Selective and quickly reversible inactivation of mammalian neurons in vivo using the Drosophila allatostatin receptor

Genetic strategies for perturbing activity of selected neurons hold great promise for understanding circuitry and behavior. Several such strategies exist, but there has been no direct demonstration of reversible inactivation of mammalian neurons in vivo. We previously reported quickly reversible inactivation of neurons in vitro using expression of the Drosophila allatostatin receptor (AlstR). Here, adeno-associated viral vectors are used to express AlstR in vivo in cortical and thalamic neurons of rats, ferrets, and monkeys. Application of the receptor's ligand, allatostatin (AL), leads to a dramatic reduction in neural activity, including responses of visual neurons to optimized visual stimuli. Additionally, AL eliminates activity in spinal cords of transgenic mice conditionally expressing AlstR. This reduction occurs selectively in AlstR-expressing neurons. Inactivation can be reversed within minutes upon washout of the ligand and is repeatable, demonstrating that the AlstR/AL system is effective for selective, quick, and reversible silencing of mammalian neurons in vivo.     

Upregulation of thromboxane synthase in human colorectal carcinoma and the cancer cell proliferation by thromboxane A2

Tumor growth of colorectal cancers accompanies upregulation of cyclooxygenase-2, which catalyzes a conversion step from arachidonic acid to prostaglandin H(2) (PGH(2)). Here, we compared the expression levels of thromboxane synthase (TXS), which catalyzes the conversion of PGH(2) to thromboxane A(2) (TXA(2)), between human colorectal cancer tissue and its accompanying normal mucosa. It was found that TXS protein was consistently upregulated in the cancer tissues from different patients. TXS was also highly expressed in human colonic cancer cell lines. Depletion of TXS protein by the antisense oligonucleotide inhibited proliferation of the cancer cells. This inhibition was rescued by the direct addition of a stable analogue of TXA(2). The present results suggest that overexpression of TXS and subsequent excess production of TXA(2) in the cancer cells may be involved in the tumor growth of human colorectum.     

A geographical model of high species diversity

Several cases of high species diversity, for example in tropical rain forests, imply that speciation has been frequent or rapid. However, how speciation could proceed so frequently as to generate extraordinary diversity still remains unsolved, despite recent advancements of diverse theories of allopatric and sympatric speciation. This paper presents a theoretical model that demonstrates the process of frequent speciation by means of geographical fragmentation. We focus on allopatric speciation and explore the evolutionary effect of fragmentation and extinction of demes (subpopulations) in a widespread species or species group. After a large contagious population of a single species is fragmented into demes, extinction of some demes could result in isolation of multiple demes. Thus, several demes could become good species simultaneously through the process of allopatric speciation. We apply the random extinction method to this fragmentation process where demes become randomly extinct. The present model illustrates that frequent speciation could occur in communities where large environmental changes frequently take place.     

5′-O-Dephosphorylated 2′,5′-oligoadenylate (2-5A) with 8-methyladenosine at the 2′-terminus activates human RNase L

Human ribonuclease L (RNase L), an interferon-induced endoribonuclease, becomes enzymatically active after binding to 2-5A. The 5′-phosphoryl group of 2-5A is reportedly necessary for the conformational change leading to RNase L activation. However, we found that 5′-O-dephosphorylated 2-5A tetramer analogs with 8-methyladenosine at the 2′-terminus were more effective as an activator of RNase L than the parent 2-5A tetramer. Introduction of 8-methyladenosine is thought to induce a dramatic shift of 2-5A in the binding site of RNase L.     

Biochemical screening of stable dinucleosomes using DNA fragments from a dinucleosome DNA library

The dinucleosome is an informative unit for analysis of the higher-order chromatin structure. DNA fragments forming stable dinucleosomes were screened from a dinucleosome DNA library after the reconstitution of nucleosomes in vitro and digestion with micrococcal nuclease. Reconstituted dinucleosomes showed a diversity of sensitivity to micrococcal nuclease, suggesting that the biochemical stability of a dinucleosome depends, in part, on the DNA fragments. The DNA fragments after the screening were classified into three groups represented by clones bf10, af14 and af32 according to the sensitivity to micrococcal nuclease. Mapping of the nucleosome boundaries by Southern blotting of the DNA after restriction digestion and by primer extension analysis showed that each nucleosome position of clone af32 was fixed. Analysis of reconstituted dinucleosomes using mutant DNA fragments of clone af32 revealed a unique property characteristic of a key nucleosome, given that the replacement of a DNA fragment corresponding to the right nucleosome position resulted in marked sensitivity to micrococcal nuclease, whereas the replacement of the other nucleosome fragment had almost no effect on sensitivity as compared to the original af32 construct. The mutant construct in which the right nucleosome was removed showed multiple nucleosome phases, suggesting that the right nucleosome stabilized first each mononucleosome and then the dinucleosome. An oligonucleotide bending assay revealed that the DNA fragment in the right nucleosome included curved DNA, suggesting that the positioning activity of the nucleosome was attributed to its DNA structure. These results suggest that information for forming stable dinucleosome is embedded in the genomic DNA and that a further characterization of the key nucleosome is useful for understanding the building up of the chromatin structure.     

Rice plant development: from zygote to spikelet

Rice is becoming a model plant in monocotyledons and a model cereal crop. For better understanding of the rice plant, it is essential to elucidate the developmental programs of the life cycle. To date, several attempts have been made in rice to categorize the developmental processes of some organs into substages. These studies are based exclusively on the morphological and anatomical viewpoints. Recent advancement in genetics and molecular biology has given us new aspects of developmental processes. In this review, we first describe the phasic development of the rice plant, and then describe in detail the developmental courses of major organs, leaf, root and spikelet, and specific organs/tissues. Also, for the facility of future studies, we propose a staging system for each organ.