Psychiatry has proven to be among the least penetrable clinical disciplines for the development of satisfactory in vivo model systems for evaluating novel treatment approaches. However, mood and anxiety disorders remain poorly understood and inadequately treated. With the explosion in the use of genetically modified mice, enormous research efforts have been focused on developing mouse models of psychiatric disorders. The success of this approach is largely contingent on the usefulness of available behavioural models of depression- and anxiety-related behaviours in mice. Here, we assess the current status of research into developing appropriate tests for assessing such behaviours.

The ascent of mouse: advances in modelling human depression and anxiety.

During the past decade, the molecular mechanisms underlying the mammalian circadian clock have been defined. A core set of circadian clock genes common to most cells throughout the body code for proteins that feed back to regulate not only their own expression, but also that of clock output genes and pathways throughout the genome. The circadian system represents a complex multioscillatory temporal network in which an ensemble of coupled neurons comprising the principal circadian pacemaker in the suprachiasmatic nucleus of the hypothalamus is entrained to the daily light/dark cycle and subsequently transmits synchronizing signals to local circadian oscillators in peripheral tissues. Only recently has the importance of this system to the regulation of such fundamental biological processes as the cell cycle and metabolism become apparent. A convergence of data from microarray studies, quantitative trait locus analysis, and mutagenesis screens demonstrates the pervasiveness of circadian regulation in biological systems. The importance of maintaining the internal temporal homeostasis conferred by the circadian system is revealed by animal models in which mutations in genes coding for core components of the clock result in disease, including cancer and disturbances to the sleep/wake cycle.

/pdf/mammalian-circadian-biology-elucidating-genome-wide-levels-5fs9zyaexz.pdf

Mammalian circadian biology: elucidating genome-wide levels of temporal organization.

https://www.cell.com/developmental-cell/pdf/S1534-5807(03)00399-X.pdf

Talking about a Revolution: The Impact of Site-Specific Recombinases on Genetic Analyses in Mice

Classical genetic methods, driven by phenotype rather than hypotheses, generally permit the identification of all proteins that serve nonredundant functions in a defined biological process. Long before this goal is achieved, and sometimes at the very outset, genetics may cut to the heart of a biological puzzle. So it was in the field of mammalian innate immunity. The positional cloning of a spontaneous mutation that caused lipopolysaccharide resistance and susceptibility to Gram-negative infection led directly to the understanding that Toll-like receptors (TLRs) are essential sensors of microbial infection. Other mutations, induced by the random germ line mutagen ENU (N-ethyl-N-nitrosourea), have disclosed key molecules in the TLR signaling pathways and helped us to construct a reasonably sophisticated portrait of the afferent innate immune response. A still broader genetic screen--one that detects all mutations that compromise survival during infection--is permitting fresh insight into the number and types of proteins that mammals use to defend themselves against microbes.

Genetic analysis of host resistance: Toll-like receptor signaling and immunity at large

In the post-genome era, the mouse will have a major role as a model system for functional genome analysis. This requires a large number of mutants similar to the collections available from other model organisms such as Drosophila melanogaster and Caenorhabditis elegans. Here we report on a systematic, genome-wide, mutagenesis screen in mice. As part of the German Human Genome Project, we have undertaken a large-scale ENU-mutagenesis screen for dominant mutations and a limited screen for recessive mutations1. In screening over 14,000 mice for a large number of clinically relevant parameters, we recovered 182 mouse mutants for a variety of phenotypes. In addition, 247 variant mouse mutants are currently in genetic confirmation testing and will result in additional new mutant lines. This mutagenesis screen, along with the screen described in the accompanying paper2, leads to a significant increase in the number of mouse models3 available to the scientific community. Our mutant lines are freely accessible to non-commercial users (for information, see http://www.gsf.de/ieg/groups/enu-mouse.html
 ).

Genome-wide, large-scale production of mutant mice by ENU mutagenesis

The progress of human genome sequencing is driving genetic approaches to define gene function. Strategies such as gene traps and chemical mutagenesis will soon generate a large mutant mouse resource. Point mutations induced by N -ethyl- N -nitrosourea (ENU) provide a unique mutant resource because they: (i) reflect the consequences of single gene change independent of position effects; (ii) provide a fine-structure dissection of protein function; (iii) display a range of mutant effects from complete or partial loss of function to exaggerated function; and (iv) discover gene functions in an unbiased manner. Phenotype-driven ENU screens in the mouse are emphasizing relevance to human clinical disease by targeting cardiology, physiology, neurology, immunity, hematopoiesis and mammalian development. Such approaches are extremely powerful in understanding complex human diseases and traits: the base-pair changes may accurately model base changes found in human diseases, and subtle mutant alleles in a standard genetic background provide the ability to analyze the consequences of compound genotypes. Ongoing mouse ENU mutagenesis experiments are generating a treasure trove of new mutations to allow an in-depth study of a single gene, a chromosomal region or a biological system.

Mouse ENU Mutagenesis

The mouse mutant quaking
 viable
 (qk
 v
 ) has been studied for almost four decades as a model for dysmyelination of the central nervous system (CNS). The genetic lesion associated with the qk
 v
 phenotype is a large deletion of approximately 1 Megabase on mouse Chromosome (Chr) 17. This deficiency alters the expression of transcripts from the qkI locus in oligodendrocytes, resulting in improper myelination of the CNS in animals homozygous for the deletion. To determine whether other genes within the deletion contribute to the quaking
 viable
 phenotype, we physically mapped and sequenced the deleted interval. We determined that the mouse Parkin gene, as well as the Parkin co-regulated gene (Pacrg), lies within the qk
 v
 deletion. We determined that qk
 v
 mutants completely lack the expression of the Parkin gene product. Loss-of-function mutations in the human PARKIN gene cause autosomal juvenile Parkinson’s disease (AR-JP). Our studies show that the deletion of Parkin in qk
 v
 brains does not result in the loss of dopaminergic neurons typical of AR-JP patients. Also, α-synuclein, a target of Parkin-dependent ubiquitination, does not accumulate in qk
 v
 mutant brains. Despite the lack of AR-JP-like neuropathology in qk
 v
 mice, this mutant may constitute a readily available model for the study of the cellular function of Parkin. This is the first report of a gene distinct from qkI affected by the qk
 v
 deletion. The discovery of the multigenic nature of this classical mouse mutation calls for the re-evaluation of its phenotypic characterization.

Janice K. Noveroske

Papers

Mouse ENU Mutagenesis

The neurological mutant quaking(viable) is Parkin deficient.