Mitochondrial DNA sequences of various species of the genus Equus with special reference to the phylogenetic relationship between Przewalskii's wild horse and domestic horse

The noncoding region between tRNA^Pro and the large conserved sequence block is the most variable region in the mammalian mitochondrial DNA D-loop region. This variable region (ca. 270 bp) of four species of Equus, including Mongolian and Japanese native domestic horses as well as Przewalskii's (or Mongolian) wild horse, were sequenced. These data were compared with our recently published Thoroughbred horse mitochondrial DNA sequences. The evolutionary rate of this region among the four species of Equus was estimated to be 2–4 × 10^–8 per site per year. Phylogenetic trees of Equus species demonstrate that Przewalskii's wild horse is within the genetic variation among the domestic horse. This suggests that the chromosome number change (probably increase) of the Przewalskii's wild horse occurred rather recently.Correspondence to: N. Ishida     

Inducible ablation of melanopsin-expressing retinal ganglion cells reveals their central role in non-image forming visual responses

Rod/cone photoreceptors of the outer retina and the melanopsin-expressing retinal ganglion cells (mRGCs) of the inner retina mediate non-image forming visual responses including entrainment of the circadian clock to the ambient light, the pupillary light reflex (PLR), and light modulation of activity. Targeted deletion of the melanopsin gene attenuates these adaptive responses with no apparent change in the development and morphology of the mRGCs. Comprehensive identification of mRGCs and knowledge of their specific roles in image-forming and non-image forming photoresponses are currently lacking. We used a Cre-dependent GFP expression strategy in mice to genetically label the mRGCs. This revealed that only a subset of mRGCs express enough immunocytochemically detectable levels of melanopsin. We also used a Cre-inducible diphtheria toxin receptor (iDTR) expression approach to express the DTR in mRGCs. mRGCs develop normally, but can be acutely ablated upon diphtheria toxin administration. The mRGC-ablated mice exhibited normal outer retinal function. However, they completely lacked non-image forming visual responses such as circadian photoentrainment, light modulation of activity, and PLR. These results point to the mRGCs as the site of functional integration of the rod/cone and melanopsin phototransduction pathways and as the primary anatomical site for the divergence of image-forming and non-image forming photoresponses in mammals.     

Formation and stability of complex organic compounds in space environments.

Complex organic compounds have been found in extraterrestrial bodies such as meteorites and comets. We confirmed the formation of complex organic compounds that contained amino acid precursors from a mixture of carbon monoxide (or methanol), ammonia and water by radiation or UV. Molecular weights of the complex organics were several thousands. Stability of the complex precursors was studied. When free amino acids were irradiated with gamma rays or synchrotron radiation, they easily decomposed. The complex precursors were, however, much more stable than free amino acid against irradiation. We propose to examine the formation and alteration of amino acid precursors in space by using exposed facility of ISS.     

Pfaffosides,nortriterpenoid saponins,from Pfaffia paniculata

Three new nortriterpene saponins having inhibitory effects on the growth of cultured tumor cells, named pfaffosides D, E and F, have been isolated from Pfaffia paniculata. Their structures have been established as 3β-O-[β-d-xylopyranosyl-(1 → 2)-β-d-(6-O-n-butyl) glucuronopyranosyl]-pfaffic acid-(28 → 1)-β-d-glucopyranosyl ester, 3β-O-[β-d-xylopyranosyl-(1 → 2)-β-d(6-O-methyl)glucuronopyranosyl]-pfaffic acid-(28 → 1)-β-d glucopyranosyl ester and 3β-O[β-d-glucuronopyranosyl]-pfaffic acid respectively, based on their chemical and spectroscopic properties     

Disruption of a single copy of the p38alpha MAP kinase gene leads to cardioprotection against ischemia-reperfusion

The p38 mitogen-activated protein kinase (p38) is activated in the heart during ischemia-reperfusion. However, it is not clear whether the activation of p38 is the protective response or the kinase mediates the cellular damage by ischemia-reperfusion. We examined the role of p38alpha in ischemia-reperfusion injury by studying p38alpha(+/-) mice. The p38alpha protein level in the p38alpha(+/-) heart was 50+/-8.7% compared with that in the p38alpha(+/+) heart. Upon reperfusion following ischemia for 25min, p38alpha activity was transiently increased. The maximum level of p38 activity in p38alpha(+/-) was 60+/-10.5% compared with that in p38alpha(+/+). In the p38alpha(+/+) heart, 25min ischemia and 2h reperfusion resulted in necrotic injury (37.1+/-2.7% of the area at risk), whereas infarct size was drastically reduced to 7.2+/-0.7% in the p38alpha(+/-) heart. These suggested that p38alpha plays a pivotal role in the signal transduction pathway mediating myocardial cell death caused by ischemia-reperfusion.     

Chk1 is activated transiently and targets Cdc25A for degradation at the Xenopus midblastula transition

In Xenopus embryos, cell cycle elongation and degradation of Cdc25A (a Cdk2 Tyr15 phosphatase) occur naturally at the midblastula transition (MBT), at which time a physiological DNA replication checkpoint is thought to be activated by the exponentially increased nucleo-cytoplasmic ratio. Here we show that the checkpoint kinase Chk1, but not Cds1 (Chk2), is activated transiently at the MBT in a maternal/zygotic gene product-regulated manner and is essential for cell cycle elongation and Cdc25A degradation at this transition. A constitutively active form of Chk1 can phosphorylate Cdc25A in vitro and can target it rapidly for degradation in pre-MBT embryos. Intriguingly, for this degradation, however, Cdc25A also requires a prior Chk1-independent phosphorylation at Ser73. Ectopically expressed human Cdc25A can be degraded in the same way as Xenopus Cdc25A. Finally, Cdc25A degradation at the MBT is a prerequisite for cell viability at later stages. Thus, the physiological replication checkpoint is activated transiently at the MBT by developmental cues, and activated Chk1, only together with an unknown kinase, targets Cdc25A for degradation to ensure later development.     

Inducible nitric oxide synthase augments injury elicited by oxidative stress in rat cardiac myocytes

The effects of nitric oxide (NO) produced by cardiac inducibleNO synthase (iNOS) on myocardial injury after oxidative stress wereexamined. Interleukin-1 induced cultured rat neonatal cardiac myocytes to express iNOS. After induction of iNOS,L-arginine enhanced NOproduction in a concentration-dependent manner. Glutathione peroxidase(GPX) activity in myocytes was attenuated by elevated iNOS activity andby an NO donor,S-nitroso-N-acetyl-penicillamine (SNAP). Although NO production by iNOS did not induce myocardial injury, NO augmented release of lactate dehydrogenase from myocyte cultures after addition ofH₂O₂(0.1 mM, 1 h). Inhibition of iNOS withN-nitro-L-argininemethyl ester ameliorated the effects of NO-enhancing treatments onmyocardial injury and GPX activity. SNAP augmented the myocardialinjury induced byH₂O₂.Inhibition of GPX activity with antisense oligodeoxyribonucleotide forGPX mRNA increased myocardial injury byH₂O₂.Results suggest that the induction of cardiac iNOS promotes myocardialinjury due to oxidative stress via inactivation of the intrinsicantioxidant enzyme, GPX.