Genetic background influences timing, morphology and dissemination of lymphomas in p53-deficient mice

Autosomal dominant inheritance of brain cardiolipin fatty acid abnormality in VM/DK mice: association with hypoxic-induced cognitive insensitivity

Cardiolipin is a complex polyglycerol phospholipid found almost exclusively in the inner mitochondrial membrane and regulates numerous enzyme activities especially those related to oxidative phosphorylation and coupled respiration. Abnormalities in cardiolipin can impair mitochondrial function and bioenergetics. We recently demonstrated that the ratio of shorter chain saturated and monounsaturated fatty acids (C16:0; C18:0; C18:1) to longer chain polyunsaturated fatty acids (C18:2; C20:4; C22:6) was significantly greater in the brains of adult VM/DK (VM) inbred mice than in the brains of C57BL/6 J (B6) mice. The cardiolipin fatty acid abnormalities in VM mice are also associated with alterations in the activity of mitochondrial respiratory complexes. In this study we found that the abnormal brain fatty acid ratio in the VM strain was inherited as an autosomal dominant trait in reciprocal B6 × VM F1 hybrids. To evaluate the potential influence of brain cardiolipin fatty acid composition on cognitive sensitivity, we placed the parental B6 and VM mice and their reciprocal male and female B6VMF1 hybrid mice (3-month-old) in a hypoxic chamber (5 % O2). Cognitive awareness (conscientiousness) under hypoxia was significantly lower in the VM parental mice and F1 hybrid mice (11.4 ± 0.4  and 11.0 ± 0.4 min, respectively) than in the parental B6 mice (15.3 ± 1.4 min), indicating an autosomal dominant inheritance like that of the brain cardiolipin abnormalities. These findings suggest that impaired cognitive awareness under hypoxia is associated with abnormalities in neural lipid composition.

Deficiency in PER proteins has no effect on the rate of spontaneous and radiation-induced carcinogenesis

There is a growing body of evidence that components of the circadian clock are involved in modulation of numerous signaling pathways, and that clock deregulation due to environmental or genetic factors contributes to the development of various pathologies, including cancer. Previous work performed in tissue culture and in in vivo mouse models defined mammalian PERIOD proteins as tumor suppressors, although some experimental inconsistencies (the use of mice on mixed genetic background, lack of sexual discrimination) did not allow a definitive conclusion. To address this issue in a systematic way, we performed a detailed analysis comparing the incidence of tumor development after low-dose ionizing radiation in male and female wild-type, Per1^−/−, and Per2^−/− mice. We showed that in contrast to previous reports deficiency in either Per1 or Per2 genes by itself does not make mice more tumor-prone; moreover, some of the long-term effects of ionizing radiation in Per2-deficient mice are reminiscent more of accelerated aging rather than tumor-prone phenotype. Our histopathological analysis also revealed significant sexual dimorphism both in the rate of radiation-induced tumorigenesis and in the spectrum of tumors developed, which underscores the importance of using sex-matched experimental groups for in vivo studies. Based on our results, we suggest that the role of PER proteins as bona fide tumor suppressors needs to be reevaluated.

Strain-specific modifier genes governing craniofacial phenotypes

BACKGROUND

The presence of strain-specific modifier genes is known to modulate the phenotype and pathophysiology of mice harboring genetically engineered mutations. Thus, identification of genetic modifier genes is requisite to understanding control of phenotypic expression. c-Ski is a transcriptional regulator. Ski(-/-) mice on a C57BL6J (B6) background exhibit facial clefting, while Ski(-/-) mice on a 129P3 (129) background present with exencephaly.

METHODS

In the present study, oligonucleotide-based gene expression profiling was used to identify potential strain-specific modifier gene candidates present in wild type mice of B6 and 129 genetic backgrounds. Changes in gene expression were verified by TaqMan quantitative real-time PCR.

RESULTS

Steady-state levels of 89 genes demonstrated a significantly higher level of expression, and those of 68 genes demonstrated a significantly lower level of expression in the developing neural tubes from embryonic day (E) 8.5, B6 embryos when compared to expression levels in neural tubes derived from E 8.5, 129 embryos.

CONCLUSIONS

Based on the results from the current comparative microarray study, and taking into consideration a number of relevant published reports, several potential strain-specific gene candidates, likely to modify the craniofacial phenotypes in various knockout mouse models have been identified.

Transgenic mice carrying the H258N mutation in the gene encoding the beta-subunit of phosphodiesterase-6 (PDE6B) provide a model for human congenital stationary night blindness

Mutations in the beta-subunit of cGMP-phosphodiesterase (PDE6beta) can lead to either progressive retinal disease, such as human retinitis pigmentosa (RP), or stationary disease, such as congenital stationary night blindness (CSNB). Individuals with CSNB in the Rambusch pedigree were found to carry the H258N allele of PDE6B (MIM# 180072); a similar mutation was not found in RP patients. This report describes an individual carrying the H258N allele, who presented with generalized retinal dysfunction affecting the rod system and a locus of dysfunction at the rod-bipolar interface. Also described are preclinical studies in which transgenic mice with the H258N allele were generated to study the pathophysiological mechanisms of CSNB. While Pde6b(rd1)/Pde6b(rd1) mice have severe photoreceptor degeneration, as in human RP, the H258N transgene rescued these cells. The cGMP-PDE6 activity of dark-adapted H258N mice showed an approximate three-fold increase in the rate of retinal cGMP hydrolysis: from 130.1 nmol x min(-1) x nmol(-1) rhodopsin in wild-type controls to 319.2 nmol x min(-1) x nmol(-1) rhodopsin in mutants, consistent with the hypothesis that inhibition of the PDE6beta activity by the regulatory PDE6gamma subunit is blocked by this mutation. In the albino (B6CBA x FVB) F2 hybrid background, electroretinograms (ERG) from H258N mice were similar to those obtained from affected Rambusch family members, as well as humans with the most common form of CSNB (X-linked), demonstrating a selective loss of the b-wave with relatively normal a-waves. When the H258N allele was introduced into the DBA background, there was no evidence of selective reduction in b-wave amplitudes; rather a- and b-wave amplitudes were both reduced. Thus, factors other than the PDE6B mutation itself could contribute to the variance of an electrophysiological response. Therefore, caution is advisable when interpreting physiological phenotypes associated with the same allele on different genetic backgrounds. Nevertheless, such animals should be of considerable value in further studies of the molecular pathology of CSNB.