C3H Background Research Articles

Network-based analysis predicts interacting genetic modifiers from a meta-mapping study of spike-wave discharge in mice.

Absence seizures are characterized by brief lapses in awareness accompanied by a hallmark spike-and-wave discharge (SWD) electroencephalographic pattern and are common to genetic generalized epilepsies (GGEs). While numerous genes have been associated with increased risk, including some Mendelian forms with a single causal allele, most cases of GGE are idiopathic and there are many unknown genetic modifiers of GGE influencing risk and severity. In a previous meta-mapping study, crosses between transgenic C57BL/6 and C3HeB/FeJ strains, each carrying one of three SWD-causing mutations (Gabrg2tm1Spet(R43Q) , Scn8a8j or Gria4spkw1 ), demonstrated an antagonistic epistatic interaction between loci on mouse chromosomes 2 and 7 influencing SWD. These results implicate universal modifiers in the B6 background that mitigate SWD severity through a common pathway, independent of the causal mutation. In this study, we prioritized candidate modifiers in these interacting loci. Our approach integrated human genome-wide association results with gene interaction networks and mouse brain gene expression to prioritize candidate genes and pathways driving variation in SWD outcomes. We considered candidate genes that are functionally associated with human GGE risk genes and genes with evidence for coding or non-coding allele effects between the B6 and C3H backgrounds. Our analyses output a summary ranking of gene pairs, one gene from each locus, as candidates for explaining the epistatic interaction. Our top-ranking gene pairs implicate microtubule function, cytoskeletal stability and cell cycle regulation as novel hypotheses about the source of SWD variation across strain backgrounds, which could clarify underlying mechanisms driving differences in GGE severity in humans.

Does Background Matter? A Comparative Characterization of Mouse Models of Autosomal Retinitis Pigmentosa rd1 and Pde6b-KO.

Many retinal degenerative diseases result in vision impairment or permanent blindness due to photoreceptor loss or dysfunction. It has been observed that Pde6brd1 mice (rd1), which carry a spontaneous nonsense mutation in the pde6b gene, have a strong phenotypic similarity to patients suffering from autosomal recessive retinitis pigmentosa. In this study, we present a novel mouse model of retinitis pigmentosa generated through pde6b gene knockout using CRISPR/Cas9 technology. We compare this Pde6b-KO mouse model to the rd1 mouse model to gain insights into the progression of retinal degeneration. The functional assessment of the mouse retina and the tracking of degeneration dynamics were performed using electrophysiological methods, while retinal morphology was analyzed through histology techniques. Interestingly, the Pde6b-KO mouse model demonstrated a higher amplitude of photoresponse than the rd1 model of the same age. At postnatal day 12, the thickness of the photoreceptor layer in both mouse models did not significantly differ from that of control animals; however, by day 15, a substantial reduction was observed. Notably, the decline in the number of photoreceptors in the rd1 model occurred at a significantly faster rate. These findings suggest that the C3H background may play a significant role in the early stages of retinal degeneration.

The Genetic Background Is Shaping Cecal Enlargement in the Absence of Intestinal Microbiota.

Germ-free (GF) rodents have become a valuable tool for studying the role of intestinal microbes on the host physiology. The major characteristic of GF rodents is an enlarged cecum. The accumulation of mucopolysaccharides, digestion enzymes and water in the intestinal lumen drives this phenotype. Microbial colonization normalizes the cecum size in ex-GF animals. However, whether strain genetics influences the cecal enlargement is unknown. Here we investigated the impact of mouse genetic background on the cecal size in five GF strains frequently used in biomedical research. The cecal weight of GF mice on B6 background (B6J and B6N) represented up to 20% of total body weight. GF NMRI and BALBc mice showed an intermediate phenotype of 5-10%, and those on the C3H background of up to 5%. Reduced cecal size in GF C3H mice correlated with decreased water content, increased expression of water transporters, and reduced production of acidic mucins, but was independent of the level of digestive enzymes in the lumen. In contrast, GF B6J mice with greatly enlarged cecum showed increased water content and a distinct metabolic profile characterized by altered amino acid and bile acid metabolism, and increased acidic mucin production. Together, our results show that genetic background influences the cecal enlargement by regulating the water transport, production of acidic mucins, and metabolic profiles.

Modification of an aggressive model of Alport Syndrome reveals early differences in disease pathogenesis due to genetic background

The link between mutations in collagen genes and the development of Alport Syndrome has been clearly established and a number of animal models, including knock-out mouse lines, have been developed that mirror disease observed in patients. However, it is clear from both patients and animal models that the progression of disease can vary greatly and can be modified genetically. We have identified a point mutation in Col4a4 in mice where disease is modified by strain background, providing further evidence of the genetic modification of disease symptoms. Our results indicate that C57BL/6J is a protective background and postpones end stage renal failure from 7 weeks, as seen on a C3H background, to several months. We have identified early differences in disease progression, including expression of podocyte-specific genes and podocyte morphology. In C57BL/6J mice podocyte effacement is delayed, prolonging normal renal function. The slower disease progression has allowed us to begin dissecting the pathogenesis of murine Alport Syndrome in detail. We find that there is evidence of differential gene expression during disease on the two genetic backgrounds, and that disease diverges by 4 weeks of age. We also show that an inflammatory response with increasing MCP-1 and KIM-1 levels precedes loss of renal function.

Excess hydrogen sulfide and polysulfides production underlies a schizophrenia pathophysiology

Mice with the C3H background show greater behavioral propensity for schizophrenia, including lower prepulse inhibition (PPI), than C57BL/6 (B6) mice. To characterize as‐yet‐unknown pathophysiologies of schizophrenia, we undertook proteomics analysis of the brain in these strains, and detected elevated levels of Mpst, a hydrogen sulfide (H2S)/polysulfide‐producing enzyme, and greater sulfide deposition in C3H than B6 mice. Mpst‐deficient mice exhibited improved PPI with reduced storage sulfide levels, while Mpst‐transgenic (Tg) mice showed deteriorated PPI, suggesting that “sulfide stress” may be linked to PPI impairment. Analysis of human samples demonstrated that the H2S/polysulfides production system is upregulated in schizophrenia. Mechanistically, the Mpst‐Tg brain revealed dampened energy metabolism, while maternal immune activation model mice showed upregulation of genes for H2S/polysulfides production along with typical antioxidative genes, partly via epigenetic modifications. These results suggest that inflammatory/oxidative insults in early brain development result in upregulated H2S/polysulfides production as an antioxidative response, which in turn cause deficits in bioenergetic processes. Collectively, this study presents a novel aspect of the neurodevelopmental theory for schizophrenia, unraveling a role of excess H2S/polysulfides production.

Increased susceptibility to mammary carcinogenesis and an opposite trend in endometrium in <i>Trp53</i> heterozygous knockout female mice by backcrossing the BALB/c strain onto the background C3H strain

Patients with dominantly inherited Li-Fraumeni syndrome have a loss-of-function mutation in TP53 and develop diverse mesenchymal and epithelial neoplasms at multiple sites. Trp53+/− female mice with the BALB/c background provide unique characteristics for the study of breast cancer in Li-Fraumeni syndrome; however, we previously found that female C3H-Trp53+/− mice did not spontaneously develop mammary tumors. Therefore, we obtained F1 and N2-N4 female mice by backcrossing the BALB/c strain and examined the incidence of mammary and other tumors in lifetime studies. Malignant lymphomas, osteosarcomas, and uterine adenocarcinomas spontaneously developed in approximately 20% or more of Trp53+/− mice with the C3H background. In contrast, the incidence of uterine adenocarcinomas showed a tendency to decrease, while that of mammary adenocarcinomas gradually increased in mice with the BALB/c strain backcross. Wild-type BALB/c female mice are predisposed to a wide spectrum of neoplasms, including mammary tumors, partly due to genetic factors, whereas uterine tumors are uncommon not only in BALB/c mice but also C3H mice. Thus, genetic factors appear to contribute to a strain-specific predisposition to malignant neoplasms in Trp53+/− mice, and further studies are needed to clarify the detailed mechanisms.

Verification That Mouse Chromosome 14 Is Responsible for Susceptibility to Streptozotocin in NSY Mice.

Introduction Streptozotocin- (STZ-) induced diabetes is under polygenic control, and the genetic loci for STZ susceptibility are mapped to chromosome (Chr) 11 in Nagoya-Shibata-Yasuda (NSY) mice. In addition to Chr11, other genes on different chromosomes may contribute to STZ susceptibility in NSY mice. The aim of this study was to determine whether NSY-Chr14 contributes to STZ susceptibility and contains the STZ-susceptible region. Materials and Methods A consomic C3H-14NSY strain (R0: homozygous for NSY-derived whole Chr14 on the control C3H background), two congenic strains (R1: the region retained proximal and middle segments of NSY-Chr14 and R2: the region retained a proximal segment of NSY-Chr14), and parental NSY and C3H mice were intraperitoneally injected with a single injection of STZ at a dose of 175 mg/kg body weight at 12 weeks of age. Blood glucose levels and body weights were measured at days 0, 1, 2, 4, 5, 7, 8, and 14 after STZ injection. At day 14 after STZ injection, pancreata were dissected and fixed. Results After STZ injection, blood glucose levels were significantly higher in R0 mice than in C3H mice. However, blood glucose levels in R0 mice were not as severely affected as those in NSY mice. In R1 and R2 mice, blood glucose levels were similar to those in C3H mice and were significantly lower than those in R0 mice. Body weights were decreased in NSY and R0 mice; however, this change was not observed in R1, R2, and C3H mice. Although islet tissues in all strains exhibited degeneration and cellular infiltration, histological changes in NSY and R0 mice were more severe than those in R1, R2, and C3H mice. Conclusions These data demonstrated that NSY-Chr14 was a STZ-susceptible chromosome and that STZ susceptibility was mapped to the distal segment of NSY-Chr14.

Cryptochrome deficiency enhances transcription but reduces protein levels of pineal Aanat

Cryptochrome (Cry) 1 and 2 are essential for circadian rhythm generation, not only in the suprachiasmatic nucleus, the site of the mammalian master circadian clock, but also in peripheral organs throughout the body. CRY is also known as a repressor of arylalkylamine-N-acetyltransferase (Aanat) transcription; therefore, Cry deficiency is expected to induce constantly high pineal melatonin content. Nevertheless, we previously found that the content was consistently low in melatonin-proficient Cry1 and Cry2 double-deficient mice (Cry1−/−/Cry2−/−) on C3H background. This study aims to clarify the mechanism underlying this discrepancy. In the Cry1−/−/Cry2−/− pineal, expression levels of Aanat and clock gene Per1 were consistently high with no circadian fluctuation on the first day in constant darkness, demonstrating that CRY acts in vivo as a repressor of the pineal circadian clock and AANAT. In contrast, the enzyme activity and protein levels of AANAT remained low throughout the day, supporting our previous observation of continuously low melatonin. Thus, effects of Cry deficiency on the responses of β-adrenergic receptors were examined in cultured pineal glands. Isoproterenol, a β-adrenergic stimulant, significantly increased melatonin content, although the increase was smaller in Cry1−/−/Cry2−/− than in WT mice, during both the day and night. However, the increase in cAMP in response to forskolin was similar in both genotypes, indicating that CRY deficiency does not affect the pathway downstream of the β-adrenergic receptor. These results suggest that a lack of circadian adrenergic input due to CRY deficiency decreases β-receptor activity and cAMP levels, resulting in consistently low AANAT levels despite abundant Aanat mRNA.

Microphthalmia-associated transcription factor ensures the elongation of axons and dendrites in the mouse frontal cortex.

Long interspersed element-1 (LINE-1) is a mammalian transposable element, and its genomic insertion could cause neurological disorders in humans. Incidentally, LINE-1 is present in intron 3 of the microphthalmia-associated transcription factor (Mitf) gene of the black-eyed white mouse (Mitfmi-bw allele). Mice homozygous for the Mitfmi-bw allele show the white coat color with black eye and deafness. Here, we explored the functional consequences of the LINE-1 insertion in the Mitf gene using homozygous Mitfmi-bw mice on the C3H background (C3H-bw mice) or on the C57BL/6 background (bw mice). The open-field test showed that C3H-bw mice moved more irregularly in an unfamiliar environment during the 20-min period, compared to wild-type mice, suggesting the altered emotionality. Moreover, C3H-bw mice showed the lower serum creatinine levels, which may reflect the creatine deficiency. In fact, morphologically abnormal neurons and astrocytes were detected in the frontal cortex of bw mice. The immunohistochemical analysis of bw mouse tissues showed the lower intensity for expression of guanidinoacetate methyltransferase, a key enzyme in creatine synthesis, in neurons of the frontal cortex and in glomeruli and renal tubules. Thus, Mitf may ensure the elongation of axons and dendrites by maintaining creatine synthesis in the frontal cortex.

Immune Response to FIX Is Dependent on Mouse Background Strain and Modulated By TLR4

IntroductionMany investigators rely on mouse models to study immune responses against factor IX protein (FIX) products. While it is recognized that there are distinct differences in immune responses towards FIX in different mouse strains, there is an absence of studies conducted on mice with a F9 gene deletion. Our laboratory has developed protocols to prevent or reverse ongoing anti-hFIX IgG inhibitors in hemophilia B mice with a F9 gene deletion (F9-/Y) on both a BALB/c and C3H/HeJ background. Interestingly C3H/HeJ F9-/Y mice develop high titer anti-FIX IgG1 inhibitors and anaphylaxis, while BALB/c F9-/Y mice have mild anti-hFIX IgG1 inhibitors without anaphylaxis. The C3H/HeJ mouse strain is deficient for the innate immune sensor toll like receptor 4 (TLR4) while a congenic C3H/OuJ strain has functional TLR4. Several recent studies have indicated an important link between coagulation and innate immunity and TLR4 has been linked to sensitivity in food allergy models. Together these studies suggest that TLR4 may have a role in modulating FIX immunity. Here we report results from a study exploring B and T cell responses against FIX protein therapy on two different mouse strains BALB/c and C3H/HeJ with the same F9 gene deletion and the role of TLR4 in modulating FIX immunity.MethodsBALB/c and C3H/HeJ F9-/Y mice were challenged weekly with recombinant FIX protein. Humoral immune responses were determined by IgG1 and IgG2a anti-hFIX ELISA, Bethesda assay for inhibitors and B cell ELISpot on bone marrow and spleen cells to measure FIX specific antibody secreting B cells. T cell studies measured the TH1 (IFN-γ) and TH2 (IL-4) cytokine responses in splenocytes at the mRNA and protein level in response to FIX protein. Antibody responses were also measured in C3H/HeJ/OuJ F9-/Y mice with restored TLR4 function following FIX challenge.ResultsBALB/c F9-/Y mice have a TH2 skewed response and a reduction in anti-hFIX secreting plasma cells in the bone marrow. Independent antigen challenge revealed both strains generated equivalent IgG1 antibody titers to an intravenously delivered antigen suggesting the reduced anti-FIX response in BALB/c mice is antigen specific. C3H/HeJ F9-/Y mice have a mixed TH1 and TH2 response (mainly TH2). Importantly TLR4 signaling has an important modulatory role in the C3H background on the levels of anti-hFIX IgG1 and incidence of anaphylaxis.ConclusionsThe background strain has an important impact on FIX immune responses, which in permissive strains can be modulated by mutations in innate immune sensors. [Display omitted] [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Immune responses to human factor IX in haemophilia B mice of different genetic backgrounds are distinct and modified by TLR4.

Our laboratory develops protocols to prevent or reverse ongoing anti-hFIX IgG inhibitors in haemophilia B mice with a F9 gene deletion on BALB/c and C3H/HeJ backgrounds. C3H/HeJ F9−/Y mice develop high titre anti-hFIX IgG1 inhibitors and anaphylaxis, whereas most BALB/c F9−/Y mice have mild anti-hFIX IgG1 inhibitors and no anaphylaxis. Our aim was to determine if hFIX-specific B- and T-cell responses in BALB/c and C3H/HeJ F9−/Y mice trigger the difference in anti-hFIX immune responses. BALB/c and C3H/HeJ F9−/Y mice were challenged weekly with recombinant hFIX protein. Humoral immune responses were determined by IgG1 and IgG2a anti-hFIX ELISA, Bethesda assay for inhibitors and B-cell ELISpot on bone marrow and spleen cells. T-cell studies measured the TH1 (IFN-γ) and TH2 (IL-4) cytokine responses in splenocytes at the mRNA and protein level in response to hFIX protein. Antibody responses were also measured in C3H/HeJ/OuJ F9−/Y mice with restored toll-like receptor 4 (TLR4) function. BALB/c F9−/Y mice have a TH2 skewed response and a reduction in anti-hFIX secreting plasma cells in the bone marrow. Independent antigen challenge revealed both strains generated equivalent IgG1 antibody titres to an intravenously delivered antigen. C3H/HeJ F9−/Y mice have a mixed TH1 and TH2 response (mainly TH2). Importantly, TLR4 signalling has a modulatory role in the C3H background on the levels of anti-hFIX IgG1 and incidence of anaphylaxis. The background strain strongly impacts the immune response to hFIX, which can be significantly impacted by mutations in innate immune sensors.

Decline in muscle strength and running endurance in klotho deficient C57BL/6 mice

Alpha klotho (known as klotho) is a multifunctional protein that may be linked to age-associated decline in tissue homeostasis. The original klotho hypomorphic (klotho (hm) ) mouse, produced on a mixed C57BL/6 and C3H background, is short lived and exhibits extensive aging-like deterioration of several body systems. Differently, klotho (hm) mice on a pure C57BL/6 background do not appear sickly nor die young, which has permitted us to gain insight into the effect of klotho deficiency in adult life. First, analyzing klotho transcript levels in the kidney, the main site of klotho production, we demonstrated a 71-fold decline in klotho (hm) females compared to wildtype females versus only a 4-fold decline in mutant males. We then examined the effect of klotho deficiency on muscle-related attributes in adult mice, focusing on 7-11month old females. Body weight and forelimb grip strength were significantly reduced in klotho (hm) mice compared to wildtype and klotho overexpressing mice. The female mice were also subjected to voluntary wheel running for a period of 6days. Running endurance was markedly reduced in klotho (hm) mice, which exhibited a sporadic running pattern that may be characteristic of repeated bouts of exhaustions. When actually running, klotho (hm) females ran at the same speed as wildtype and klotho overexpressing mice, but spent about 65% less time running compared to the other two groups. Our novel results suggest an important link between klotho deficiency and muscle performance. This study provides a foundation for further research on klotho involvement as a potential inhibitor of age-associated muscle deterioration.

Type of uromodulin mutation and allelic status influence onset and severity of uromodulin-associated kidney disease in mice

Uromodulin-associated kidney disease (UAKD) is a dominant heritable renal disease in humans which is caused by mutations in the uromodulin (UMOD) gene and characterized by heterogeneous clinical appearance. To get insights into possible causes of this heterogeneity of UAKD, we describe the new mutant mouse line Umod(C93F), leading to disruption of a putative disulfide bond which is also absent in a known human UMOD mutation, and compare the phenotype of this new mouse line with the recently published mouse line Umod(A227T). In both mutant mouse lines, which were both bred on the C3H background, the Umod mutations cause a gain-of-toxic function due to a maturation defect of the mutant uromodulin leading to a dysfunction of thick ascending limb of Henle's loop (TALH) cells of the kidney. Umod mutant mice exhibit increased plasma urea and Cystatin levels, impaired urinary concentration ability, reduced fractional excretion of uric acid and nephropathological alterations including uromodulin retention in TALH cells, interstitial fibrosis and inflammatory cell infiltrations, tubular atrophy and occasional glomerulo- und tubulocystic changes, a phenotype highly similar to UAKD in humans. The maturation defect of mutant uromodulin leads to the accumulation of immature uromodulin in the endoplasmic reticulum (ER) and to ER hyperplasia. Further, this study was able to demonstrate for the first time in vivo that the severity of the uromodulin maturation defect as well as onset and speed of progression of renal dysfunction and morphological alterations are strongly dependent on the particular Umod mutation itself and the zygosity status.

Cd72c Is a Modifier Gene that Regulates Faslpr-Induced Autoimmune Disease

Although modifier genes are extensively studied in various diseases, little is known about modifier genes that regulate autoimmune diseases. Autoimmune disease caused by the Fas(lpr) mutation depends on the genetic background of mouse strains, suggesting a crucial role of modifier genes. MRL/MpJ-Fas(lpr) (MRL/lpr) and AKR/lpr mice develop severe and mild lupus-like autoimmune disease, respectively, whereas this mutation does not cause disease on C57BL/6 (B6) or C3H background. Both MRL and AKR carry the same haplotype of the Cd72 gene encoding an inhibitory BCR coreceptor (CD72(c)), and CD72(c) contains several amino acid substitutions and a deletion in the extracellular region compared with CD72(a) and CD72(b). To address the role of Cd72(c) locus in the regulation of Fas(lpr)-induced autoimmune disease, we generated B6.CD72(c)/lpr and MRL.CD72(b)/lpr congenic mice. Introduction of the chromosomal interval containing Cd72(c) did not cause disease in B6 mice by itself, but caused development of lupus-like disease in the presence of Fas(lpr) on B6 background, clearly demonstrating that this interval contains the modifier gene that regulates Fas(lpr)-induced autoimmune disease. Conversely, MRL.CD72(b)/lpr congenic mice showed milder disease compared with MRL/lpr mice. We further demonstrated that Cd72(c) is a hypofunctional allele in BCR signal inhibition and that CD72 deficiency induces severe autoimmune disease in the presence of Fas(lpr). These results strongly suggest that the Cd72(c) is a crucial modifier gene that regulates Fas(lpr)-induced autoimmune disease due to its reduced activity of B cell signal regulation.

Dose Effect and Mode of Inheritance of Diabetogenic Gene on Mouse Chromosome 11

The quantitative trait locus (QTL) mapping in segregating crosses of NSY (Nagoya-Shibata-Yasuda) mice, an animal model of type 2 diabetes, with nondiabetic strain C3H/He mice has identified diabetogenic QTLs on multiple chromosomes. The QTL on chromosome 11 (Chr11) (Nidd1n) showing the largest effect on hyperglycemia was confirmed by our previous studies with homozygous consomic mice, C3H-11NSY, in which the NSY-derived whole Chr11 was introgressed onto control C3H background genes. C3H-11NSY mice also showed a streptozotocin (STZ) sensitivity. In the present study, we constructed heterozygous C3H-11NSY mice and the phenotypes were analyzed in detail in comparison with those of homozygous C3H-11NSY and C3H mice. Heterozygous C3H-11NSY mice had significantly higher blood glucose levels and STZ sensitivity than those in C3H mice. Hyperglycemia and STZ sensitivity in heterozygous C3H-11NSY mice, however, were not as severe as in homozygous C3H-11NSY mice. The body weight and fat pad weight in heterozygous C3H-11NSY mice were similar to those in C3H and homozygous C3H-11NSY mice. These data indicated that the introgression of Chr11 of the diabetes-susceptible NSY strain onto diabetes-resistant C3H caused marked changes in the glucose tolerance and STZ susceptibility even in a heterozygous state, and suggested that the mode of inheritance of a gene or genes on Chr11 for hyperglycemia and STZ sensitivity is additive.

Congenic Strain Analysis Reveals Genes That Are Rapidly Evolving Components of a Prezygotic Isolation Mechanism Mediating Incipient Reinforcement

Two decades ago, we developed a congenic strain of Mus musculus, called b-congenic, by replacing the androgen-binding protein Abpa27a allele in the C3H/HeJ genome with the Abpa27b allele from DBA/2J. We and other researchers used this b-congenic strain and its C3H counterpart, the a-congenic strain, to test the hypothesis that, given the choice between signals from two strains with different a27 alleles on the same genetic background, test subjects would prefer the homosubspecific one. It was our purpose in undertaking this study to characterize the segment transferred from DBA to the C3H background in producing the b-congenic strain on which a role for ABPA27 in behavior has been predicated. We determined the size of the chromosome 7 segment transferred from DBA and the genes it contains that might influence preference. We found that the “functional" DBA segment is about 1% the size of the mouse haploid genome and contains at least 29 genes expressed in salivary glands, however, only three of these encode proteins identified in the mouse salivary proteome. At least two of the three genes Abpa27, Abpbg26 and Abpbg27 encoding the subunits of androgen-binding protein ABP dimers evolved under positive selection and the third one may have also. In the sense that they are subunits of the same two functional entities, the ABP dimers, we propose that their evolutionary histories might not be independent of each other.

Serum xylosyltransferase 1 level increases during early posttraumatic osteoarthritis in mice with high bone forming potential

Increased proteoglycan (PG) synthesis is essential for the stimulation of cartilage repair processes that take place during the reversible phase of osteoarthritis (OA). In articular cartilage, xylosyltransferase 1 (Xylt1) is the key enzyme that initiates glycosaminoglycan (GAG) chain synthesis by transferring the first sugar residue to the PG core protein. Biological activity of PGs is closely linked to GAG biosynthesis since their polyanionic nature directly contributes to the proper hydration and elastic properties of the cartilage tissue present at the articular interface. The aim of this study was to investigate whether variations in the level of Xylt1 present in serum can be used to predict OA disease progression. The influence of bone forming activity on the systemic release of this enzyme was addressed by experimentally-inducing OA in mice of two different genetic backgrounds that were previously characterized for their distinct bone metabolism: C57BL/6J (B6, high bone remodelers) or C3H/HeJ (C3H, high bone formers). Serum was collected after medial meniscectomy or sham surgeries in young adult mice of these two strains over a period of 3.5months at which point knee histopathology was assessed. A significant increase in serum Xylt1 levels observed shortly after meniscectomy positively correlated with severe cartilage damage evaluated by histological assessment at later time points in mice of the C3H background. In contrast, no temporal regulation of Xylt1 level was found between meniscectomies and control surgeries in B6 mice, which developed OA at a slower rate. Additionally, longitudinal evaluation of the serum levels of other markers of cartilage/bone metabolism (C1,2C, osteocalcin) did not reveal any association with late knee damages. Our results strongly support the idea that serum Xylt1 has a clinical value for monitoring risk of OA progression in young adults with high bone forming potential. Ultimately, the understanding of posttraumatic mechanisms regulating PG synthesis and their modification by GAG will be essential so that interventions that stimulate cartilage regrowth can be undertaken prior to irreversible destruction of the joint tissue. This article is part of a Special Issue entitled "Osteoarthritis".

DNA damage-induced apoptosis and genetic background of the host: host-specific signaling enhancers of apoptosis.

Radiation therapy, inducing DNA damage, is one of the most effective tools for treatments of human cancers, but the effectiveness of the therapy is largely depending on the host specific conditions. Recently genetic constitution has proven to be important for apoptosis-induction responding to DNA damage. Regarding the host-specific manner of responses against DNA-damage in animal model, we have reported that infection with Friend leukemia virus (FLV) enhances the DNA damage-induced apoptosis in hematopoietic cells derived from C3H but DBA/2 mice. Furthermore, p53 or ATM knockout mice of C3H background and DNA-PK-deficient C3H SCID mice did not show the enhanced apoptosis by FLV. Recently, we could show that this host-specific apoptosis was mediated by the kinase activity of DNA-PK in association with FLV env-coding protein, gp70. Interestingly, two host proteins, acinus and MCM2, were also associated with DNA-PK and gp70 and were host-specifically overexpressed in C3H-derived cells. Our data suggest that gp70 enhances cellular DNA damage-induced signaling in association with host-specific cellular proteins, including acinus and MCM2, resulting in the activation of DNA-PK to phosphorylate P53. By introducing gp70/acinus/MCM2-associated pathways into tumor cells, cancer therapy with DNA damage-inducing agents might become much more effective. Our aim is to develop a novel form of targeted therapy that can be combined with other treatment modalities, such as radiotherapy and chemotherapy, using the host-specific regulatory mechanisms of apoptotic enhancement.

Effect of genetic background on phenotype variability in transgenic mouse models of amyotrophic lateral sclerosis: A window of opportunity in the search for genetic modifiers

Transgenic (Tg) mouse models of FALS containing mutant human SOD1 genes (G37R, G85R, D90A, or G93A missense mutations or truncated SOD1) exhibit progressive neurodegeneration of the motor system that bears a striking resemblance to ALS, both clinically and pathologically. The most utilized and best characterized Tg mice are the G93A mutant hSOD1 (Tg(hSOD1-G93A)1GUR mice), abbreviated G93A. In this review we highlight what is known about background-dependent differences in disease phenotype in transgenic mice that carry mutated human or mouse SOD1. Expression of G93A-hSOD1Tg in congenic lines with ALR, NOD.Rag1KO, SJL or C3H backgrounds show a more severe phenotype than in the mixed (B6xSJL) hSOD1Tg mice, whereas a milder phenotype is observed in B6, B10, BALB/c and DBA inbred lines. We hypothesize that the background differences are due to disease-modifying genes. Identification of modifier genes can highlight intracellular pathways already suspected to be involved in motor neuron degeneration; it may also point to new pathways and processes that have not yet been considered. Most importantly, identified modifier genes provide new targets for the development of therapies.

Highlighted article: “A Novel Null Allele of Mouse Dscam Survives to Adulthood on an Inbred C3H Background With Reduced Phenotypic Variability” by Fuerst, Harris, Johnson and Burgess

Highlighted article: “A Novel Null Allele of Mouse Dscam Survives to Adulthood on an Inbred C3H Background With Reduced Phenotypic Variability” by Fuerst, Harris, Johnson and Burgess