Computer simulation of engulfment and other movements of embryonic tissues

Using a model proposed earlier by Goel et al. and a set of plausible motility rules, a computer simulation of engulfment of two or more intact embryonic tissues is successfully carried out. The same motility rules are used to simulate the rounding up of a tissue, centralization of one tissue within another tissue (a phenomenon not yet observed), and phase inversion, a process which may have relevance to differentiation. The finnal structures bear a good resemblance to those observed experimentally. The software, in conjunction with an appropriate hardware configuration, allows a visual display of the dynamics of cellular movement. These simulations indicate that the range of inter-cellular interactions controlling these tissue rearrangements extends only one or two cell diameters.     

Action of alkyl cations and the natural ATPase inhibitor from mitochondria on soluble mitochondrial ATPase

The effect of the natural ATPase inhibitor and octylguanidine on the ATPase activity of soluble oligomycin-insensitive mitochondrial F₁ were compared. Both compounds induced a maximal inhibition of 60–80% in various preparations of F₁ studied. The inhibition was of the uncompetitive type with respect to MgATP, and the action of the compounds was partially additive. The data suggest that octylguanidine reproduces the action of the natural ATPase inhibitor. Alkylammonium salts also affect the ATPase activity in a similar form. F₁ bound to Sepharose-hexylammonium is largely inactive, whilst free hexylammonium at higher concentrations induces only a partial inhibition of the activity. This suggests that the degree of immobilization of F₁ is related to the magnitude of inhibition of ATPase activity induced by alkyl cations. The binding of F₁ to Sepharose-hexylammonium is prevented by high concentrations of Na⁺ or K⁺.     

Purification of membrane-bound polyvinyl alcohol oxidase in Pseudomonas sp. VM15C

Abstract Polyvinyl alcohol (PVA) was utilized by a symbiotic mixed culture which was composed of Pseudomonas putida VM15A and Pseudomonas sp. VM14C. The PVA oxidase was found in the culture fluid, membrane, and cytosol fractions of VM15C. The membrane-bound PVA oxidase was purified by several steps of chromatography. The enzyme (p I = 9.6) exhibited the maximum activity at pH 8.0 to 8.4 and 45°C, and utilized secondary alcohol as well as PVA. The enzyme showed the PVA dehydrogenating activity linking with phenazine ethosulfate, indicating the possibility that PVA oxidation is coupled with an electron transport chain on the bacterial membrane.     

Prolactin modifies the prostaglandin synthesis, prolactin binding and fluidity of mouse liver membranes

The objective of these studies was to determine if prolactin, known to induce its own receptors, alters the prostaglandin (PG) synthesis which could, in turn, modify the fluidity of the membrane and thus alter the functionality of prolactin receptors. Adult male C₃H mice were injected subcutaneously with 100 μg of oPRL every 4 h for 0, 24 or 48 h and sacrificed 8 h after receiving the last injection. Liver 100,000 × $\text{g}$ membrane pellets were used in the measurement of these parameters. The amount of binding of prolactin to these membranes increased with the duration of injections, the values being 179 and 244% of control values after 24 and 48 h of injections, respectively. The amounts of PGF_2α and PGE synthesized also increased after these injections, the values being 127 and 270% of control for PGF_2α and 634 and 695% of control values for PGE after 24 and 48 h of injections, respectively. Fluorescence polarization, an index of microviscosity, was decreased by 14 and 20% after 24 and 48 h of PRL administration, respectively. Previous studies have demonstrated simultaneous in vitro effects of prostaglandin on both prolactin receptors and membrane fluidity. The current data are in agreement with those observations and suggest that prolactin may modulate its own receptor by increasing the fluidity of the membrane in which it exists by alterations within the PG cascade. Such biochemical changes may then modify existing restraints and allow the hormone receptor to assume a more functional configuration.     

Intraspecific variation in the response of rice (Oryza sativa) to increased CO2– photosynthetic, biomass and reproductive characteristics

Two rice ( Oryza sativa L.) cultivars of contrasting morphologies, IR-36 and Fujiyama-5, were exposed to ambient (360 μl l⁻¹) and ambient plus 300 μl l⁻¹ CO₂ from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO₂ resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO₂ environment. The photosynthetic response at 5% CO₂ and the response of CO₂ assimilation (A) to internal CO₂ (C_i) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO₂ were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO₂ environment with a significant increase in harvest index for IR-36 but not for Fujiyama-5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO₂ environment.     

Occurrence of 28- and 27-Carbon ecdysteroids and sterols in developing worker pupae of the leaf-cutting ant acromyrmex octospinosus (reich) (hymenoptera,formicidae: Attini)

The major ecdysteroids in large worker pupae of the leaf-cutting ant Acromyrmex octospinosus were characterized at the peak ecdysteroid concentration by using high-performance liquid chromatography, enzyme immunoassay, and mass spectrometry. In decreasing amounts, they were determined to be makisterone A, an unidentified C₂₈ ecdysteroid bearing a molecular weight of 494, 20-hydroxyecdysone (ratio of 1 to 6 as compared to makisterone A), and putative but negligible ecdysone. The presence of both C₂₈ and C₂₇ ecdysteroids is discussed in relation to the content of 4-desmethylsterols determined by gas chromatography and mass spectrometry to be ergosta-5,7,24 (28)-trien-3β-ol, ergosterol, ergosta-5,7-dien-3β-ol and ergosta-7,24(28)-dien-3β-ol for the main sterols, and with a small amount of cholesterol.     

Concentration-dependent inducing activity of activin A

Summary Human recombinant activin A, which is identical with erythroid differentiation factor (EDF), was tested for its mesoderm-inducing activity in concentrations from 0.3–50 ng/ml, using ectoderm of Xenopus late blastula (Stage 9) as the responding tissue. At a low concentration of activin A, blood-like cells, mesenchyme, and coelomic epithelium were induced; at a moderate concentration muscle and neural tissue, and at a high concentration notochord. Activin A thus induced all mesodermal tissues in a dose-dependent manner, such that a low dose induced ventral structures and a high dose induced dorsal structures. Activin may act as an intrinsic inducing molecule responsible for establishing the dorso-ventral axis in early Xenopus development. Offprint requests to: M. Asashima