Widespread expression of the Supv3L1 mitochondrial RNA helicase in the mouse.

Supv3L1 is an evolutionarily conserved helicase that plays a critical role in the mitochondrial RNA surveillance and degradation machinery. Conditional ablation of Supv3L1 in adult mice leads to premature aging phenotypes including loss of muscle mass and adipose tissue and severe skin abnormalities. To get insights into the spatial and temporal expression of Supv3L1 in the mouse, we generated knock-in and transgenic strains in which an EGFP reporter was placed under control of the Supv3L1 native promoter. During development, expression of Supv3L1 begins at the blastocyst stage, becomes widespread and strong in all fetal tissues and cell types, and continues during postnatal growth. In mature animals reporter expression is only slightly diminished in most tissues and continues to be highly expressed in the brain, peripheral sensory organs, and testis. Together, these data confirm that Supv3L1 is an important developmentally regulated gene, which continues to be expressed in all mature tissues, particularly the rapidly proliferating cells of testes, but also in the brain and sensory organs. The transgenic mice and cell lines derived from them constitute a valuable tool for the examination of the spatial and temporal aspects of Supv3L1 promoter activity, and should facilitate future screens for small molecules that regulate Supv3L1 expression.

The chromatin-targeting protein Brd2 is required for neural tube closure and embryogenesis.

Chromatin modifications are essential for directing transcription during embryonic development. Bromodomain-containing protein 2 (Brd2; also called RING3 and Fsrg1) is one of four BET (bromodomain and extra-terminal domain) family members known to selectively bind acetylated histones H3 and H4. Brd2 associates with multiple subunits of the transcriptional apparatus including the mediator, TFIID and Swi/Snf multiprotein complexes. While molecular interactions of Brd2 are known, the functions of Brd2 in mammalian embryogenesis remain unknown. In developing a mouse model deficient in Brd2, we find that Brd2 is required for the completion of embryogenesis and proper neural tube closure during development. Embryos lacking Brd2 expression survive up to embryonic day 13.5, soon after mid-gestation, and display fully penetrant neurulation defects that largely result in exencephaly of the developing hindbrain. In this study, we find that highest expression of Brd2 is detected in the developing neural tube, correlating with the neural tube defects found in Brd2-null embryos. Additionally, embryos lacking Brd2 expression display altered gene expression programs, including the mis-expression of multiple genes known to guide neuronal development. Together these results implicate essential roles for Brd2 as a critical integrator of chromatin structure and transcription during mammalian embryogenesis and neurogenesis.

Disruption of Supv3L1 damages the skin and causes sarcopenia, loss of fat, and death.

Supv3L1 is a conserved and ubiquitously expressed helicase found in numerous tissues and cell types of many species. In human cells, SUPV3L1 was shown to suppress apoptotic death and sister chromatid exchange, and impair mitochondrial RNA metabolism and protein synthesis. In vitro experiments revealed binding of SUPV3L1 to BLM and WRN proteins, suggesting a role in genome maintenance processes. Disruption of the Supv3L1 gene in the mouse has been reported to be embryonic lethal at early developmental stages. We generated a conditional mouse in which the phenotypes associated with the removal of exon 14 can be tested in a variety of tissues. Disruption mediated by a Mx1 promoter-driven Cre displayed a postnatal growth delay, reduced lifespan, loss of adipose tissue and muscle mass, and severe skin abnormalities manifesting as ichthyosis, thickening of the epidermis, and atrophy of the dermis and subcutaneous tissue. Using a tamoxifen-activatable Esr1/Cre driver, Supv3L1 disruption resulted in growth retardation and aging phenotypes, including loss of adipose tissue and muscle mass, kyphosis, cachexia, and premature death. Many of the abnormalities seen in the Mx1-Cre mice, such as hyperkeratosis characterized by profound scaling of feet and tail, could also be detected in tamoxifen-inducible Cre mice. Conditional ablation of Supv3L1 in keratinocytes confirmed atrophic changes in the skin and ichthyosis-like changes. Together, these data indicate that Supv3L1 is important for the maintenance of the skin barrier. In addition, loss of Supv3L1 function leads to accelerated aging-like phenotypes.

Forced expression of the cell cycle inhibitor p57Kip2 in cardiomyocytes attenuates ischemia-reperfusion injury in the mouse heart.

BACKGROUND: Myocardial hypoxic-ischemic injury is the cause of significant morbidity and mortality worldwide. The cardiomyocyte response to hypoxic-ischemic injury is known to include changes in cell cycle regulators. The cyclin-dependent kinase inhibitor p57Kip2 is involved in cell cycle control, differentiation, stress signaling and apoptosis. In contrast to other cyclin-dependent kinase inhibitors, p57Kip2 expression diminishes during postnatal life and is reactivated in the adult heart under conditions of cardiac stress. Overexpression of p57Kip2 has been previously shown to prevent apoptotic cell death in vitro by inhibiting stress-activated kinases. Therefore, we hypothesized that p57Kip2 has a protective role in cardiomyocytes under hypoxic conditions. To investigate this hypothesis, we created a transgenic mouse (R26loxpTA-p57k/+) that expresses p57Kip2 specifically in cardiac tissue under the ventricular cardiomyocyte promoter Mlc2v. RESULTS: Transgenic mice with cardiac specific overexpression of p57Kip2 are viable, fertile and normally active and their hearts are morphologically indistinguishable from the control hearts and have similar heart weight/body weight ratio. The baseline functional parameters, including left ventricular systolic pressure (LVSP), left ventricular end diastolic pressure (LVEDP), LVdp/dtmax, heart rate (HR) and rate pressure product (RPR) were not significantly different between the different groups as assessed by the Langendorff perfused heart preparation. However, after subjecting the heart ex vivo to 30 minutes of ischemia-reperfusion injury, the p57Kip2 overexpressing hearts demonstrated preserved cardiac function compared to control mice with higher left ventricular developed pressure (63 +/- 15 vs 30 +/- 6 mmHg, p = 0.05), rate pressure product (22.8 +/- 4.86 vs 10.4 +/- 2.1 x 103bpm x mmHg, p < 0.05) and coronary flow (3.5 +/- 0.5 vs 2.38 +/- 0.24 ml/min, p <0.05). CONCLUSION: These data suggest that forced cardiac expression of p57Kip2 does not affect myocardial growth, differentiation and baseline function but attenuates injury from ischemia-reperfusion in the adult mouse heart.