently developed zebrafish behavioral paradigms that may have relevance for a spectrum of complex human brain disorders including those associated with abnormalities of learning and memory, fear and anxiety, and social behavior. Although at this point co-application of the genetics and behavioral approaches is rare with zebrafish, I argue that the rapid accumulation of knowledge in both of these disciplines will make zebrafish a prominent research tool for the genetic analysis of complex brain disorders.

At last - rats lacking B cells

The rat model is a widely used animal model in research, its popularity perhaps only surpassed by the mouse model. Rats are the preferred models for the study of transplantation and certain tumor and autoimmune diseases. In particular, the understanding of cardiovascular-related diseases and chronic inflammation has depended widely on the rat, from which models for both multiple sclerosis and rheumatoid arthritis have been derived. Until now, research in the rat has been hampered by a lack of precise gene-targeting technology in this model. This limitation, however, is rapidly changing; a recent example is the availability of B-cell-deficient rat strains obtained by the newly established zinc finger nucleases-targeting technology. As described in this issue of the European Journal of Immunology, genetic targeting of the rat, for example, using zinc finger nucleases-targeting technology, is likely to rapidly drive progress in the understanding of not only B-cell biology but also in the general understanding of rat disease models.

Targeted integration in rat and mouse embryos with zinc-finger nucleases

Gene targeting is indispensible for reverse genetics and the generation of animal models of disease. The mouse has become the most commonly used animal model system owing to the success of embryonic stem cell-based targeting technology, whereas other mammalian species lack convenient tools for genome modification. Recently, microinjection of engineered zinc-finger nucleases (ZFNs) in embryos was used to generate gene knockouts in the rat and the mouse by introducing nonhomologous end joining (NHEJ)-mediated deletions or insertions at the target site. Here we use ZFN technology in embryos to introduce sequence-specific modifications (knock-ins) by means of homologous recombination in Sprague Dawley and Long-Evans hooded rats and FVB mice. This approach enables precise genome engineering to generate modifications such as point mutations, accurate insertions and deletions, and conditional knockouts and knock-ins. The same strategy can potentially be applied to many other species for which genetic engineering tools are needed.

Neurogenetics: advancing the "next-generation" of brain research

There can be little doubt that genetics has transformed our understanding of mechanisms mediating brain disorders. The last two decades have brought tremendous progress in terms of accurate molecular diagnoses and knowledge of the genes and pathways that are involved in a large number of neurological and psychiatric disorders. Likewise, new methods and analytical approaches, including genome array studies and "next-generation" sequencing technologies, are bringing us deeper insights into the subtle complexities of the genetic architecture that determines our risks for these disorders. As we now seek to translate these discoveries back to clinical applications, a major challenge for the field will be in bridging the gap between genes and biology. In this Overview of Neuron's special review issue on neurogenetics, we reflect on progress made over the last two decades and highlight the challenges as well as the exciting opportunities for the future.

Gene targeting in the rat: advances and opportunities

The rat has long been a model favored by physiologists, pharmacologists and neuroscientists. However, over the past two decades, many investigators in these fields have turned to the mouse because of its gene modification technologies and extensive genomic resources. Although the genomic resources of the rat have nearly caught up, gene targeting has lagged far behind, limiting the value of the rat for many investigators. In the past two years, advances in transposon- and zinc finger nuclease (ZFN)-mediated gene knockout as well as the establishment and culturing of embryonic and inducible pluripotent stem cells have created new opportunities for rat genetic research. Here, we provide a high-level description and the potential uses of these new technologies for investigators using the rat for biomedical research.

Rat traps: filling the toolbox for manipulating the rat genome

The laboratory rat is rapidly gaining momentum as a mammalian genetic model organism. Although traditional forward genetic approaches are well established, recent technological developments have enabled efficient gene targeting and mutant generation. Here we outline the current status, possibilities and application of these techniques in the rat.