Strain difference in the radiosensitivity of immunocompetent cells and its influence on the residual host-vs-graft reaction in lethally irradiated mice grafted with semiallogeneic bone marrow

A striking difference in radiosensitivity was noted between C3H/He (H-2k) and C57BL/6J (H-2b) strain mice when assessed by primary anti-SRBC PFC response of intact animals and primary cell-mediated lympholysis (CML) response of spleen cells to allogeneic cells in vitro, the C3H strain being more radioresistant. On the other hand, when C3H and B6 mice were exposed to 6.62 to 10.40 grays (Gy) of x-rays and then were transplanted with 2 X 10(6) bone marrow cells from B6C3F1 (H-2b/k) donor mice within 3 hr or at 24 hr after radiation exposure, the early mortality caused by residual host-vs-graft (HVG) reaction was much higher when C3H mice were used as recipients. Furthermore, the proportion of surviving animals manifesting host-type lymphohemopoiesis, i.e., host-type revertants, was much higher in B6C3F1 to C3H than in B6C3F1 to B6 combination. Spleen cells from such host-type revertants manifested strong anti-donor reactivity when assessed by mixed lymphocyte reaction (MLR) and/or CML in vitro. Increase of radiation doses to the recipients to 10.40 Gy resulted in 100% survival and 100% donor-type lymphohemopoiesis in both groups of chimeras. These results indicate strongly that a genetic difference in radiosensitivity of immune system of the recipients can greatly influence the magnitude of residual HVG reactions observed in hybrid to parental strain bone marrow transplantation in mice.     

Asexual reproductive organ-specific expression of the glyceraldehyde-3-phosphate dehydrogenase 2 gene of Pilobolus crystallinus

Pilobolus crystallinus has three putative glyceraldehyde-3-phosphate dehydrogenase (gapdh) genes (pcgapdh1, pcgapdh2 and pcgapdh3). The results of this study demonstrate that expression of pcgapdh2 was increased by irradiation and that this increased expression was correlated with the formation of asexual reproductive organs (trophocysts). Interestingly, expression of pcgapdh2 was restricted to trophocysts. The formation of trophocysts was likely promoted by light, and the expression of pcgapdh2 was increased as a result of trophocyst formation. This is the first report that shows the regulation of a gapdh gene in an organ-specific manner in fungi.     

Retinal Attachment Instability Is Diversified among Mammalian Melanopsins

Melanopsins play a key role in non-visual photoreception in mammals. Their close phylogenetic relationship to the photopigments in invertebrate visual cells suggests they have evolved to acquire molecular characteristics that are more suited for their non-visual functions. Here we set out to identify such characteristics by comparing the molecular properties of mammalian melanopsin to those of invertebrate melanopsin and visual pigment. Our data show that the Schiff base linking the chromophore retinal to the protein is more susceptive to spontaneous cleavage in mammalian melanopsins. We also find this stability is highly diversified between mammalian species, being particularly unstable for human melanopsin. Through mutagenesis analyses, we find that this diversified stability is mainly due to parallel amino acid substitutions in extracellular regions. We propose that the different stability of the retinal attachment in melanopsins may contribute to functional tuning of non-visual photoreception in mammals.     

RNA-Induced Interference with Animal Virus Infection

Some RNAs, including both single- and double-stranded RNAs, when incubated with chick embryo cell culture induce cellular resistance against viruses. Evidence was now obtained indicating that the induction of cellular resistance by RNA depends on the cellular metabolic activity, especially on the synthesis of cellular RNA and protein. Thus, inhibitors of RNA and protein synthesis, actinomycin D and cycloheximide, were found to inhibit the development of an antiviral state when added before, or during the relatively early period of, incubation of the cells with RNA. In the course of induction of cellular resistance, three stages may be distinguished, the priming stage, the developing stage, and the established resistant stage.     

Organic Acid Metabolism in Aluminum-Phosphate Utilizing Cells of Carrot (Daucus carota L.)

Carbohydrate metabolism in Al-phosphate utilizing cells of carrot[designated as IPG, Koyama et al. (1992) Plant Cell Physiol.33: 171], which grow normally in Al-phosphate medium accompaniedby citrate excretion, was investigated. The excretion of citratewas strongly related to the availability of sucrose in medium,indicating that citrate excretion was severely limited by sucrosein medium. The ratio of the amount of carbon in the excretedcitrate to the consumed sucrose, was significantly higher inIPG cells than in wild-type cells. When 50% of the sucrose inthe medium was consumed, the ratio was 0.6% for the IPG cellsand 0.2% the wild-type cells. Under these conditions, IPG cellsshowed altered citrate synthesis metabolism, which resultedin increased citrate production. Specific activity of mitochondrialcitrate synthase was higher in IPG cells than in wild-type cells,whereas the activity of cytosolic NADP-specific isocitrate dehydrogenasewas lower in IPG cells than in wild-type cells. (Received August 27, 1998; Accepted February 21, 1999)     

Pr-SNTX,a short-chain three-finger toxin from Papuan pigmy mulga snake,is an antagonist of muscle-type nicotinic acetylcholine receptor (α2βδε)

Three-finger toxins (3FTxs) are one of the major components in snake venoms. In this study, we isolated a cDNA encoding a short-chain 3FTx, Pr-SNTX, from Pseudechis rossignolii. The amino acid sequence of Pr-SNTX is nearly identical to that of its ortholog in Pseudechis australis. Pr-SNTX protein inhibited muscle-type (α₂βδε), but not neuronal α7 nicotinic acetylcholine receptor (nAChR) activity.