A Mammalian Mitophagy Receptor,Bcl2-L-13, Recruits the ULK1 Complex to Induce Mitophagy

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Tet-on inducible system combined with in ovo electroporation dissects multiple roles of genes in somitogenesis of chicken embryos

The in ovo electroporation technique in chicken embryos has enabled investigators to uncover the functions of numerous developmental genes. In this technique, the ubiquitous promoter, CAGGS (CMV base), has often been used for overexpression experiments. However, if a given gene plays a role in multiple steps of development and if overexpression of this gene causes fatal consequences at the time of electroporation, its roles in later steps of development would be overlooked. Thus, a technique with which expression of an electroporated DNA can be controlled in a stage-specific manner needs to be formulated. Here we show for the first time that the tetracycline-controlled expression method, "tet-on" and "tet-off", works efficiently to regulate gene expression in electroporated chicken embryos. We demonstrate that the onset or termination of expression of an electroporated DNA can be precisely controlled by timing the administration of tetracycline into an egg. Furthermore, with this technique we have revealed previously unknown roles of RhoA, cMeso-1 and Pax2 in early somitogenesis. In particular, cMeso-1 appears to be involved in cell condensation of a newly forming somite by regulating Pax2 and NCAM expression. Thus, the novel molecular technique in chickens proposed in this study provides a useful tool to investigate stage-specific roles of developmental genes.     

Stable integration and conditional expression of electroporated transgenes in chicken embryos

The in ovo electroporation in chicken embryos has widely been used as a powerful tool to study roles of genes during embryogenesis. However, the conventional electroporation technique fails to retain the expression of transgenes for more than several days because transgenes are not integrated into the genome. To overcome this shortcoming, we have developed a transposon-mediated gene transfer, a novel technique in chicken manipulations. It was previously reported that the transposon Tol2, originally found in medaka fish, facilitates an integration of a transgene into the genome when co-acting with Tol2 transposase. In this study, we co-electroporated a plasmid containing a CAGGS-EGFP cassette cloned in the Tol2 construct along with a transposase-encoding plasmid into early presomitic mesoderm or optic vesicles of chicken embryos. This resulted in persistent expression of EGFP at least until embryonic day 8 (E8) and E12 in somite-derived tissues and developing retina, respectively. The integration of the transgene was confirmed by genomic Southern blotting using chicken cultured cells. We further combined this transposon-mediated gene transfer with the tetracycline-dependent conditional expression system that we also developed recently. With this combined method, expression of a stably integrated transgene could be experimentally induced upon tetracycline administration at relatively late stages such as E6, where a variety of organogenesis are underway. Thus, the techniques proposed in this study provide a novel approach to study the mechanisms of late organogenesis, for which chickens are most suitable model animals.     

Function of FGF signaling in the developmental process of the median fin fold in zebrafish

Median fins, unpaired appendages in fish, are fundamental locomotory organs that are believed to have evolved before paired lateral appendages in vertebrates. However, the early process of median fin development remains largely unknown. We investigated the early development of the median fin fold, a rudiment of median fins, and report here the process in zebrafish embryos and the function of FGF signaling in the process. Using expressions of three genes, dlx5a, sp9 and fgf24, as markers of different phases of fold development, our findings suggest that the early process of median fin fold development can be divided into two steps, specification of the median fin fold territory and construction of the fold structure. Both loss-of-function and gain-of-function assays revealed that FGF signaling plays roles in each step, suggesting a common mechanism for the development of median appendages and paired lateral appendages.     

Direct neurite-osteoblastic cell communication, as demonstrated by use of an in vitro co-culture system

Using an in vitro co-culture approach comprising cultured murine superior cervical ganglia and MC3T3-E1 osteoblast-like cells, we found that the addition of scorpion venom (SV) elicited neurite activation via intracellular Ca2+ mobilization and, after a lag period, osteoblastic Ca2+ mobilization. SV did not have any direct effect on the osteoblastic cells in the absence of neurites. The addition of an alpha1-adrenergic receptor (AR) antagonist, prazosin, dose-dependently prevented the osteoblastic activation that resulted as a consequence of neural activation by SV. These results demonstrate that osteoblastic activation occurred as a direct response to neuronal activation, which activation was mediated by alpha1-ARs in the osteoblastic cells.     

Splicing factor 3b subunit 4 binds BMPR-IA and inhibits osteochondral cell differentiation

Bone morphogenetic protein (BMP)-2/4 play critical roles in early embryogenesis and skeletal development. BMP-2/4 signals conduct into cells via two types of serine/threonine kinase receptors, known as BMPR-I (IA and IB) and BMPR-II. Here we identified splicing factor 3b subunit 4 (SF3b4) as a molecule that interacts with BMPR-IA, using a yeast two-hybrid screening with a human fetal brain cDNA library. Co-immunoprecipitation/immunoblot analysis confirmed their interaction in mammalian cells. By separation of the cell components, SF3b4 was present in the cell membrane fraction with BMPR-IA as well as in the nucleus. Overexpression of SF3b4 inhibited BMP-2-mediated osteogenic and chondrocytic differentiation of C2C12 and ATDC5 cells, respectively, and the endogenous expression level of SF3b4 decreased during differentiation in ATDC5 cells. By reporter gene assay, SF3b4 suppressed Id reporter gene activity, specific to the Smad1/5/8 pathway, but not TGFbeta-mediated reporter gene activity. Biotin labeling of the cell surface proteins followed by their immunoblot revealed that SF3b4 decreased the cell surface BMPRI-A levels. Further analysis by molecular modeling of the intracellular domain of BMPR-IA, coupled with binding studies of its several mutants, indicated that the site(s) for SF3b4 binding is not directly associated with the C-terminal lobe and the activation segment. Taken together, these results suggest that SF3b4, known to be localized in the nucleus and involved in RNA splicing, binds BMPR-IA and specifically inhibits BMP-mediated osteochondral cell differentiation.     

Thrombomodulin is a clock-controlled gene in vascular endothelial cells

Cardiovascular diseases are closely related to circadian rhythm, which is under the control of an internal biological clock mechanism. Although a biological clock exists not only in the hypothalamus but also in each peripheral tissue, the biological relevance of the peripheral clock remains to be elucidated. In this study we searched for clock-controlled genes in vascular endothelial cells using microarray technology. The expression of a total of 229 genes was up-regulated by CLOCK/BMAL2. Among the genes that we identified, we examined the thrombomodulin (TM) gene further, because TM is an integral membrane glycoprotein that is expressed primarily in vascular endothelial cells and plays a major role in the regulation of intravascular coagulation. TM mRNA and protein expression showed a clear circadian oscillation in the mouse lung and heart. Reporter analyses, gel shift assays, and chromatin immunoprecipitation analyses using the TM promoter revealed that a heterodimer of CLOCK and BMAL2 binds directly to the E-box of the TM promoter, resulting in TM promoter transactivation. Indeed, the oscillation of TM gene expression was abolished in clock mutant mice, suggesting that TM expression is regulated by the clock gene in vivo. Finally, the phase of circadian oscillation of TM mRNA expression was altered by temporal feeding restriction, suggesting TM gene expression is regulated by the peripheral clock system. In conclusion, these data suggest that the peripheral clock in vascular endothelial cells regulates TM gene expression and that the oscillation of TM expression may contribute to the circadian variation of cardiovascular events.     

Accumulation of 8-oxo-deoxyguanosine in cardiovascular tissues with the development of hypertension

Accumulation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in DNA is associated with mutagenesis and cell death. Little attention has been given to the biological significance of 8-oxo-dG accumulation in cardiovascular tissues during the different stage of hypertension and its prevention. We thus investigated the levels and localization of both 8-oxo-dG accumulation and expression of MTH1, which hydrolyzes 8-oxo-dGTP to prevent its incorporation into DNA, in the thoracic aorta prepared from stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wister-Kyoto rats (WKY), aged 5-32 weeks. HPLC-MS/MS analysis revealed that the levels of nuclear 8-oxo-dG in the aorta increased significantly in SHRSP, but not WKY, with aging. Immunohistochemical study revealed that both TUNEL reactivity and 8-oxo-dG immunoreactivity were increased in smooth muscle cells (SMC) and endothelial cells (EC) of the aorta with aging, and they exhibited similar distributions in serial sections. The number of 8-oxo-dG and TUNEL positive cells in EC, but not in SMC, was significantly higher in SHRSP than WKY at 32 weeks of age. In contrast, the expression levels of Mth1mRNA and MTH1 protein in the aorta were similarly decreased both in SHRSP and WKY with aging. However, the number of MTH1 expressing EC was remarkably increased in the older SHRSP compared to the younger ones or age-matched WKY. Hypertension significantly increased not only 8-oxo-dG accumulation but also the expression of MTH1 in EC of the aorta during aging. While accumulation of 8-oxo-dG in SMC of the aorta was slightly increased, the expression of MTH1 protein in SMC was rather decreased by hypertension. We thus suggest that MTH1 may protect EC in the aorta from the oxidative damage increased by hypertension.