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Patricia A Hunt

Publications and source records attributed to Patricia A Hunt.

At least 19 recordsLinked to original sources
PubMed2007

Bisphenol A exposure in utero disrupts early oogenesis in the mouse.

Estrogen plays an essential role in the growth and maturation of the mammalian oocyte, and recent studies suggest that it also influences follicle formation in the neonatal ovary. In the course of studies designed to assess the effect of the estrogenic chemical bisphenol A (BPA) on mammalian oogenesis, we uncovered an estrogenic effect at an even earlier stage of oocyte development--at the onset of meiosis in the fetal ovary. Pregnant mice were treated with low, environmentally relevant doses of BPA during mid-gestation to assess the effect of BPA on the developing ovary. Oocytes from exposed female fetuses displayed gross aberrations in meiotic prophase, including synaptic defects and increased levels of recombination. In the mature female, these aberrations were translated into an increase in aneuploid eggs and embryos. Surprisingly, we observed the same constellation of meiotic defects in fetal ovaries of mice homozygous for a targeted disruption of ERbeta, one of the two known estrogen receptors. This, coupled with the finding that BPA exposure elicited no additional effects in ERbeta null females, suggests that BPA exerts its effect on the early oocyte by interfering with the actions of ERbeta. Together, our results show that BPA can influence early meiotic events and, importantly, indicate that the oocyte itself may be directly responsive to estrogen during early oogenesis. This raises concern that brief exposures during fetal development to substances that mimic or antagonize the effects of estrogen may adversely influence oocyte development in the exposed female fetus.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Characterising the electronic structure of ionic liquids: an examination of the 1-butyl-3-methylimidazolium chloride ion pair.

In this paper we analyse the electronic properties of gas-phase 1-butyl-3-methylimidazolium Cl ion pairs, [C(4)C(1)im]Cl, in order to deepen our understanding of ionic liquids in general. Examination of charge densities, natural bond orbitals (NBO), and delocalised molecular orbitals computed at the B3LYP and MP2/6-31(++)G(d,p) levels have enabled us to explain a number of experimental phenomena: the relative acidity of different sites on the imidazolium ring, variations in hydrogen-bond donor and acceptor abilities, the apparent contradiction of the hydrogen-bond-donor parameters for different types of solute, the low probability of finding a Cl(-) anion at the rear of the imidazolium ring and the expansion of the imidazolium ring in the presence of a strong hydrogen-bond acceptor. The unreactive but coordinating environment and large electrochemical window have also been accounted for, as has the strong electron-donating character of the carbon atoms to the rear of the ring in associated imidazolylidenes. The electronic structure of the [C(4)C(1)im](+) cation is best described by a C(4)==C(5) double bond at the rear, and a delocalised three-centre 4 e(-) component across the front (N(1)-C(2)-N(3)) of the imidazolium ring; delocalisation between these regions is also significant. Hydrogen-bond formation is driven by Coulombic stabilisation, which compensates for an associated destabilisation of the electronic part of the system. Interactions are dominated by a large positive charge at C(2) and the build up of pi-electron density above and below the ring, particularly that associated with the double bond between C(4) and C(5). The NBO partial charges have been computed and compared with those used in a number of classical simulations.

Journal Article↗
PubMed2006

Cooperativity in ionic liquids.

Cooperativity in ionic liquids is investigated by means of static quantum chemical calculations. Larger clusters of the dimethylimidazolium cation paired with a chloride anion are calculated within density functional theory combined with gradient corrected functionals. Tests of the monomer unit show that density functional theory performs reasonably well. Linear chain and ring aggregates have been considered and geometries are found to be comparable with liquid phase structures. Cooperative effects occur when the total energy of the oligomer differs from a simple sum of monomer energies. Cooperative effects have been found in the structural motifs examined. A systematic study of linear chains of increasing length (up to nine monomer units) has shown that cooperativity plays a more important role than expected and is stronger than in water. The Cl...H distance of the chloride to the most acidic proton increases with an increasing number of monomer units. The average bond distance approaches 218.9 pm asymptotically. The dipole moment grows almost linearly and the dipole moment per monomer unit reaches the asymptotic value of 16.3 D. The charge on the chloride atoms decreases with an increasing chain length. In order to detect local hydrogen bonding in the clusters a new parametrization of the shared-electron number method is introduced. We find decreasing hydrogen bond energies with an increasing cluster size for both the first hydrogen bond to the most acidic proton and the average hydrogen bond.

Journal Article↗
PubMed2006

Structural characterization of the 1-butyl-3-methylimidazolium chloride ion pair using ab initio methods.

Ab initio theoretical methods are used to investigate the gas-phase ion pairs of the ionic liquid 1-butyl-3-methylimidazolium chloride. Multiple stable conformers with the chloride anion positioned (in-plane) around the imidazolium ring or above the C2-H bond are determined. The relative energy ordering of the conformers is examined at the B3LYP, MP2, and CCSD(T) levels. Zero-point energies, BSSE, and basis set effects are examined. For accurate results, correlation (dispersion) effects must be included. The most stable conformers are essentially degenerate and have the chloride H-bonding to, or lying above, the C2-H bond. Other conformers are found to lie approximately 30 and approximately 60 kJ mol(-1) higher in energy. Results are compared with those from recent simulations and experimental studies. The effect of the chloride anion on rotation of the butyl chain is investigated and found to lower some rotational barriers while enhancing others. The origin of the rotational barriers is determined. The number and type of hydrogen bonds formed between the imidazolium cation and chloride anion is found to vary significantly among conformers. No evidence of a possible intra C(alkyl)-H...pi interaction is obtained; however, hints of a Cl...pi interaction are found. The vibrational spectrum of each conformer is examined, and the origin of multiple (H-bonding) features in the vibrational spectrum of the ionic liquid explained.

Journal Article↗
PubMed2005

SMC1beta-deficient female mice provide evidence that cohesins are a missing link in age-related nondisjunction.

Mitotic chromosome segregation is facilitated by the cohesin complex, which maintains physical connections between sister chromatids until anaphase. Meiotic cell division is considerably more complex, as cohesion must be released sequentially to facilitate orderly segregation of chromosomes at both meiosis I and meiosis II. This necessitates meiosis-specific cohesin components; recent studies in rodents suggest that these influence chromosome behavior during both cell division and meiotic prophase. To elucidate the role of the meiosis-specific cohesin SMC1beta (encoded by Smc1l2) in oogenesis, we carried out meiotic studies of female SMC1beta-deficient mice. Our results provide the first direct evidence that SMC1beta acts as a chiasma binder in mammals, stabilizing sites of exchange until anaphase. Additionally, our observations support the hypothesis that deficient cohesion is an underlying cause of human age-related aneuploidy.

Age Factors↗
PubMed2005

Systematic control of photochemistry: the dynamics of photoisomerization of a model cyanine dye.

On-the-fly CASSCF nonadiabatic dynamics have been used to model the trans-cis isomerization of a model cyanine dye. Our results show that the photochemical generation of the trans versus cis product is dynamically controlled by the presence of an extended cis-trans conical intersection seam that persists along all torsional angles. This in turn suggests that the photochemistry could be completely controlled by controlling the distribution of momentum components in a wave packet excited by laser photolysis in a coherent control experiment.

Journal Article↗
PubMed2004

Cisplatin disrupts mammalian spermatogenesis, but does not affect recombination or chromosome segregation.

Meiotic recombination is initiated by a series of double-strand breaks (DSBs) in areas of the genome that generally contain promoters and feature an open chromatin configuration [T.D. Petes, Meiotic recombination hot spots and cold spots, Nat. Rev. Genet. 2 (2001) 360-369]. To investigate whether induced DSBs likewise lead to recombinational repair and whether the placement of new exchange events alters normal patterns of recombination, we used the chemotherapeutic drug cisplatin (CP) to generate additional DSBs throughout the mouse genome. Treatment with CP impaired spermatogenesis, as exhibited by reductions in sperm counts, reductions in both testicular size and weight, changes in the distribution of cells at various prophase I substages, prolonged increases in germ cell apoptosis, and an increased incidence of synaptic abnormalities. Unexpectedly, however, no obvious effect on genome-wide recombination levels in CP-treated animals was observed, nor was the level of aneuploidy increased in sperm from exposed males.

Animals↗
PubMed2004

Cohesin SMC1 beta is required for meiotic chromosome dynamics, sister chromatid cohesion and DNA recombination.

Sister chromatid cohesion ensures the faithful segregation of chromosomes in mitosis and in both meiotic divisions. Meiosis-specific components of the cohesin complex, including the recently described SMC1 isoform SMC1 beta, were suggested to be required for meiotic sister chromatid cohesion and DNA recombination. Here we show that SMC1 beta-deficient mice of both sexes are sterile. Male meiosis is blocked in pachytene; female meiosis is highly error-prone but continues until metaphase II. Prophase axial elements (AEs) are markedly shortened, chromatin extends further from the AEs, chromosome synapsis is incomplete, and sister chromatid cohesion in chromosome arms and at centromeres is lost prematurely. In addition, crossover-associated recombination foci are absent or reduced, and meiosis-specific perinuclear telomere arrangements are impaired. Thus, SMC1 beta has a key role in meiotic cohesion, the assembly of AEs, synapsis, recombination, and chromosome movements.

Animals↗
PubMed2003

Bisphenol a exposure causes meiotic aneuploidy in the female mouse.

BACKGROUND: There is increasing concern that exposure to man-made substances that mimic endogenous hormones may adversely affect mammalian reproduction. Although a variety of reproductive complications have been ascribed to compounds with androgenic or estrogenic properties, little attention has been directed at the potential consequences of such exposures to the genetic quality of the gamete. RESULTS: A sudden, spontaneous increase in meiotic disturbances, including aneuploidy, in studies of oocytes from control female mice in our laboratory coincided with the accidental exposure of our animals to an environmental source of bisphenol A (BPA). BPA is an estrogenic compound widely used in the production of polycarbonate plastics and epoxy resins. We identified damaged caging material as the source of the exposure, as we were able to recapitulate the meiotic abnormalities by intentionally damaging cages and water bottles. In subsequent studies of female mice, we administered daily oral doses of BPA to directly test the hypothesis that low levels of BPA disrupt female meiosis. Our results demonstrated that the meiotic effects were dose dependent and could be induced by environmentally relevant doses of BPA. CONCLUSIONS: Both the initial inadvertent exposure and subsequent experimental studies suggest that BPA is a potent meiotic aneugen. Specifically, in the female mouse, short-term, low-dose exposure during the final stages of oocyte growth is sufficient to elicit detectable meiotic effects. These results provide the first unequivocal link between mammalian meiotic aneuploidy and an accidental environmental exposure and suggest that the oocyte and its meiotic spindle will provide a sensitive assay system for the study of reproductive toxins.

Aneuploidy↗
PubMed2003

Checkpoint failure and chromosomal instability without lymphomagenesis in Mre11(ATLD1/ATLD1) mice.

In this study, mice expressing one of the two Mre11 alleles inherited in the human ataxia-telangiectasia like disorder (A-TLD) were derived. The mutation had a profound maternal effect on embryonic viability, revealing an acute requirement for Mre11 complex function in early embryogenesis. Mre11(ATLD1/ATLD1) mice exhibited several indices of impaired ATM function. The mice also exhibited pronounced chromosomal instability. Despite this phenotypic spectrum, the animals were not prone to malignancy. These data indicate that defective cell cycle checkpoints and chromosomal instability are insufficient to significantly enhance the initiation of tumorigenesis. In contrast, the latency of malignancy in p53(+/-) mice was dramatically reduced. We propose that in Mre11(ATLD1/ATLD1) mice, genome instability and cell cycle checkpoint defects reduce viability in early embryos and in proliferating cells, while promoting malignancy in the context of an initiating lesion.

Animals↗
PubMed2002

Sex matters in meiosis.

In mammals, fertilization typically involves the ovulation of one or a few eggs at one end of the female reproductive tract and the entry of millions of sperm at the other. Given this disparity in numbers, it might be expected that the more precious commodity-eggs-would be subject to more stringent quality-control mechanisms. However, information from engineered mutations of meiotic genes suggests just the opposite. Specifically, the available mutants demonstrate striking sexual dimorphism in response to meiotic disruption; for example, faced with adversity, male meiosis grinds to a halt, whereas female meiosis soldiers on. This female "robustness" comes with a cost, however, because aneuploidy appears to be increased in the resultant oocytes.

Aneuploidy↗
PubMed2002

Covariation of synaptonemal complex length and mammalian meiotic exchange rates.

Analysis of recombination between loci (linkage analysis) has been a cornerstone of human genetic research, enabling investigators to localize and, ultimately, identify genetic loci. However, despite these efforts little is known about patterns of meiotic exchange in human germ cells or the mechanisms that control these patterns. Using recently developed immunofluorescence methodology to examine exchanges in human spermatocytes, we have identified remarkable variation in the rate of recombination within and among individuals. Subsequent analyses indicate that, in humans and mice, this variation is linked to differences in the length of the synaptonemal complex. Thus, at least in mammals, a physical structure, the synaptonemal complex, reflects genetic rather than physical distance.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Simultaneous analysis of chromosomes and chromosome-associated proteins in mammalian oocytes and embryos.

Cytogenetic analyses of mammalian eggs and preimplantation embryos have been limited by the difficult and tedious task of preparing chromosomes from single cells or small numbers of cells. In this report we describe a new technique that is both reliable and comparatively simple. Further, since the technique does not use the conventional 3:1 methanol:acetic acid fixative, it has the advantage of producing high-resolution chromosome preparations without destroying chromosome-associated proteins. Thus, this method provides a sensitive means of conducting studies of a heretofore inaccessible period of mammalian development, and of studying proteins thought to mediate both meiotic chromosome segregation and chromatin modifications in the preimplantation embryo.

Animals↗
PubMed2002

Dihydroazulene/vinylheptafulvene photochromism: a model for one-way photochemistry via a conical intersection.

Dihydroazulene (DHA)/vinylheptafulvene (VHF) photochromism has been investigated by studying the isomerization of 1,2,3,8a,9-pentahydrocyclopent[a]azulene-9,9-dicarbonitrile through complete active space-self consistent field calculations on the ground (S(0)) and first excited (S(1)) states of smaller model compounds. In each case, the S(1) reaction coordinate is characterized by a transition structure for adiabatic ring opening, connecting a DHA-like intermediate to a much more stable VHF-like structure. This VHF-like structure is not a real S(1) minimum but a crossing (i.e., a conical intersection) between the excited- and ground-state potential energy surfaces. The existence of such a crossing is consistent with the lifetime of approximately 600 fs recently measured for the DHA-like intermediate on S(1) (Ern, J.; Petermann, M.; Mrozek, T.; Daub, J.; Kuldova, K.; Kryschi, C. Chem. Phys. 2000, 259, 331-337). The shape of the crossing is also crucial; it not only explains the fact that the quantum yield approaches 1.0 for the forward DHA --> VHF reaction, but also the lack of any fluorescence or photochemical back-reaction from VHF. These findings are supported by ab initio direct dynamics calculations. This work suggests that calculating and understanding the topology of excited-state potential energy surfaces will be useful in designing photochromic molecules.

Journal Article↗
PubMed2002

Genetic control of mammalian meiotic recombination. I. Variation in exchange frequencies among males from inbred mouse strains.

Genetic background effects on the frequency of meiotic recombination have long been suspected in mice but never demonstrated in a systematic manner, especially in inbred strains. We used a recently described immunostaining technique to assess meiotic exchange patterns in male mice. We found that among four different inbred strains--CAST/Ei, A/J, C57BL/6, and SPRET/Ei--the mean number of meiotic exchanges per cell and, thus, the recombination rates in these genetic backgrounds were significantly different. These frequencies ranged from a low of 21.5 exchanges in CAST/Ei to a high of 24.9 in SPRET/Ei. We also found that, as expected, these crossover events were nonrandomly distributed and displayed positive interference. However, we found no evidence for significant differences in the patterns of crossover positioning between strains with different exchange frequencies. From our observations of >10,000 autosomal synaptonemal complexes, we conclude that achiasmate bivalents arise in the male mouse at a frequency of 0.1%. Thus, special mechanisms that segregate achiasmate chromosomes are unlikely to be an important component of mammalian male meiosis.

Animals↗
PubMed2002

Sex-specific differences in meiotic chromosome segregation revealed by dicentric bridge resolution in mice.

The meiotic properties of paracentric inversion heterozygotes have been well studied in insects and plants, but not in mammalian species. In essence, a single meiotic recombination event within the inverted region results in the formation of a dicentric chromatid, which usually breaks or is stretched between the two daughter nuclei during the first meiotic anaphase. Here, we provide evidence that this is not the predominant mode of exchange resolution in female mice. In sharp contrast to previous observations in other organisms, we find that attempts to segregate the dicentric chromatid frequently result not in breakage, stretching, or loss, but instead in precocious separation of the sister centromeres of at least one homolog. This often further results in intact segregation of the dicentric into one of the meiotic products, where it can persist into the first few embryonic divisions. These novel observations point to an unusual mechanism for the processing of dicentric chromosomes in mammalian oogenesis. Furthermore, this mechanism is rare or nonexistent in mammalian spermatogenesis. Thus, our results provide additional evidence of sexual dimorphism in mammalian meiotic chromosome behavior; in "stressful" situations, meiotic sister chromatid cohesion is apparently handled differently in males than in females.

Animals↗