Redistribution of Mitochondria Leads to Bursts of ATP Production During Spontaneous Mouse Oocyte Maturation

During mammalian oocyte maturation there are marked changes in the distribution of mitochondria that supply the majority of the cellular ATP. Such redistribution of mitochondria is critical for oocyte quality, as oocytes with a poor developmental potential display aberrant mitochondrial distribution and lower ATP levels. Here we have investigated the dynamics of mitochondrial ATP production throughout spontaneous mouse oocyte maturation, using live measurements of cytosolic and mitochondrial ATP levels. We have observed three distinct increases in cytosolic ATP levels temporally associated with discrete events of oocyte maturation. These changes in cytosolic ATP levels are mirrored by changes in mitochondrial ATP levels, suggesting that mitochondrial ATP production is stimulated during oocyte maturation. Strikingly, these changes in ATP levels correlate with the distribution of mitochondria undergoing translocation to the peri-nuclear region and aggregation into clusters. Mitochondrial clustering during oocyte maturation was concomitant with the formation of long cortical microfilaments and could be disrupted by cytochalasin B treatment. Furthermore, the ATP production bursts observed during oocyte maturation were also inhibited by cytochalasin B suggesting that mitochondrial ATP production is stimulated during oocyte maturation by microfilament-driven, sub-cellular targeting of mitochondria. J. Cell. Physiol. 224: 672–680, 2010. © 2010 Wiley-Liss, Inc

Mitochondria directly influence fertilisation outcome in the pig

The mitochondrion is explicitly involved in cytoplasmic regulation and is the cell's major generator of ATP. Our aim was to determine whether mitochondria alone could influence fertilisation outcome. In vitro, oocyte competence can be assessed through the presence of glucose-6-phosphate dehydrogenase (G6PD) as indicated by the dye, brilliant cresyl blue (BCB). Using porcine in vitro fertilisation (IVF), we have assessed oocyte maturation, cytoplasmic volume, fertilisation outcome, mitochondrial number as determined by mtDNA copy number, and whether mitochondria are uniformly distributed between blastomeres of each embryo. After staining with BCB, we observed a significant difference in cytoplasmic volume between BCB positive (BCB+) and BCB negative (BCB-) oocytes. There was also a significant difference in mtDNA copy number between fertilised and unfertilised oocytes and unequal mitochondrial segregation between blastomeres during early cleavage stages. Furthermore, we have supplemented BCB- oocytes with mitochondria from maternal relatives and observed a significant difference in fertilisation outcomes following both IVF and intracytoplasmic sperm injection (ICSI) between supplemented, sham-injected and non-treated BCB- oocytes. We have therefore demonstrated a relationship between oocyte maturity, cytoplasmic volume, and fertilisation outcome and mitochondrial content. These data suggest that mitochondrial number is important for fertilisation outcome and embryonic development. Furthermore, a mitochondrial pre-fertilisation threshold may ensure that, as mitochondria are diluted out during post-fertilisation cleavage, there are sufficient copies of mtDNA per blastomere to allow transmission of mtDNA to each cell of the post-implantation embryo after the initiation of mtDNA replication during the early postimplantation stages

The consequences of nuclear transfer for mammalian foetal development and offspring survival : a mitochondrial DNA perspective

Review of the articleThe introduction of nuclear transfer (NT) and other technologies that involve embryo reconstruction require us to reinvestigate patterns of mitochondrial DNA (mtDNA) transmission, transcription and replication. MtDNA is a 16.6 kb genome located within each mitochondrion. The number of mitochondria and mtDNA copies per organelle is specific to each cell type. MtDNA is normally transmitted through the oocyte to the offspring. However, reconstructed oocytes often transmit both recipient oocyte mtDNA and mtDNA associated with the donor nucleus. We argue that the transmission of two populations of mtDNA may have implications for offspring survival as only one allele might be actively transcribed. This could result in the offspring phenotypically exhibiting mtDNA depletion-type syndromes. A similar occurrence could arise when nucleo-cytoplasmic interactions fail to regulate mtDNA transcription and replication, especially as the initiation of mtDNA replication post-implantation is a key developmental event. Furthermore, failure of the donor somatic nucleus to be reprogrammed could result in the early initiation of replication and the loss of cellular mtDNA specificity. We suggest investigations should be conducted to enhance our understanding of nucleo-cytoplasmic interactions in order to improve NT efficiency

Fine Scale Temperature Fluctuations in the the Orion Nebula and the t^2 Problem

We present a high spatial resolution map of the columnar electron temperature (Tc) of a region to the south west of the Trapezium in the Orion Nebula. This map was derived from Hubble Space Telescope images that isolated the primary lines of HI for determination of the local extinction and of the OIII lines for determination of Tc. Although there is no statistically significant variation of Tc with distance from the dominant ionizing star theta1-Ori-C, we find small scale variations in the plane of the sky down to a few arcseconds that are compatible with the variations inferred from comparing the value of Te derived from forbidden and recombination lines, commonly known as the t^2 problem. We present other evidence for fine scale variations in conditions in the nebula, these being variations in the surface brightness of the the nebula, fluctuations in radial velocities, and ionization changes. From our Tc map and other considerations we estimate that t^2=0.028 +-0.006 for the Orion nebula. Shadowed regions behind clumps close to the ionization front can make a significant contribution to the observed temperature fluctuations, but they cannot account for the t^2 values inferred from several methods of temperature determination. It is shown that an anomalous broadening of nebular emission lines appears to have the same sense of correlation as the temperature anomalies, although a causal link is not obvious.Comment: 53 pages, 13 images, many of the images have been downgraded to be able to fit within the astro-ph file size limit

The qWR star HD 45166. II. Fundamental stellar parameters and evidence of a latitude-dependent wind

The enigmatic object HD 45166 is a qWR star in a binary system with an orbital period of 1.596 day, and presents a rich emission-line spectrum in addition to absorption lines from the companion star (B7 V). As the system inclination is very small (i=0.77 +- 0.09 deg), HD 45166 is an ideal laboratory for wind-structure studies. The goal of the present paper is to determine the fundamental stellar and wind parameters of the qWR star. A radiative transfer model for the wind and photosphere of the qWR star was calculated using the non-LTE code CMFGEN. The wind asymmetry was also analyzed using a recently-developed version of CMFGEN to compute the emerging spectrum in two-dimensional geometry. The temporal-variance spectrum (TVS) was calculated for studying the line-profile variations. Abundances, stellar and wind parameters of the qWR star were obtained. The qWR star has an effective temperature of Teff=50000 +- 2000 K, a luminosity of log(L/Lsun)=3.75 +- 0.08, and a corresponding photospheric radius of Rphot=1.00 Rsun. The star is helium-rich (N(H)/N(He) = 2.0), while the CNO abundances are anomalous when compared either to solar values, to planetary nebulae, or to WR stars. The mass-loss rate is Mdot = 2.2 . 10^{-7} Msun/yr, and the wind terminal velocity is vinf=425 km/s. The comparison between the observed line profiles and models computed under different latitude-dependent wind densities strongly suggests the presence of an oblate wind density enhancement, with a density contrast of at least 8:1 from equator to pole. If a high velocity polar wind is present (~1200 km/s), the minimum density contrast is reduced to 4:1. The wind parameters determined are unusual when compared to O-type stars or to typical WR stars. (abridged)Comment: 16 pages, 13 figures, accepted for publication in A&

Analysis of proteins expressed at the time of murine organogenesis

Two-dimensional electrophoretograms were prepared from wild-type C57BL/6J embryos from day 7.5 through day 9.0 of development. This time period encompasses a critical window of development as the embryo traverses from an egg cylinder through major organogenesis. Consequently, we term this resource MOPED (for mouse organogenesis protein electrophoresis database). By resolving and analyzing the behavior of approximately 1,000 polypeptides per time point, we were able to track many of these polypeptides through this time period in development. Of special note was a burst of induced protein synthesis that was observed on day 8.5 of development. Polypeptides observed in mouse embryos that match those identified previously in mouse fibroblasts were noted. Two of them (the intermediate filament-associated protein and tropomyosin-4) were significantly altered in 8.5 day embryos. As more polypeptides are designated, it will be possible to expand the known proteins in the database. MOPED establishes the patterns of synthesis of a large number of polypeptides during a crucial period of development. Thus MOPED is designed to analyze proteins relevant to mouse embryogenesis in the future.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50418/1/1080290207_ftp.pd

The tails in the Helix Nebula NGC 7293

We have examined a stream-source model for the production of the cometary tails observed in the Helix Nebula NGC 7293 in which a transonic or moderately supersonic stream of ionized gas overruns a source of ionized gas. Hydrodynamic calculations reveal velocity structures which are in good agreement with the observational data on tail velocities and are consistent with observations of the nebular structure. The results also are indicative of a stellar atmosphere origin for the cometary globules. Tail remnants persist for timescales long enough for their identification with faint striations visible in the nebula gas to be plausible.Comment: 7 pages, 6 figures, accepted for publication in A&

Age-Associated Metabolic and Morphologic Changes in Mitochondria of Individual Mouse and Hamster Oocytes

Background: In human oocytes, as in other mammalian ova, there is a significant variation in the pregnancy potential, with approximately 20% of oocyte-sperm meetings resulting in pregnancies. This frequency of successful fertilization decreases as the oocytes age. This low proportion of fruitful couplings appears to be influenced by changes in mitochondrial structure and function. In this study, we have examined mitochondrial biogenesis in both hamster (Mesocricetus auratus) and mouse (Mus musculus) ova as models for understanding the effects of aging on mitochondrial structure and energy production within the mammalian oocyte. Methodology/Principal Findings: Individual metaphase II oocytes from a total of 25 young and old mice and hamsters were collected from ovarian follicles after hormone stimulation and prepared for biochemical or structural analysis. Adenosine triphosphate levels and mitochondrial DNA number were determined within individual oocytes from young and old animals. In aged hamsters, oocyte adenosine triphosphate levels and mitochondrial DNA molecules were reduced 35.4% and 51.8%, respectively. Reductions of 38.4% and 44% in adenosine triphosphate and mitochondrial genomes, respectively, were also seen in aged mouse oocytes. Transmission electron microscopic (TEM) analysis showed that aged rodent oocytes had significant alterations in mitochondrial and cytoplasmic lamellae structure. Conclusions/Significance: In both mice and hamsters, decreased adenosine triphosphate in aged oocytes is correlated with a similar decrease in mtDNA molecules and number of mitochondria. Mitochondria in mice and hamsters undergo significant morphological change with aging including mitochondrial vacuolization, cristae alterations, and changes in cytoplasmic lamellae