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Using modern DNA engineering techniques, geneticists are now able to precisely alter the genomic structure of domestic animals and, in order to describe these kinds of changes, it has become common to speak of " gene or genomic editing". In most cases these genomic changes result in more or less significant changes in the phenotypes, which is why the subject is of interest to the veterinary community and many other professions in the rural world. However, while this new approach certainly opens up interesting perspectives, it is also controversial. Based on published examples, this review presents an inventory of how the genomic structure of domestic mammals can be modified and discusses the value of such a venture. The last part is a plea to urge legislators, especially European ones, to review in the light of recent data the orders and laws, which have been in force concerning genomic edition for now over twenty years. The current status quo has become difficult to accept., En utilisant les techniques modernes d''ingénierie de l''ADN, les généticiens sont aujourd''hui capables de modifier précisément la structure du génome des animaux domestiques et, pour qualifier ce genre de modifications, il est désormais convenu de parler " d''édition génique" ou " d''édition génomique". Dans la plupart des cas ces modifications se traduisent par des modifications plus ou moins importantes du phénotype : c''est pourquoi le sujet intéresse la profession vétérinaire et beaucoup d''autres professions du monde rural. Cependant, si cette nouvelle approche ouvre assurément des perspectives nouvelles et intéressantes, elle soulève aussi des controverses. Sur la base d''exemples publiés, cette revue présente un inventaire des moyens utilisables pour modifier la structure du génome des mammifères domestiques et discute l''intérêt d''une telle entreprise. La dernière partie est un plaidoyer pour inciter les législateurs, notamment européens, à reconsidérer les directives en vigueur, depuis plus de vingt ans, à la lumière de données récentes. Le statu quo actuel est devenu difficilement acceptable, Guénet Jean-Louis. L'édition génomique des animaux domestiques : quels enjeux et quel avenir ?. In: Bulletin de l'Académie Vétérinaire de France tome 174, 2021. pp. 167-179.

International audience; Here we describe a spontaneous mutation in the Zdhhc13 (zinc finger, DHHC domain containing 13) gene (also called Hip14l), one of 24 genes encoding palmitoyl acyltransferase (PAT) enzymes in the mouse. This mutation (Zdhhc13luc) was identified as a nonsense base substitution, which results in a premature stop codon that generates a truncated form of the ZDHHC13 protein, representing a potential loss-of-function allele. Homozygous Zdhhc13luc/Zdhhc13luc mice developed generalized hypotrichosis, associated with abnormal hair cycle, epidermal and sebaceous gland hyperplasia, hyperkeratosis, and increased epidermal thickness. Increased keratinocyte proliferation and accelerated transit from basal to more differentiated layers were observed in mutant compared with wild-type (WT) epidermis in untreated skin and after short-term 12-O-tetradecanoyl-phorbol-13-acetate treatment and acute UVB exposure. Interestingly, this epidermal phenotype was associated with constitutive activation of NF-κB (RelA) and increased neutrophil recruitment and elastase activity. Furthermore, tumor multiplicity and malignant progression of papillomas after chemical skin carcinogenesis were significantly higher in mutant mice than WT littermates. To our knowledge, this is the first report of a protective role for PAT in skin carcinogenesis.

International audience; Ion channel-controlled cell volume regulation is of fundamental significance to the physiological function of sperm. In addition to volume regulation, LRRC8A-dependent volume-regulated anion channel (VRAC) activity is involved in cell cycle progression, insulin signaling, and cisplatin resistance. Nevertheless, the contribution of LRRC8A and its dependent VRAC activity in the germ cell lineage remain unknown. By utilizing a spontaneous Lrrc8a mouse mutation (c.1325delTG, p.F443*) and genetically engineered mouse models, we demonstrate that LRRC8A-dependent VRAC activity is essential for male germ cell development and fertility. Lrrc8a-null male germ cells undergo progressive degeneration independent of the apoptotic pathway during postnatal testicular development. Lrrc8a-deficient mouse sperm exhibit multiple morphological abnormalities of the flagella (MMAF), a feature commonly observed in the sperm of infertile human patients. Importantly, we identified a human patient with a rare LRRC8A hypomorphic mutation (c.1634G>A, p.Arg545His) possibly linked to Sertoli cell-only syndrome (SCOS), a male sterility disorder characterized by the loss of germ cells. Thus, LRRC8A is a critical factor required for germ cell development and volume regulation in the mouse, and it might serve as a novel diagnostic and therapeutic target for SCOS patients.

G protein–coupled receptor 84 (GPR84) is a 7-transmembrane protein expressed on myeloid cells that can bind to medium-chain free fatty acids in vitro. Here, we report the discovery of a 2-bp frameshift deletion in the second exon of the Gpr84 gene in several classical mouse inbred strains. This deletion generates a premature stop codon predicted to result in a truncated protein lacking the transmembrane domains 4-7. We sequenced Gpr84 exon 2 from 58 strains representing different groups in the mouse family tree and found that 14 strains are homozygous for the deletion. Some of these strains are DBA/1J, DBA/2J, FVB/NJ, LG/J, MRL/MpJ, NOD/LtJ, and SJL/J. However, the deletion was not found in any of the wild-derived inbred strains analyzed. Haplotype analysis suggested that the deletion originates from a unique mutation event that occurred more than 100 years ago, preceding the development of the first inbred strain (DBA), from a Mus musculus domesticus source. As GPR84 ostensibly plays a role in the biology of myeloid cells, it could be relevant 1) to consider the existence of this Gpr84 nonsense mutation in several mouse strains when choosing a mouse model to study immune processes and 2) to consider reevaluating data obtained using such strains.

A mutation in the HERC2 gene has been linked to a severe neurodevelopmental disorder with similarities to the Angelman syndrome. This gene codifies a protein with ubiquitin ligase activity that regulates the activity of tumor protein p53 and is involved in important cellular processes such as DNA repair, cell cycle, cancer, and iron metabolism. Despite the critical role of HERC2 in these physiological and pathological processes, little is known about its relevance in vivo. Here, we described a mouse with targeted inactivation of the Herc2 gene. Homozygous mice were not viable. Distinct from other ubiquitin ligases that interact with p53, such as MDM2 or MDM4, p53 depletion did not rescue the lethality of homozygous mice. The HERC2 protein levels were reduced by approximately one-half in heterozygous mice. Consequently, HERC2 activities, including ubiquitin ligase and stimulation of p53 activity, were lower in heterozygous mice. A decrease in HERC2 activities was also observed in human skin fibroblasts from individuals with an Angelman-like syndrome that express an unstable mutant protein of HERC2. Behavioural analysis of heterozygous mice identified an impaired motor synchronization with normal neuromuscular function. This effect was not observed in p53 knockout mice, indicating that a mechanism independent of p53 activity is involved. Morphological analysis showed the presence of HERC2 in Purkinje cells and a specific loss of these neurons in the cerebella of heterozygous mice. In these animals, an increase of autophagosomes and lysosomes was observed. Our findings establish a crucial role of HERC2 in embryonic development and motor coordination.

International audience; Susceptibility of inbred strains to infection with West Nile virus (WNV) has been genetically associated with an arginine-to-a nonsense codon substitution at position 253 (R253X) in the predicted sequence of the murine 2',5'-oligoadenylate synthetase 1B (OAS1B) protein. We introduced by transgenesis the Oas1b cDNA from MBT/Pas mice carrying the R253 codon (Oas1b(MBT)) into BALB/c mice homozygous for the X253 allele (Oas1b(BALB/c)). Overexpression of Oas1b(MBT) mRNA in the brain of transgenic mice prior and in the time course of infection provided protection against the neuroinvasive WNV strain IS-98-ST1. A 200-fold induction of Oas1b(MBT) mRNA in the brain of congenic BALB/c mice homozygous for a MBT/Pas segment encompassing the Oas1b gene was also efficient in reducing both viral growth and mortality, whereas a 200-fold induction of Oas1b(BALB/c) mRNA was unable to prevent virally-induced encephalitis, confirming the critical role of the R253X mutation on Oas1b activity in live mice.

With the advances in molecular genetics, animal models of human diseases are becoming more numerous and more refined every year. Despite this, one must recognize that they generally do not faithfully and comprehensively mimic the homologous human disease. Faced with these imperfections, some geneticists believe that these models are of little value, while for others, on the contrary, they are important tools. We agree with this second statement, and in this review, we examine the reasons that may explain the observed differences and suggest means to circumvent or even exploit them. Our opinion is that animal models should be regarded more as tools capable of answering specific questions rather than mere replicas, at a smaller scale, of a given human disease. Far from disappointing they are probably called for a promising future.

Le rat et la souris sont, depuis deja longtemps, des modeles de choix pour l’etude de la biologie des mammiferes : faciles d’entretien, ils offrent aussi toute une panoplie de lignees genetiquement pures et de mutants bien caracterises. Bien que longtemps prefere a la souris en raison de sa taille et de sa physiologie, le rat a progressivement ete delaisse au profit de la souris, espece chez laquelle les techniques de mutagenese dirigee alimentent depuis plus de vingt ans le repertoire des modeles d’etudes. Aujourd’hui, deux avancees techniques devraient changer la donne : l’utilisation de nucleases artificielles a doigts de zinc pour inactiver un gene d’interet des les premiers stades du developpement et la derivation et la manipulation genetique de cellules ES (embryonic stem cells ) de rat. Nul doute que les annees qui viennent verront se multiplier les modeles de maladies humaines etablies chez le rat.

International audience; Citrullinemia type I (CTLN1, OMIM# 215700) is an inherited urea cycle disorder that is caused by an argininosuccinate synthetase (ASS) enzyme deficiency. In this report, we describe two spontaneous hypomorphic alleles of the mouse Ass1 gene that serve as an animal model of CTLN1. These two independent mouse mutant alleles, also described in patients affected with CTLN1, interact to produce a range of phenotypes. While some mutant mice died within the first week after birth, others survived but showed severe retardation during postnatal development as well as alopecia, lethargy, and ataxia. Notable pathological findings were similar to findings in human CTLN1 patients and included citrullinemia and hyperammonemia along with delayed cerebellar development, epidermal hyperkeratosis, and follicular dystrophy. Standard treatments for CTLN1 were effective in rescuing the phenotype of these mutant mice. Based on our studies, we propose that defective cerebellar granule cell migration secondary to disorganization of Bergmann glial cell fibers cause cerebellar developmental delay in the hyperammonemic and citrullinemic brain, pointing to a possible role for nitric oxide in these processes. These mouse mutations constitute a suitable model for both mechanistic and preclinical studies of CTLN1 and other hyperammonemic encephalopathies and, at the same time, underscore the importance of complementing knockout mutations with hypomorphic mutations for the generation of animal models of human genetic diseases.

Using an inter-specific subcongenic strain, Nested Recombinant Haplotype 3 (NRH3), generated between two mouse strains showing extreme differences in γ-radiation-induced thymic lymphoma susceptibility (SEG/Pas and C57BL/6J), we have identified a critical region on chromosome 19 that regulates survival of mice suffering from T-cell lymphoblastic lymphomas. Mapped on this region, the gene encoding the Cd274 ligand is able to trigger an inhibitory effect that modulates T-cell receptor (TCR) signalling and affects thymocyte maturation. Interestingly, this gene shows differential expression between thymic stromal cells from both strains in early response to a single sublethal γ-ray dose, but is inhibited in T-cell lymphoblastic lymphomas. Furthermore, we have identified several polymorphisms in the complementary DNA sequence of this gene that affect the affinity for its Cd279 receptor and are able to induce a differential rate of thymocyte apoptosis. Taken together, our data are consistent with Cd274 acting as a genetic modifier that influences the survival of γ-radiation-induced T-cell lymphoma-bearing mice. The data similarly support the idea of a co-evolution of tumour cells and associated stromal cells to generate a favourable microenvironment for T-cell lymphoma growth.

Cancer susceptibility is essentially attributable to multiple low-penetrance genes. Using interspecific consomic and congenic mice between the tumour-resistant SEG/Pas and the tumour-sensitive C57BL/6J strains, a region on chromosome 19 involved in the genetic resistance to γ-irradiation-induced T-cell lymphomas (Tlyr1) has been identified. Through the development of non-overlapping sub-congenic strains, it has been further demonstrated that Anxa1 may be a candidate resistance gene on the basis of its differential expression in thymus stroma cells after γ-radiation exposure. In addition, thymus-stroma cells of thymic lymphomas exhibited a significant reduction in the expression levels of Anxa1. Interestingly, the activity of Anxa1 relies on prostaglandin E2 (PGE2) induction that brings about apoptosis in thymocytes. In fact, in vitro transfection experiments revealed that PGE2 production was enhanced when HEK 293 cells were transfected with full-length cDNAs of Anxa1, with PGE2 production in the cells transfected with the allele of the resistant strain (Anxa1Tyr) being higher than that in cells transfected with the allele of the susceptible strain (Anxa1Phe). Furthermore, the presence of this compound in the medium induced apoptosis of immature CD4+CD8+CD3low cells in a dose-dependent manner. These results improve our knowledge of the molecular mechanisms triggering T-cell lymphoblastic lymphoma development, while highlighting the relevance of the stroma in controlling genetic susceptibility, and the use of PGE2 as a new therapeutic approach in T-cell haematogical malignancies., The work was supported by the European Commission contract number FI6R-CT-2003- 508842 to JS and by the Spanish Ministry of Education and Science contract number SAF-2006-09437 to JFP.

The recessive mutation oligotriche (olt) affects the coat and male fertility in the mouse. In homozygous (olt/olt) mutants, the coat is sparse, most notably in the inguinal and medial femoral region. In these regions, almost all hair shafts are bent and distorted in their course through the dermis and rarely penetrate the epidermis because the hair cortex is not fully keratinized. During hair follicle morphogenesis, mutant hair follicles exit from anagen one day before those of normal littermates and show a prolongation of the catagen stage. The oligotriche (olt) locus was mapped to distal chromosome 9 within a 5-Mbp interval distal to D9Mit279. Analysis of candidate gene expression revealed that olt/olt mutant mice do not express functional phospholipase C delta 1 (Plcd1) mRNA. This deficiency is the consequence of a 234-kbp deletion involving not only the Plcd1 locus but also the chromosomal segment harboring the genes Vill (villin-like), Dlec1 (deleted in lung and esophageal cancer 1), Acaa1b (acetyl-Coenzyme A acyltransferase 1B, synonym thiolase B), and parts of the genes Ctdspl (carboxy-terminal domain RNA polymerase II polypeptide A small phosphatase-like) and Slc22a14 (solute carrier family 22 member 14). Offspring of olt/olt females, mated with Plcd1 ( -/- ) knockout males, exhibit coat defects similar to those observed in homozygous olt/olt mutant mice but the spermiogenesis in male offspring is normal. We conclude that the 234-kbp deletion from chromosome 9 harbors a gene involved in spermiogenesis and we propose that the oligotriche mutant be used as a model for the study of the putative tumor suppressor genes Dlec1, Ctdspl, and Vill. We also suggest that the oligotriche locus be named Del(9Ctdspl-Slc22a14)1Pas.

Inbred SPRET/Ei mice, derived from Mus spretus, were found to be extremely resistant to infection with a mouse adapted influenza A virus. The resistance was strongly linked to distal chromosome 16, where the interferon-inducible Mx1 gene is located. This gene encodes for the Mx1 protein which stimulates innate immunity to Orthomyxoviruses. The Mx1 gene is defective in most inbred mouse strains, but PCR revealed that SPRET/Ei carries a functional allele. The Mx1 proteins of M. spretus and A2G, the other major resistant strain derived from Mus musculus, share 95.7% identity. We were interested whether the sequence variations between the two Mx1 alleles have functional significance. To address this, we used congenic mouse strains containing the Mx1 gene from M. spretus or A2G in a C57BL/6 background. Using a highly pathogenic influenza virus strain, we found that the B6.spretus-Mx1 congenic mice were better protected against infection than the B6.A2G-Mx1 mice. This effect may be due to different Mx1 induction levels, as was shown by RT-PCR and Western blot. We conclude that SPRET/Ei is a novel Mx1-positive inbred strain useful to study the biology of Mx1.

Lipids play major biological roles as components of cell membranes (Vance and Vance, 1991). They are involved in cell proliferation, differentiation and survival (Cutler and Mattson, 2001). Impairment of lipid functions has direct consequences on cell functions, as demonstrated by nutritional and genetic pathologies related to lipid metabolism. As components of the extracellular matrix (ECM) of mineralized tissues, lipids have been far less studied. Their presence is now well recognized, but their role in biological and pathological mineralizations is far from being elucidated. The total lipid content of bones has been reported to range from 1–10%. In dental tissues, the total lipid content is 0.26–0.36% in dentin, 0.014% of which are phospholipids, and 0.60% in enamel, among which 12.5% are phospholipids (0.075% of total enamel) (see for review Goldberg and Boskey, 1996). Compared with the major dentin ECM components, namely the phosphorylated proteins of the SIBLING family, lipids appear as minor components. Due to the low ratio between lipids and the total ECM molecules and to the fact that the major part of the lipid fraction is lost after routine fixation and processing for light and electron microscopy, they have been less investigated than other matrix components easier to preserve and analyze.

In this article we describe the main characteristics and peculiarities of the different strains and stocks of laboratory animals from the genetic point of view. We explain how they are produced and maintained as well as their advantages and disadvantages in the context of animal experiments. We also provide some guidance to make the best possible choice when establishing an experimental protocol. Curr. Protoc. Mouse Biol. 1:213-238. © 2011 by John WileySons, Inc.

International audience; Mary F. Lyon est décédée le jour de Noël 2014, au terme d'une carrière scientifique exceptionnelle à la fois par sa longueur (plus d'un demi-siècle) et par sa qualité. Elle restera universellement connue pour avoir, la première, émis l'hypothèse qu'un seul chromosome X est exprimé dans les cellules somatiques des femelles de mammifères, tandis que l'autre est fonctionnellement inactivé grâce à un mécanisme intervenant au cours du développement embryonnaire et qui permet d'équilibrer le dosage génique X/autosomes. Cette hypothèse, formulée en 1961, annonçait la découverte, plus récente, d'un mécanisme épigénétique plus général de régulation de l'expression de nombreux gènes chez les mammifères.

When compared to other model organisms whose genome is sequenced, the number of mutations identified in the mouse appears extremely reduced and this situation seriously hampers our understanding of mammalian gene function(s). Another important consequence of this shortage is that a majority of human genetic diseases still await an animal model. To improve the situation, two strategies are currently used: the first makes use of embryonic stem cells, in which one can induce knockout mutations almost at will; the second consists of a genome-wide random chemical mutagenesis, followed by screening for mutant phenotypes and subsequent identification of the genetic alteration(s). Several projects are now in progress making use of one or the other of these strategies. Here, we report an original effort where we mutagenized BALB/c males, with the mutagen ethylnitrosourea. Offspring of these males were screened for dominant mutations and a three-generation breeding protocol was set to recover recessive mutations. Eleven mutations were identified (one dominant and ten recessives). Three of these mutations are new alleles (Otop1mlh, Foxn1sepe and probably rodador) at loci where mutations have already been reported, while 4 are new and original alleles (carc, eqlb, frqz, and Sacc). This result indicates that the mouse genome, as expected, is far from being saturated with mutations. More mutations would certainly be discovered using more sophisticated phenotyping protocols. Seven of the 11 new mutant alleles induced in our experiment have been localized on the genetic map as a first step towards positional cloning.

Although recent progress in identifying genes involved in deafness has been remarkable, the genetic basis of progressive hearing loss (or age-related hearing loss) is poorly understood because of the extreme difficulty in studying such a late-onset, complex disease in human populations. Several inbred strains of mice such as 129P1/ReJ, C57BL/6J, DBA/2J, and BALB/cByJ have been reported to exhibit age-related hearing loss and provide valuable models for human nonsyndromic progressive deafness. In this article we show that 101/H mice also exhibit progressive deafness with early onset. Linkage analysis of F(2) populations derived from crosses between the 101/H and the MAI/Pas and MBT/Pas wild-derived mice suggested at least two major quantitative trait loci (QTLs) that influence progressive hearing loss. A first QTL, designated Phl1, was mapped with a maximum LOD score of 6.7 to the centromeric region of Chromosome 17, where no deafness-related QTL has been mapped so far. A second QTL, designated Phl2, mapped to Chromosome 10 and exhibited a maximum LOD score of 5.3. The map position of Phl2 near the well-known QTL of age-related hearing loss (Ahl) suggested the possibility of allelism, although the Ahl mutation itself did not segregate in these crosses. Finally, we found some evidence of epistatic interaction between Phl1 and Phl2.

CMV can cause life-threatening disease in immunodeficient hosts. Experimental infection in mice has revealed that the genetically determined natural resistance to murine CMV (MCMV) may be mediated either by direct recognition between the NK receptor Ly49H and the pathogen-encoded glycoprotein m157 or by epistatic interaction between Ly49P and the host MHC H-2Dk. Using stocks of wild-derived inbred mice as a source of genetic diversity, we found that PWK/Pas (PWK) mice were naturally resistant to MCMV. Depletion of NK cells subverted the resistance. Analysis of backcrosses to susceptible BALB/c mice revealed that the phenotype was controlled by a major dominant locus effect linked to the NK gene complex. Haplotype analysis of 41 polymorphic markers in the Ly49h region suggested that PWK mice may share a common ancestral origin with C57BL/6 mice; in the latter, MCMV resistance is dependent on Ly49H-m157 interactions. Nevertheless, PWK mice retained viral resistance against m157-defective mutant MCMV. These results demonstrate the presence of yet another NK cell-dependent viral resistance mechanism, named Cmv4, which most likely encodes for a new NK activating receptor. Identification of Cmv4 will expand our understanding of the specificity of the innate recognition of infection by NK cells.

The 2',5'-oligoadenylate synthetase (OAS) proteins associated with endoribonuclease RNase L are components of the interferon-regulated OAS/RNase L system, which is an RNA decay pathway known to play an important role in the innate antiviral immunity. A large body of evidence suggests a critical role for the 1b isoform of the mouse Oas gene (Oas1b) in resistance to West Nile virus (WNV) infection in vivo. WNV is a positive, single-stranded RNA virus responsible for severe encephalitis in a large range of animal species and humans. To investigate the molecular basis for the sensitivity of WNV to the Oas1b antiviral pathway, we established a stable mouse fibroblastic cell clone that up-regulates Oas1b protein expression under the control of the Tet-Off expression system. We showed that murine cells respond to Oas1b expression by efficiently inhibiting WNV replication. The antiviral action of Oas1b was essentially restricted to the early stages in virus life cycle. We found that the inability of WNV to productively infect the Oas1b-expressing cells was attributable to a dramatic reduction in positive-stranded viral RNA level. Thus, Oas1b represents an antiviral pathway that exerts its inhibitory effect on WNV replication by preventing viral RNA accumulation inside infected cells.

The house mouse has been used as a privileged model organism since the early days of genetics, and the numerous experiments made with this small mammal have regularly contributed to enrich our knowledge of mammalian biology and pathology, ranging from embryonic development to metabolic disease, histocompatibility, immunology, behavior, and cancer. Over the past two decades, a number of large-scale integrated and concerted projects have been undertaken that will probably open a new era in the genetics of the species. The sequencing of the genome, which will allow researchers to make comparisons with other mammals and identify regions conserved by evolution, is probably the most important project, but many other initiatives, such as the massive production of point or chromosomal mutations associated with comprehensive and standardized phenotyping of the mutant phenotypes, will help annotation of the ∼25,000 genes packed in the mouse genome. In the same way, and as another consequence of the sequencing, the discovery of many single nucleotide polymorphisms and the development of new tools and resources, like the Collaborative Cross, will contribute to the development of modern quantitative genetics. It is clear that mouse genetics has changed dramatically over the last 10-15 years and its future looks promising.

Summary Our objective was to study the teeth of a mutant mice fro/fro that display severe forms of osteogenesis imperfecta . One day and 8 week-old fro/fro and +/ fro heterozygote mice (wild type, WT) were processed for light and scanning electron microscopy. The genetic defect, shown to be located on chromosome 8, induced alveolar bone and teeth hypomineralisation. Due to defective cell proliferation in the fro/fro, the distal growth of the mandibular incisors was impaired. Immunolabelling revealed an increase of chondroitin/dermatan sulphate, whereas no difference was detected in dental tissues for decorin and biglycan. Amelogenin expression was decreased in the incisor and enhanced in the molar. Dentin sialoprotein was below the level of detection in the fro/fro , whereas osteonectin and osteopontin were unchanged. The main target of the mutation was seen in the lingual part of the incisor near the apex where dentine formation was delayed. In the molars, bulbous roots with obliteration of the pulp chamber were seen. In the TGFβ1 overexpressing mice, the lingual root-analogue part of the incisor was missing. In the molar, short roots, circumpulpal dentine of the osteodentine type and pulp obliteration were seen. It may be noted that, although the mutant and transgenic strains mutations are two different genetic alterations not related to the same defective gene, in both cases the expression of the dentin sialoprotein is altered. Altogether, the present data suggest that the lingual forming part of the incisor seems to be an anatomical entity bearing its own biological specificities.

Laboratory mice often exhibit wide differences in susceptibility when infected experimentally with viruses. Based on such observations, experiments have been designed to investigate the determinism of these differences at the molecular level, and a few genes that play a major role in the innate mechanisms of defence of the species toward viral aggressions have been characterised. For example, the extraordinary resistance of SJL mice to experimental infections with hepatitis virus strain A59 is the consequence of a structural alteration of a cell adhesion molecule which normally binds to the spikes of the virus, allowing its entry into the cells. If the virus cannot bind to the molecule, or if the molecule is absent, epithelial cells of the intestine and liver are not infected and mice are resistant. In the same way, most — not to say all — laboratory strains of mice are susceptible to infections with orthomyxoviruses or flaviviruses because essential molecules, the synthesis of which is normally triggered by interferon, are defective in these mice. Wild mice, by contrast — probably because they are constantly exposed to natural infections — are resistant. Finally, some mouse strains resist experimental infections by the mouse cytomegalovirus 1 (MCMV-1) because, once infected, these mice synthesise a molecule at the surface of infected cells which allows immediate recognition and killing by natural killer (NK) cells. With the exuberant development of mouse genetics and the constant generation of new mutant alleles, it is likely that many more genes with an impact on the phenotype of resistance or susceptibility will be identified in the forthcoming years. These genes are probably numerous, however, and many of them presumably interact with each other and/or have additive effects. This might slow down progress in our understanding of the innate mechanism of defence.

Pluridigite ( Pdt) is a semi-dominant mutation obtained after a mutagenesis experiment with ethyl-nitroso-urea (ENU). The mutant exhibits abnormal skeletal pattern formation characterized by the formation of extra digits (polydactyly) in the preaxial (anterior) part of the hindlimbs. The phenotype shows incomplete penetrance, depending on the genetic background. In an F2 cross with C57BL/6, the phenotype could not be associated with a single locus. Strong linkage was observed with markers located on Chromosome (Chr) 12, in a 2-cM interval between D12Mit136 and D12Mit153. This region contains the Twist gene, and we show that the [Pdt] phenotype is dependent upon a new allele of Twist. We further identified that the whole Chr 4 is associated with the [Pdt] phenotype. The Pluridigite phenotype thus results from the combination of a Twist mutant allele and at least two additional loci.

2',5'-Oligoadenylate synthetases (2',5'-OASs) are interferon-inducible enzymes. Some of these proteins play an important role in cellular physiology, in particular, in the innate defense mechanisms against RNA virus infections. In the present publication we report the complete genomic structure of the cluster of genes encoding mouse 2',5'-OAS, with all its transcription units, their predicted functions, and their evolutionary relationships. We found that mouse Oas2/Oas3 genes have a genomic structure similar to that of human OAS2/OAS3, while the mouse equivalent of human OAS1 is composed of eight (Oas1a to Oas1h) tandemly arranged transcription units. For all these eight genes a specific inducible promoter controls transcription. The possible functions of this family of proteins are discussed.

Over the past 7 years, West Nile zoonosis has been an emerging concern for public health in Europe, Middle East and more recently in North America. West Nile virus causes epidemic outbreaks in humans and infected patients may exhibit severe neurological symptoms. Because susceptibility and sensitivity to West Nile virus infections may depend on host genetic factors, a mouse model has been established to investigate the genetic determinism of host susceptibility to West Nile virus. A nonsense mutation in gene encoding the 1b isoform of the 2'-5'oligoadenylate synthetase (OAS1b) was constantly associated with the susceptibility of mouse strains to experimental West Nile virus infection. Oligoadenylate synthetase are interferon-inducible proteins playing a role in the endogeneous antiviral pathway. It was of interest to establish whether interferon-alpha and OAS 1B were sufficient to mediate resistance to West Nile virus infection. In the present study, we showed that interferon-alpha had the ability to modulate West Nile virus infection in mouse. In vitro, interferon-alpha protected mouse neuroblastoma cells against West Nile virus infection if cells have been pretreated with the cytokine for several hours. As a consequence of the presence of a stop codon, the Oas1b gene of the susceptible mice encodes a truncated and presumably inactive form, while resistant mice have a normal copy of the gene. Stable mouse neuroblastoma cell clones overexpressing mutant or wild-type OAS 1B were established. Replication of West Nile virus was less efficient in cells that produce the normal copy of OAS 1B as compared to those expressing the truncated form. Our data illustrate the notion that interferon-alpha and Oas genes may be critical for West Nile virus pathogenesis.

A spontaneous mouse hair mutation was identified in a C3H/HeN colony. The mode of inheritance of the mutation was semidominant, with incomplete penetrance when heterozygous. The trait is controlled by a single locus hague (Hag), which was mapped to the telomeric region of chromosome 15. This mutation was shown to be unstable, since its transmission could be switched from semidominant to recessive. To identify the causative gene and the nature of the mutation, hague was introduced into a high-resolution and high-density molecular genetic map. Over 2000 meioses were analyzed and the mutation was mapped to the keratin 2 complex genes. A YAC and BAC physical map of the critical region was then constructed and the gene involved was located in a 600- to 800-kb-long segment. Fourteen genes were mapped to this region; of these, 11 were expressed in the skin (5 epidermic cytokeratin and 6 hard keratin genes), but none were mutated in hague mice.

A mouse model has been established to investigate the genetic determinism of host susceptibility to West Nile (WN) virus, a member of the genus flavivirus and family Flaviviridae . Whereas WN virus causes encephalitis and death in most laboratory inbred mouse strains after peripheral inoculation, most strains derived from recently trapped wild mice are completely resistant. The phenotype of resistance/susceptibility is determined by a major locus, Wnv , mapping to chromosome 5 within the 0.4-cM-wide interval defined by markers D5Mit408 and D5Mit242 . We constructed a high resolution composite/consensus map of the interval by merging the data from the mouse T31 Radiation Hybrid map and those from the homologous region of human chromosome 12q, and found the cluster of genes encoding 2′-5′-oligoadenylate synthetases (2′-5′-OAS) to be the most prominent candidate. This cluster encodes a multimember family of IFN-inducible proteins that is known to play an important role in the established endogenous antiviral pathway. Comparing the cDNA sequences of 2′-5′-OAS L1, L2, and L3 isoforms, between susceptible and resistant strains, we identified a STOP codon in exon 4 of the gene encoding the L1 isoform in susceptible strains that can lead to a truncated form with amputation of one domain, whereas all resistant mice tested so far have a normal copy of this gene. The observation that WN virus sensitivity of susceptible mice was completely correlated with the occurrence of a point mutation in 2′-5′-OAS L1 suggests that this isoform may play a critical role in WN pathogenesis.

We previously described an autosomal-recessive mutation named nackt (nkt) exhibiting partial alopecia associated with CD4(+) T-cell deficiency. Also, we recently reported that nkt (now Ctsl(nkt)) comprises a deletion in the cathepsin L (Ctsl) gene. Another recent study reported that Ctsl knockout mice have CD4(+) T-cell deficiency and periodic shedding of hair, which recapitulate the nkt mutation and the old furless (fs) mutation. The current study focuses on the dermatological aspects of the nkt mutation. Careful histological analysis of skin development of homozygous nkt mice revealed a delayed hair follicle morphogenesis and late onset of the first catagen stage. The skin of Ctsl(nkt)/Ctsl(nkt) mice showed mild epidermal hyperplasia and hyperkeratosis, severe hyperplasia of the sebaceous glands, and structural alterations of hair follicles. Epidermal differentiation seems to be affected in nkt skin, with overexpression of involucrin and profilaggrin/filaggrin along with focal areas of keratin 6 expression in the interfollicular epidermis. Severe epidermal hyperplasia, acanthosis, orthokeratosis, and hyperkeratosis were only observed in mice maintained in nonpathogen-free environments. The analysis of Rag2-/- Ctsl(nkt)/Ctsl(nkt) double-mutant mice indicates that the skin defect remains under the absence of T and B cells. This animal model provides in vivo evidence that cysteine protease cathepsin L plays a critical role in hair follicle morphogenesis and cycling, as well as epidermal differentiation.

The neurological syndrome caused by Plasmodium berghei ANKA in rodents partially mimics the human disease. Several rodent models of cerebral malaria (CM) exist for the study of the mechanisms that cause the disease. However, since common laboratory mouse strains have limited gene pools, the role of their phenotypic variations causing CM is restricted. This constitutes an obstacle for efficient genetic analysis relating to the pathogenesis of malaria. Most common laboratory mouse strains are susceptible to CM, and the same major histocompatibility complex (MHC) haplotype may exhibit different levels of susceptibility. We analyzed the influence of the MHC haplotype on overcoming CM by using MHC congenic mice with C57BL/10 and C3H backgrounds. No correlation was found between MHC molecules and the development of CM. New wild-derived mouse strains with wide genetic polymorphisms were then used to find new models of resistance to CM. Six of the twelve strains tested were resistant to CM. For two of them, F 1 progeny and backcrosses performed with the reference strain C57BL/6 showed a high level of heterogeneity in the number and characteristics of the genetic factors associated with resistance to CM.

Chemical mutagenesis followed by screening for abnormal phenotypes in the mouse holds much promise as a method for revealing gene function. This method is particularly well-suited for discovering genes involved in hearing or balance function, as these defects are relatively easy to screen for in the mouse. We report here the inner ear abnormalities and genetic localization of seven new dominant mutations created by ENU mutagenesis. All seven mutant stocks were identified because of circling and/or head-weaving behavior, which is an indication of balance dysfunction. Investigation of the inner ears of the seven mutant stocks revealed very similar lateral and posterior semicircular canal defects. Studies of the development of the canals in one mutant stock revealed that the affected canals showed reduced outgrowth and delayed canal fusion. Physiological studies performed in one mutant stock showed raised average compound-action-potential thresholds of approximately 10-20 dB sound pressure level (SPL) (depending on frequency), indicating a mild hearing impairment, although scanning electron microscopy performed in several of the mutant stocks revealed no obvious structural defects in the organ of Corti. All seven mutations mapped to the proximal portion of Chromosome (Chr) 4, near the centromere. On the basis of their similar phenotype and map location, we suggest that the seven mutant genes may be allelic and represent a highly mutable locus on Chr 4 that may be particularly susceptible to ENU-induced mutation on the BALB/c genetic background.

In the early 1980s, the expression of transgenic animals was proposed to define animals having foreign DNA sequences stably and deliberately inserted into their genome through human intermediaries. With time and the advent of new techniques, this concept has progressively evolved, and nowadays, it is probably more appropriate to consider that transgenic animals are animals whose genetic characteristics have been altered using one of the techniques of genetic engineering. Whatever the definition, transgenic animals belong to the category of genetically modified or genetically engineered organisms (GMOs).

At the beginning of the twentieth century when genetics began to emerge as an experimental science, laboratory mouse resources were extremely limited. Aside from a few coat color mutants, which were bred by fanciers as pets, the only animals available for experiments were “albino” mice. These mice were bred with no specific mating protocol and were, in most cases, genetically heterogeneous. At that time, and based on the experience of dog and horse breeders, inbreeding was a practice to be avoided by all possible means because it was thought to lead to a decline in vigor and ultimately to the extinction of the colony. In fact, it is not an exaggeration to say that the only qualities that were required of these “albino” mice were prolificacy, robustness, and tameness.

Because they are often closely associated with humans and sometimes “share” food with them, zoologists consider the mouse as a commensal species (from the Latin cum mensa, which means eating at the same table). For the same reason, mice are often referred to as “house” mice in the English literature, as opposed to wild or feral mice even though, in fact, they are the same species. Because they have been described as “invasive,” “prolific,” “troublesome,” and “devastating,” farmers consider mice to be pests. Physicians and epidemiologists don’t like mice (and rodents more generally) because they are natural reservoirs of many pathogens, some of them deadly. For some other people, on the contrary, mice are cute pets, easy to breed, cheap to buy, and with beautiful coat colors.

This chapter brings together a variety of information and concepts that are important for understanding the following chapters. The first section is an overview concerning mouse reproductive biology and embryology. This topic is important because, nowadays, many experiments in genetics require the manipulation of embryos at different stages of development, either to study their phenotype or for the production of chimeras with other embryos or with genetically engineered embryonic stem (ES) cells. The second part is a compilation of concepts of general or molecular genetics related to the phenotypic expression of mutations. More information can also be retrieved from several websites, where books and manuals are freely available online.