Precursor Bodies Research Articles

Parent body depth–pressure–temperature relationships and the style of the ureilite anatexis

Abstract– New analyses of mafic silicates from 14 ureilite meteorites further constrain a strong correlation (Singletary and Grove 2003) between olivine‐core Fo ratio and the temperature of equilibration (TE) recorded by the composition of pigeonite. This correlation may be compared with relationships implied by various postulated combinations of Fo and pressure P in models for ureilite genesis by a putative process of anatectic (depth‐linked, P‐controlled) smelting. In such models, any combination of Fo and P together fixes the temperature of smelting. Agreement between the observed correlation and these models is poor. The anatectic smelting model also carries implausible implications for the depth range at which ureilites of a given composition (Fo) form. Actual ureilites (and polymict ureilite clasts: Downes et al. 2008) show a distribution strongly skewed toward the low‐Fo end of the compositional range, with approximately 58% in the range Fo76–81. In contrast, the P‐controlled smelting model implies that the Fo76–81 region is a small fraction of the volume of the parent body: not more than 3.2%, in a model consistent with the Fo‐TE observations; and even ignoring the Fo‐TE evidence not more than 11% (percentages cited require optimal assumptions concerning the size of the parent body). This region also must occur deep within the body, where no straightforward model would imply a strong bias in the impact‐driven sampling process. The ureilites did not derive preponderantly from one atypical “largest offspring” disruption survivor, because cooling history evidence shows that after the disruption (whose efficiency was increased by gas jetting), all of the known ureilites cooled in bodies that were tiny (mass of order 10−9) in comparison with the precursor body. The Ca/Al ratio of the ureilite starting matter cannot be 2.5 times chondritic, as has been suggested, unless the part of the body from which ureilites come is at most 50% of the whole body. Published variants of the anatectic, P‐controlled smelting model have the ureilites coming from a region that is >50 vol% of their parent body; and to invoke a larger body would have the drawback of implying that the Fo76–81 spike represents an even smaller fraction of the parent body’s interior. The ureilites’ moderate depletions in incompatible elements are difficult to reconcile with a fractional fusion model. It is not plausible that melt formed grossly out of equilibrium with the medium‐sized ureilite crystals. The alternative to pressure‐controlled smelting, i.e., a model of gasless or near‐gasless anatexis, has very different implications for the size and evolution of the original parent body. To yield internal pressures prohibitive of smelting in even the shallowest and most ferroan portion of its anatectic mantle, the body would have to be larger than roughly 690 km in diameter. A 400 km body would have approximately 12 vol% of the interior (or 13 vol% of the interior apart from the thermal “skin” that never undergoes anatexis) prone, if both extremely shallow and extremely ferroan, to mild smelting. Gasless anatexis also implies that this large parent body was compositionally, at least in terms of mg, grossly heterogeneous before anatexis, probably (in view of the oxygen isotopic diversity) as a result of mixed accretion.

Production of Giant Mouse Oocyte Nucleoli and Assessment of Their Protein Content

Compared with advanced developmental stage embryos and somatic cells, fully grown mammalian oocytes contain specific nucleolus-like structures (NPB - nucleolus precursor bodies). It is commonly accepted that they serve as a store of material(s) from which typical nucleoli are gradually formed. Whilst nucleoli from somatic cells can be collected relatively easily for further biochemical analyses, a sufficient number of oocyte nucleoli is very difficult to obtain. We have found that isolated oocytes nucleoli fuse very efficiently when contact is established between them. Thus, well visible giant nucleoli can be obtained, relatively easily handled and then used for further biochemical analyses. With the use of colloidal gold staining, we estimated that a single fully grown mouse oocyte nucleolus contains approximately 1.6 ng of protein. We do believe that this approach will accelerate further research aiming at analyzing the composition of oocyte nucleoli in more detail.

Regulation of fusion of the nucleolar precursor bodies following activation of mouse oocytes: roles of the maturation-promoting factors and mitogen-activated protein kinases

Fusion of nucleoli or nucleolus precursor bodies (NPBs) has been observed during somatic cell interphase and pronuclear development of human zygotes; however, the underlying mechanism is unknown. NPB fusion and its regulation by mitogen-activated protein kinase (MAPK) and maturation-promoting factor (MPF) were studied in activated mouse oocytes. Small NPBs appeared about 4 h after ethanol activation, and took about 1.5 h to fuse into a large NPB, which persisted for about 10 h before disappearance. Analysis of the temporal windows for kinase action indicated that a high MAPK activity during the first 2 h and a low MPF activity during the first 3-4 h after activation were essential for subsequent NPB fusion. A preactivation decline in MAPK activity was associated with decreased NPB fusion following activation of aged oocytes. While MAPK inactivation by regulator U0126 prevented NPB fusion in oocytes activated by ethanol or 5 min Sr2+ treatments, it had no effect on oocytes fertilized or activated by 6 h Sr2+ treatment. In most cases, while rates of pronuclear formation did not differ, rates of NPB fusion differed significantly between different treatments. Our results suggest that: (i) the MAPK and MPF activities at the initial stage of activation regulate NPB fusion after pronuclear formation; (ii) pronuclear assembly and NPB fusion are two separable events that might be controlled by different mechanisms; and (iii) high MAPK activity and low MPF activity at the initial stage of activation is essential for NPB fusion when only one calcium rise is induced by ethanol, while inhibition of MAPK activity does not affect NPB fusion when the repetitive intracellular Ca2+ rises are induced after fertilization.

Role of Ooplasm in Nuclear and Nucleolar Remodeling of Intergeneric Somatic Cell Nuclear Transfer Embryos during the First Cell Cycle

Initially, development of the zygote is under control of the oocyte ooplasm. However, it is presently unknown if and to what extent is the ooplasm able to interact with a transferred somatic cell from another species in the context of interspecies somatic cell nuclear transfer (SCNT). Here, one-cell stage embryos were processed at different points in time post activation (2 hpa, 4 hpa, 8 hpa, and 12 hpa) for detailed nuclear and nucleolar analysis by TEM, and immunofluorescence for visualization of nucleolar proteins related to transcription (UBF) and processing (fibrillarin). Bovine and porcine intergeneric SCNT embryos were compared to their parthenogenetic counterparts to assess the effects of the introduced somatic cell. Despite the absence of morphological remodeling (premature chromatin condensation, nuclear envelope breakdown), reconstructed embryos showed nuclear and nucleolar precursor body (NPB) morphology similar to the host ooplasm, which, together with detected posttranslational activity of somatic cell introduced into the bovine ooplasm, suggests a universal function of ooplasmic factors. However, the lack of distinct UBF localization in intergeneric embryos indicates failures in sequence-specific interactions between the ooplasm and chromatin of another genus. In conclusion, the results demonstrate a possible reason why the intergeneric SCNT embryos never reached the full term.

Formation of nucleoli in interspecies nuclear transfer embryos derived from bovine, porcine, and rabbit oocytes and nuclear donor cells of various species

The most successful development of interspecies somatic cell nuclear transfer (iSCNT) embryos has been achieved in closely related species. The analyses of embryonic gene activity in iSCNT embryos of different species combinations have revealed the existence of significant aberrations in expression of housekeeping genes and genes dependent on the major embryonic genome activation (EGA). However, there are many studies with successful blastocyst (BL) development of iSCNT embryos derived from donor cells and oocytes of animal species with distant taxonomical relations (inter-family/inter-class) that should indicate proper EGA at least in terms of RNA polymerase I activation, nucleoli formation, and activation of genes engaged in morula and BL formation. We investigated the ability of bovine, porcine, and rabbit oocytes to activate embryonic nucleoli formation in the nuclei of somatic cells of different mammalian species. In iSCNT embryos, nucleoli precursor bodies originate from the oocyte, while most proteins engaged in the formation of mature nucleoli should be transcribed from genes de novo in the donor nucleus at the time of EGA. Thus, the success of nucleoli formation depends on species compatibility of many components of this complex process. We demonstrate that the time and cell stage of nucleoli formation are under the control of recipient ooplasm. Oocytes of the studied species possess different abilities to support nucleoli formation. Formation of nucleoli, which is a complex but small part of the whole process of EGA, is essential but not absolutely sufficient for the development of iSCNT embryos to the morula and BL stages.

37 LIMITATION OF BOVINE OOPLASM IN REPROGRAMMING OF PORCINE SOMATIC CELLS

Ooplasm posses several, undefined factors allowing for reprogramming of somatic genome into pluripotent state. However, it is presently unknown if and to what extent the ooplasm is able to interact with a transferred somatic cell from another species in the context of interspecies somatic cell nuclear transfer (SCNT). The 1-cell stage embryos were processed at different time points (2, 4, 8, and 12 h post-activation) for detailed nuclear and nucleolar analysis by TEM, and immunofluorescence for visualisation of nucleolar proteins related to transcription (UBF) and processing (fibrillarin). The embryos produced by SCNT of porcine fibroblast into non-activated bovine ooplasm were compared to bovine parthenogenetic counterparts. In the absence of morphological remodelling features (premature chromatin condensation, nuclear envelope break-down), intergeneric embryos showed bovine nuclear and nucleolar precursor body (NPB) morphology. The somatic cell introduced into the bovine ooplasm displayed intranuclear activity at the post-translational level signalling a universal function of ooplasmic factors. The lack of distinct UBF localization in intergeneric embryos, however, suggests failures in sequence-specific interactions between the ooplasm and transferred cell from another genus. We conclude that sperm or a somatic cell of the same species is required for successful embryonic development. Clonet MRTN-CT-2006-035468; MedRat LSHG-CT-2006-518240; PluriSys FP7-HEALTH-2007-223485; DFG, Alexander von Humboldt fellowship, VEGA 1/0057/08; VEGA 1/0012/10.

Fine structure of the vomeronasal organ in the grass lizard, Takydromus tachydromoides

The squamates are composed of many taxa, among which there is morphological variation in the vomeronasal organ (VNO). To elucidate the evolution of chemoreception in squamate reptiles, morphological data from the VNO from a variety of squamate species is required. In this study, the morphology of the VNO of the grass lizard Takydromus tachydromoides was examined using light and electron microscopy. The VNO consists of a pair of dome-shaped structures, which communicate with the oral cavity. There are no associated glandular structures. Microvilli are present on the apical surfaces of receptor cells in its sensory epithelium, as well as on supporting cells, and there are centrioles and ciliary precursor bodies on the dendrites. In addition to ciliated cells and basal cells in the non-sensory epithelium, there is a novel type of non-ciliated cell in T. tachydromoides. They have constricted apical cytoplasm and microvilli instead of cilia, and are sparsely distributed in the epithelium. Based on these results, the variation in the morphology of the VNO in scincomorpha, a representative squamate taxon, is discussed.

Human zygote morphological indicators of higher rate of arrest at the first cleavage stage

A little studied aspect of developmental arrest (DA) in ART is zygote arrest (ZA). Etiologically, blockage at the first cleavage stage includes molecular and chromosomal anomalies, some of which manifest morphologically. Given considerations on embryo culture, transfer and cryopreservation, optimal zygote selection is very important. The aim of this study was to ascertain whether zygote morphological features were indicators of increased ZA. In this study we performed a prospective, observational study of 2105 zygotes obtained from consecutive patients who were undergoing IVF/ICSI treatment, of which 43 (2%) suffered ZA. Morphological features observed under the inverted microscope were qualitatively categorized: pronuclear size, nucleolar precursor bodies (NPB) alignment, light and dark halos, polar body placement and fragmentation observed at 16-18 h post-insemination. We compared these features in blocked versus cleaved zygotes at 48 h and found significant correlations (p < 0.05) between ZA and three features: the absence of a light halo (p = 0.001), the absence of a dark halo (p < 0.005), and non-aligned NPB (p < 0.05). We can say that certain morphological features are indicators of significantly increased zygote arrest. These findings may be of utility for optimal zygote selection and culture strategies, especially in countries under restrictive conditions.

Silicon oxycarbide ceramics with reduced carbon by pyrolysis of polysiloxanes in water vapor

SiOC ceramics pyrolyzed from polysiloxanes are usually black because of the formation of excess carbon in the ceramic network. Here we show that the pyrolysis of polysiloxanes in water vapor significantly reduces carbon from SiOC and yields a white SiOC ceramic. Chemical analysis shows the amount of carbon in the white ceramic is only half of that in the black one pyrolyzed in argon. 29Si nuclear magnetic resonance spectral (NMR) analysis indicates the reduction of the carbon-rich [SiC 4] and [SiC 2O 2] units with the enhanced formation of the oxygen-rich [SiO 4] and [SiCO 3] units by the water pyrolysis. Importantly, this water pyrolysis resultant carbon reduction is realized in a bulk polysiloxane, and the white SiOC ceramic is obtained in a bulk body with the retained shape of the precursor body. The water pyrolysis can be adopted as an effective mean to tailor the structure of PDCs via the simple introduction of water vapor in pyrolysis.

The role of RNA-polymerase II transcription in embryonic nucleologenesis by bovine embryos

The early stages of embryonic development are maternally driven. As development proceeds, maternally inherited informational molecules decay, and embryogenesis becomes dependent on de novo synthesized RNAs of embryonic genome. The aim of the present study is to investigate the role of de novo transcription in the development of embryos during embryonic genome activation. Autoradiography for detection of transcriptional activity and transmission electron microscopy were applied in in vitro produced bovine embryos cultured to the late 8-cell stage with or without (control group) α-amanitin, specific inhibitor of RNA-polymerases II and III transcription. The α-amanitin (AA) groups presented three sets of embryos cultivated with AA in different time intervals (6, 9 and 12 h). In control group, nucleoplasm and nucleolar structures displayed strong autoradiographic labeling and showed initial development of fibrillo-granular nucleoli. In α-amanitin groups, lack of autoradiographic labeling and disintegrated nucleolus precursor bodies (NPBs) stage were observed. Inhibition of RNA polymerase II (RNA pol II) already in the early phases of embryonic genome activation has detrimental effect on nucleolar formation and embryo survival, what was shown for the first time.

THE FORMATION OF THE COLLISIONAL FAMILY AROUND THE DWARF PLANET HAUMEA

Haumea, a rapidly rotating elongated dwarf planet (~ 1500 km in diameter), has two satellites and is associated with a "family" of several smaller Kuiper Belt objects (KBOs) in similar orbits. All members of the Haumea system share a water ice spectral feature that is distinct from all other KBOs. The relative velocities between the Haumea family members are too small to have formed by catastrophic disruption of a large precursor body, which is the process that formed families around much smaller asteroids in the Main Belt. Here we show that all of the unusual characteristics of the Haumea system are explained by a novel type of giant collision: a graze-and-merge impact between two comparably sized bodies. The grazing encounter imparted the high angular momentum that spun off fragments from the icy crust of the elongated merged body. The fragments became satellites and family members. Giant collision outcomes are extremely sensitive to the impact parameters. Compared to the Main Belt, the largest bodies in the Kuiper Belt are more massive and experience slower velocity collisions; hence, outcomes of giant collisions are dramatically different between the inner and outer solar system. The dwarf planets in the Kuiper Belt record an unexpectedly large number of giant collisions, requiring a special dynamical event at the end of solar system formation.

51 DELAYED NUCLEOLOGENESIS IN PORCINE PREIMPLANTATION EMBRYOS DEVELOPED IN VIVO AND PRODUCED BY SOMATIC CELL NUCLEAR TRANSFER

Nucleolus is known to be a well-suited morphological marker for embryo technologies. Failure in de novo nucleolar formation during embryonic genome activation (EGA) has been observed in many species. The aim of the present study was to investigate nuclear changes and nucleolar formation during EGA in the porcine preimplantation embryos developed in vivo and produced by somatic cell nuclear transfer (SCNT). Embryos were collected at early and late 1-cell stage, 2-, 4-, and 8-cell stage, early and late blastocyst stage, fixed in 3% glutaraldehyde for 1 h, and processed for transmission electron microscopy. In vivo embryos from 1- and 2-cell stages showed electron dense, spherical nucleolar precursor bodies (NPB) in centrally located nuclei with well-developed nuclear envelope and condensed chromatin. Two 1-cell-stage embryos, however, had represented metaphase chromosomes in the periphery. At the 4-cell stage, in vivo embryos displayed fibrillo-granular nucleoli containing all 3 functional nucleolar compartments: fibrillar centers (FC), dense fibrillar component (DFC), and granular component (GC). The nuclei were centrally located, round, and had complete nuclear envelopes. The same types of nuclei and nucleoli were observed for all following stages. On the other hand, embryos produced by SCNT at early 1-cell stage showed centrally located, irregular-shaped nuclei with incomplete nuclear envelopes and condensed chromatin with large intact NPB. Exceptionally, 1 out of the 5 embryos presented a peripheral nucleus with partially condensed chromatin lacking nuclear envelope and fibrillo-granular nucleolus probably persisting from donor fibroblast. Only 2 out of 5 late-1-cell SCNT embryos showed nuclear structures. The nuclei had irregular shapes, complete nuclear membranes, and contained large NPB. At the 2- and 4-cell stages, the embryos presented central nuclei with complete nuclear envelopes. Some of the embryos showed more than one nucleus of varying shapes and sizes. The fibrillo-granular nucleoli were first observed toward the 8-cell stage. The embryos from this stage contained irregularly shaped nuclei with well-developed nuclear envelopes. The nucleoli displayed fibrillar and granular compartments in SCNT 8-cell stage embryos, but lacked the typically structured functional nucleoli observed in in vivo embryos. The absence of formation of functional nucleoli at the 4-cell stage and altered nuclear ultrastructure during the EGA in SCNT embryos, thus, may be one of the main reasons for decreased developmental competence of SCNT embryos.

Dynamical constraints on the origin of Main Belt comets

Abstract— In an effort to understand the origin of Main Belt comets (MBCs) 7968 Elst‐Pizzaro, 118401, and P/2005 U1, the dynamics of these three icy asteroids and a large number of hypothetical MBCs were studied. Results of extensive numerical integrations of these objects suggest that they were formed in place through the collisional breakup of a larger precursor body. Simulations point specifically to the Themis family of asteroids as the origin of these objects and rule out the possibility of a cometary origin (i.e., inward scattering of comets from outer solar system and their primordial capture in the asteroid belt). Results also indicate that while 7968 Elst‐Pizzaro and 118401 maintain their orbits for 1 Gyr, P/2005 U1 diffuses chaotically in eccentricity and becomes unstable in ˜20 Myr. The latter suggest that this MBC used to be a member of the Themis family and is now escaping away. Numerical integrations of the orbits of hypothetical MBCs in the vicinity of the Themis family show a clustering of stable orbits (with eccentricities smaller than 0.2 and inclinations less than 25°) suggesting that many more MBCs may exist in the vicinity of this family (although they might have not been activated yet). The details of the results of simulations and the constraints on the models of the formation and origins of MBCs are presented and their implications for the detection of more of these objects are discussed.

Component-resolved near-infrared spectra of the (22) Kalliope system

We observed (22) Kalliope and its companion Linus with the integral-field spectrograph OSIRIS, which is coupled to the adaptive optics system at the W.M. Keck 2 telescope on March 25, 2008. We present, for the first time, component-resolved spectra acquired simultaneously in each of the Zbb (1–1.18 μm), Jbb (1.18–1.42 μm), Hbb (1.47–1.80 μm), and Kbb (1.97–2.38 μm) bands. The spectra of the two bodies are remarkably similar and imply that both bodies were formed at the same time from the same material; such as via incomplete re-accretion after a major impact on the precursor body.

Localization of satellite DNA and associated proteins in respect to nucleolar precursor bodies in one- and two-cell mouse embryos

Nucleolar precursor bodies (NPB) are characteristic structures in the nuclei of one- and two cell mouse embryos. The alignment of centromeric (CEN) and pericentromeric (periCEN) chromosome regions to the chromatin layer surrounding NPB is known. Mus musculus 4 satellite DNA (satDNA) types are known to be located in CEN region--mouse minor satellite (MiSat) and mouse satellite 3 (MS3); and periCEN region--mouse major satellite (MaSat) and mouse satellite (MS4). We determined the localization of 4 types of mouse satDNA CEN and periCEN regions and associated proteins: RNA-helicase p68, SMC3, Rad21 subunits of the cohesin complex and SYCP3 subunit of the synaptonemal complex (SC). Partially flattened nuclei of the one- and two-cell embryos and embryos treated with ocadaic acids (OA) were used. Different satDNA fragments revealed distinct domains at the surface of NPB: periCEN MaSat was always localized in NPB more internally covering almost entire surface of NPB while CEN MiSat, MS3 and periCEN MS4 showed more peripheral localization. All 4 satDNA did not cover the entire areas of the NPB, indicating the presence of other DNA sequence involved in its formation. RNA-helicase p68 and components of multiprotein cohesin and synaptonemal complexes are the necessary components of NPB. Our results support the opinion that NPB serve as a precursor of chromocenters.

RBM19 is essential for preimplantation development in the mouse

BackgroundRNA-binding motif protein 19 (RBM19, NCBI Accession # NP_083038) is a conserved nucleolar protein containing 6 conserved RNA recognition motifs. Its biochemical function is to process rRNA for ribosome biogenesis, and it has been shown to play a role in digestive organ development in zebrafish. Here we analyzed the role of RBM19 during mouse embryonic development by generating mice containing a mutation in the Rbm19 locus via gene-trap insertion.ResultsHomozygous mutant embryos failed to develop beyond the morula stage, showing defective nucleologenesis, activation of apoptosis, and upregulation of P53 target genes. A unique feature of RBM19 is its localization to the cytoplasm in morula stage-embryos, whereas most other nucleolar proteins are localized to the nucleolar precursor body (NPB). The nucleoli in the Rbm19 mutant embryos remain immature, yet they can carry out rRNA synthesis. The timing of developmental arrest occurs after expression of the inner cell mass markers OCT3/4 and NANOG, but prior to the specification of trophectoderm as reflected by CDX2 expression.ConclusionThe data indicate that RBM19 is essential for preimplantation development, highlighting the importance of de novo nucleologenesis during this critical developmental stage.

Papillary thyroid carcinoma: Evidence for intracytoplasmic formation of precursor substance for calcification and its release from well‐preserved neoplastic cells

Psammoma bodies (PBs) are believed to represent a process of dystrophic calcification over nonviable and dying tissues. Light microscopic and ultrastructural observations suggest that PB formation follows the intracellular assembly of precursor substances and their calcification leading to death of tumor cells and their release. It may also be the result of local secretion of precursor substances like collagen by tumor cells into extracellular space and their calcification. In an earlier reported study, we demonstrated the extracellular localization of various precursor forms of PBs and of irregular calcification in fine-needle aspiration (FNA) smears of papillary thyroid carcinoma (PTC). In this report, we describe a PTC case with intracellular formation precursor substances for calcification and their release from the well-preserved neoplastic cells before undergoing calcification. Ultrasound-guided FNA smears from a small nodule in the left lobe of thyroid in a 40-year-old woman revealed a PTC with numerous intracytoplasmic targetoid bodies, which were magenta colored in MGG stain. On their release from the neoplastic cells, these targetoid precursor bodies were found to be forming pools of matrix material, some of which showed evidence of calcification. The cytologic findings were confirmed by histopathology of the tumor in the thyroidectomy specimen. For the first time, we demonstrate through cytomorpholgy the intracytoplasmic formation of targetoid bodies as precursor substances for calcification and their release from well-preserved cells in PTC. We suggest that the calcification in PTC may not necessarily be taking place over nonviable and dying cells.

Quantitative morphometrical characterization of human pronuclear zygotes

Identification of embryos with high implantation potential remains a challenge in in vitro fertilization (IVF). Subjective pronuclear (PN) zygote scoring systems have been developed for that purpose. The aim of this work was to provide a software tool that enables objective measuring of morphological characteristics of the human PN zygote. A computer program was created to analyse zygote images semi-automatically, providing precise morphological measurements. The accuracy of this approach was first validated by comparing zygotes from two different IVF centres with computer-assisted measurements or subjective scoring. Computer-assisted measurement and subjective scoring were then compared for their ability to classify zygotes with high and low implantation probability by using a linear discriminant analysis. Zygote images coming from the two IVF centres were analysed with the software, resulting in a series of precise measurements of 24 variables. Using subjective scoring, the cytoplasmic halo was the only feature which was significantly different between the two IVF centres. Computer-assisted measurements revealed significant differences between centres in PN centring, PN proximity, cytoplasmic halo and features related to nucleolar precursor bodies distribution. The zygote classification error achieved with the computer-assisted measurements (0.363) was slightly inferior to that of the subjective ones (0.393). A precise and objective characterization of the morphology of human PN zygotes can be achieved by the use of an advanced image analysis tool. This computer-assisted analysis allows for a better morphological characterization of human zygotes and can be used for classification.

Nucleolar re‐activation is delayed in mouse embryos cloned from two different cell lines

Aim of this study was to evaluate and compare embryonic genome activation (EGA) in mouse embryos of different origin using nucleolus as a marker. Early and late 2-cell and late 4-cell stage embryos, prepared by in vitro fertilization (IVF), parthenogenetic activation (PG), and nuclear transfer of mouse embryonic fibroblast (MEF) and mouse HM1 embryonic stem cells (HM1), were processed for autoradiography following (3)H-uridine incubation (transcriptional activity), transmission electron microscopy (ultrastructure) and immunofluorescence (nucleolar proteins; upstream binding factor, UBF and nucleophosmin, B23). All early 2-cell embryos showed transcriptional activity only in nucleoplasm, not over nucleolar precursor bodies (NPBs). UBF was diffusely localized to cytoplasm and B23 to cytoplasm and nucleoplasm. Late 2-cell IVF and PG embryos displayed transcription over nucleoplasm and NPBs. Ultrastructurally, the latter were developing into functional nucleoli. NT-MEF and NT-HM1 embryos displayed transcription over nucleoplasm, but not over NPBs. Development of NPBs into nucleoli was lacking. UBF was in both groups localized to nucleoplasm or distinctly to presumptive NPBs. B23 was distinctly localized to NPBs. All 4-cell embryos presented nucleoplasmic transcription and developing fibrillo-granular nucleoli. UBF and B23 were distinctly localized to nucleoli. However, whereas fully transformed reticulated fibrillo-granular nucleoli were found in IVF and PG embryos, NT-MEF and -HM1 embryos displayed early NPBs transformation. In conclusion, despite normal onset of EGA in cloned embryos, activation of functional nucleoli was one cell cycle delayed in NT embryos. NT-MEF embryos displayed normal targeting but delayed activation of nucleolar proteins. Contrary, in NT-HM1 embryos, both of these processes were delayed.

Coincidental Compositional and Orbital Correspondences Among Some Ordinary Chondrites: No Strong Evidence for Meteoroid Streams

Previous attempts to assign ordinary chondrites (OC) to meteoroid streams have been unsuccessful because the orbits of the proposed members had different radiants and, in some cases, the meteorites had significantly different cosmic-ray exposure (CRE) ages. Using more conservative criteria, we have identified four pairs of equilibrated OC (L6 Nejo, Salem; L6 Perpeti, Vouille; L6 Drake Creek, Forsyth; H5 Okabe, Kerilis) wherein each member of the pair could conceivably have been derived from the same immediate precursor body (IPB). The members of each pair are of the same chondrite group and petrologic type; they have similar CRE ages and fell within 1 calendar day of each other (in different years). Because there is a moderate range in oxidation state (represented by mean olivine Fa) among equilibrated OC in each group, similarities in this intrinsic geochemical property between the members of two of the proposed pairs offer some support for the hypothesis that these rocks were derived from the same IPB. If the pairs are genuine, their precursor bodies were probably meter-size near-Earth asteroids (NEAs) with aphelia within or beyond the Main Asteroid Belt. Fragmentation of such NEAs is most likely to have occurred near aphelia; in principle, the ejecta could have spread somewhat along the NEAs’ orbits and collided with Earth on approximately the same calendar date but in different years. However, literature data show that, although ∼670 meteorites with masses ≥10 kg reach the Earth’s surface each year, only five or six falls (typically in this mass range) are observed and recovered. This suggests that the chances of recovering more than one meteorite from a disrupted meter-size body in Earth-crossing orbit are small. It thus seems likely that the similar properties of the proposed OC pairs are due to coincidence.