BackgroundExtant cubozoans are voracious predators characterized by their square shape, four evenly spaced outstretched tentacles and well-developed eyes. A few cubozoan fossils are known from the Middle Cambrian Marjum Formation of Utah and the well-known Carboniferous Mazon Creek Formation of Illinois. Undisputed cubozoan fossils were previously unknown from the early Cambrian; by that time probably all representatives of the living marine phyla, especially those of basal animals, should have evolved.MethodsMicroscopic fossils were recovered from a phosphatic limestone in the Lower Cambrian Kuanchuanpu Formation of South China using traditional acetic-acid maceration. Seven of the pre-hatched pentamerous cubozoan embryos, each of which bears five pairs of subumbrellar tentacle buds, were analyzed in detail through computed microtomography (Micro-CT) and scanning electron microscopy (SEM) without coating.ResultsThe figured microscopic fossils are unequivocal pre-hatching embryos based on their spherical fertilization envelope and the enclosed soft-tissue that has preserved key anatomical features arranged in perfect pentaradial symmetry, allowing detailed comparison with modern cnidarians, especially medusozoans. A combination of features, such as the claustrum, gonad-lamella, suspensorium and velarium suspended by the frenula, occur exclusively in the gastrovascular system of extant cubozoans, indicating a cubozoan affinity for these fossils. Additionally, the interior anatomy of these embryonic cubozoan fossils unprecedentedly exhibits the development of many new septum-derived lamellae and well-partitioned gastric pockets unknown in living cubozoans, implying that ancestral cubozoans had already evolved highly specialized structures displaying unexpected complexity at the dawn of the Cambrian. The well-developed endodermic lamellae and gastric pockets developed in the late embryonic stages of these cubozoan fossils are comparable with extant pelagic juvenile cubomedusae rather than sessile cubopolyps, whcih indicates a direct development in these fossil taxa, lacking characteristic stages of a typical cnidarian metagenesis such as planktonic planula and sessile polyps.

To elucidate the mechanism whereby liganded receptor molecules enhance nucleotide exchange of GTPbinding regulatory proteins (G proteins), changes in the secondary structure of the recombinant G i1 ␣ subunit (G i1 ␣) upon binding with receptor mimetics, compound 48/80 and mastoparan, were analyzed by circular dichroism spectroscopy. Compound 48/80 enhanced the initial rate of GTP␥S binding to soluble G i1 ␣ 2.6-fold with an EC 50 of 30 g/ml. With the same EC 50 , the mimetic decreased the magnitude of ellipticity, which is ascribed to a reduction in ␣ helix content of the G i1 ␣ by 7%. Likewise, mastoparan also enhanced the rate of GTP␥S binding by 3.0-fold and decreased the magnitude of ellipticity of G i1 ␣ similar to compound 48/80. In corresponding experiments using a K349P-G i1 ␣, a G i1 ␣ counterpart of the unc mutant in G s ␣ in which Pro was substituted for Lys 349 , enhancement of the GTP␥S binding rate by both activators was quite small. In addition, compound 48/80 showed a negligible effect on the circular dichroism spectrum of the mutant. On the other hand, a proteolytic fragment of G i1 ␣ lacking the N-terminal 29 residues was activated and showed decreased ellipticity upon interaction with the compound, as did the wild-type G i1 ␣. Taken together, our results strongly suggest that the activator-induced unwinding of the ␣ helix of the G protein ␣ subunit is mechanically coupled to the enhanced release of bound GDP from the ␣ subunit.The central role played by trimeric GTP-binding regulatory proteins (G proteins) 1 in signal transduction in membranes has received considerable research attention (reviewed in Refs.1-3). Upon ligand binding, a G protein-coupled receptor promotes the release of GDP from inactive trimeric G␣␤␥, which allows binding of cytosolic GTP to the remaining G␣ subunit, thereby resulting in dissociation of trimeric G␣(GTP)␤␥ complex into active G␣⅐GTP and a ␤␥ subunit complex. In this activation process of G protein, the release of bound GDP is of particular interest as it is the rate-limiting step (4). The analyses of x-ray crystallographic structures of the ␣ subunit of G t and G i1 have indicated the presence of two domains, i.e. a GTPase (or Ras-like) domain comprised of ␣ helices and ␤ strands and a highly ␣ helical domain. In addition, the conformational changes induced in the ␣ subunit by nucleotide exchange (GDP 3 GTP␥S) and the mechanism of GTP hydrolysis have been determined (5-9). Conformational changes in the ␣ subunit upon binding with a ␤␥ subunit complex have been determined as well (10, 11). However, the mechanism whereby liganded receptor molecules enhance the GDP release from the ␣ subunit remains unclear, as pointed out previously (3, 12). Likewise, the conformational change of the ␣ subunit upon receptor binding is unknown. The use of physicochemical methods to gain further insight into these key reactions presents difficulties due to the facts that (i) only small amounts of G protein-coupled receptor proteins are expressed in cells, and (ii) no method exists ...

We investigated the symbiont-bearing benthic foraminifer Palaeonummulites venosus to determine the chamber building rate (CBR), test diameter increase rate (DIR), reproduction time and longevity using the 'natural laboratory' approach. This is based on the decomposition of monthly obtained frequency distributions of chamber number and test diameter into normally distributed components. Test measurements were taken using MicroCT. The shift of the mean and standard deviation of component parameters during the 15-month investigation period was used to calculate Michaelis-Menten functions applied to estimate the averaged CBR and DIR under natural conditions. The individual dates of birth were estimated using the inverse averaged CBR and the inverse DIR fitted by the individual chamber number or the individual test diameter at the sampling date. Distributions of frequencies and densities (i.e., frequency divided by sediment weight) based on both CBR and DIR revealed continuous reproduction throughout the year with two peaks, a stronger one in June determined as the onset of the summer generation (generation 1) and a weaker one in November determined as the onset of the winter generation (generation 2). This reproduction scheme explains the presence of small and large specimens in the same sample. Longevity, calculated as the maximum difference in days between the individual's birth date and the sampling date, is approximately 1.5 yr, an estimation obtained by using both CBR and DIR.

X‐ray microtomography has been applied successfully to obtain reliable microstructural information of many insect species. Nonetheless, the technique has not been widely applied to ambrosia beetles. The ambrosia beetle Euwallacea interjectus (Blandford) was first recorded as a vector of plant pathogenic fungus Ceratocystis ficicola Kajitani & Masuya, which has caused serious wilt disease in many fig orchards in Japan since 1999. Previous studies of E. interjectus have not described the mycangia (fungus‐storing organ) in detail. In this study, we non‐destructively examined the internal structure of an adult female of E. interjectus through computed microtomography scans. Paired mycangia were observed on typical computed tomography cross‐sections of the head. Each mycangium, ovoid in shape, was located in tissues just posterior to emarginated notch of eyes, adjacent to pharynx. Three dimensions (length × width × depth) of the mycangia were measured on stereography. We confirmed the absence of mycangia in the other body parts, such as elytra, prothorax and coxa of legs.

Representatives of the foraminifer Nummulites are important in Earth history for timing Cenozoic shallow-water carbonates. Taphonomic complexity explains the construction of carbonate buildups, but reproduction and life span of the constructing individuals are unknown. During the 15-month investigation period, asexually reproduced schizonts and gamonts showed equal proportions in the first half of this period, whereas gamonts predominated in the second half. Oscillations in cell growth are mainly caused by light intensities during chamber construction when minor differences in water depth increase the photosynthetic rate of endosymbiotic diatoms during neap tides. The continuous reproduction rate of N . venosus throughout the year is increased in subtropical calms by higher summer temperatures and the marginal input of inorganic nutrients during rainy seasons. The expected life span of both gamonts and schizonts are 18 months.